Exigências e eficiência energética de vacas de corte Nelore e de cruzamento Bos Taurus x Nelore. / Energy requirements and energetic efficiency of nellore and crossbred bos taurus x nellore beef cows.

AUTOR(ES)
DATA DE PUBLICAÇÃO

2004

RESUMO

Forty mature, lactating and non-pregnant cows (10 Nellore – NL; 10 Canchim x Nellore – CN; 10 Angus x Nellore – AN; and 10 Simmental x Nellore – SN) were randomized in blocks by calving date. Calves out of crossbred cows were sired by Canchim bulls, while calves out of NL cows were sired by Nellore bulls. Cows were individually fed from postpartum to weaning (15-180 d) a pelleted diet made of 50% hay (15% alfalfa and 35% Coastcross) and 50% concentrate. Diet had 16.1% CP and 2.24 Mcal of metabolizable energy (ME) on a DM basis. Amount offered to each individual cow was adjusted every 14 days to maintain shrunk body weight (SBW) and body condition score (BCS). SBW and BCS were 430 and 4.7, 449 and 4.8, 496 and 5.0, and 507 and 5.1 for NL, CN, AN and SN, respectively. At 40 days of age calves had access to the same diet of their dams ad libitum. Milk yields were determined at 52, 66, 94, 122 and 178 days postpartum by weighting calves before and after suckling. Cows were milked at 80 and 150 days postpartum and the samples analyzed for fat, protein, and lactose. Daily ME intake by NL cows (19.7 Mcal/d) was lower (P<0.05) compared to CN (20.6Mcal/d), AN (23.1 Mcal/d) and SN (23.7 Mcal/d). These results were positively correlated with milk yield (P<0.05). Nellore calves had lower weaning weight than crossbreds (P<0.05): 165.8 vs. 205.5 for ¾Canchim¼Nellore (¾C¼N), 216.4 for ½Canchim¼Angus¼Nellore (½C¼A¼N) and 215.4 kg for ½Canchim¼Simmental¼Nellore (½C¼S¼N). In association with the lowest weight gain, Nellore calves had lower (P<0.05) metabolizable energy intake (ME from milk plus ration, Mcal). Calves were slaughtered at weaning and body composition estimated using the 9-10-11th rib section. Body energy at weaning (Mcal) was higher (P<0.05) for ½C¼A¼N than ¾C¼N and Nellore calves: 462.6 vs. 384.0 and 321.8 Mcal, respectively. Calves ½C¼S¼N had intermediate body energy at weaning: 429.8 Mcal. Cow/calf energetic efficiency was higher (P<0.05) for AN compared to NL cow/calf pairs: 124.4 vs. 95.8 kcal deposited/Mcal of ME consumed by cow and calf. Results for Canchim and Simmental were intermediate: 105.2 and 107.0 kcal/Mcal, respectively. The higher ME intakes by Angus cow/calf pairs were more than compensated by the higher energy retention and body weight gain compared to NL. In an unrestricted nutritional setting, crossbreeding improved cow efficiency as measured by body energy/total feed energy input to cow and calf. Reproduction was not evaluated, and the lower intakes and daily energy requirements demonstrated for Nellore could be beneficial in a nutritionally limited environment.

ASSUNTO(S)

body composition animal nutrition milk yield nutrição animal calf genotype genótipo leite (produção) cruzamento animal beef cattle bezerro composição corporal crossbreeding bovino de corte

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