Energy requirements and cow/calf efficiency of Nellore and Continental and British Bos taurus x Nellore crosses

¹ Department of Animal Production, College of Agriculture "Luiz de Queiroz", University of Sao Paulo, Piracicaba, SP, Brazil
² Southeast-Cattle Research Center, Embrapa, Sao Carlos, SP, Brazil

^* To whom correspondence should be addressed. E-mail: dplanna{at}esalq.usp.br.

	Abstract

The objective of this work was to compare different breed types with increasing percentage of B. taurus on cow/calf energy requirements and pre-weaning efficiency. Forty mature, lactating, 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 from crossbred cows were sired by Canchim bulls ( Charolais + Zebu), while calves out of NL cows were sired by Nellore bulls. Cows were individually fed a pelleted diet with 50% hay (alfalfa and coastcross) and 50% concentrate from calving to weaning (20 to 180 d postpartum). Estimated diet metabolizable energy (ME) content was 2.24 Mcal/kg DM. Individual cow DMI was adjusted every 14 d to keep shrunk body weight (SBW) and body condition score (BCS) constant. Shrunk BW and BCS were 430 ± 12 kg and 4.7 ± .09 for NL, 449 ± 10 kg and 4.8 ± .09 for CN, 496 ± 10 kg and 5.0 ± .09 for AN, and 507 ± 12 kg and 5.1 ± .09 for SN. At 40 d calves were allowed ad libitum access to the same diet. Milk yield was recorded using a weigh-suckle-weigh technique. Increasing B. taurus percentage had a linear effect (P < .01) on MEI of cow/calf pairs: 21.9 ± 0.38 for Nellore, 23.6 ± 0.35 for 31.5% B. taurus (CN) and 25.6 ± 0.27 Mcal/d for 50% B. taurus (AN and SN). B. taurus percentage was also positively associated with milk production. Nellore calves had lower (P < .05) weaning weight (kg) than crossbreds: 167 ± 12 vs. 206 ± 10 for Canchim Nellore (C), 220 ± 11 for Canchim Angus Nellore (A) and 228 ± 11 for Canchim Simmental Nellore (S). Calf body composition was estimated at weaning using the 9-10-11^th rib section. Retained energy (Mcal) was higher (P < .05) in A (384 ± 19.9) than in Nellore (298 ± 21.6) and C calves (312 ± 19.8), and intermediate in S calves (333 ± 21.6). Cow/calf energetic efficiency (kcal deposited/Mcal of MEI by the pair) was higher (P < .05) for AN (103 ± 5.3) than NL (84.9 ± 5.9), CN (83 ± 5.3) and SN pairs (83.5 ± 6.1). Difference (P < .05) between Continental and British crosses was shown in linear contrast; SN pairs had higher MEI and lower RE than AN. Increasing B. taurus percentage increased inputs as well as outputs. However, a relatively greater increase in outputs resulted in significantly greater pre-weaning efficiency. Purebred Nellore had lower ME requirements, however, in an environment without nutritional constraints, crossbreeding improved pre-weaning biological efficiency.

Key Words: biological efficiency, body composition, crossbreeding, milk production, weaning weight