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Effects of milk replacer feeding rate and frequency on metabolic responses of dairy calves during summer and winter.

R. M. Orellana Rivas

Abstract:

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Effects of milk replacer feeding rate and frequency on metabolic responses of dairy calves during summer and winter.
R. M. Orellana Rivas*, T. Rodrigues, J. Silveira, V. Lacerda, J. Gao, D. Ferreira de Ara�jo, J. Souza, T. N. Marins, J. K. Bernard, S. Tao. University of Georgia Tifton, GA.

Holstein calves (n = 48/season) were enrolled at 7 d of age in the summer (June to Aug, BW = 40.6 � 0.7 kg) and winter (Nov to Jan, BW = 41.9 � 0.8 kg) to evaluate the effect of milk replacer (MR) feeding rate (FR) and frequency (FF) on metabolic responses. In each season, calves were randomly assigned to 1 of 4 treatments (TRT) in a 2 � 2 factorial arrangement including 2 FR (0.68 [LOW] or 0.79 kg of solid/d [HIGH] of a 26% CP and 17% fat MR) and 2 FF (2 � [0700 and 1600 h] or 3 � [0700, 1600, and 2200 h]). Calves were managed similarly and housed in polyethylene hutches with sand bedding. Milk replacer (12.5%) was fed until d 42 when FR was reduced by half and offered 1 � /d (0700 h) for 7 d. Average ambient temperatures were 23.3 � 2.4 in summer and 10.5 � 5.5�C in winter. A subset of calves (n = 8/TRT/season) was subjected to an intravenous glucose tolerance test (GTT) on d 28 and insulin challenge (IC) on d 29 of age at 1000 h. Plasma was collected at −15, −5, 0, 5, 10, 15, 20, 30, 40, 50, 60, 75, 90, 120 min relative to glucose (GLC) or insulin (INS) infusion to analyze GLC, nonesterified fatty acids (NEFA) and INS. Data were analyzed using PROC GLM of SAS. Following GTT in both seasons, 3 � reduced (P ≤ 0.05) INS increment and area under the curve (AUC) than 2 � . Calves fed HIGH tended to have lower (P = 0.07) GLC AUC from 0 to 30 min following GTT than LOW only during winter. In both seasons, INS clearance following IC was similar among TRT (P > 0.10). During IC in the summer, 3 � lowered (P < 0.01) GLC AUC and NEFA AUC from 0 to 30 min than 2 �; and LOW with 2 � lowered NEFA AUC from 0 to 60 or 0—120 min than LOW with 3 �, both of which were similar to HIGH regardless of FF (FF � FR: P = 0.04). During IC in the winter, 3 � lowered (P ≤ 0.03) GLC AUC from 0 to 60 or 0—120 min compared with 2 �, and HIGH calf with 3 � had lowest decrement of NEFA and greatest AUC from 0 to 30 or 0—60 min than other TRT (FF � FR: P ≤ 0.04). In conclusion, increasing FF from 2 to 3 � /d reduced pancreatic INS secretion but improved INS dependent GLC uptake in both summer and winter, but the inhibitory effect on lipolysis was inconsistent between seasons.

Keywords: calf, season, metabolism.