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

The objective of this work was to compare breed types with increasing percentage of Bos taurus on cow/ calf energy requirements and preweaning efficiency. Forty mature, lactating, nonpregnant 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 ( 5/ 8 Charolais + 3/8 Zebu), whereas calves from 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 ME content was 2.24 Mcal/ kg of DM. Individual cow DMI was adjusted every 14 d to keep shrunk BW and BCS constant. Shrunk BW and BCS were 430 +/- 12 kg and 4.7 +/- 0.09 for NL, 449 +/- 10 kg and 4.8 +/- 0.09 for CN, 496 +/- 10 kg and 5.0 +/- 0.09 for AN, and 507 +/- 12 kg and 5.1 +/- 0.09 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 < 0.01) on ME intake ( 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). Bos taurus percentage was also positively associated with milk production. Nellore calves had lower ( P < 0.05) weaning weight ( kg) than crossbreds: 167 +/- 12 vs. 206 +/- 10 for 3/4 Canchim 1/4 Nellore (3/4C), 220 +/- 11 for 1/2 Canchim 1/4 Angus 1/4 Nellore (1/4A) and 228 +/- 11 for 1/2 Canchim 1/4 Simmental 1/4 Nellore (1/4S). Calf body composition was estimated at weaning using the 9- 10- 11th- rib section. Retained energy ( Mcal) was greater ( P < 0.05) in 1/4A ( 384 +/- 19.9) than in Nellore ( 298 +/- 21.6) and 3/4C calves ( 312 +/- 19.8), and was intermediate in 1/4S calves ( 333 +/- 21.6). Cow/calf energetic efficiency ( kcal deposited/ Mcal of MEI by the pair) was greater ( P < 0.05) for AN ( 103 +/- 5.3) than NL ( 84.9 +/- 5.9), CN ( 83 +/- 5.3), and SN pairs ( 83.5 +/- 6.1). Difference ( P < 0.05) between Continental and British crosses was shown in linear contrasts; SN pairs had greater MEI and lower retained energy than AN. Increasing the B. taurus percentage increased inputs as well as outputs. However, a relatively greater increase in outputs resulted in significantly greater preweaning efficiency. Purebred Nellore had lower ME requirements; however, in an environment without nutritional constraints, crossbreeding improved preweaning biological efficiency.