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Research| Volume 103, ISSUE 9, P8143-8150, September 2020

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Postweaning response on growth and nutrient digestion to using different weaning strategies when feeding moderate and high amounts of milk replacer to Holstein calves

Open ArchivePublished:July 16, 2020DOI:https://doi.org/10.3168/jds.2019-17704

      ABSTRACT

      Many changes occur in the rumen as calves transition from consuming a liquid diet to a completely solid diet. These changes can influence growth and calf health, being greatly affected by preweaning diet as well as the transitional steps used to wean calves. A 2 × 2 factorial design of moderate [MOD; 0.66 kg of dry matter (DM)] or high (HI; up to 1.1 kg of DM) feeding rates of milk replacer (MR) and abrupt (AB; 7-d step-down) or gradual weaning (GR; 21-d step-down) was used to study how preweaning program affects calf performance from 2 to 4 mo of age. Calves (n = 50) were randomly assigned to 1 of the 4 preweaning treatments. For the following 56-d grower portion of the experiment, calves were grouped into 12 pens based on MR program, with 4 to 5 calves per pen. Data were analyzed as a completely randomized design, with repeated measures when applicable, by PROC MIXED in SAS (version 9.4; SAS Institute Inc., Cary, NC). All calves received ad libitum access to water and a textured starter [42% starch and 20% crude protein (CP)] blended with 5% chopped grass hay. Overall, apparent digestibility coefficients (dC) of DM, neutral detergent fiber, and acid detergent fiber were greater for MOD compared with HI, and apparent dC of DM and ADF were greater for GR than for AB. No significant differences were detected between organic matter, CP, fat, starch, or sugar dC based on treatment, and no interactions were observed. However, by d 56 only starch dC differed by treatment. Weaning body weight (BW), hip width (HW), and hip height (HH) were greater for HI compared with MOD calves. Weaning HH was greater for AB than for GR calves. However, final BW, HW, HH, and body condition score, as well as average daily gain, did not differ among treatments. An interaction occurred where feed efficiency (gain/feed) was reduced with GR weaning in MOD, whereas the opposite occurred in the HI group. When feeding calves a moderate level of MR, a several-step gradual weaning is not necessary to ensure growth and development; however, calves should be gradually weaned when offered a high level of MR.

      Key words

      INTRODUCTION

      There is an increasing interest in the amount of milk or milk replacer (MR) that should be fed to dairy calves to ensure a healthy animal with rapid and efficient prepubertal growth. Furthermore, several studies have reported epigenetic responses linking preweaning plane of nutrition with enhanced lactation performance (
      • Fischer A.J.
      • Villot C.
      • van Niekerk J.K.
      • Yohe T.T.
      • Renaud D.L.
      • Steele M.A.
      Invited review: Nutritional regulation of gut function in dairy calves: From colostrum to weaning.
      ). A concern about feeding calves large quantities for milk or MR is that the intensified preweaning ADG and greater BW at weaning (
      • Appleby M.C.
      • Weary D.M.
      • Chua B.
      Performance and feeding behaviour of calves on ad libitum milk from artificial teats.
      ;
      • Diaz M.C.
      • Van Amburgh M.E.
      • Smith J.M.
      • Kelsey J.M.
      • Hutten E.L.
      Composition of growth of Holstein calves fed milk replacer from birth to 105-kilogram body weight.
      ;
      • Jasper J.
      • Weary D.M.
      Effects of ad libitum milk intake on dairy calves.
      ) is usually lost by 4 mo of age compared with a moderate MR feeding regimen (
      • Hill T.M.
      • Quigley J.D.
      • Suarez-Mena F.X.
      • Bateman II, H.G.
      • Schlotterbeck R.L.
      Effect of milk replacer feeding rate and functional fatty acids on dairy calf performance and digestion of nutrients.
      ,
      • Hill T.M.
      • Quigley J.D.
      • Bateman II, H.G.
      • Suarez-Mena F.X.
      • Dennis T.S.
      • Schlotterbeck R.L.
      Effect of milk replacer program on calf performance and digestion of nutrients in dairy calves to 4 months of age.
      ). This has been attributed to a rudimentary rumen as a result of the lower starter consumption preweaning. Hence, calves not adequately adapted to solid feed intake exhibit slower postweaning growth (
      • Terré M.
      • Devant M.
      • Bach A.
      Effect of level of milk replacer fed to Holstein calves on performance during the preweaning period and starter digestibility at weaning.
      ;
      • Hill T.M.
      • Bateman II, H.G.
      • Aldrich J.M.
      • Schlotterbeck R.L.
      Effect of milk replacer program on digestion of nutrients in dairy calves.
      ,
      • Hill T.M.
      • Quigley J.D.
      • Bateman II, H.G.
      • Suarez-Mena F.X.
      • Dennis T.S.
      • Schlotterbeck R.L.
      Effect of milk replacer program on calf performance and digestion of nutrients in dairy calves to 4 months of age.
      ).
      • Bach A.
      • Terré M.
      • Pinto A.
      Performance and health responses of dairy calves offered different milk replacer allowances.
      reported that calves fed 8 L/d of MR (25% CP, 19% fat with 12.5% solids), had a BW at 52 d that was 3.7 kg greater than that of calves fed 6 L/d of MR. However, BW at d 73 (weaning) and d 228 were similar between the 2 MR rates.
      Reports conflict regarding the effect of increased MR feeding rate on postweaning ADG. Some studies report reduced ADG (
      • Hill T.M.
      • Quigley J.D.
      • Bateman II, H.G.
      • Suarez-Mena F.X.
      • Dennis T.S.
      • Schlotterbeck R.L.
      Effect of milk replacer program on calf performance and digestion of nutrients in dairy calves to 4 months of age.
      ;
      • Hu W.
      • Hill T.M.
      • Dennis T.S.
      • Suarez-Mena F.X.
      • Quigley J.D.
      • Schlotterbeck R.L.
      Intake, nutrient digestibility, and growth performance of Holstein dairy calves consuming a milk replacer at moderate or high feeding rates.
      ), whereas others report no short-term effects (
      • Terré M.
      • Devant M.
      • Bach A.
      Effect of level of milk replacer fed to Holstein calves on performance during the preweaning period and starter digestibility at weaning.
      ;
      • Rosenberger K.
      • Costa J.H.C.
      • Neave H.W.
      • von Keyserlingk M.A.G.
      • Weary D.M.
      The effect of milk allowance on behavior and weight gains in dairy calves.
      ). A reduction in structural growth postweaning has been reported in most studies where it was measured (
      • Hill T.M.
      • Quigley J.D.
      • Suarez-Mena F.X.
      • Bateman II, H.G.
      • Schlotterbeck R.L.
      Effect of milk replacer feeding rate and functional fatty acids on dairy calf performance and digestion of nutrients.
      ,
      • Hill T.M.
      • Quigley J.D.
      • Bateman II, H.G.
      • Suarez-Mena F.X.
      • Dennis T.S.
      • Schlotterbeck R.L.
      Effect of milk replacer program on calf performance and digestion of nutrients in dairy calves to 4 months of age.
      ). This decreased ADG and structural growth could be associated with the reduction in solid feed digestion. Concurrently, it has also been reported that intensive MR regimens reduce the digestion of an exclusively solid diet postweaning (
      • Terré M.
      • Devant M.
      • Bach A.
      Effect of level of milk replacer fed to Holstein calves on performance during the preweaning period and starter digestibility at weaning.
      ;
      • Hill T.M.
      • Bateman II, H.G.
      • Aldrich J.M.
      • Schlotterbeck R.L.
      Effect of milk replacer program on digestion of nutrients in dairy calves.
      ), not allowing all the available nutrients to be absorbed and utilized by the body for growth and development, resulting in lower BW gains and structural growth. Another factor to consider for an optimal transition during weaning is an adequate adaptation to a completely solid diet. Several studies have evaluated the effects postweaning of pairing a high-MR feeding program with gradual weaning; nonetheless, these did not report diet digestibility (
      • Hill T.M.
      • Bateman II, H.G.
      • Aldrich J.M.
      • Schlotterbeck R.L.
      Effects of the feeding rate of high protein calf milk replacers.
      ;
      • Sweeney B.C.
      • Rushen J.
      • Weary D.M.
      • de Passillé A.M.
      Duration of weaning, starter intake, and weight gain of dairy calves fed large amounts of milk.
      ). One experiment (
      • Hill T.M.
      • Quigley J.D.
      • Bateman II, H.G.
      • Suarez-Mena F.X.
      • Dennis T.S.
      • Schlotterbeck R.L.
      Effect of milk replacer program on calf performance and digestion of nutrients in dairy calves to 4 months of age.
      ) reported that calves fed a high-MR diet and weaned gradually (step-down over 3 wk) increased postweaning digestion and growth compared with calves fed high levels of MR and weaned using a 1-wk step-down
      These results suggest that increased starter consumption when calves are gradually weaned from high MR intake prepares their gastrointestinal tracts to enhance nutrient digestibility, resulting in greater overall performance. The present experiment aimed to evaluate the carryover effects of MR feeding rate and weaning strategy on growth and nutrient digestibility of weaned dairy calves to 4 mo of age. We hypothesized that gradual weaning could help mitigate the negative effects observed postweaning when high amounts of MR are offered to calves.

      MATERIALS AND METHODS

      Pre-Trial Animals, Facilities, and Treatments

      All animals were cared for as described in the Guide for the Care and Use of Agricultural Animals in Research and Teaching (
      • FASS
      Guide for the Care and Use of Agricultural Animals in Research and Teaching.
      ) and under the approval of the Institutional Animal Care and Use Committee. Pre-trial data have been reported elsewhere (
      • Klopp R.N.
      • Suarez-Mena F.X.
      • Dennis T.S.
      • Hill T.M.
      • Schlotterbeck R.L.
      • Lascano G.J.
      Effects of feeding different amounts of milk replacer on growth performance and nutrient digestibility in Holstein calves to 2 months of age using different weaning strategies.
      ). Fifty Holstein bull calves, 2 to 3 d of age, were obtained from a single farm and transported 3.5 h to the Provimi Nurture Research Center (Brookville, OH). At the source farm, calves were housed in individual hutches with wire pens. They were fed 3 L of fresh colostrum within 1 h of birth, followed by another 3 L 12 h later. Calves then received 2 L of pasteurized whole milk twice daily until they left. Upon arrival at the Nurture Research Center, calves were sorted into individual pens (1.2 m × 2.4 m) with a rock tile-drained base, bedded with wheat straw inside the facility with no added heat, natural ventilation, and curtain sides. Calves were fed 0.66 kg of DM from MR (24.9% CP, 17.8% fat) the first p.m. and the next a.m. Then, calves were randomly assigned to 1 of 4 treatments in a 2 × 2 factorial arrangement. Treatments were moderate MR rate and abrupt (1 step-down) weaning strategy (MOD-AB; 0.66 kg for the first 42 d, and 0.33 kg for the last 7 d, a.m. only), moderate MR rate and gradual (2 step-down) weaning strategy (MOD-GR; 0.66 kg for 28 d, then 0.33 kg for 14 d, a.m. only; then 0.17 kg for 7 d, a.m. only), high MR rate and abrupt weaning strategy (HI-AB; 0.66 kg for 7 d, 0.82 kg for 7 d, 1.1 kg for 28 d, then 0.66 kg for the last 7 d, a.m. only), and high MR rate and gradual weaning strategy (HI-GR; 0.66 kg for 7 d, 0.82 kg for 7 d, 1.1 kg for 14 d, 0.66 kg for 14 d, a.m. only, then 0.33 kg for the last 7 d, a.m. only). All calves remained in individual pens with no MR consumption until d 56. The MOD treatments had 13 calves each, and the HI treatments had 12 calves each. During the preweaning phase, all calves received the same MR (25% CP, 17% fat, DM basis; 14% solids; Table 1), which was formulated with added synthetic amino acids (
      • Hill T.M.
      • Bateman II, H.G.
      • Aldrich J.M.
      • Schlotterbeck R.L.
      • Tanan K.G.
      Optimal concentrations of lysine, methionine, and threonine in milk replacers for calves less than five weeks of age.
      ) and fatty acids (
      • Hill T.M.
      • VandeHaar M.J.
      • Sordillo L.M.
      • Catherman D.R.
      • Bateman II, H.G.
      • Schlotterbeck R.L.
      Fatty acid intake alters growth and immunity in milk-fed calves.
      ). Milk replacer was fed in equal amounts twice daily at 0630 and 1530 h. Calves were given ad libitum access to a textured calf starter (20% CP, 42% starch, DM basis; Table 1) and water during the preweaning phase (56 d).
      Table 1Chemical composition of experimental feeds
      ItemMR
      MR = milk replacer; manufactured from whey, whey protein concentrate, and animal fat, and used in the preweaning experiment (Klopp et al., 2019).
      StarterHay
      DM, % as fed96.8 ± 1.1087.9 ± 2.1090.2 ± 2.20
      DM basis, %
       Ash6.0 ± 0.626.3 ± 0.499.8 ± 1.05
       CP24.9 ± 2.1220.7 ± 2.255.8 ± 0.62
       Fat17.8 ± 1.993.5 ± 0.341.9 ± 0.24
       ADF7.5 ± 0.9740.8 ± 0.39
       NDF14.2 ± 1.9662.4 ± 0.69
       Starch42.4 ± 0.540.7 ± 0.13
      1 MR = milk replacer; manufactured from whey, whey protein concentrate, and animal fat, and used in the preweaning experiment (
      • Klopp R.N.
      • Suarez-Mena F.X.
      • Dennis T.S.
      • Hill T.M.
      • Schlotterbeck R.L.
      • Lascano G.J.
      Effects of feeding different amounts of milk replacer on growth performance and nutrient digestibility in Holstein calves to 2 months of age using different weaning strategies.
      ).

      Trial Feed and Growth Measurements

      At d 56 of the preweaning phase (d 0 of the current phase), after calves spent 7 d housed individually indoors, consuming only starter (weaned on d 49), calves were moved to 12 group pens, with 4 to 5 calves per pen, 3 pens per treatment. The pens consisted of 6.5 m2 of outside space with concrete pad and rock tile-drained yard and 1.35 m2 of inside space bedded with wheat straw. During the postweaning phase, all calves were fed the same calf starter used during the prior trial, blended with 5% chopped grass hay (mean particle size of 2.5 cm) offered ad libitum, as well as free choice water. Refusals were weighted back daily to determine DMI. Body weight and hip width (HW) were measured on d 0, 14, 35, and 56, and body condition was scored. Calves remained in group pens until the trial ended. This experiment took place from Jun. 7 to Aug. 2, 2017. The average temperature during the trial was 22°C, with a range of 9 to 33°C. The average humidity during this period was 80%, with a range of 25 to 100%.

      Digestibility Estimates

      During the postweaning phase of the study, fecal samples were collected to estimate diet apparent digestibility coefficients (dC). Sampling was performed on d 10 to 14, 31 to 35, and 52 to 56 (indicated as d 14, 35, and 56), and samples were composited on an equal wet-weight basis to estimate total-tract diet digestibility, as described by
      • Hill T.M.
      • Quigley J.D.
      • Suarez-Mena F.X.
      • Bateman II, H.G.
      • Schlotterbeck R.L.
      Effect of milk replacer feeding rate and functional fatty acids on dairy calf performance and digestion of nutrients.
      ,
      • Hill T.M.
      • Quigley J.D.
      • Bateman II, H.G.
      • Suarez-Mena F.X.
      • Dennis T.S.
      • Schlotterbeck R.L.
      Effect of milk replacer program on calf performance and digestion of nutrients in dairy calves to 4 months of age.
      ). Briefly, fecal samples were collected from the ground of each pen, with care not to sample bed materials or other contaminants. Acid-insoluble ash was used as an internal marker for feed and fecal samples composited by pen (
      • Van Keulen J.V.
      • Young B.A.
      Evaluation of acid-insoluble ash as a natural marker in ruminant digestibility studies.
      ).

      Feed and Digestibility Analyses

      Every bale of grass hay and every other bag of MR and starter was sampled and composited for nutrient analysis. Feeds and feces were analyzed according to
      • AOAC International
      Official Methods of Analysis.
      for DM (oven method, 930.15), ash (oven method, 942.05), CP (Kjeldahl method, 988.05), fat (alkaline treatment with Roese-Gottlieb method, 932.06 for MR; diethyl ether extraction method, 2003.05, for starters and hay), NDF with ash (
      • Van Soest P.J.
      • Robertson J.B.
      • Lewis B.A.
      Symposium: Carbohydrate methodology, metabolism and nutritional implications in dairy cattle: Methods for dietary fiber, neutral detergent fiber, non-starch polysaccharides in relation to animal nutrition.
      ) without sodium sulfite or α-amylase, ADF with ash (
      • Robertson J.B.
      • Van Soest P.J.
      The Detergent System of Analysis and its Application to Human Foods.
      ), starch (α-amylase method,
      • Hall M.B.
      Analysis of starch, including maltooligosaccharides, in animal feeds: A comparison of methods and a method recommended for AOAC collaborative study.
      ), sugar (colorimetric method,
      • DuBois M.
      • Gilles K.A.
      • Hamilton J.K.
      • Rebers P.A.
      • Smith F.
      Colorimetric method for determination of sugars and related substances.
      ), and acid-insoluble ash (
      • Van Keulen J.V.
      • Young B.A.
      Evaluation of acid-insoluble ash as a natural marker in ruminant digestibility studies.
      ).

      Statistical Analyses

      Data were analyzed as a complete randomized design with repeated measures, when applicable, to identify changes over time, using PROC MIXED in SAS (version 9.4; SAS Institute Inc., Cary, NC). A statistical model was developed for the analysis that included terms for the fixed factor of MR rate (Mi; i = 1, 2), weaning strategy (Sg; g = 1, 2), and day [Dj; j = 1 to 8 for BW and DMI, 1 to 4 for HW, HH, and BCS, and 1 to 3 for dC, DMI %BW, and feed efficiency (FE; 3 periods from d 10 to 14, 31 to 35, and 52 to 56)]; MS(ig) is the interaction of M and S, DM(ji) is the interaction of D and M, DS(jg) is the interaction of D and S, and DMS(jig) is the interaction of D, M, and S; Ck(ig) is the random effect of calf within treatment (M and S), and eigjk is the residual error. The model was represented as follows:
      Yigjk = µ + Mi + Sg + Dj + MS(ig) + DM(ji) + DS(jg) + DMS(jig) + Ck(ig) + eigjk,


      where Yigjk is a continuous, dependent response variable and µ is the overall mean. Pen was the experimental unit (n = 3). Body measurements were taken individually but averaged together and analyzed based on pen. Body weight and intake data were grouped by week, and HW and BCS data were grouped by 14-d periods. The digestibility data were analyzed by individual 5-d collection periods (average measures from 5-d collection; d 10 to 14, 31 to 35, and 52 to 56) as well as overall with repeated measurements (
      • Hill T.M.
      • Quigley J.D.
      • Bateman II, H.G.
      • Suarez-Mena F.X.
      • Dennis T.S.
      • Schlotterbeck R.L.
      Effect of milk replacer program on calf performance and digestion of nutrients in dairy calves to 4 months of age.
      ). No interactions between D × M × S were significant for any of the growth performance-dependent variables and thus were not presented in tables nor discussed. In the mixed models with repeated measurements, the first-order autoregressive structure was selected as the appropriate covariance structure based on Akaike's information criterion.
      We used ANOVA followed by Fisher's protected least significant difference test to evaluate the terms in the model. The P-values, least squares means, and standard errors of least squares means are presented in tables. Statistical significance was declared at P ≤ 0.05 and trends discussed at 0.10 ≥ P ≥ 0.05.

      RESULTS AND DISCUSSION

      Chemical composition of feeds is presented in Table 1. Treatments were planned to differ mainly in MR intake rate and weaning strategy during the preweaning phase, and a common diet was offered during the postweaning phase.

      Milk Replacer Feeding Rate Effect

      Growth Performance

      Weaning BW, HW, and hip height (HH) were greater for HI compared with MOD calves (Table 2). These differences are due to the treatments implemented during the preweaning phase of this trial and reported elsewhere (
      • Klopp R.N.
      • Suarez-Mena F.X.
      • Dennis T.S.
      • Hill T.M.
      • Schlotterbeck R.L.
      • Lascano G.J.
      Effects of feeding different amounts of milk replacer on growth performance and nutrient digestibility in Holstein calves to 2 months of age using different weaning strategies.
      ). However, final BW, HW, and HH (d 56) did not differ among treatments. We observed an MR rate trend (P = 0.07) for average BW, where HI calves had a greater average BW compared with MOD calves. This could be attributed to MOD calves weighing less after weaning compared with HI calves. No differences were seen for weaning or final BCS. Change in HH (P < 0.01) was greater for MOD than for HI calves. This is due to MOD calves having a lower HH at the start of the postweaning phase but then the same HH as HI calves at the end of the postweaning phase, accounting for the greater overall change during this period. These results indicate that during the postweaning phase, HI calves lost their growth advantage over MOD calves, as a result of an inadequate amount of starter consumption before weaning causing an underdeveloped rumen that is not fully capable of digesting the nutrients in the starter (
      • Khan M.A.
      • Lee H.J.
      • Lee W.S.
      • Kim H.S.
      • Kim S.B.
      • Ki K.S.
      • Ha J.K.
      • Lee H.G.
      • Choi Y.J.
      Pre- and postweaning performance of Holstein female calves fed milk through step-down and conventional methods.
      ,
      • Khan M.A.
      • Lee H.J.
      • Lee W.S.
      • Kim H.S.
      • Ki K.S.
      • Hur T.Y.
      • Suh G.H.
      • Kang S.J.
      • Choi Y.J.
      Structural growth, rumen development, and metabolic and immune responses of Holstein male calves fed milk through step-down and conventional methods.
      ). This allowed the MOD calves, which were more accustomed to starter intake and likely possessed a more developed rumen (microbial establishment, papillae formation, initiation of rumination, and epithelial muscularization and vascularization;
      • Khan M.A.
      • Bach A.
      • Weary D.M.
      • von Keyserlingk M.A.G.
      Invited review: Transitioning from milk to solid feed in dairy heifers.
      ), greater BW gain to make up the difference in BW.
      • Dennis T.S.
      • Suarez-Mena F.X.
      • Hill T.M.
      • Quigley J.D.
      • Schlotterbeck R.L.
      • Hulbert L.
      Effect of milk replacer feeding rate, age at weaning, and method of reducing milk replacer to weaning on digestion, performance, rumination, and activity in dairy calves to 4 months of age.
      compared the effects of MOD and HI MR and also reported no differences in final BW and HW. At the start of the trial, HI calves had greater BW compared with MOD calves, but by the end of the trial, HI calves no longer had greater BW.
      Table 2Postweaning growth performance of calves, as influenced by the 4 preweaning treatments
      ItemPreweaning treatment
      Calves assigned to the moderate milk replacer (MR), abrupt weaning group, MOD-AB (n = 3), were fed 0.66 kg (DM basis) of MR for the first 42 d, then 0.33 kg for the last 7 d. The moderate MR, gradual weaning group, MOD-GR (n = 3), were fed 0.66 kg of MR for 28 d, 0.33 kg for 14 d, and 0.17 kg for the last 7 d. The high MR, abrupt weaning group, HI-AB (n = 3), were fed 0.66 kg of MR for 7 d, 0.82 kg for 7 d, 1.1 kg for 28 d, and 0.66 kg for the last 7 d. The high MR, gradual weaning group, HI-GR (n = 3), were fed 0.66 kg of MR for 7 d, 0.82 kg for 7 d, 1.1 kg for 14 d, 0.66 kg for 14 d, and 0.33 kg for the last 7 d.
      SEMP-value
      MOD-ABMOD-GRHI-ABHI-GRRateWeaningRate × Weaning
      Weaning BW, kg75.073.580.677.21.920.040.240.62
      Final BW, kg1331301351333.330.440.510.71
      Average BW, kg99.9298.75105.92102.742.440.070.400.69
      Weaning hip width, cm20.920.821.321.30.190.030.670.93
      Final hip width, cm25.925.725.926.40.20.110.530.18
      Weaning hip height, cm83.081.184.983.00.680.020.020.96
      Final hip height, cm95.394.195.394.10.720.950.130.98
      Weaning BCS2.202.302.302.300.040.260.260.26
      Final BCS2.702.732.672.730.100.870.620.87
      Overall DMI, % BW3.013.202.982.920.100.150.530.25
      Overall ADG, kg/d1.041.010.971.010.030.330.940.25
      Overall feed efficiency
      BW gain divided by DMI.
      0.330.310.300.330.010.610.950.03
      Hip width change, cm5.005.004.605.030.190.360.290.29
      Hip height change, cm12.313.010.411.10.36<0.010.080.89
      BCS change0.500.470.330.470.080.340.560.34
      1 Calves assigned to the moderate milk replacer (MR), abrupt weaning group, MOD-AB (n = 3), were fed 0.66 kg (DM basis) of MR for the first 42 d, then 0.33 kg for the last 7 d. The moderate MR, gradual weaning group, MOD-GR (n = 3), were fed 0.66 kg of MR for 28 d, 0.33 kg for 14 d, and 0.17 kg for the last 7 d. The high MR, abrupt weaning group, HI-AB (n = 3), were fed 0.66 kg of MR for 7 d, 0.82 kg for 7 d, 1.1 kg for 28 d, and 0.66 kg for the last 7 d. The high MR, gradual weaning group, HI-GR (n = 3), were fed 0.66 kg of MR for 7 d, 0.82 kg for 7 d, 1.1 kg for 14 d, 0.66 kg for 14 d, and 0.33 kg for the last 7 d.
      2 BW gain divided by DMI.
      No main effect differences in DMI occurred, as a percentage of BW or as kilograms per day, based on preweaning MR amount or weaning strategy during the grower phase (Table 2; P > 0.15). Interestingly, an interaction (P = 0.03) was detected for FE: it was lower for MOD calves that were weaned GR but greater for HI calves that were GR weaned. This could be because MOD-GR calves received the lowest overall amount of MR preweaning. Thus, under MOD feeding regimens, the advantage of providing more readily available nutrients is maintained through the postweaning period without the need for GR strategy (
      • Appleby M.C.
      • Weary D.M.
      • Chua B.
      Performance and feeding behaviour of calves on ad libitum milk from artificial teats.
      ;
      • Khan M.A.
      • Lee H.J.
      • Lee W.S.
      • Kim H.S.
      • Ki K.S.
      • Hur T.Y.
      • Suh G.H.
      • Kang S.J.
      • Choi Y.J.
      Structural growth, rumen development, and metabolic and immune responses of Holstein male calves fed milk through step-down and conventional methods.
      ). During the preweaning experiment (
      • Klopp R.N.
      • Suarez-Mena F.X.
      • Dennis T.S.
      • Hill T.M.
      • Schlotterbeck R.L.
      • Lascano G.J.
      Effects of feeding different amounts of milk replacer on growth performance and nutrient digestibility in Holstein calves to 2 months of age using different weaning strategies.
      ), HI MR had greater FE compared with MOD, and AB weaning had greater FE than GR. This could indicate that MOD MR regimens might not need to be gradually weaned for 3 wk, whereas gradual weaning provides a major advantage for HI MR regimens.

      Diet Digestibility

      Table 3 shows the apparent dC for d 14, 35, and 56, as well as overall. Overall apparent dC of DM, NDF, and ADF were greater (P < 0.05) for MOD than for HI.
      • Hill T.M.
      • Quigley J.D.
      • Bateman II, H.G.
      • Suarez-Mena F.X.
      • Dennis T.S.
      • Schlotterbeck R.L.
      Effect of milk replacer program on calf performance and digestion of nutrients in dairy calves to 4 months of age.
      reported the same results when comparing MOD with HI MR feeding programs from 2 to 4 mo of age. This reflects increased development in the digestive tract of MOD calves, promoting nutrient digestion, including digestion of fiber. Based on our results, no significant differences occurred between OM, CP, fat, starch, or sugar apparent dC based on treatment, and no interactions were observed overall. These results suggest that calves receiving MOD amounts of MR preweaning are more adapted to consuming more complex nutrients, such as the ones present in the cell wall matrix of forages (
      • Hill T.M.
      • Quigley J.D.
      • Suarez-Mena F.X.
      • Bateman II, H.G.
      • Schlotterbeck R.L.
      Effect of milk replacer feeding rate and functional fatty acids on dairy calf performance and digestion of nutrients.
      ;
      • Dennis T.S.
      • Suarez-Mena F.X.
      • Hill T.M.
      • Quigley J.D.
      • Schlotterbeck R.L.
      • Hulbert L.
      Effect of milk replacer feeding rate, age at weaning, and method of reducing milk replacer to weaning on digestion, performance, rumination, and activity in dairy calves to 4 months of age.
      ). This increased nutrient digestion allowed MOD calves to converge the BW and structural growth gap with HI calves by 56 d postweaning.
      Table 3Postweaning apparent digestibility coefficients (dC) of nutrients in calves as influenced by the 4 preweaning treatments
      Digestibility, %Preweaning treatments
      Calves assigned to the moderate milk replacer (MR), abrupt weaning group, MOD-AB (n = 3), were fed 0.66 kg (DM basis) of MR for the first 42 d, then 0.33 kg for the last 7 d. The moderate MR, gradual weaning group, MOD-GR (n = 3), were fed 0.66 kg of MR for 28 d, 0.33 kg for 14 d, and 0.17 kg for the last 7 d. The high MR, abrupt weaning group, HI-AB (n = 3), were fed 0.66 kg of MR for 7 d, 0.82 kg for 7 d, 1.1 kg for 28 d, and 0.66 kg for the last 7 d. The high MR, gradual weaning group, HI-GR (n = 3), were fed 0.66 kg of MR for 7 d, 0.82 kg for 7 d, 1.1 kg for 14 d, 0.66 kg for 14 d, and 0.33 kg for the last 7 d.
      SEMP-value
      MOD-ABMOD-GRHI-ABHI-GRRateWeaningRate × Weaning
      d 14 Postweaning
       DM83.683.381.280.50.39<0.010.260.65
       OM85.385.285.483.40.710.270.180.23
       NDF57.756.550.448.82.490.020.600.94
       ADF56.155.147.849.02.680.030.960.69
       CP84.184.085.083.80.830.680.430.53
       Fat80.281.981.882.41.310.450.400.68
       Starch97.797.798.095.61.090.430.300.31
       Sugar97.897.397.794.81.120.280.170.30
      d 35 Postweaning
       DM83.084.078.583.30.54<0.01<0.010.01
       OM85.385.581.786.01.040.170.060.09
       NDF58.161.348.055.62.570.020.070.42
       ADF56.961.340.356.02.860.010.010.09
       CP84.683.480.685.51.100.400.120.02
       Fat87.787.985.187.51.470.330.420.47
       Starch96.797.394.997.00.660.170.070.27
       Sugar97.296.993.796.80.640.020.060.03
      d 56 Postweaning
       DM80.381.081.281.30.790.460.590.74
       OM81.482.382.682.90.880.320.510.77
       NDF51.653.052.152.22.270.950.750.78
       ADF50.651.851.151.52.210.980.740.85
       CP82.581.882.983.50.760.230.900.42
       Fat82.282.884.985.61.230.060.600.98
       Starch93.896.195.497.20.550.040.010.63
       Sugar94.794.696.197.31.170.110.680.59
      Combined
       DM82.382.880.381.70.35<0.010.010.16
       OM84.084.383.284.10.610.440.340.66
       NDF55.856.950.252.21.440.010.300.76
       ADF54.556.146.452.21.50<0.010.020.17
       CP83.883.182.884.20.710.860.620.18
       Fat83.484.283.985.10.820.390.250.82
       Starch96.097.096.196.60.550.770.220.69
       Sugar96.696.395.896.30.630.600.900.55
      1 Calves assigned to the moderate milk replacer (MR), abrupt weaning group, MOD-AB (n = 3), were fed 0.66 kg (DM basis) of MR for the first 42 d, then 0.33 kg for the last 7 d. The moderate MR, gradual weaning group, MOD-GR (n = 3), were fed 0.66 kg of MR for 28 d, 0.33 kg for 14 d, and 0.17 kg for the last 7 d. The high MR, abrupt weaning group, HI-AB (n = 3), were fed 0.66 kg of MR for 7 d, 0.82 kg for 7 d, 1.1 kg for 28 d, and 0.66 kg for the last 7 d. The high MR, gradual weaning group, HI-GR (n = 3), were fed 0.66 kg of MR for 7 d, 0.82 kg for 7 d, 1.1 kg for 14 d, 0.66 kg for 14 d, and 0.33 kg for the last 7 d.
      At d 14 and 35, apparent dC of DM, NDF, and ADF were greater (P < 0.05) for MOD than for HI calves (Table 3).
      • Hill T.M.
      • Quigley J.D.
      • Bateman II, H.G.
      • Suarez-Mena F.X.
      • Dennis T.S.
      • Schlotterbeck R.L.
      Effect of milk replacer program on calf performance and digestion of nutrients in dairy calves to 4 months of age.
      measured digestibility on d 21 postweaning and reported greater NDF and ADF dC in MOD compared with HI, and a trend for greater DM dC in MOD calves. The lower digestibility but higher FE seen in HI calves could be explained by gut fill, leading to increased ADG but not structural growth (
      • Hill T.M.
      • Quigley J.D.
      • Bateman II, H.G.
      • Suarez-Mena F.X.
      • Dennis T.S.
      • Schlotterbeck R.L.
      Effect of milk replacer program on calf performance and digestion of nutrients in dairy calves to 4 months of age.
      ).
      • Dennis T.S.
      • Suarez-Mena F.X.
      • Hill T.M.
      • Quigley J.D.
      • Schlotterbeck R.L.
      • Hulbert L.
      Effect of milk replacer feeding rate, age at weaning, and method of reducing milk replacer to weaning on digestion, performance, rumination, and activity in dairy calves to 4 months of age.
      also reported increased dC of DM, NDF, and ADF for MOD compared with HI calves at d 35 postweaning. Calves fed high amounts of MR preweaning do not have an adequately developed rumen (lesser establishment of the microbiome, papillae formation, and muscularization and vascularization of the rumen wall) to effectively digest the nutrients found in starter, causing them to have lower DM, NDF, and ADF dC up to 6 wk postweaning (weaned on d 49). We detected no other differences in digestibility at d 14. At d 35 postweaning, apparent dC of sugar (P = 0.02) was greater for MOD than for HI. An interaction was also observed between MR feeding rate and weaning strategy for apparent dC of DM, CP, and sugar (P < 0.05). The combination of HI MR with GR weaning seems to drastically improve nutrient digestion compared with HI MR and AB weaning. This indicates that the combination of feeding calves increased amounts of MR and then gradually reducing it until weaning both promotes the growth of the animal preweaning and adequately prepares the rumen for solid feed consumption (
      • Khan M.A.
      • Lee H.J.
      • Lee W.S.
      • Kim H.S.
      • Ki K.S.
      • Hur T.Y.
      • Suh G.H.
      • Kang S.J.
      • Choi Y.J.
      Structural growth, rumen development, and metabolic and immune responses of Holstein male calves fed milk through step-down and conventional methods.
      ). Apparent dC of all reported nutrients for HI-AB appears to be less than the other 3 treatments. At d 56, apparent dC for starch was greater for HI compared with MOD (P = 0.04).
      • Dennis T.S.
      • Suarez-Mena F.X.
      • Hill T.M.
      • Quigley J.D.
      • Schlotterbeck R.L.
      • Hulbert L.
      Effect of milk replacer feeding rate, age at weaning, and method of reducing milk replacer to weaning on digestion, performance, rumination, and activity in dairy calves to 4 months of age.
      also observed increased starch digestion in high-MR regimens compared with moderate at d 56 of the postweaning phase. No other differences or interactions were reported. Calves receiving HI MR were initially reported to have lower dC for DM, NDF, and ADF compared with MOD calves until d 35.
      • Chapman C.E.
      • Erickson P.S.
      • Quigley J.D.
      • Hill T.M.
      • Bateman II, H.G.
      • Suarez-Mena F.X.
      • Schlotterbeck R.L.
      Effect of milk replacer program on calf performance and digestion of nutrients with age of the dairy calf.
      also reported lower dC postweaning in calves fed an increased amount of MR, which resulted in reduced ADG and structural growth. However, by the end of 56 d, no differences were seen for nutrient apparent dC except for starch, which was greater for HI than for MOD MR.
      During the 56 d of this study, DM, NDF, and ADF overall digestibility were greater for MOD than for HI calves. Moreover, looking at individual sampling times, DM, NDF, and ADF dC were greater for MOD than HI calves for d 14 and 35, but no significant differences were observed in the last sampling period (d 56; Table 3), indicating that all calves were adapted to solid feed consumption (
      • Hill T.M.
      • Quigley J.D.
      • Bateman II, H.G.
      • Suarez-Mena F.X.
      • Dennis T.S.
      • Schlotterbeck R.L.
      Effect of milk replacer program on calf performance and digestion of nutrients in dairy calves to 4 months of age.
      ;
      • Dennis T.S.
      • Suarez-Mena F.X.
      • Hill T.M.
      • Quigley J.D.
      • Schlotterbeck R.L.
      • Hulbert L.
      Effect of milk replacer feeding rate, age at weaning, and method of reducing milk replacer to weaning on digestion, performance, rumination, and activity in dairy calves to 4 months of age.
      ). The DM apparent dC was greater for MOD than for HI calves over the entire 56-d postweaning period. We detected no significant difference in starch digestibility based on MR feeding rate overall, at d 14 or 35, but at d 56 starch apparent dC was significantly greater for HI than for MOD calves. By the end of the postweaning phase, HI calves were able to adapt to solid feed consumption, allowing their rumens to develop and increasing nutrient digestibility. This is evidenced by MOD calves no longer having greater dC for any nutrient at d 56 and HI calves having greater starch dC compared with MOD, indicating that MR effect on diet digestibility is lost by 4 mo of age.

      Weaning Strategy Effect

      Growth Performance

      Only weaning HH was greater for AB than GR calves (P = 0.02; Table 2). These differences are due to the treatments implemented during the preweaning phase. This is likely because AB-weaned calves received MR at higher amounts for longer compared with GR, leading to increased structural growth. However, final HH based on weaning strategy was not different. Even though calves weaned abruptly consumed more MR and had increased structural growth, they may not have been adequately adapted to solid feed consumption, causing their structural growth advantage to be lost postweaning.
      • Khan M.A.
      • Lee H.J.
      • Lee W.S.
      • Kim H.S.
      • Ki K.S.
      • Hur T.Y.
      • Suh G.H.
      • Kang S.J.
      • Choi Y.J.
      Structural growth, rumen development, and metabolic and immune responses of Holstein male calves fed milk through step-down and conventional methods.
      compared how conventional (reduced milk and abrupt weaning) and step-down (increased milk and gradual weaning) feeding methods affected structural growth. They reported that both at weaning (d 49) and after weaning (d 63), step-down had increased HH compared with conventional. This differed from our results and could be due to our study having a HI and MOD MR amount offered with AB and GR weaning, whereas in the study by Khan and colleagues, calves only had a moderate level of milk with abrupt weaning (10% of BW for 44 d) and a high level of milk with gradual weaning (20% of BW for 23 d, reduced over 5 d, and then 10% of BW for 16 d). No other differences were detected between weaning methods in the present study. Final BW, HW, and HH did not differ among treatments. However, the advantages seen at weaning (greater ADG, BW, and FE;
      • Klopp R.N.
      • Suarez-Mena F.X.
      • Dennis T.S.
      • Hill T.M.
      • Schlotterbeck R.L.
      • Lascano G.J.
      Effects of feeding different amounts of milk replacer on growth performance and nutrient digestibility in Holstein calves to 2 months of age using different weaning strategies.
      ) were lost, and all calves are the same in BW and structural growth by d 56 of the experiment (
      • Dennis T.S.
      • Suarez-Mena F.X.
      • Hill T.M.
      • Quigley J.D.
      • Schlotterbeck R.L.
      • Hulbert L.
      Effect of milk replacer feeding rate, age at weaning, and method of reducing milk replacer to weaning on digestion, performance, rumination, and activity in dairy calves to 4 months of age.
      ).

      Diet Digestibility

      Table 3 shows the apparent dC for d 14, 35, and 56, as well as these measurements combined, to identify digestibility differences over the entire 56-d postweaning phase and by sampling period. At d 14, no dC differences were detected between AB and GR weaning for NDF or ADF.
      • Hill T.M.
      • Quigley J.D.
      • Bateman II, H.G.
      • Suarez-Mena F.X.
      • Dennis T.S.
      • Schlotterbeck R.L.
      Effect of milk replacer program on calf performance and digestion of nutrients in dairy calves to 4 months of age.
      also reported no differences in NDF or ADF based on a more abruptly weaned and a more gradually weaned treatment at d 14, indicating that, early in the postweaning phase, weaning strategy did not help stimulate rumen development enough to increase fiber digestion. At d 35, apparent dC of DM and ADF were greater for GR than for AB. The same increase in ADF dC for gradual compared with abrupt weaning was reported by
      • Dennis T.S.
      • Suarez-Mena F.X.
      • Hill T.M.
      • Quigley J.D.
      • Schlotterbeck R.L.
      • Hulbert L.
      Effect of milk replacer feeding rate, age at weaning, and method of reducing milk replacer to weaning on digestion, performance, rumination, and activity in dairy calves to 4 months of age.
      at d 35. This shift from no differences seen in ADF dC at d 14 to greater ADF dC in GR compared with AB at d 35 could be the result of cellulolytic bacteria within the rumen taking a longer time to establish (
      • Anderson K.L.
      • Nagaraja T.G.
      • Morrill J.L.
      • Avery T.B.
      • Galitzer S.J.
      • Boyer J.E.
      Ruminal microbial development in conventionally or early-weaned calves.
      ), causing GR weaning to have a delayed increase in ADF dC. At d 56, apparent dC for starch was greater for GR than for AB weaning (P = 0.01). Again, this transition, from no differences seen initially (d 14 and 35) in starch dC to greater starch dC in GR compared with AB weaning at d 56, indicates that gradual weaning has a positive carryover effect on dC for both structural and nonstructural carbohydrates. The only differences seen over the entire 56 d were greater DM and ADF dC for GR than for AB. This indicates that gradual weaning can have a positive influence on nutrient digestion by promoting starter consumption and stimulating rumen development before weaning, better preparing the animal to transition to solid fed digestion after weaning.

      CONCLUSIONS

      Evaluating postweaning responses to milk replacer amount and weaning strategy revealed that gradual weaning is significantly effective when used to transition calves on a high milk replacer regimen. Postweaning, we observed that the increased growth parameters seen before weaning lasted through d 35 (∼91 d of age), but all treatments converged by d 56 of the study (∼112 d of age). No significant differences were detected for ADG, final BW, final hip height, final hip width, or final BCS based on milk replacer amount or weaning strategy by d 56 (∼112 d of age). This confirms our hypothesis that calves fed high levels of MR would experience less growth postweaning than calves fed moderate MR, allowing the moderate-MR calves to reduce the growth gap by d 56 postweaning. We also found no apparent differences in digestibility coefficients at d 56 (∼112 d of age) between treatments, except for starch. In conclusion, calves on a program of moderate milk replacer did not benefit from an extended weaning period of 3 wk, as in gradual weaning, compared with 1 wk as in a single-step weaning. However, when calves are administered a high amount of milk replacer, the regimen should be paired with a gradual weaning process, to ensure successful growth and development.

      ACKNOWLEDGMENTS

      The authors thank members of the Clemson Ruminant Nutrition Team (Clemson University, Clemson, SC) and personnel at the Provimi Nurture Research Center (Brookville, OH) for their assistance throughout the duration of this project. The authors thank Provimi North America (Brookville, OH). This work was supported by the USDA National Institute of Food and Agriculture (Washington, DC; NC-2042) and Provimi North America. The authors have not stated any conflicts of interest.

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