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* Current address: Functional Nutrition, Gainesville, FL 32606. † Current address: Micronutrients, Indianapolis, IN 46241. ‡ Current address: Department of Animal Science, Delaware Valley University, Doylestown, PA 18901. § Current address: Eli Lilly and Company, Indianapolis, IN 46225.
Our objectives were to evaluate the effects of prepartum monensin supplementation and dry-period nutritional strategy on the postpartum productive performance of cows fed monensin during lactation. A total of 102 Holstein cows were enrolled in the experiment (32 primiparous and 70 multiparous). The study was a completely randomized design, with randomization restricted to balance for parity, body condition score, and expected calving date. A 2 × 2 factorial arrangement of prepartum treatments was used; the variables of interest were prepartum feeding strategy [controlled-energy diet throughout the dry period (CE) vs. controlled-energy diet from dry-off to 22 d before expected parturition, followed by a moderate-energy close-up diet from d 21 before expected parturition through parturition (CU)] and prepartum monensin supplementation [0 g/t (control, CON) or 24.2 g/t (MON); Rumensin; Elanco Animal Health, Greenfield, IN]. Lactation diets before and after the dry period contained monensin at 15.4 g/t. During the close-up period, cows fed CU had greater DM and NEL intakes than cows fed CE. Calf BW at birth tended to be greater for cows fed CU than for those fed CE but was not affected by MON supplementation. Diet did not affect calving difficulty score, but cows supplemented with MON had an increased calving difficulty score. We found a tendency for a MON × parity interaction for colostral IgG concentration, such that multiparous MON cows tended to have lower IgG concentration than CON cows, but colostral IgG concentration for primiparous MON and CON cows did not differ. Postpartum milk yield did not differ between diets but tended to be greater for cows supplemented with MON. Milk fat and lactose content were greater for cows fed CU than for those fed CE, and lactose content and yield were increased for cows supplemented with MON. Solids-corrected and fat-corrected milk yields were increased by MON supplementation, but were not affected by diet. Overall means for postpartum DMI did not differ by diet or MON supplementation. The CU diet decreased the concentration of nonesterified fatty acids during the close-up period but increased it postpartum. Neither diet nor monensin affected β-hydroxybutyrate or liver composition. Overall, postpartum productive performance differed little between prepartum dietary strategies, but cows fed MON had greater energy-corrected milk production. In herds fed monensin during lactation, monensin should also be fed during the dry period.
Association between the proportion of sampled transition cows with increased nonesterified fatty acids and beta-hydroxybutyrate and disease incidence, pregnancy rate, and milk production at the herd level.
Associations of elevated nonesterified fatty acids and beta-hydroxybutyrate concentrations with early lactation reproductive performance and milk production in transition dairy cattle in the northeastern United States.
Evaluation of nonesterified fatty acids and beta-hydroxybutyrate in transition dairy cattle in the northeastern United States: Critical thresholds for prediction of clinical diseases.
) in several recent studies. Prepartum dietary energy intake has a large effect on the degree of negative energy balance that cows experience during the immediate postpartum period. The overconsumption of energy throughout the dry period has been shown to decrease postpartum DMI and result in impaired metabolic status and liver function postpartum (
demonstrated that overconsumption of energy during the far-off dry period appeared to be more detrimental for postpartum production outcomes than overconsumption of energy during the close-up period.
Several studies have investigated the feeding of a controlled-energy diet during the dry period (
) and have observed a significant improvement in postpartum cow health and metabolic status after feeding a high-fiber, controlled-energy diet during the dry period. Together, these data indicate that cows that are modestly feed-restricted during the dry period have improved postpartum metabolism. Most of the available data are based on studies in which intakes were restricted to control energy; however, in the group-fed housing that is today's industry standard, restricting energy intake for a group of cows is not practical. Limiting feed access in group-fed cows can lead to increased competition at the feed bunk and create large variations in DMI among individual cows within the group. This can decrease DMI in at least a part of the feed-restricted group, leading energy intake restricted much below target intakes in some cows. In contrast, increased inclusion of low-energy forages in the prepartum diet raises the NDF content of the ration and limits animal energy intake without restricting DMI. This high-forage, controlled-energy prepartum feeding strategy has been shown to result in lower postpartum nonesterified fatty acid (NEFA) mobilization, similar to that after restriction of prepartum feed intake (
). However, few studies have compared the high-forage, controlled-energy diet to a high-forage close-up diet designed to be intermediate in composition between the far-off and lactation diets.
Monensin is an ionophore that increases ruminal propionate production (
), likely from changes in the populations of gram-positive bacteria, along with changes in the metabolism of gram-negative bacteria in the rumen that occur with ionophore treatment (
). The efficacy of monensin in decreasing health disorders associated with periparturient negative energy balance, improving energy metabolism, and enhancing lactation performance has been demonstrated (
). However, to the best of our knowledge, the interactions of monensin and diet during the prepartum period have not yet been studied. Previous research has shown that excessive prepartum dietary energy intake negatively affects postpartum metabolism, and because feeding monensin prepartum should increase the amount of propionate available to the cow, it is of interest to determine whether the effects of prepartum monensin supplementation on the performance of postpartum cows are independent of prepartum diet. Data from studies that examined monensin and diet in cows in early lactation (
) have observed that the effects of monensin are independent of diet, but this has not yet been studied in dry cows. Moreover, field discussions have questioned whether cows should be given a “rest” from monensin during the dry period to help maintain efficacy during lactation. Studies have compared monensin-supplemented and unsupplemented diets during the dry period without monensin in the postpartum diet (
). Research has not investigated whether removing monensin during the dry period in cows fed monensin before and after the dry period would be advantageous or detrimental.
The objective of this study was to evaluate the effects of prepartum monensin supplementation on postpartum productive performance and metabolism when fed as part of a single-group controlled-energy diet, or as a 2-group approach with a controlled-energy diet during the far-off dry period and a moderate-energy diet during the close-up dry period. Cows were fed monensin in the lactation diet before and after the dry period. Our hypotheses were that cows fed monensin would have greater postpartum DMI and milk production; that cows fed the higher-forage NDF diet throughout the dry period would have greater postpartum DMI and milk production; and that the effects of prepartum monensin would be independent of prepartum dietary treatment.
MATERIALS AND METHODS
Animals and Treatments
The study was conducted at the University of Illinois Dairy Research and Teaching Unit. All animal procedures were approved by the University of Illinois Institutional Animal Care and Use Committee (protocol 08225). The study had a completely randomized design, with randomization restricted to balance for parity, BCS, and expected calving date. A 2 × 2 factorial arrangement of prepartum treatments was used; the factors of interest were prepartum feeding strategy [a controlled-energy diet throughout the dry period (CE) or a controlled-energy diet from dry-off to 22 d before expected parturition and a moderate-energy diet of intermediate nutrient density from d 21 before expected parturition through parturition (CU)] and prepartum monensin supplementation [0 g/t (CON) or 24.2 g/t (MON); Rumensin; Elanco Animal Health, Greenfield, IN]. Postpartum, all cows were fed the same lactating diet containing 15.4 g/t monensin (Table 1). The lactating diet consumed by cows before dry-off also contained monensin at 15.4 g/t.
Contained 0 or 568 g/t monensin (from Rumensin 90, Elanco Animal Health, Greenfield, IN) in carrier of ground corn and mineral oil depending on monensin treatment assignment.
1 CE = controlled-energy prepartum diet; CU = close-up prepartum diet.
2 Landus Cooperative, Ames, IA.
3 Church & Dwight Co. Inc., Princeton, NJ.
4 Contained 0 or 568 g/t monensin (from Rumensin 90, Elanco Animal Health, Greenfield, IN) in carrier of ground corn and mineral oil depending on monensin treatment assignment.
5 Milk Specialties Global Animal Nutrition, Eden Prairie, MN.
6 Contained a minimum of 5.0% Mg, 10.0% S, 7.5% K, 2.0% Fe, 3.0% Zn, 3.0% Mn, 5,000 mg/kg Cu, 250 mg/kg I, 40 mg/kg Co, 150 mg/kg Se, 2,200,000 IU/kg vitamin A, 660,000 IU/kg vitamin D3, and 22,000 IU/kg vitamin E.
A total of 102 Holstein cows were enrolled in the experiment (32 primiparous and 70 multiparous). Cows were dried off at least 50 d before expected parturition, and both primiparous and multiparous cows were moved to the experimental freestall barn at least 50 d before expected parturition. Throughout the dry-period portion of the experiment, all cows were housed in a barn with 4 pens that each had 10 sand-bedded freestalls. Primi- and multiparous cows were grouped together (up to 10 cows per pen). At enrollment on the experimental diet, cows were moved to the freestall pens and assigned a Calan feed gate (American Calan, Northwood, NH). At parturition, cows were moved to individual calving pens located in the freestall pens; immediately postpartum, cows were moved to a tiestall barn and assigned an individual stall, where they were housed for the duration of the study, through 84 DIM.
Diet Formulation, Nutrient Composition, and Feeding
The ingredient composition of the diets is shown in Table 1. Forage and byproduct compositions are shown in Supplemental Tables S1 and S2, respectively (http://dx.doi.org/10.17632/vhvz87yrdg.1). Diets were balanced using
recommendations and were fed for ad libitum intake as TMR. The CE and the CU diets were formulated for a DMI of 12.2 and 10.5 kg/d (for multiparous cows) with an energy density of 1.30 and 1.49 Mcal of NEL/kg of DM, respectively. Our strategy in formulating the dry-period diets was to keep the proportion of corn silage similar to the lactation diet, with smaller amounts of alfalfa silage and a larger amount of wheat straw to dilute the energy content. The CU diet was designed to be intermediate in ingredients and nutrient profile to the far-off and lactating diets. Both the CE and CU dry period diets were formulated without monensin, or with monensin at a targeted inclusion of 24.2 g/t of total dietary DM, which would equate to a daily dose of approximately 300 mg/d for multiparous cows. After calving, all cows were fed the same lactating diet, formulated for a DMI of 22.7 kg/d for multiparous cows with an energy density of 1.70 Mcal of NEL/kg of DM. All cows received monensin during the postpartum period at 15.4 g/t of dietary DM, for a target intake of approximately 300 mg/d. The concentration of monensin in the lactating and dry-period concentrate mixes was verified by independent analysis (Covance Laboratories, Greenfield, IN).
All diet ingredients were sampled weekly for determination of DM content by drying at 55°C for 48 h, and values were used weekly to adjust ration formulation. For CE and CU diets, if the ration DM content was more than 46% DM, water was added to the diets at mixing to adjust DM to 46% and minimize sorting of the ration.
Cows were fed once daily at 0600 h for ad libitum intake to provide a target of 2 to 3 kg/d (as fed) of refusal. Feed was pushed up 3 or more times daily; refusals were removed each day before feeding, and then weighed and recorded. Water was available for ad libitum consumption.
Data Collection, Sampling Procedures, and Analytical Methods
Samples of all TMR were obtained weekly and composited monthly for analysis at a commercial laboratory (Cumberland Valley Analytical Services, Hagerstown, MD). Procedures for all analyses (Table 2) are described at https://www.foragelab.com/Lab-Services/Forage-and-Feed/Lab-Procedures/. Contents of NEL and NEM were predicted from chemical composition. As well, 3 to 5 samples of individual feed ingredients were obtained throughout the experiment and analyzed by the same laboratory for the same constituents.
Table 2Analyzed composition of TMR experimental diets (mean ± SD)
). The scores were averaged before statistical analysis. Daily observations and general health records were maintained throughout the study. Each cow and her calf were weighed within 12 h of calving.
Dry cows were observed at least 4 times daily for signs of calving and possible calving difficulties. Calving ease was scored on a scale of 1 to 5: a score of 1 was assigned when a cow calved between observations without showing signs of parturition; a score of 2 was assigned when a cow showed signs of parturition and calved without assistance in less than 6 h from the first observation; a score of 3 was assigned when a cow was observed for 6 h and the calving progressed naturally without assistance; a score of 4 was assigned when the calving lasted more than 6 h and the cow required intervention without the use of mechanical assistance for calving; and a score of 5 was assigned when the cow required intervention with mechanical extraction because of the position or size of the calf.
All cows were first milked within 8 h of parturition, and the total colostrum harvested was stored at 4°C. The stored colostrum was weighed within the first 12 h after calving and sampled for IgG analysis. Colostrum samples were stored at −20°C until analysis for IgG by single radial-immunodiffusion techniques by the University of Illinois Veterinary Diagnostic Laboratory (Urbana).
All cows were milked 3 times daily throughout the 84 d of the lactation phase of the experiment. Milk yield was measured electronically for each milking (DairyPlan; Westfalia Surge Inc., Naperville, IL), and daily milk yield was the sum of the 3 milkings; weekly means were calculated from daily production. Milk samples were collected from 3 consecutive milkings obtained over a 24-h period once weekly. Within 12 h after the last samples were collected, the samples were composited by equal volumes for each cow, and composite samples were shipped to a commercial laboratory (Dairy Lab Services, Dubuque, IA) for analysis of milk composition. Samples were analyzed for fat, true protein, lactose, TS, and urea N content, and for SCC using mid-infrared analysis. Weekly yields of milk components were calculated. Yields were calculated as follows: solids-corrected milk (SCM) = milk kg × [(12.24 × fat % × 0.01) + (7.10 × protein % × 0.01) + (6.35 × lactose % × 0.01) −0.0345]; 3.5% FCM = (milk kg × 0.4324) + (fat kg × 16.216); and 4% FCM = (milk kg × 0.4) + (fat % × 0.15). Milk samples from weeks 2 and 6 after calving were analyzed for fatty acid composition as described previously (
). In brief, milk samples from each of the 3 daily milkings during the sampling period were composited based on milk fat yield. Following extraction and methylation of lipids, GLC was used to determine the composition of FAME.
Blood samples were obtained by puncture of a tail vein or artery 3 times weekly (Monday, Wednesday, and Friday) from all cows before the morning feeding. Serum aliquots were obtained within 4 h of the time the last sample was collected. Serum was stored in a freezer at −20°C. At the end of the trial, samples were identified based on time relative to actual calving that corresponded to 1 sample per week during the far-off period (up to 4 wk, sample from mid-point of week used) and samples that corresponded to −13 d (−14 to −12 d), −10 d (−11 to −9 d), −7 d (−8 to −6 d), −4 d (−5 to −3 d), and −1 d (−2 or −1 d) relative to calving during the close-up period. Postpartum, samples were identified that corresponded to +1 d (+1 or +2 d), +4 d (+3 to +5 d), +7 d (+6 to +8 d), +10 d (9 to +11 d), +13 d (+12 to +14 d), +16 d (+15 to +17 d), and +19 (+18 to +20 d) relative to calving, and then 1 sample per week from wk 4 through wk 12. These samples were analyzed for concentrations of BHB (
) from cows under local anesthesia at approximately 0900 h on d −10 and 7 relative to parturition. Biopsies were obtained from at least 10 second-lactation or greater cows selected randomly from each treatment. Liver-tissue samples were frozen immediately in liquid nitrogen. A portion of the tissue samples was later analyzed for concentrations of glycogen (
For prepartum data during the far-off dry period, data were analyzed from the 28 d before the switch to the close-up diet. During the close-up period, only data from the 14 d before the actual calving date were analyzed, because not all cows completed 21 d on the close-up diet before calving.
A total of 15 cows were removed from the postpartum analysis [hock infection (n = 2), severe mastitis (n = 2), severe dystocia (n = 2), displaced abomasum (n = 2), liver biopsy complications (n = 2), fatty liver (n = 2), hypocalcemia (n = 1), and poor milk production (n = 1)]. The final postpartum data set included 86 cows (CE + CON: n = 23, 8 primiparous; CE + MON: n = 20, 8 primiparous; CU + CON: n = 22, 8 primiparous; CU + MON: n = 21, 7 primiparous).
Statistical analyses were performed using SAS software (version 9.2; SAS Institute Inc., Cary, NC). Far-off, close-up, and postpartum data were analyzed separately. Prepartum data were analyzed as a completely randomized design with a 2 × 2 factorial arrangement of treatments using the MIXED procedure of SAS. Fixed effects included diet, monensin treatment, parity, time (week or day), and all 2-, 3-, and 4-way interactions. The random effect was cow nested within diet and MON treatment. For variables with repeated measures (week or day), the MIXED procedure with the REPEATED statement was used. For variables with measurements repeated over time, 4 covariance structures were tested (compound symmetry, heterogeneous compound symmetry, first-order autoregressive, and heterogeneous first-order autoregressive), and the covariance structure that resulted in the smallest Akaike's information criterion was used (
). Degrees of freedom were estimated using the Kenward–Roger option in the model statement. The presence or absence of measurable C18:2 trans-10,cis-12 was tested as a binomial variable using Fisher's exact test. Significant differences were declared when P ≤ 0.05. Trends were discussed when P > 0.05 but ≤ 0.15.
RESULTS AND DISCUSSION
Prepartum DMI, BW, and BCS
Diet chemical composition is shown in Table 2. Prepartum DMI, BW, and BCS results are presented in Table 3. We found no effect of treatment during the far-off dry period for DMI, NEL intake, BW, or BCS. During the far-off dry period, cows were fed CE with or without MON depending on dietary treatment assignment, and the CE or CU dietary treatments did not commence until the close-up period. As such, we expected to observe minimal differences during the far-off dry period.
Table 3Main effects of prepartum diet and monensin supplementation on prepartum DMI, NEL intake, BW, and BCS for cows in the lactation experiment
During the close-up period, cows fed CU had greater DM and NEL intake than cows fed CE (P < 0.001 for both variables); cows fed MON tended to have lower DMI (P = 0.07; Supplemental Figure S1; http://dx.doi.org/10.17632/vhvz87yrdg.1). These observations were consistent with those of previous researchers, who also noted that cows fed a dry-period ration with a higher energy density had higher DMI prepartum than those fed a diet with a lower energy density (
), although in both studies the observed decrease in prepartum DMI did not inhibit postpartum DMI. Other studies have shown no effect of MON on prepartum DMI (
). We found no difference between diet or MON treatments in BW or BCS during the close-up period.
Calving Data
Results for post-calving BW, calving ease, calf birth BW, colostrum yield, and colostrum quality are presented in Table 4. Post-calving BW was not affected by diet or MON treatment. Calf birth BW tended (P = 0.09) to be greater for cows fed CU (45.1 ± 1.0 kg) than for those fed CE (42.7 ± 1.0 kg). The increased DMI for cows fed CU, along with the increased energy density of the diet, may have provided increased energy for fetal growth in CU cows. However, most studies from our laboratory (
Effect of dry period dietary energy level in dairy cattle on volume, concentration of immunoglobulin G, insulin, and fatty acid composition of colostrum.
) have reported no effect of prepartum energy on calf birth BW. Calf birth BW tended (P = 0.08) to be greater for calves born to multiparous cows than for those born to primiparous cows (45.2 ± 0.66 vs. 42.7 ± 1.26 kg), and birth BW was greater (P = 0.02) for male calves than for female calves (45.6 ± 1.22 vs. 42.2 ± 0.74 kg).
Table 4Main effects of prepartum diet and monensin supplementation on calving data for cows in the lactation experiment
Although we found no effect of prepartum diet on calving difficulty score, MON cows had increased calving difficulty (P = 0.04). Although some research has indicated increased dystocia with monensin treatment in close-up cows (
The effect of a monensin controlled-release capsule on the incidence of retained fetal membranes, milk yield and reproductive responses in Holstein cows.
showed an overall increase in dystocia with monensin treatment, but the included studies showed heterogeneity. In the current study, although the effect of monensin on calving difficulty was statistically significant, the numeric difference in calving difficulty score was only 0.3 points and should not be over-interpreted.
The weight of first-milking colostrum, colostral IgG concentration, and mass of IgG secreted in the first milking were not affected by diet. However, we found a tendency (P = 0.09) for a MON × parity interaction for colostral IgG concentration: multiparous cows supplemented with MON tended to have lower IgG concentration than CON cows (60.0 ± 11.9 vs. 91.4 ± 11.9 g/L), but colostral IgG concentration for primiparous MON cows did not differ from primiparous cows fed CON (61.4 ± 8.4 vs. 65.5 ± 8.4 g/L for CON vs. MON). The concentration of Ig in colostrum (i.e., colostrum quality) is highly variable among cows, and the total mass of Ig accumulated within the mammary gland during late gestation and around calving is independent of colostrum volume (
). The timing of secretory cell activation and the interval between calving and removal of colostrum affect dilution of the colostral Ig; however, mass transfer of IgG into colostrum does not appear to be related to mammary gland size (
). To the best of our knowledge, this is the first study to examine the effects of monensin on colostral IgG concentrations, and our results warrant further study. However, we note that colostrum from multiparous cows fed MON was still considered to be of good quality as per industry standard recommendations (
Results for milk yield, milk composition, and milk fatty acid composition are presented in Table 5. Milk yield did not differ significantly between diets but tended (P = 0.06; Supplemental Figure S2; http://dx.doi.org/10.17632/vhvz87yrdg.1) to be greater for cows supplemented with MON. A lack of a significant effect of CU on milk yield has been observed by others (
Influence of prepartum and postpartum supplementation of a yeast culture and monensin, or both, on ruminal fermentation and performance of multiparous dairy cows.
De novo fatty acids originate from de novo synthesis in the mammary gland (<16 carbons); preformed fatty acids originate from extraction from circulating plasma fatty acids (>16 carbons); mixed fatty acids originate from both sources (C16:0 + cis-9 C16:1).
% of FA
De novo
18.07
18.19
0.49
17.87
18.39
0.49
0.87
0.46
0.44
Preformed
51.56
52.16
0.55
52.38
52.34
0.55
0.61
0.96
0.32
Mixed
29.36
29.65
0.22
29.75
29.27
0.36
0.13
0.45
0.42
C18:1 trans-10
1.11
0.70
0.17
0.96
0.85
0.17
0.09
0.66
0.62
1 CE = controlled energy prepartum diet; CU = close-up prepartum diet; MON = contained 24.2 g/t monensin.
3 3.5% FCM = milk kg × 0.4324 + milk fat kg × 16.216.
4 4.0% FCM = milk kg × (0.4 + 0.15 × milk fat %).
5 De novo fatty acids originate from de novo synthesis in the mammary gland (<16 carbons); preformed fatty acids originate from extraction from circulating plasma fatty acids (>16 carbons); mixed fatty acids originate from both sources (C16:0 + cis-9 C16:1).
Milk fat content was greater for cows fed CU than for those fed CE (P = 0.04). We found a diet × MON × week interaction (P = 0.001; Figure 1) for milk fat content that reflected differences during the first few weeks postpartum, in which cows fed CU + CON had the highest milk fat content, those fed CE + CON had the lowest, and those fed either diet supplemented with MON had intermediate milk fat content. Higher milk fat content in the CU group may have been due in part to increased mobilization of adipose tissue triglycerides in the first weeks of lactation (
). During this period, the dietary supply of the precursors for fatty acids such as acetate is decreased and the mammary tissue synthesizes lower amounts of short-chain fatty acids compared with a state of positive energy balance (
). Plasma NEFA can be taken up directly by the mammary gland, as reflected by a positive correlation between plasma NEFA concentration and milk fat percentage (
). In the current study, we found no effect of treatment on de novo, preformed, or mixed fatty acid content. However, concentration of C18:1 trans-10 tended (P = 0.09) to be greater for cows fed CE than for those fed CU. The C18:1 trans-10 is a marker of fatty acid isomers arising from altered conditions in the rumen that inhibit milk fat synthesis in the mammary gland (
). Concentrations of C18:2 trans-10,cis-12, an isomer that is a potent inhibitor of milk fat synthesis, were detectable only in 32 of the 127 milk samples tested from wk 2 and 6 of the study. Measurable concentrations of C18:2 trans-10,cis-12 were more likely to be found (P < 0.05) in cows fed CE than in those fed CU, but monensin had no effect. It is possible that without the transition diet, rumen conditions in CE cows were altered postpartum, leading to alternate biohydrogenation products with trans-10 double bonds. This possibility deserves additional research, because
also observed decreased milk fat content in cows fed a controlled-energy prepartum diet without a close-up diet.
Figure 1Least squares means ± SEM for postpartum milk fat content (%) from cows fed a controlled-energy diet throughout the dry period (CE) or a higher-energy close-up diet prepartum (CU), with monensin (Mon) or without (Con). Panel A shows diet × Mon × week interactions for multiparous cows (Multi). Panel B shows diet × Mon × week interactions for primiparous cows (Primi). P-values: week, P < 0.001; parity, P = 0.74; diet, P = 0.03; Mon, P = 0.86; diet × Mon, P = 0.69; diet × Mon × parity, P = 0.18; diet × Mon × week, P = 0.001; Mon × parity × week, P = 0.32; all other 2- and 3-way interactions of main effects, P > 0.35.
Interactions of diet × parity × week (P = 0.006) and diet × MON × parity × week (P = 0.02; Figure 2) were present for milk true protein content, such that multiparous cows fed CE + CON and primiparous cows fed CU + CON had the highest milk protein in early lactation relative to other treatments. Milk lactose content was greater for cows fed CU (P = 0.04), and lactose content and yield were increased for cows supplemented with MON (P = 0.06 and P = 0.02, respectively).
Figure 2Least squares means ± SEM for postpartum milk protein content (%) for cows fed a controlled-energy diet throughout the dry period (CE) or a higher-energy close-up diet prepartum (CU), with monensin (Mon) or without (Con). Panel A shows diet × Mon × week interactions for multiparous cows (Multi). Panel B shows diet × Mon × week interactions for primiparous cows (Primi). P-values: week, P < 0.001; parity, P = 0.50; diet, P = 0.30; Mon, P = 0.34; diet × Mon, P = 0.86; diet × parity, P = 0.31; parity × week, P = 0.21; diet × parity × week, P = 0.006; diet × Mon × parity × week, P = 0.02; all other 2- and 3-way interactions of main effects, P > 0.35.
Milk TS content was lower for cows fed CE than for those fed CU (P = 0.01), reflecting the lower fat and lactose concentrations. Figure 3 shows the interaction of diet × MON × week (P = 0.005), which reflected differences early postpartum, where cows fed CU + CON had the greatest TS content, those fed CE + CON had the lowest, and those fed either diet supplemented with MON were intermediate.
Figure 3Least squares means ± SEM for postpartum milk TS content (%) for cows fed a controlled-energy diet throughout the dry period (CE) or a higher-energy close-up diet prepartum (CU), with monensin (Mon) or without (Con). Panel A shows diet × Mon × week interactions for multiparous cows (Multi). Panel B shows diet × Mon × week interactions for primiparous cows (Primi). P-values: week, P < 0.001; parity, P = 0.53; diet, P = 0.01; Mon, P = 0.81; diet × Mon, P = 0.61; all other 2- and 3-way interactions of main effects, P > 0.35.
Milk SCC and urea N concentration did not differ by dietary treatment or parity. Yields of SCM, 3.5% FCM, and 4.0% FCM were increased by MON supplementation but were not affected by diet. Greater yields of milk, SCM, and FCM in cows fed monensin indicate that removal of monensin during the dry period (CON) was detrimental to subsequent milk production. Monensin should continue to be fed during the dry period if supplemented during lactation.
Postpartum DMI, BW, BCS, and Efficiency
Results for postpartum DMI, BW, BCS, and efficiency are presented in Table 6. Postpartum DMI was lower for primiparous cows (P < 0.001; 16.8 ± 0.51 kg/d) than for multiparous cows (21.0 ± 0.38 kg/d), and a tendency (P = 0.08; Figure 4) for a diet × parity × week interaction indicated that postpartum DMI tended to be greater for primiparous cows fed CE than CU but did not differ in multiparous cows. Differences in DMI prepartum did not carry over to the postpartum period. The absence of an effect on early postpartum DMI in multiparous cows in the current study after feeding a controlled-energy diet supports descriptions by other researchers (
). A tendency (P = 0.11) for a MON × parity × week interaction showed that prepartum MON supplementation tended to increase DMI postpartum in primiparous cows but not in multiparous cows (Figure 4).
Table 6Main effects of prepartum diet and monensin supplementation on postpartum DMI, NEL intake, BW, BCS, and efficiencies for cows in the lactation experiment
Figure 4Least squares means ± SEM for postpartum DMI (kg/d) for cows fed a controlled-energy diet throughout the dry period (CE) or a higher-energy close-up diet prepartum (CU), with monensin (Mon) or without (Con). Panel A shows diet × Mon × week interactions for multiparous cows (Multi). Panel B shows diet × Mon × week interactions for primiparous cows (Primi). P-values: week, P < 0.001; parity, P < 0.001; diet, P = 0.65; Mon, P = 0.40; diet × Mon, P = 0.42; diet × parity, P = 0.20; diet × week, P = 0.20; parity × week, P = 0.25; diet × parity × week, P = 0.08; Mon × parity × week, P = 0.11; all other 2- and 3-way interactions of main effects, P > 0.35.
Results for NEL intake were similar to those for DMI; tendencies for diet × parity × week (P = 0.08) and MON × parity × week (P = 0.11) interactions reflected the same differences as for DMI (Figure 4). Neither BW nor BCS postpartum was affected overall by diet or MON supplementation.
Metabolic Indicators
Results for metabolic indicators in blood and liver are shown in Table 7. Concentrations of BHB and NEFA in blood were not different between diet groups during the far-off dry period when both groups were consuming the CE diet and were not affected by monensin supplementation. During the close-up period, NEFA concentration was greater for cows fed CE, an observation that has been reported previously (
). Concentration of BHB did not differ, and neither BHB nor NEFA was affected by monensin prepartum. After parturition, concentrations of NEFA were greater for cows that had been fed CU than for those fed CE, in agreement with previous reports (
), although unlike the present study, postpartum monensin supplementation was compared with an unsupplemented control. In contrast to a previous study with a controlled-energy diet (
, the close-up diet was much higher in energy, and this may have increased the liver lipid composition for that group compared to CU in our study. Similarly, monensin did not affect liver composition, unlike the results of previous (
detected a parity × monensin interaction, such that monensin decreased liver triglyceride content in multiparous cows but increased it in primiparous cows.
Table 7Main effects of prepartum diet and monensin supplementation on variables in blood and liver before and after parturition for cows in the lactation experiment
Effect of day was significant for all liver measurements, analyzed in a repeated-measures model; no interactions were significant. The P-values for the repeated-measures analysis are presented under d −10, which is why no values appear for d 7.
d −10
Total lipid, % wet weight
4.59
4.16
1.00
4.67
4.08
1.00
0.42
0.55
0.89
Triacylglycerol, % wet weight
1.15
0.47
0.43
0.99
0.63
0.43
0.33
0.91
0.73
Glycogen, % wet weight
2.88
3.19
0.44
2.96
3.12
0.44
0.40
0.83
0.22
d 7
Total lipid, % wet weight
11.63
10.29
1.19
10.00
11.92
1.16
—
—
—
Triacylglycerol, % wet weight
5.95
5.66
0.52
5.56
6.05
0.56
—
—
—
Glycogen, % wet weight
0.76
1.28
0.49
0.99
1.05
0.49
—
—
—
1 CE = controlled energy prepartum diet; CU = close-up prepartum diet; MON = contained 24.2 g/t monensin; NEFA = nonesterified fatty acids.
2 No interactions with time were significant.
3 Effect of day was significant for all liver measurements, analyzed in a repeated-measures model; no interactions were significant. The P-values for the repeated-measures analysis are presented under d −10, which is why no values appear for d 7.
The occurrence of adverse health events during the study is shown in Table 8. Because of limited cow numbers, no conclusions should be drawn about differences among treatments. The relatively high incidence of problems across treatments may have been due to lack of optimal cow comfort in the prepartum free stalls. The stalls had a high brisket board, and the beds were deeply pitted and uneven. Stalls were renovated after this trial was completed.
Table 8Incidence of postpartum health disorders and diseases for cows fed either prepartum diet (controlled-energy or higher-energy close-up) without or with monensin
Overall, supplementation of monensin prepartum increased SCM, FCM, milk fat, lactose, and TS yields, and tended to increase milk yield. This effect was consistent regardless of prepartum diet strategy. We conclude from our results that in herds where monensin is fed during lactation, it should also be fed throughout the dry period. In this study, prepartum dietary feeding strategy had little effect on postpartum production variables. Therefore, a single-diet dry-cow approach can be successful in herds where implementing 2 prepartum groups is difficult.
ACKNOWLEDGMENTS
The authors greatly appreciate the assistance from staff at the University of Illinois Dairy Research Unit in animal care and data collection. Appreciation is extended to Landus Cooperative (Ames, IA) for donations of SoyPlus and SoyChlor, and to Milk Specialties Global Animal Nutrition (Eden Prairie, MN) for donation of Energy Booster 100. The authors also gratefully acknowledge Elanco Animal Health (Greenfield, IN) for financial support of this study. Other funds were provided through state and federal contributions to the Illinois Agricultural Experiment Station (Urbana). The authors have not stated any conflicts of interest.
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