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Effects of continuous milking during the dry period or once daily milking in the first 4 weeks of lactation on metabolism and productivity of dairy cows

      Abstract

      The objective was to compare the effects of 3 management systems in high-yielding dairy cows on metabolic profiles and milk production. Thirty-six multiparous Brown Swiss cows were randomly assigned to 1 of 3 treatment groups (n = 12 cows/group): the control (C) group, in which cows were dried off 56 d before calving and milked twice daily throughout next lactation (305 d); the once daily milking (ODM) group, in which cows were dried off 56 d before calving and milked once daily for the first 4 wk of lactation and twice daily for the remaining lactation; and the continuous milking (CM) group, in which cows were milked twice daily until calving and also during the subsequent lactation. Serum glucose concentrations decreased between wk 1 and 4 exclusively in C cows. Serum concentrations of NEFA and BHBA in the first 4 wk of lactation were highest in C cows compared with ODM and CM cows. Decreased backfat thickness during early lactation and reduction of body condition score were markedly more pronounced in C cows compared with ODM and CM cows. Mean lactational milk yield of C cows [11,310 ± 601 kg of energy-corrected milk (ECM)/305 d] was approximately 16% higher compared with ODM cows (9,531 ± 477 kg of ECM/305 d) and CM cows (9,447 ± 310 kg of ECM/305 d). The lactation curve of CM cows compared with C cows was characterized by a similar time of peak yield (wk 3), a reduced peak yield, and no obvious differences in persistency. Mean percentage of milk protein was significantly higher for CM cows (3.91%) compared with C cows (3.52%). In contrast, once daily milking was accompanied by a reduced and significantly delayed peak yield (wk 8) compared with the control treatment, whereas persistency was better and milk protein (3.79%) was higher in ODM cows than in C cows. In conclusion, continuous milking and once daily milking, targeting the interval before or after calving, respectively, substantially reduced the metabolic challenge of fresh cows and improved milk protein percentage. Continuous milking and once daily milking increased milk protein percentage markedly; furthermore, once daily milking during the first 4 wk of lactation improved the lactation curve.

      Key words

      Introduction

      The critical challenge in high-cost, high-return dairy production systems is attaining high lactational milk yield while simultaneously achieving sustainable production by maintaining an appropriate level of animal health and fertility. Producing milk with high protein percentage to meet market demands and addressing society's concerns regarding animal welfare are also priorities. Genetic selection for greater milk production is a risk factor for a variety of production diseases because increases in feed intake lag behind increases in milk production in early lactation (
      • Ingvartsen K.L.
      • Andersen J.B.
      Integration of metabolism and intake regulation: A review focusing on periparturient animals.
      ;
      • Ingvartsen K.L.
      • Dewhurst R.J.
      • Friggens N.C.
      On the relationship between lactational performance and health: Is it yield or metabolic imbalance that cause production diseases in dairy cattle?.
      ;
      • Mulligan F.J.
      • Doherty M.L.
      Production diseases of the transition cow.
      ). Therefore, efforts have been made to optimize housing, feeding, and management of high-yielding dairy cows (
      • Distl O.
      Epidemiologic and genetic analysis of veterinary data of German Brown cattle.
      ;
      • Drackley J.K.
      ADSA Foundation Scholar Award. Biology of dairy cows during the transition period: The final frontier?.
      ;
      • Grummer R.R.
      • Mashek D.G.
      • Hayirli A.
      Dry matter intake and energy balance in the transition period.
      ).
      A successful transition from late pregnancy to early lactation is essential for animal health and productivity (
      • Grant R.J.
      • Albright J.L.
      Feeding behavior and management factors during the transition period in dairy cattle.
      ;
      • Drackley J.K.
      ADSA Foundation Scholar Award. Biology of dairy cows during the transition period: The final frontier?.
      ). One way to reduce the risk of metabolic imbalance during this is time is to omit the dry period (DP;
      • Rémond B.
      • Bonnefoy J.C.
      Performance of a herd of Holstein cows managed without the dry period.
      ;
      • Andersen J.B.
      • Madsen T.G.
      • Larsen T.
      • Ingvartsen K.L.
      • Nielsen M.O.
      The effects of dry period versus continuous lactation on metabolic status and performance in periparturient cows.
      ). In a study by
      • Andersen J.B.
      • Madsen T.G.
      • Larsen T.
      • Ingvartsen K.L.
      • Nielsen M.O.
      The effects of dry period versus continuous lactation on metabolic status and performance in periparturient cows.
      , plasma concentrations of glucose and insulin were higher and plasma concentrations of NEFA and BHBA were lower in cows with an omitted DP than in control cows with a conventional DP during the first 5 wk of early lactation. However, in other studies, continuous milking compromised colostrum quality (
      • Grummer R.R.
      • Rastani R.R.
      Why reevaluate dry period length?.
      ;
      • Caja G.
      • Salama A.A.
      • Such X.
      Omitting the dry-off period negatively affects colostrum and milk yield in dairy goats.
      ) and caused a 12 to 25% decrease in milk yield during the subsequent lactation (
      • Swanson E.W.
      Comparing continuous milking with sixty-day dry periods in successive lactations.
      ;
      • Rémond B.
      • Ollier A.
      • Miranda G.
      Milking of cows in late pregnancy: Milk production during this period and during the succeeding lactation.
      ;
      • Rémond B.
      • Bonnefoy J.C.
      Performance of a herd of Holstein cows managed without the dry period.
      ). Therefore, it was concluded that the DP is needed to enhance secretory function of the mammary gland (
      • Rémond B.
      • Rouel J.
      • Pinson N.
      • Jabet S.
      An attempt to omit the dry period over three consecutive lactations in dairy cows.
      ;
      • Ingvartsen K.L.
      • Dewhurst R.J.
      • Friggens N.C.
      On the relationship between lactational performance and health: Is it yield or metabolic imbalance that cause production diseases in dairy cattle?.
      ), enabling involution, proliferation, and redifferentiation of mammary tissue (
      • Capuco A.V.
      • Akers R.M.
      • Smith J.J.
      Mammary growth in Holstein cows during the dry period: Quantification of nucleic acids and histology.
      ;
      • Wilde C.J.
      • Addey C.V.
      • Li P.
      • Fernig D.G.
      Programmed cell death in bovine mammary tissue during lactation and involution.
      ;
      • Capuco A.V.
      • Ellis S.E.
      • Hale S.A.
      • Long E.
      • Erdman R.A.
      • Zhao X.
      • Paape M.J.
      Lactation persistency: Insights from mammary cell proliferation studies.
      ). It was previously recommended that the DP last at least 6 to 8 wk because shorter intervals reduced milk yield in the following lactation (
      • Schaeffer L.R.
      • Henderson C.R.
      Effects of days dry and days open on Holstein milk production.
      ;
      • Coppock C.E.
      • Everett R.W.
      • Natzke R.P.
      • Ainslie H.R.
      Effect of dry period length on Holstein milk production and selected disorders at parturition.
      ;
      • O’Connor Jr., J.J.
      • Oltenacu P.A.
      Determination of optimum drying off time for dairy cows using decision analysis and computer simulation.
      ). Conversely, it was recently established that mammary involution is completed within 25 d, suggesting that a 30-d DP was adequate to ensure high milk production (
      • Capuco A.V.
      • Akers R.M.
      • Smith J.J.
      Mammary growth in Holstein cows during the dry period: Quantification of nucleic acids and histology.
      ;
      • Gulay M.S.
      • Hayen M.J.
      • Bachman K.C.
      • Belloso T.
      • Liboni M.
      • Head H.H.
      Milk production and feed intake of Holstein cows given short (30-d) or normal (60-d) dry periods.
      ). Moreover, cows assigned to a shortened DP (28 d) had an improved energy status for the first 10 wk of lactation compared with cows with a 56-d DP (
      • Rastani R.R.
      • Grummer R.R.
      • Bertics S.J.
      • Gumen A.
      • Wiltbank M.C.
      • Mashek D.G.
      • Schwab M.C.
      Reducing dry period length to simplify feeding transition cows: Milk production, energy balance, and metabolic profiles.
      ). Primiparous cows assigned to a 35-d DP after the first lactation had lower peripheral NEFA concentrations immediately after parturition than those given a 56-d DP (
      • Pezeshki A.
      • Mehrzad J.
      • Ghorbani G.R.
      • Rahmani H.R.
      • Collier R.J.
      • Burvenich C.
      Effects of short dry periods on performance and metabolic status in Holstein dairy cows.
      ). Multiparous cows with a 28-d DP had an improved energy status based on total milk production and BCS at 150 DIM (
      • Pezeshki A.
      • Mehrzad J.
      • Ghorbani G.R.
      • De Spiegeleer B.
      • Collier R.J.
      • Burvenich C.
      The effect of dry period length reduction to 28 days on the performance of multiparous dairy cows in the subsequent lactation.
      ).
      Another approach to reducing the metabolic challenge during early lactation is to alter milking frequency. The interval from calving to peak yield, its magnitude, and the rate of increase of milk yield per day during the first weeks of lactation are important risk factors for production diseases in early lactation (
      • Ingvartsen K.L.
      • Andersen J.B.
      Integration of metabolism and intake regulation: A review focusing on periparturient animals.
      ). However, the time that peak yield occurs can be influenced only slightly by the feeding regimen, but may depend more on milking frequency. In several studies, increased frequency enhanced milk yield (
      • van der Iest R.
      • Hillerton J.E.
      Short-term effects of frequent milking of dairy cows.
      ;
      • Rastani R.R.
      • Del Rio N.S.
      • Gressley T.F.
      • Dahl G.E.
      • Grummer R.R.
      Effects of increasing milking frequency during the last 28 days of gestation on milk production, dry matter intake, and energy balance in dairy cows.
      ;
      • Wall E.H.
      • McFadden T.B.
      Use it or lose it: Enhancing milk production efficiency by frequent milking of dairy cows.
      ). In contrast, in a study by
      • Carruthers V.R.
      • Davis S.R.C.P.J.A.
      Response of Jersey and Friesian cows to once a day milking and prediction of response based on udder characteristics and milk composition.
      , once daily milking for 2 wk in early lactation reduced milk yield by 16% compared with twice daily milking. Although milking thrice daily for the first 28 d of lactation increased milk yield by 19.6% compared with once daily milking, it was accompanied by more severe losses of body weight by d 60 of lactation (
      • Davis S.R.
      • Farr V.C.
      • Stelwagen K.
      Regulation of yield loss and milk composition during once-daily milking: A review.
      ;
      • Patton J.
      • Kenny D.A.
      • Mee J.F.
      • O’Mara F.P.
      • Wathes D.C.
      • Cook M.
      • Murphy J.J.
      Effect of milking frequency and diet on milk production, energy balance, and reproduction in dairy cows.
      ). Energy status was improved in cows milked once daily during the first 3 wk of lactation (
      • Patton J.
      • Kenny D.A.
      • Mee J.F.
      • O’Mara F.P.
      • Wathes D.C.
      • Cook M.
      • Murphy J.J.
      Effect of milking frequency and diet on milk production, energy balance, and reproduction in dairy cows.
      ), reducing the risk of metabolic disorders (
      • Rauw W.M.
      • Kanis E.
      • Noordhuizen-Stassen E.N.G.F.J.
      Undesiderable side effects of selection for high production efficiency in farm animals: A review.
      ).
      To date, continuous milking has not been compared with once daily milking in early lactation as a way to easier cope with the metabolic challenge of high-yielding dairy cows. Thus, the objective of the present study was to compare the effects of continuous milking without DP and milking frequency during early lactation on the metabolic profile, fertility, and productivity of the subsequent lactation. The hypothesis to be tested was that metabolic profile and, as a consequence, parameters of productivity were different among cows that were milked either continuously or once daily for the first 4 wk of lactation compared with those managed with a traditional 56-d DP and twice daily milking after calving.

      Materials and Methods

      Animals and Experimental Design

      The study was conducted at the research farm Veitshof of the Technische Universitaet Muenchen (Freising, Germany) from December 2006 to December 2008 using 45 multiparous Brown Swiss dairy cows.
      Cows were assigned at random to 1 of 3 treatment groups. In the control group (C; n = 16), cows were dried off 56 d before expected calving and milked twice daily throughout the entire lactation (305 d). Cows in the once daily milking group (ODM; n = 16) were dried off 56 d before expected calving and milked only once daily for the first 4 wk of lactation and twice daily for the remainder of lactation. Cows of the continuous milking group (CM; n = 13) were milked twice daily up to the day of calving and throughout the subsequent 305-d lactation (i.e., they were not dried off).
      One cow from the CM group, 4 cows from the ODM group, and 4 cows from the C group did not finish the entire lactation; they were removed because of various health disorders. Ultimately, complete data sets (305-d lactation) for 12 cows in each treatment group were used for statistical analysis (Table 1).
      Table 1Experimental design, animals excluded from the study and reasons for removal, and animals used for statistical analysis
      C=control group: cows were dried off 56 d before calving and milked twice daily throughout next lactation (305 d; n=12); ODM=once daily milking group: cows were dried off 56 d before calving and milked once daily for the first 4 wk of lactation and twice daily for the remaining lactation (n=12); CM=continuous milking group: cows were milked twice daily until calving and also during the subsequent lactation (n=12).
      ItemCODMCM
      Cows assigned to study, n161613
      Daily milking frequency
      Numbers indicate days relative to calving.
       d −56 to 0drydry2
       d 1 to 28212
       d 29 to 305222
      Cows removed from study, n441
       Downer cow syndrome1 (4)
      Values in parentheses represent days of lactation when cows were removed from the study.
      1 (1)
       Severe injuries1 (29)1 (48)
       Lameness1 (194)1 (159)1 (106)
       Mastitis1 (137)
       Abortion1 (239)
      Cows with complete data sets, n121212
      Previous energy-corrected 305-d milk yield,
      Mean ± SEM.
      kg
      8,826 ± 3778,725 ± 3608,664 ± 336
      Parity
      Mean ± SEM.
      3.5 ± 1.63.8 ± 1.83.3 ± 2.1
      1 C = control group: cows were dried off 56 d before calving and milked twice daily throughout next lactation (305 d; n = 12); ODM = once daily milking group: cows were dried off 56 d before calving and milked once daily for the first 4 wk of lactation and twice daily for the remaining lactation (n = 12); CM = continuous milking group: cows were milked twice daily until calving and also during the subsequent lactation (n = 12).
      2 Numbers indicate days relative to calving.
      3 Values in parentheses represent days of lactation when cows were removed from the study.
      4 Mean ± SEM.

      Housing and Feeding

      All cows were kept in a cubicle housing system fitted with rubber-coated slatted floors and bedded with wood shavings. Cows were milked in a 2 × 2 tandem milking parlor (GEA WestfaliaSurge GmbH, Boenen, Germany) either once (1545 h) or twice (0415 and 1545 h) daily. For drying-off (C and ODM cows only), milking was done once daily (1545 h) for 3 d and then an intramammary antibiotic treatment containing 1 g of cloxacillin (Orbenin, Pfizer, Berlin, Germany) was given 56 d before expected calving. Thereafter, C and ODM cows were transferred to a separate stable and fed the DP ration (Table 2). Approximately 1 wk before expected calving, all cows were moved to single calving pens bedded with barley straw. After calving, cows were moved to the lactating herd and fed the lactation diet. The CM cows were not separated from the herd during the last 2 mo of pregnancy because they were milked throughout the entire pregnancy–lactation cycle. All lactating cows were fed the partly mixed ration formulated to meet nutrient requirements, as indicated by
      GfE
      Empfehlungen zur Energie und Nährstoffversorgung der Milchkühe und Aufzuchtrinder.
      (Table 2), and had ad libitum access to fresh water.
      Table 2Ingredients and chemical composition of the partial mixed ration
      Lactation diet (LD) was fed to all cows; dry period diet (DPD) was fed only to cows having a 56-d dry period (control and once daily milking cows, not continuous milking cows).
      ItemLDDPD
      Ingredient, %
       Corn silage6043
       Grass silage2325
       Hay432
       Feed pellets
      Composition: corn gluten, 18.4%; turnips molasses chips, 13.8%; wheat, 10.0%; triticale, 10.0%; rape cake, 10.0%; maize, 8.8%; malt germ, 6.0%; grain distillation residual (ProtiGrain), 5%; rape extraction grist, 5%; rumen protected rape extraction grist, 5%; palm corn cake, 3.3%; soy extraction grist, 2.8%; sodium bicarbonate, 1.0%; calcium bicarbonate, 0.99%; plant oil (palm coconut), 0.40% (Raiffeisen Kraftfutterwerke Süd GmbH, Würzburg, Germany).
      12
       Mineral mix
      Ingredients: Ca, 14%; Na, 10.0%; P, 5.0%; Mg, 5.0% (Josera, Kleinheubach, Germany).
      1
      Chemical composition, % unless noted
       DM45.252.0
       CP12.212.9
       Crude fiber18.619.2
       NFC26.49.92
       Ether extract3.163.16
       NEL,
      Estimates determined from tabulated values of feeds (GfE, 2007) and according to the following formula: NEL (Mcal/kg)=0.6 × [1+0.004 × (q − 57)] × ME(Mcal/kg), where q=ME/GE. Here, q=88.9.
      Mcal/kg
      1.551.36
      1 Lactation diet (LD) was fed to all cows; dry period diet (DPD) was fed only to cows having a 56-d dry period (control and once daily milking cows, not continuous milking cows).
      2 Composition: corn gluten, 18.4%; turnips molasses chips, 13.8%; wheat, 10.0%; triticale, 10.0%; rape cake, 10.0%; maize, 8.8%; malt germ, 6.0%; grain distillation residual (ProtiGrain), 5%; rape extraction grist, 5%; rumen protected rape extraction grist, 5%; palm corn cake, 3.3%; soy extraction grist, 2.8%; sodium bicarbonate, 1.0%; calcium bicarbonate, 0.99%; plant oil (palm coconut), 0.40% (Raiffeisen Kraftfutterwerke Süd GmbH, Würzburg, Germany).
      3 Ingredients: Ca, 14%; Na, 10.0%; P, 5.0%; Mg, 5.0% (Josera, Kleinheubach, Germany).
      4 Estimates determined from tabulated values of feeds (
      GfE
      Empfehlungen zur Energie und Nährstoffversorgung der Milchkühe und Aufzuchtrinder.
      ) and according to the following formula: NEL (Mcal/kg) = 0.6 × [1 + 0.004 × (q − 57)] × ME(Mcal/kg), where q = ME/GE. Here, q = 88.9.
      In addition, hay was fed immediately after milking (0600 h). The partly mixed ration, formulated on the basis of a milk yield of 22 kg/d, was delivered once daily (0700 h) and was intended to provide ad libitum intake (>5% residual feed). Cows producing more than 22 kg/d were fed additional concentrates (0.5 kg of concentrate/kg of milk, maximal 9 kg/d; Raiffeisen Kraftfutterwerke Süd, Würzburg, Germany) in feeding stations.

      Health and Occurrence of Diseases

      Health status was assessed daily. Retained fetal membranes, periparturient paresis, primary ketosis, mastitis, and lameness occurred during the study. Nine cows were removed from the study (Table 1) because they were severely affected with the following disorders: downer cow syndrome (n = 2; 1 C and 1 ODM cow), severe injuries (n = 2; 1 C and 1 ODM cow), lameness (n = 3; 1 C, 1 ODM, and 1 CM cow), mastitis (n = 1; 1 ODM cow), or abortion (n = 1; 1 C cow).

      Records and Sampling

      Milk yield was measured twice daily with electronic milk meters (Metatron P21, GEA WestfaliaSurge GmbH) and stored electronically (DairyPlan C21, GEA WestfaliaSurge GmbH). Daily milk yield was standardized to ECM (4.0% fat and 3.4% protein content) by ECM (kg/d) = [(0.38 × fat % + 0.21 × protein % + 1.05)/3.28] × milk yield (kg/d) (
      • Fischer B.
      • Mäurer H.
      • Engelhard T.
      • Haacker W.
      Feed intake and energy supplementation of far-off dry cows.
      ). Analysis of milk components (protein, fat, and SCC) was done on samples collected at the afternoon milking. Because milking intervals were similar between morning and afternoon milkings, measurements in afternoon samples were reliable estimations of the contents in daily milk in agreement with
      • Lee A.J.
      • Wardrop J.
      Predicting daily milk yield, fat percent, and protein percent from morning or afternoon tests.
      . Samples (∼1 L) were collected during milking. The amount of milk separated into the sample pot was controlled by milk flow-rate and total amount of milk to get a proportional subsample (Metatron P21, GEA WestfaliaSurge GmbH). A 50-mL aliquot was taken and stored at 4°C for a maximum of 10 d with a preservative (acidiol) until analyses. Milk composition of cows in CM was analyzed twice weekly until calving. After parturition, milk composition of all cows was determined daily for the first week, twice weekly to 56 DIM, once weekly from 57 to 100 DIM, and then once every 2 wk to 305 DIM.
      Blood samples from all cows were collected by jugular venipuncture at wk −4, −2, and −1 before expected calving, within 24 h postpartum (wk 0), and at wk 1, 2, 4, 6, 8, 12, 16, 24, 36, and 44. Samples were collected into 7-mL vacuum tubes (Vacuette, Greiner Bio-One, Kremsmünster, Austria) at 0700 (after milking); within 1 h, blood serum was separated by centrifugation (2,000 × g; 4°C; 15 min). Three aliquots (1.5 mL) of serum were stored at −20°C.

      Backfat Thickness and BCS

      Subcutaneous adipose tissue (backfat thickness) was assessed with ultrasonography (Sonovet 2000, Universal Ultrasound, Bedford Hills, NY) near the pelvic region (
      • Schröder U.J.
      • Staufenbiel R.
      Invited review: Methods to determine body fat reserves in the dairy cow with special regard to ultrasonographic measurement of backfat thickness.
      ). The BCS was determined by the same person once every 2 wk from wk −8 to the end of the study (wk 44) using a scale from 1 to 5 (1 = emaciated, 5 = obese) in increments of 0.25 (
      • Edmonson A.J.
      • Lean I.J.
      • Weaver L.D.
      • Farver T.
      • Webster G.
      A body condition scoring chart for Holstein dairy cows.
      ).

      Analyses

      Milk protein and fat were analyzed by infrared spectrophotometry (MilkoScan FT6000, Foss, Hillerød, Denmark), and SCC was determined with a fluorescence optical counting system (Fossomatic FC, Foss) in the laboratories of Milchprüfring Bayern e.V. (Wolnzach, Germany). Serum concentrations of glucose, NEFA, BHBA, and total bilirubin (TB) were determined with an automated clinical chemistry analyzer (ABX Pentra 400, Horiba, Montpellier, France); precision of 20 measurements of 1 sample was expressed as the respective relative coefficient of variation. Glucose concentrations were analyzed by using hexokinase method (Hoffmann La-Roche, Basel, Switzerland; CV = 2.3%), NEFA concentrations were measured using colorimetric enzymatic reactions (CV = 6.2%), BHBA was determined using a spectrophotometric enzymatic analysis (Sigma-Aldrich Diagnostics, Munich, Germany; CV = 7.1%), and TB was determined with the Jandrassik/Grof reaction (
      • Jandrassik J.
      • Grof P.
      Quantitative determination of total and direct bilirubin in serum and plasma.
      ). Calibration and quality controls were done daily. The threshold values are based on
      • Macrae A.I.
      • Whitaker D.A.
      • Bourrough E.
      • Dowell A.
      • Kelly J.M.
      Use of metabolic profiles for the assessment of dietary adequacy in UK dairy herds.
      .

      Statistics

      End points measured repeatedly (daily milk yield, milk composition) were pooled to weekly means before statistical analysis. For BCS and backfat, an average value for every 4 wk from wk −8 to wk 40 was used.
      For any metabolic key parameters in blood, as for milk yield, percentage milk protein, milk fat content, and milk protein and fat yield, treatment effects, and differences among groups were determined using REML in the MIXED procedure in SAS (
      SAS Institute
      SAS/STAT User's Guide.
      ). The model contained fixed effects of treatment and week and random effects of cow within treatment. For the repeated measurements, the model also contained weeks relative to calving and the interaction between treatment and weeks relative to calving. The effects of time, group, and time × group interactions were tested.
      For each variable analyzed, 3 covariance structures were evaluated: compound symmetry, autoregressive order 1, and unstructured. The covariance structure of repeated measurements that resulted in the Akaike's information criterion or Schwarz's Bayesian criterion closest to zero was used (
      • Littell R.C.
      • Henry P.R.
      • Ammerman C.B.
      Statistical analysis of repeated measures data using SAS procedures.
      ). Differences between treatments were determined using the PDIFF option.
      Incidence of health disorders and the proportion of blood samples from wk 1 to 4 with low glucose, high NEFA, and high BHBA were tested for differences with PROC ANOVA using Dunnett's one-tailed t-test to locate differences. Results are reported as least squares means ± standard error of means. Means were considered to differ significantly in case of P < 0.05.

      Results

      Milk Yield

      Total lactational ECM yield (305 d) was highest for C cows (11,310 ± 601 kg of ECM). Compared with C cows, total ECM was 15.7 and 16.5% lower for ODM cows (9,531 ± 477 kg of ECM) and CM cows (9,447 ± 310 kg of ECM), respectively (Figure 1A; Table 3).
      Figure thumbnail gr1
      Figure 1A) Energy-corrected daily milk yield (kg/d), B) milk protein concentration (%), C) milk fat concentration (%), and D) SCC pattern (log10/mL) from wk −8 before parturition up to wk 44 of lactation for Brown Swiss dairy cows assigned to 1 of 3 management strategies: 56-d dry period (DP) and twice daily milking after parturition (control, C; ●), 56-d DP and once daily milking (ODM) for the first 28 d of lactation (♦), and 0-d DP with continuous milking (CM) twice daily throughout lactation (□). Asterisks indicate differences between C and CM; plus signs indicate differences between C and ODM (P < 0.05); circles indicate differences between ODM and CM. Values are LSM ± SEM. The gray box indicates time of different milking regimens in early lactation from 1 to 28 DIM.
      Table 3Energy-corrected milk yield (LSM ± SEM) during the last 56 d before calving for CM cows and for the first, second, and third 100-d interval of a 305-d lactation period compared among experimental groups
      Treatment group
      C=control group: cows were dried off 56 d before calving and milked twice daily throughout next lactation (305 d; n=12); ODM=once daily milking group: cows were dried off 56 d before calving and milked once daily for the first 4 wk of lactation and twice daily for the remaining lactation (n=12); CM=continuous milking group: cows were milked twice daily until calving and also during the subsequent lactation (n=12).
      P-value
      Means are different among groups (P<0.05).
      ItemCODMCMC vs. ODMC vs. CMODM vs. CM
      56 to 0 DIM
       Average/d21.2 ± 1.5
       Total1,186 ± 82
      1 to 100 DIM
       Average kg/d44.9 ± 2.837.6 ± 1.237.8 ± 0.90.0250.0210.99
       Total4,349 ± 2783,514 ± 903,706 ± 950.0020.0160.46
      101 to 200 DIM
       Average kg/d39.2 ± 1.932.5 ± 2.133.6 ± 1.30.0170.0050.6256
       Total3,987 ± 1863,323 ± 2123,434 ± 1310.0130.0400.67
      201 to 305 DIM
       Average kg/d31.8 ± 2.328.5 ± 2.325.0 ± 1.60.0430.0030.31
       Total2,975 ± 2302,694 ± 2292,306 ± 1540.290.0120.14
      305-d lactation yield
       Average kg/d38.2 ± 0.5632.4 ± 0.4130.5 ± 0.450.040.0050.12
       Total11,310 ± 6019,531 ± 4779,447 ± 3100.0130.0090.90
      1 C = control group: cows were dried off 56 d before calving and milked twice daily throughout next lactation (305 d; n = 12); ODM = once daily milking group: cows were dried off 56 d before calving and milked once daily for the first 4 wk of lactation and twice daily for the remaining lactation (n = 12); CM = continuous milking group: cows were milked twice daily until calving and also during the subsequent lactation (n = 12).
      2 Means are different among groups (P < 0.05).
      Total milk yield of CM cows from d −56 to parturition was 1,186 ± 82 kg of ECM. Daily ECM yield declined by 57.3% from wk −8 to wk −1 relative to calving. During the last week before calving, average daily milk yield of CM cows was 14.4 ± 2.1 kg of ECM. The average dry-off milk yield was 17.7 ± 2.0 kg/d for C cows and 17.4 ± 1.8 kg/d for ODM cows.
      Within the first 28 DIM, average daily milk yield was highest for C cows (43.3 ± 1.8 kg of ECM/d), which was 38% more than for ODM cows (31.3 ± 1.1 kg of ECM/d; P < 0.001) and 24% more than for CM cows (35.0 ± 1.1 kg of ECM/d; P = 0.005). During this time, ECM yield did not differ between ODM and CM cows. Milk yield for ODM cows increased from the start of twice daily milking at wk 5 (P < 0.001), but remained approximately 8.1 kg/d of ECM (18%) lower than for C cows (P = 0.01) until wk 8. From wk 5 to wk 20, ODM cows produced about 7.3 kg/d (15.7%) and CM cows about 6.5 kg/d (13.7%) less ECM than C cows. Yield of ECM peaked at wk 2 for C cows (46.4 ± 3.6 kg of ECM/d), at wk 5 for CM cows (39.4 ± 1.5 kg of ECM/d), and at wk 8 for ODM cows (38.4 ± 1.2 kg of ECM/d).

      Milk Composition

      Milk protein and milk fat content increased for CM cows from wk −8 to wk −1 relative to calving (3.90 ± 0.06% to 7.49 ± 0.41%, P < 0.001, and 5.20 ± 0.18% to 6.42 ± 0.35%, P = 0.001, for milk protein and milk fat content, respectively; Figure 1B and C). From wk −8 to wk −1, daily fat yield decreased (1.02 ± 0.40 kg/d to 0.64 ± 0.31 kg/d; P < 0.01) in milk of CM cows, whereas daily protein yield remained constant (0.75 ± 0.26 kg/d to 0.71 ± 0.32 kg/d; P = 0.19).
      Milk protein concentration decreased steeply for C cows from wk 1 (4.91 ± 0.8%) to wk 4 (3.05 ± 0.23%; P < 0.001). For the first 4 wk postpartum, milk protein concentration was higher in both ODM cows (3.97 ± 1.07%; P = 0.041) and CM cows (4.06 ± 0.63%; P = 0.009) compared with C cows (3.65 ± 0.12%). However, reduced milk volume for ODM cows resulted in lower daily protein yield for these cows (0.83 ± 0.22 kg/d) compared with C cows (1.13 ± 0.3 kg/d; P = 0.007) and CM cows (1.15 ± 0.14 kg/d; P = 0.007). The CM cows had a higher weekly milk protein concentration for the first 20 wk of lactation compared with C cows (3.85 ± 0.07% vs. 3.34 ± 0.07%; P = 0.005).
      During the first 4 wk of lactation, milk fat concentration was highest for ODM cows (7.67 ± 0.20%) compared with C cows (7.07 ± 0.20%; P < 0.02) and CM cows (5.84 ± 0.13%; P < 0.001; Figure 1C). Daily fat yield was 36% higher for C cows (2.23 ± 0.73 kg/d) compared with ODM cows (1.64 ± 0.47 kg/d; P < 0.001) and 33% higher compared with CM cows (1.68 ± 0.32 kg/d; P < 0.001; Table 4).
      Table 4Milk protein yield, milk fat yield, milk protein concentration, and milk fat concentration (LSM ± SEM) compared among treatment groups for 305-d lactation
      Data in relation to control (set 100) are given in parentheses.
      ItemTreatment group
      C=control group: cows were dried off 56 d before calving and milked twice daily throughout next lactation (305 d; n=12); ODM=once daily milking group: cows were dried off 56 d before calving and milked once daily for the first 4 wk of lactation and twice daily for the remaining lactation (n=12); CM=continuous milking group: cows were milked twice daily until calving and also during the subsequent lactation (n=12). CM+=CM group, but for calculation of LSM of total lactation values, the extra days of milking (from wk −8 up to day of calving) were included. Values in parentheses represent the timeframe relative to calving from which data were obtained.
      P-value
      Means are different among groups (P<0.05).
      CODMCM (1 to 305 DIM)CM+ (−56 to 305 DIM)ODM vs. CMC vs. ODMC vs. CMC vs. CM+
      Protein, %3.52 ± 0.3 (100)3.79 ± 0.41 (107)3.91 ± 0.28 (110)4.04 ± 0.27 (115)0.070.06<0.001<0.001
      Fat, %5.50 ± 0.2 (100)5.15 ± 0.1 (94)4.70 ± 0.1 (85)5.33 ± 0.30 (97)0.030.05<0.0010.13
      Protein yield, kg342 ± 15 (100)311 ± 16 (91)325 ± 12 (95)367 ± 14 (107)0.520.140.390.26
      Fat yield, kg541 ± 37 (100)437 ± 23 (81)417 ± 16 (77)484 ± 25 (89)0.9240.0060.0050.13
      Daily fat yield, kg1.87 ± 0.081.42 ± 0.081.38 ± 0.081.26 ± 0.080.780.0020.004<0.001
      Daily protein yield, kg1.08 ± 0.050.99 ± 0.051.10 ± 0.041.03 ± 0.050.090.810.150.07
      SCC, log10 cells/mL5.06 ± 0.085.10 ± 0.085.13 ± 0.085.15 ± 0.080.790.770.570.59
      1 Data in relation to control (set 100) are given in parentheses.
      2 C = control group: cows were dried off 56 d before calving and milked twice daily throughout next lactation (305 d; n = 12); ODM = once daily milking group: cows were dried off 56 d before calving and milked once daily for the first 4 wk of lactation and twice daily for the remaining lactation (n = 12); CM = continuous milking group: cows were milked twice daily until calving and also during the subsequent lactation (n = 12). CM+ = CM group, but for calculation of LSM of total lactation values, the extra days of milking (from wk −8 up to day of calving) were included. Values in parentheses represent the timeframe relative to calving from which data were obtained.
      3 Means are different among groups (P < 0.05).
      Somatic cell count differed only at wk 1 between cows in group C (5.34 ± 0.4 log10SCC) and group ODM (5.47 ± 0.4 log10SCC; P = 0.042). No differences were found for SCC among treatment groups at any other time points (Figure 1D).

      Health and Occurrence of Diseases

      Five C cows, 2 ODM cows, and 3 CM cows suffered from clinical mastitis; 2 of the latter had infections of the udder during the last week before calving. A retained placenta was observed in 2 C cows, 5 ODM cows, and 1 CM cow. One ODM cow suffered from clinical hypocalcemia, and primary ketosis was diagnosed in 3 C cows. Two each of C and ODM cows became lame (Table 5).
      Table 5Occurrence of diseases (number of events) in the treatment groups during study
      Data in parentheses indicate the first day of diagnosis in relation to calving.
      DiagnosisTreatment group
      C=control group: cows were dried off 56 d before calving and milked twice daily throughout next lactation (305 d; n=12); ODM=once daily milking group: cows were dried off 56 d before calving and milked once daily for the first 4 wk of lactation and twice daily for the remaining lactation (n=12); CM=continuous milking group: cows were milked twice daily until calving and also during the subsequent lactation (n=12).
      P-value
      Means are different among groups (P<0.05).
      CODMCM
      Mastitis5 (3, 15, 109, 248, 263)2 (61, 118)3 (−7, −5, 60)0.47
      Retained placenta2 (1)5 (1)1 (1)0.61
      Hypocalcemia01 (1)00.56
      Ketosis3 (13, 31, 32)000.18
      Lameness2 (33, 53)2 (86, 88)00.21
      1 Data in parentheses indicate the first day of diagnosis in relation to calving.
      2 C = control group: cows were dried off 56 d before calving and milked twice daily throughout next lactation (305 d; n = 12); ODM = once daily milking group: cows were dried off 56 d before calving and milked once daily for the first 4 wk of lactation and twice daily for the remaining lactation (n = 12); CM = continuous milking group: cows were milked twice daily until calving and also during the subsequent lactation (n = 12).
      3 Means are different among groups (P < 0.05).

      Blood Analysis

      Before Parturition

      Before parturition there were no differences in serum concentration of glucose, NEFA, BHBA, and TB among treatment groups except during the last week before calving, when serum NEFA concentrations were higher for ODM cows compared with CM cows (467 ± 88 μmol/L vs. 216 ± 79 μmol/L; P = 0.025).

      At Parturition

      Serum glucose concentration did not differ between groups at parturition. The C cows and ODM cows had higher blood NEFA concentrations compared with CM cows. The C cows had similar blood BHBA concentrations compared with ODM cows but higher blood BHBA concentrations compared with CM cows. Total bilirubin was highest for ODM cows compared with C and CM cows (Figure 2A, B, C, and D; Table 6).
      Figure thumbnail gr2
      Figure 2A) NEFA, B), BHBA, C) total bilirubin (TB), and D) glucose concentrations in blood of cows assigned to 1 of 3 different management strategies: 56-d dry period (DP) and twice daily milking after parturition (control, C; ●), 56-d DP and once daily milking (ODM) for the first 28 d of lactation (♦), and 0-d DP with continuous milking (CM) twice daily throughout lactation (□). Asterisks indicate that blood serum concentrations differed between C and CM; plus signs indicate that blood serum concentrations differed between C and ODM; circles indicate that blood serum concentrations differed between ODM and CM (P < 0.05). Values are LSM ± SEM. The gray box indicates time of different milking regimens.
      Table 6Least squares means ± SEM of serum metabolites of dairy cows managed with different milking regimens during dry period and early lactation
      ItemTreatment group
      C=control group: cows were dried off 56 d before calving and milked twice daily throughout next lactation (305 d; n=12); ODM=once daily milking group: cows were dried off 56 d before calving and milked once daily for the first 4 wk of lactation and twice daily for the remaining lactation (n=12); CM=continuous milking group: cows were milked twice daily until calving and also during the subsequent lactation (n=12).
      P-value
      Means are different among groups (P<0.05).
      CODMCMC vs. ODMC vs. CMODM vs. CM
      Glucose, mmol/L
       Before parturition3.50 ± 0.113.51 ± 0.123.44 ± 0.110.960.730.70
       At parturition3.56 ± 0.253.76 ± 0.153.74 ± 0.150.220.510.58
       Wk 1 to 42.95 ± 0.13.29 ± 0.13.39 ± 0.050.040.010.63
       Wk 5 to 83.23 ± 0.113.49 ± 0.073.46 ± 0.070.0890.10.92
       Wk 12 to 443.55 ± 0.083.56 ± 0.093.64 ± 0.080.890.390.50
      NEFA, μmol/L
       Before parturition177 ± 50257 ± 51170 ± 490.270.920.22
       At parturition831 ± 71868 ± 71414 ± 750.48<0.001<0.001
       Wk 1 to 4778 ± 45435 ± 46266 ± 45<0.001<0.0010.008
       Wk 5 to 8389 ± 52172 ± 51137 ± 520.004<0.0010.62
       Wk 12 to 44110 ± 133129 ± 3891 ± 370.700.700.47
      BHBA, mmol/L
       Before parturition0.48 ± 0.070.40 ± 0.070.48 ± 0.070.800.520.86
       At parturition0.85 ± 0.090.72 ± 0.090.53 ± 0.090.06<0.0010.14
       Wk 1 to 41.28 ± 0.060.65 ± 0.060.43 ± 0.06<0.001<0.0010.02
       Wk 5 to 80.72 ± 0.070.57 ± 0.070.39 ± 0.070.150.0020.08
       Wk 12 to 440.49 ± 0.040.47 ± 0.050.44 ± 0.050.770.490.71
      TB,
      TB=total bilirubin.
      mmol/L
       Before parturition3.62 ± 0.463.56 ± 0.463.28 ± 0.450.920.590.67
       At parturition7.51 ± 0.589.59 ± 0.604.24 ± 0.600.026<0.001<0.001
       Wk 1 to 46.38 ± 0.425.27 ± 0.423.23 ± 0.410.07<0.0010.007
       Wk 5 to 85.23 ± 0.473.06 ± 0.473.78 ± 0.470.0020.0330.28
       Wk 12 to 444.25 ± 0.293.68 ± 0.333.39 ± 0.340.20.060.54
      1 C = control group: cows were dried off 56 d before calving and milked twice daily throughout next lactation (305 d; n = 12); ODM = once daily milking group: cows were dried off 56 d before calving and milked once daily for the first 4 wk of lactation and twice daily for the remaining lactation (n = 12); CM = continuous milking group: cows were milked twice daily until calving and also during the subsequent lactation (n = 12).
      2 Means are different among groups (P < 0.05).
      3 TB = total bilirubin.

      Wk 1 to 4 Postpartum

      Blood glucose concentration was lowest for C cows for the first 2 wk of lactation (2.62 ± 0.82 mmol/L at wk 1 and 2.72 ± 0.81 mmol/L at wk 2) compared with CM cows (3.29 ± 0.27 mmol/L at wk 1, P = 0.006, and 3.40 ± 0.30 mmol/L at wk 2, P < 0.001) and ODM cows (3.16 ± 0.5 mmol/L at wk 1, P = 0.032, and 3.29 ± 0.32 mmol/L at wk 2, P < 0.005; Figure 2D; Table 6). On average during the first 4 wk of lactation, blood glucose concentration was lowest for C cows compared with ODM and CM cows. During the first 4 wk of lactation, blood serum NEFA concentrations were 44% lower for ODM cows and 66% lower for CM cows compared with C cows. Like NEFA, blood BHBA concentrations for C cows were approximately twice as high as for ODM cows and approximately thrice as high as for CM cows. Simultaneously, CM cows had about half the TB blood concentration of C cows. The latter was comparable to the TB concentration measured in blood serum of ODM cows (Figure 2A, B, and C; Table 6).
      Furthermore, considering blood samples collected in wk 1, 2, and 4 of lactation, a proportion of samples was assessed in which established alarm levels of metabolic key parameters in herd medicine were exceeded. A higher percentage of C cows exhibited hypoglycemia compared with ODM and CM cows (47, 20, and 14%, respectively; P < 0.05). Moreover, the proportion of C cows with excessive lipomobilization and ketonemia was higher compared with those of the other treatment groups (Table 7).
      Table 7Percentage of blood samples (36 samples/group) collected in wk 1, 2, and 4 of lactation exceeding established alarm levels of metabolic key parameters in herd medicine of all treatment groups
      ParameterThreshold value
      Threshold values are based on our own experience and data of Macrae et al. (2006).
      Treatment group
      C=control group: cows were dried off 56 d before calving and milked twice daily throughout next lactation (305 d; n=12); ODM=once daily milking group: cows were dried off 56 d before calving and milked once daily for the first 4 wk of lactation and twice daily for the remaining lactation (n=12); CM=continuous milking group: cows were milked twice daily until calving and also during the subsequent lactation (n=12).
      P-value
      Means are different among groups (P<0.05).
      CODMCMC vs. ODMC vs. CMCM vs. ODM
      Glucose≤3.0 mmol/L47.120.013.9<0.001<0.0010.81
      BHBA≥1.4 mmol/L29.42.90<0.001<0.0010.62
      NEFA≥700 μmol/L41.217.18.30.012<0.0010.9
      1 Threshold values are based on our own experience and data of
      • Macrae A.I.
      • Whitaker D.A.
      • Bourrough E.
      • Dowell A.
      • Kelly J.M.
      Use of metabolic profiles for the assessment of dietary adequacy in UK dairy herds.
      .
      2 C = control group: cows were dried off 56 d before calving and milked twice daily throughout next lactation (305 d; n = 12); ODM = once daily milking group: cows were dried off 56 d before calving and milked once daily for the first 4 wk of lactation and twice daily for the remaining lactation (n = 12); CM = continuous milking group: cows were milked twice daily until calving and also during the subsequent lactation (n = 12).
      3 Means are different among groups (P < 0.05).
      From wk 5 to 8, glucose concentration did not differ between groups. Concentrations of NEFA and TB were higher for C cows than for ODM cows and CM cows. Blood serum BHBA concentrations were higher in C cows than in CM cows (Figure 2A, B, C, and D; Table 6). No differences between treatment groups were obvious for any of the analyzed blood parameters from wk 12 to 44.

      Backfat Thickness and BCS

      Backfat thickness was not different among treatments at any time point (Figure 3A). It declined from mo −2 before to mo 2 after calving by 24, 19, and 25% for C, ODM, and CM cows, respectively (i.e., a decrease of on average 5.8 ± 0.7 mm; P < 0.001). After calving, backfat thickness declined from mo 1 to 4 by approximately 40% for C cows (21.4 ± 2.3 to 13.1 ± 1.9 mm; P < 0.001) and by 17% for ODM cows (23.7 ± 3.3 to 19.6 ± 3.9 mm; P = 0.06). The C cows exhibited the most pronounced decrease between calving and mo 3 of lactation, followed by an increase of backfat thickness until mo 10 of lactation by 63% (15.6 ± 2.3 to 25.4 ± 3.3 mm; P < 0.001). Backfat thickness increased from mo 4 of lactation to mo 10 in ODM cows by approximately 28% (22.0 ± 3.8 to 29.4 ± 3.2 mm; P < 0.001). For CM cows, increase of backfat thickness started 2 mo earlier compared with ODM cows already at wk 6; backfat thickness increased by 74% (15.7 ± 2.1 to 27.3 ± 2.7 mm; P < 0.001).
      Figure thumbnail gr3
      Figure 3Changes of backfat thickness and BCS from month −2 before parturition to mo 10 of lactation for cows assigned to 1 of 3 different management strategies: 56-d dry period (DP) and twice daily milking after parturition (control, C; ●), 56-d DP and once daily milking (ODM) for the first 28 d of lactation (♦), and 0-d DP and continuous milking (CM) twice daily throughout lactation (□). Asterisks indicate differences between C and CM; plus signs indicate differences between C and ODM (P < 0.05).
      Before calving, BCS did not differ between C cows at mo −2 (3.7 ± 0.3) and mo −1 (4.0 ± 0.5) relative to calving compared with CM cows (3.5 ± 0.4, P = 0.84, and 3.6 ± 0.5, P = 0.23 for mo −2 and −1, respectively) and ODM cows (3.7 ± 0.51, P = 0.51, and 3.8 ± 0.4, P = 0.11 for mo −2 and −1, respectively; Figure 3B). The BCS was lower in the first month of lactation in C cows compared with ODM cows (2.9 ± 0.5 vs. 3.39 ± 0.5; P = 0.022) and CM cows (3.3 ± 0.5; P = 0.03). Decrease of BCS between the first and the third month of lactation was most pronounced in C cows (0.31 ± 0.09; P < 0.001). A smaller reduction in BCS was found for ODM cows (0.20 ± 0.09; P = 0.92) and CM cows (0.16 ± 0.09; P = 0.08). The BCS of CM cows steadily increased between the first (3.1 ± 0.2) and tenth (3.6 ± 0.1) month of lactation (P = 0.004). For C cows, BCS increased by 24% between the third (2.9 ± 0.1) and the tenth (3.6 ± 0.2) month of lactation (P < 0.001), whereas BCS for ODM cows increased in this timeframe by 15% (3.3 ± 0.5 to 3.8 ± 0.6; P = 0.004).

      Discussion

      The objective was to characterize the effects of 2 different approaches adopted to reduce metabolic stress throughout the transition period in high-yielding dairy cows. Brown Swiss cows for the treatment groups were recruited from the Technische Universitaet Muenchen herd in which the breeding strategy for a decade was designed to maximize milk protein. Thereby, the protein percentage in the University herd's tank milk (mean during the last 15 yr: 3.69%) is somewhat higher than that of the German Holstein population (roughly 3.38%). Furthermore, the implementation of a transponder-based concentrate feeding system and the availability of a superior maize silage induced a significant increase in milk yield during the experimental period compared with former years.
      Nine out of 45 cows left the herd because of severe health problems during the study period; this culling rate (20%) was similar to that of previous investigations (
      • Reist M.
      • Erdin D.K.
      • von Euw E.D.
      • Tschümperlin K.M.
      • Leuenberger H.
      • Hammon H.M.
      • Morel C.
      • Philipona C.
      • Zbinden Y.
      • Künzi N.
      • Blum J.W.
      Postpartum reproductive function: Association with energy, metabolic and endocrine status in high yielding dairy cows.
      ). Nevertheless, the remaining group size (n = 12 cows/group) allowed the investigation of treatment effects for blood serum parameters and parameters of milk yield and composition with a statistical power of 0.8 based on previously obtained standard deviations and generally accepted differences of means. However, the present experimental design did not provide sufficient statistical power to evaluate possible differences among groups for health disorders. Statistical power analysis revealed that at least 38 cows for each group were needed for unbiased statistical comparisons of health disorders.
      Because of the limited group size, the lower incidence of diseased CM cows compared with C cows did not allow the suggestion that this is a valid difference. Three C cows, but no CM cows, suffered from ketosis; however, with 12 animals used for each treatment, no differences could be confirmed at a significance level of 0.05.

      Continuous Milking Compared with a 56-d DP and Twice Daily Milking During Lactation

      Milk Yield

      Yield of ECM from CM cows averaged 21.2 ± 1.5 kg/d during the last 8 wk before calving. For 1 cow, however, milk yield decreased to less than 3 kg/d in the last week before calving. Two cows developed clinical mastitis at d −7 and −5 and dried off independently at d −2 relative to calving. That contrasts with the observation that up to 50% of all cows assigned to CM dry off between 7 and 2 d prepartum (
      • Andersen J.B.
      • Madsen T.G.
      • Larsen T.
      • Ingvartsen K.L.
      • Nielsen M.O.
      The effects of dry period versus continuous lactation on metabolic status and performance in periparturient cows.
      ;
      • Madsen T.G.
      • Nielsen M.O.
      • Andersen J.B.
      • Ingvartsen K.L.
      Continuous lactation in dairy cows: Effect on milk production and mammary nutrient supply and extraction.
      ).
      In our study, the 305-d lactation ECM yield was 17% lower in CM cows compared with C cows. This result was comparable with the depression in milk yield systematically entailed by the omission of the DP, as described in the literature (
      • Swanson E.W.
      Comparing continuous milking with sixty-day dry periods in successive lactations.
      ;
      • Farries E.
      • Hoheisel S.
      The influence of reduced dry periods on some performance and metabolism traits in dairy cows.
      ;
      • Rémond B.
      • Ollier A.
      • Miranda G.
      Milking of cows in late pregnancy: Milk production during this period and during the succeeding lactation.
      ).
      • Rémond B.
      • Rouel J.
      • Pinson N.
      • Jabet S.
      An attempt to omit the dry period over three consecutive lactations in dairy cows.
      assumed that high-producing cows are less sensitive to this management system compared with lower producing cows. Our results using cows of high genetic merit did not confirm this hypothesis. This result is in accordance with
      • Andersen J.B.
      • Madsen T.G.
      • Larsen T.
      • Ingvartsen K.L.
      • Nielsen M.O.
      The effects of dry period versus continuous lactation on metabolic status and performance in periparturient cows.
      . In fact, involution, proliferation, and differentiation of mammary parenchyma during DP represent decisive preconditions for a high subsequent lactation yield (
      • Capuco A.V.
      • Akers R.M.
      • Smith J.J.
      Mammary growth in Holstein cows during the dry period: Quantification of nucleic acids and histology.
      ) independently of the genetic merit of the cow (
      • Smith A.
      • Wheelock J.V.
      • Dodd F.H.
      Effect of milking throughout pregnancy on milk yield in the succeeding lactation.
      ;
      • Andersen J.B.
      • Madsen T.G.
      • Larsen T.
      • Ingvartsen K.L.
      • Nielsen M.O.
      The effects of dry period versus continuous lactation on metabolic status and performance in periparturient cows.
      ). Accordingly, continuously milking over more than 2 successive lactations reveals more severe production losses (18–29%) in the subsequent lactation (
      • Rémond B.
      • Rouel J.
      • Pinson N.
      • Jabet S.
      An attempt to omit the dry period over three consecutive lactations in dairy cows.
      ). The depression of milk yield is caused primarily by an impaired functionality of mammary parenchyma (
      • Annen E.L.
      • Collier R.J.
      • McGuire M.A.
      • Vicini J.L.
      Effects of dry period length on milk yield and mammary epithelial cells.
      ).

      Effects of Continuous Milking on Metabolic Profile

      Glucose is a key molecule in ruminant metabolism (e.g., in lactogenesis;
      • Guinard-Flament J.
      • Delamaire E.
      • Lemosquet S.
      • Boutinaud M.
      • David Y.
      Changes in mammary uptake and metabolic fate of glucose with once-daily milking and feed restriction in dairy cows.
      ). Blood glucose concentration reflects the balance between glucose input and output. Hypoglycemia is prevented under physiologic conditions by the effects of different hormones including glucagon, catecholamines, glucocorticoids, and the GH-IGF-I system. In our study, 47% of serum samples collected between wk 1 and 4 from C cows revealed hypoglycemia (<3.0 mmol/L; Table 7). In contrast, only 14% of samples of CM cows collected from wk 1 to 4 revealed hypoglycemia (Table 7). The sustained physiological serum glucose levels in early lactation for CM cows indicate a more stable metabolic status and lower blood serum NEFA concentrations. Similar results were reported by
      • Rastani R.R.
      • Del Rio N.S.
      • Gressley T.F.
      • Dahl G.E.
      • Grummer R.R.
      Effects of increasing milking frequency during the last 28 days of gestation on milk production, dry matter intake, and energy balance in dairy cows.
      during the first week of lactation and by
      • Andersen J.B.
      • Madsen T.G.
      • Larsen T.
      • Ingvartsen K.L.
      • Nielsen M.O.
      The effects of dry period versus continuous lactation on metabolic status and performance in periparturient cows.
      and
      • Madsen T.G.
      • Nielsen M.O.
      • Andersen J.B.
      • Ingvartsen K.L.
      Continuous lactation in dairy cows: Effect on milk production and mammary nutrient supply and extraction.
      during the first 5 wk of lactation for CM cows compared with C cows milked twice daily after a 56-d DP. Because higher NEFA serum concentrations of C cows reflect a higher rate of lipolysis in adipose tissue (
      • Mashek D.G.
      • Grummer R.R.
      Effects of long chain fatty acids on lipid and glucose metabolism in monolayer cultures of bovine hepatocytes.
      ), continuous milking is accompanied by reduced lipomobilization in fresh parturient cows. Simultaneously, serum BHBA concentrations were higher in C cows compared with CM cows because, in case of large amounts of NEFA entering the hepatocytes, ketogenesis represents an alternative metabolic pathway in hepatic mitochondria (
      • Heitmann R.N.
      • Fernandez J.M.
      Autoregulation of alimentary and hepatic ketogenesis in sheep.
      ). Differences in serum concentration of glucose and BHBA suggest an improved metabolic status for CM cows in early lactation.
      The DMI of CM cows was found to be similar (
      • Andersen J.B.
      • Madsen T.G.
      • Larsen T.
      • Ingvartsen K.L.
      • Nielsen M.O.
      The effects of dry period versus continuous lactation on metabolic status and performance in periparturient cows.
      ) or even higher (
      • Rastani R.R.
      • Grummer R.R.
      • Bertics S.J.
      • Gumen A.
      • Wiltbank M.C.
      • Mashek D.G.
      • Schwab M.C.
      Reducing dry period length to simplify feeding transition cows: Milk production, energy balance, and metabolic profiles.
      ) compared with 56-d dry cows. Usually, DP includes diet changes associated with facility and grouping changes. These management changes may contribute to a reduction of DMI. Feeding the same diet throughout the entire lactation–gestation cycle may reduce nutritional stress because of less frequent dietary changes at prepartum and may improve energy status in cows with short or no DP. Further on, lower postpartum milk yield of CM cows may contribute to reduced metabolic stress.

      Effects of Continuous Milking on Milk Yield, Milk Composition, and Body Condition

      The present study indicated an increased lactational milk protein concentration in CM cows (3.91 ± 0.28%) compared with C cows (3.52 ± 0.3%) in agreement with earlier results (
      • Rémond B.
      • Pomiès D.
      • Dupont D.
      • Chilliard Y.
      Once-a-day milking of multiparous Holstein cows throughout the entire lactation: Milk yield and composition, and nutritional status.
      ). This difference was apparent throughout the entire lactation as indicated by an average milk protein content of more than 4.0% for the last 6 wk of lactation in CM cows. The increased milk protein content in early lactation indicates improved availability of energy attributable to a reduced milk yield (
      • Rémond B.
      • Rouel J.
      • Pinson N.
      • Jabet S.
      An attempt to omit the dry period over three consecutive lactations in dairy cows.
      ) because milk protein content is considered an indicator for energy supply in a herd monitoring system. It is indeed well established that improvement in the energy balance increases the protein content of milk. Regarding the total produced protein yield, CM cows produced about 25 kg more milk protein than C cows because of being milked in late pregnancy. During this time, while C and ODM cows were dried off, CM cows produced about 42 kg of milk protein. In addition to the high milk protein content throughout lactation, cows of this group produced the highest lactational milk protein yield from d 56 before parturition to the end of lactation.
      However, the quality of the colostrum is poor in continuously milked goats (
      • Caja G.
      • Salama A.A.
      • Such X.
      Omitting the dry-off period negatively affects colostrum and milk yield in dairy goats.
      ) and cows (
      • Annen E.L.
      • Collier R.J.
      • McGuire M.A.
      • Vicini J.L.
      Effects of dry period length on milk yield and mammary epithelial cells.
      ) because an accumulation of immunoglobulin level requires prolonged secretion in the mammary gland before calving (
      • Wheelock J.V.
      • Rook J.A.F.
      • Dodd F.H.
      The effect of milking throughout the whole pregnancy on the composition of cow's milk.
      ). Furthermore, there is concern about higher SCC levels in milk of CM cows because SCC was increased in late pregnancy for CM cows, particularly the last week before calving (
      • Farries E.
      • Hoheisel S.
      The influence of reduced dry periods on some performance and metabolism traits in dairy cows.
      ;
      • Rémond B.
      • Ollier A.
      • Miranda G.
      Milking of cows in late pregnancy: Milk production during this period and during the succeeding lactation.
      ). In our study, SCC of CM cows did not differ from that of C cows in either early lactation or during the entire lactation. There were 2 cows with mastitis at d −7 and −1 relative to calving; this may have been caused by the very low milk yield for these cows (<2 kg/d) followed by a lack of intramammary pressure, longer stripping times, and, as a consequence, a higher risk for mastitis for these cows, which are known to be immunosuppressed before and after calving.
      In late pregnancy, the milk was progressively enriched with fat and protein, as found by
      • Wheelock J.V.
      • Rook J.A.F.
      • Dodd F.H.
      The effect of milking throughout the whole pregnancy on the composition of cow's milk.
      and
      • Rémond B.
      • Bonnefoy J.C.
      Performance of a herd of Holstein cows managed without the dry period.
      . Postpartum milk fat concentration was lower for CM cows compared with C cows for the first 5 wk of lactation. This is in contrast with
      • Rastani R.R.
      • Grummer R.R.
      • Bertics S.J.
      • Gumen A.
      • Wiltbank M.C.
      • Mashek D.G.
      • Schwab M.C.
      Reducing dry period length to simplify feeding transition cows: Milk production, energy balance, and metabolic profiles.
      , who observed that milk fat percentage increased from 3.86 to 4.08% when DP was reduced from 56 to 28 d. The higher milk fat content of C cows in our study may have been caused by a higher infiltration of long-chain fatty acids from blood into milk fat, as found for periparturient cows with a strong lipolysis (
      • Bauman D.E.
      • Mather I.H.
      • Wall R.J.
      • Lock A.L.
      Major advances associated with the biosynthesis of milk.
      ).
      The moderate decrease of BCS and backfat in CM cows in early lactation may be the consequence of an improved metabolic status for these cows as indicated by higher glucose, lower BHBA and NEFA concentrations, and higher milk protein content. The C cows, on the other hand, started into early lactation with a BCS of more than 3.5. Thus, these cows seemed to have been overfed during the DP, which is a well-known explanation for postpartum depression of appetite causing stronger lipolysis and proteolysis. The resulting sharp decrease of backfat and BCS was clearly recognizable in C cows (Figure 3).

      Once Daily Milking During the First 4 Wk of Lactation Compared with a 56-d DP and Twice Daily Milking During Lactation

      Our approach to implementing once daily milking was to improve the metabolic situation of high-yielding dairy cows after calving in a high-cost, high-return production system. This is contrast to most other studies testing the effects of once daily milking that focus on the implementation of once daily milking to improve quality of life of the farmer or as a tool to increase labor productivity, for example, in low-cost, low-return dairy systems in New Zealand (
      • Clark D.A.
      • Phyn C.V.
      • Tong M.J.
      • Collis S.J.
      • Dalley D.E.
      A systems comparison of once- versus twice-daily milking of pastured dairy cows.
      ). Few studies exist in which once daily milking was implemented during early lactation (
      • Carruthers V.R.
      • Davis S.R.C.P.J.A.
      Response of Jersey and Friesian cows to once a day milking and prediction of response based on udder characteristics and milk composition.
      ;
      • Stelwagen K.
      • Knight C.H.
      Effect of unilateral once or twice daily milking of cows on milk yield and udder characteristics in early and late lactation.
      ). Interestingly, high-producing cows do not necessarily exhibit greater reductions of milk yield because of once daily milking compared with substandard cows (
      • Davis S.R.
      • Farr V.C.
      • Stelwagen K.
      Regulation of yield loss and milk composition during once-daily milking: A review.
      ). During once daily milking compared with twice daily milking, a reduction in milk yield of 19% on average is well established (
      • Davis S.R.
      • Farr V.C.
      • Stelwagen K.
      Regulation of yield loss and milk composition during once-daily milking: A review.
      ).
      Only 1 recent study compared the effects of once daily milking with thrice daily milking on the energy status of the dairy cow in early lactation (
      • Patton J.
      • Kenny D.A.
      • Mee J.F.
      • O’Mara F.P.
      • Wathes D.C.
      • Cook M.
      • Murphy J.J.
      Effect of milking frequency and diet on milk production, energy balance, and reproduction in dairy cows.
      ). In that study, however, the production level was much lower compared with that of the high-yielding dairy cows used in our trial.

      Effects of Once Daily Milking on Metabolism and Body Condition

      Interestingly, in the study presented here, once daily milking had almost similar effects as continuous milking on metabolism and productivity in the subsequent lactation, but the effects were obviously attributable to different causes. The blood concentrations of metabolic key parameters did not differ during the first 4 wk of lactation from those of CM cows but were lower compared with C cows. In particular, the decrease of serum glucose concentration at wk 2 observed in C cows was not observed in ODM cows (Figure 2D). The higher blood serum glucose concentrations for ODM cows indicated less severe metabolic stress compared with those of C cows. The results are in agreement with previous studies that demonstrated that once daily milking for about 4 wk in early lactation results in reduced milk yield and less metabolic stress (
      • Davis S.R.
      • Farr V.C.
      • Stelwagen K.
      Regulation of yield loss and milk composition during once-daily milking: A review.
      ). At calving, ODM cows had blood NEFA concentrations more than twice as high as CM cows. At this time, ODM cows are in practically the same metabolic situation as C cows. However, just 1 wk after calving, ODM cows had higher blood glucose concentrations and lower NEFA and BHBA blood concentrations compared with C cows. The ODM cows lost less body reserves during early lactation than reported elsewhere (
      • Rémond B.
      • Aubailly S.
      • Chilliard Y.
      • Dupont D.
      • Pomies D.
      • Petit M.
      Combined effects of once-daily milking and feeding level in the first three weeks of lactation on milk production and enzyme activities, and nutritional status, Holstein cows.
      ). Even after switching to twice daily milking starting at wk 5 of lactation, body weight loss in the subsequent months was less pronounced in ODM cows compared with C and CM cows.
      • Rémond B.
      • Pomiès D.
      • Dupont D.
      • Chilliard Y.
      Once-a-day milking of multiparous Holstein cows throughout the entire lactation: Milk yield and composition, and nutritional status.
      found that BW and BCS of cows milked once daily were gradually improved compared with those of cows milked twice daily at wk 36 of lactation.

      Effects of Once Daily Milking on Animal Welfare and Health

      Animal well-being during once daily milking in fresh cows is an important issue. Generally, it is observed that high-yielding dairy cows wait near the milking parlor before milking time and seem to expect milking, probably because of high intramammary pressure. In our study, however, we did not observe in ODM cows any indicators revealing severe discomfort, a finding in agreement with other research (
      • Davis S.R.
      • Farr V.C.
      • Stelwagen K.
      Regulation of yield loss and milk composition during once-daily milking: A review.
      ;
      • Rémond B.
      • Pomiès D.
      • Dupont D.
      • Chilliard Y.
      Once-a-day milking of multiparous Holstein cows throughout the entire lactation: Milk yield and composition, and nutritional status.
      ;
      • Tucker C.B.
      • Dalley D.E.
      • Burke J.L.
      • Clark D.A.
      Milking cows once daily influences behavior and udder firmness at peak and mid lactation.
      ). One of the 12 cows mooed and lowed during the first few days of once daily milking treatment before and during afternoon milking, but after 3 d the animal accepted once daily milking without problems. There were 2 leaking cows in this group; 1 leaked because of teat damage. A typical concern in respect to once daily milking is udder health because udder distension in cows milked once daily may lead to a higher probability of inflammatory responses. One study indicated a doubled SCC in comparison with twice daily milking when cows were milked once daily for a longer time (
      • Lacy-Hulbert S.J.
      • Dalley D.E.
      • Clark D.A.
      The effects of once a day milking on mastitis and somatic cell count.
      ). However, no differences were obvious in the incidence of mastitis for ODM cows compared with C or CM cows in our study, which corresponded with others (
      • Clark D.A.
      • Phyn C.V.
      • Tong M.J.
      • Collis S.J.
      • Dalley D.E.
      A systems comparison of once- versus twice-daily milking of pastured dairy cows.
      ).
      • Rémond B.
      • Pomiès D.
      • Dupont D.
      • Chilliard Y.
      Once-a-day milking of multiparous Holstein cows throughout the entire lactation: Milk yield and composition, and nutritional status.
      found no differences in mean SCC between once and twice daily milking despite a sharp increase noted for cows milked once daily during the last third of lactation.
      • Loiselle M.C.
      • Ster C.
      • Talbot B.G.
      • Zhao X.
      • Wagner G.F.
      • Boisclair Y.R.
      • Lacasse P.
      Impact of postpartum milking frequency on the immune system and the blood metabolite concentration of dairy cows.
      found differences neither for SCC nor for chemotaxis, phagocytosis, or oxidative burst activity during once daily milking in the first week postpartum compared with twice daily milking or thereafter up to wk 14 of lactation.
      Despite the similar body condition of ODM and C cows at calving, ODM cows lost less body reserves at the onset of lactation (Figure 3B) than did C cows. The improved nutritional and metabolic condition status of ODM cows is also reflected by a lower frequency of hypoglycemia during the first 4 wk of lactation compared with C cows.

      Effects of Once Daily Milking on Productivity

      The obvious reduction of total lactation ECM yield by 16% for ODM cows compared with C cows was primarily attributable to the reduced yield during the first 4 wk of lactation, with a smaller carryover effect after resumption of twice daily milking during the following 4 wk. Losses reported in previous experiments ranged from 7 to 34% for once daily milking experiments, with an average yield loss of about 19% (
      • Davis S.R.
      • Farr V.C.
      • Stelwagen K.
      Regulation of yield loss and milk composition during once-daily milking: A review.
      ;
      • Tucker C.B.
      • Dalley D.E.
      • Burke J.L.
      • Clark D.A.
      Milking cows once daily influences behavior and udder firmness at peak and mid lactation.
      ).
      • Rémond B.
      • Pomiès D.
      • Dupont D.
      • Chilliard Y.
      Once-a-day milking of multiparous Holstein cows throughout the entire lactation: Milk yield and composition, and nutritional status.
      found a reduction of total 305-d lactation milk yield of about 30% for cows milked once daily compared with those milked twice daily throughout a 305-d lactation. This reduction of milk yield may be caused by functional changes in the mammary gland: mammary cell number and metabolic activity, tight junction permeability, regulation of alveolar cell activity by feedback inhibitor of lactation, and apoptosis stimulating factors. Because these processes are essential to the proper functioning of the mammary gland, it has been suggested that milking frequency affects secretory alveolar cell activity (
      • Vetharaniam I.
      • Davis S.R.
      • Soboleva T.K.
      • Shorten P.R.
      • Wake G.C.
      Modeling the interaction of milking frequency and nutrition on mammary gland growth and lactation.
      ) as epithelial cells begin to regress after a variable period of time and are more likely to senesce when longer intermilking intervals are imposed (
      • Capuco A.V.
      • Ellis S.E.
      • Hale S.A.
      • Long E.
      • Erdman R.A.
      • Zhao X.
      • Paape M.J.
      Lactation persistency: Insights from mammary cell proliferation studies.
      ). Changes in mammary cell activity are often measured as changes in the mRNA level and the activity of several key mammary enzymes. Furthermore, the reduced milk yield of ODM cows may be caused by a reduced alveolar capacity provoked by longer intermilking intervals (
      • Davis S.R.
      • Farr V.C.
      • Copeman P.J.
      • Carruthers V.R.
      • Knight C.H.
      • Stelwagen K.
      Partitioning of milk accumulation between cisternal and alveolar compartments of the bovine udder: Relationship to production loss during once daily milking.
      ). The effects of increasing and decreasing milking frequency on functionality of the mammary gland are excellently reviewed by
      • Stelwagen K.
      Effect of milking frequency on mammary functioning and shape of the lactation curve.
      . Interestingly, SCC was not affected by once daily milking compared with twice daily milking in C cows, in accordance with earlier reports (
      • Rémond B.
      • Pomiès D.
      • Dupont D.
      • Chilliard Y.
      Once-a-day milking of multiparous Holstein cows throughout the entire lactation: Milk yield and composition, and nutritional status.
      ).
      The lactation curve of ODM cows was remarkable compared with C cows in respect to a reduced peak yield, a 6-wk-delayed time of peak yield, and a better persistency throughout the remainder of lactation. This is exactly the lactation curve that is favorable for dairy farmers but difficult to achieve by breeding programs (
      • Togashi K.
      • Lin C.Y.
      Modifying the lactation curve to improve lactation milk and persistency.
      ;
      • Togashi K.
      • Lin C.Y.
      Efficiency of different selection criteria for persistency and lactation milk yield.
      ). Persistent cows are more desirable because they are more efficient in roughage usage and suffer less metabolic stress because of high peak yield, and thus are more resilient to production diseases (
      • Jakobsen J.H.
      • Madsen P.
      • Jensen J.
      • Pedersen J.
      • Christensen L.G.
      • Sorensen D.A.
      Genetic parameters for milk production and persistency for Danish Holsteins estimated in random regression models using REML.
      ). This may be attributable to the fact that the risk for metabolic disturbances depends largely on the increase of milk yield during the first weeks of lactation (
      • Drackley J.K.
      ADSA Foundation Scholar Award. Biology of dairy cows during the transition period: The final frontier?.
      ). Lower NEFA and BHBA concentrations combined with a later peak yield and a better persistency revoke the reduced milk production in early lactation.
      Besides milk yield, milk protein content is a matter of growing economic interest to the dairy processing industry compared with all other milk components. It must be emphasized that continuous milking as well as once daily milking are useful tools for producing milk with higher milk protein content and a higher price compared with traditional management of dairy cows. Also,
      • Patton J.
      • Kenny D.A.
      • Mee J.F.
      • O’Mara F.P.
      • Wathes D.C.
      • Cook M.
      • Murphy J.J.
      Effect of milking frequency and diet on milk production, energy balance, and reproduction in dairy cows.
      demonstrated a higher milk protein concentration (3.55%) and milk fat concentration (4.70%) during the first 28 d of lactation for cows milked once daily compared with cows milked thrice daily. In our study, once daily milking was associated with the highest fat concentration during the first 4 wk of lactation. Because of the lower milk yield, ODM cows produced only three-fourths of the daily fat yield produced by C cows. However, no changes in milk protein concentration were found in short-term studies (once daily milking for 1 wk;
      • Guinard-Flament J.
      • Delamaire E.
      • Lamberton P.
      • Peyraud J.L.
      Adaptations of mammary uptake and nutrient use to once-daily milking and feed restriction in dairy cows.
      ;
      • Loiselle M.C.
      • Ster C.
      • Talbot B.G.
      • Zhao X.
      • Wagner G.F.
      • Boisclair Y.R.
      • Lacasse P.
      Impact of postpartum milking frequency on the immune system and the blood metabolite concentration of dairy cows.
      ).

      Comparisons Between Continuous Milking and Once Daily Milking

      Both once daily milking and continuous milking exhibited profound effects on metabolism and productivity. For both treatments, an improved metabolic status in early lactation was obvious as indicated by a reduced incidence of hypoglycemia and lipomobilization. Extent of reduced lactational milk yield was comparable for both treatments.
      Once daily milking is furthermore a management system often chosen in pasture-based, low-cost, low-return farming systems. There are many economical aspects and lifestyle choices involved in the choice of milking frequency because certain fixed costs are associated with milking, including consumables and power. Our results indicate that once daily milking is furthermore appropriate in high-yielding dairy cows. In contrast, the additional milk produced during the extra 56 d in the previous lactation for the CM cows (about 1,200 kg) and the higher milk protein yield compared with prepartum dried-off C cows added additional value to this management scheme, whereas problems related to the colostral supply of calves had a negative effect. In the present study, continuous milking was conducted during 1 gestation–lactation cycle. This approach is not practical for consecutive lactations because most cows dry off independently after more than 2 successive lactations without a DP (
      • Rémond B.
      • Rouel J.
      • Pinson N.
      • Jabet S.
      An attempt to omit the dry period over three consecutive lactations in dairy cows.
      ). The well-known challenges of maintaining health and well-being in high-yielding dairy cattle suggest that there may be management alternatives to a 56-d DP and twice daily milking.

      Conclusions

      The rapid increase of milk yield after calving represents an important risk factor for metabolic disturbances in conventionally reared, high-yielding dairy cows after a 56-d DP. Both continuous milking without DP and once daily milking during the first 4 wk of lactation represent management strategies to successfully reduce the metabolic stress in fresh cows, combined with an improved metabolic balance and increased milk protein content throughout the entire lactation. The lactational ECM yield (305 d) was decreased, however, in both the ODM and CM cows by roughly 20% compared with C cows. The proportions of hypoglycemic and ketotic cows were lower in the CM group than in the C and ODM groups. The lactation curve for ODM cows peaked later and proceeded flatter. The optimal duration of once daily milking in high-yielding dairy cows remains an issue for further investigation. Milk protein content was markedly increased in CM cows (+0.5%) and, to a lesser extent, in ODM cows (+0.3%). Thus, considering the actual pricing system for milk, continuous milking and once daily milking may be meaningful, economical alternatives for dairy farmers.

      Acknowledgments

      The authors express their appreciation to Sachsenmilch AG (Leppersdorf, Germany) and Bayerisches Staatsministerium für Ernährung, Landwirtschaft und Forsten (Munich, Germany) for financial support. We thank the farm crew for their help during study and the laboratory technicians and students for analysis of samples. For proofreading the manuscript, we thank J. Hodges (speaker at the IAEA-FAO conference, Vienna, 2009).

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