Abstract
The effects of weaning age (90 days or 156 days) of female beef calves were evaluated on their subsequent performance from the beginning of the first pregnancy and the end of the second breeding season, at 22/24 months of age. During pregnancy, heifers were managed as a single group on Brachiaria brizantha cv. Marandu pasture; after calving, on bristle oats (Avena strigosa Schreb) and ryegrass (Lolium multiflorum Lam.); and on Brachiaria humidicula pasture during the second reproductive period. The characteristics studied were not influenced by calf weaning age. Heifers submitted to early or conventional weaning weighed 354.5 and 351.9 kg in the post-calving, and 363.4 and 359.2 kg when they weaned their calves. Average daily gain during the breeding season was 0.562 kg, and body condition score was 3.10 and 3.93 at the beginning and end of the experiment, respectively. Average calf birth and weaning weights were not influenced by dam weaning age, and were 28.7 ± 0.74; 86.5 ± 3.26 and 27.4 ± 0.92; 90.3 ± 4.04 kg, respectively, for dams submitted to early or conventional weaning. Dystocia, calving, birth, and weaning rates were not different between weaning ages, with mean values of 29.5; 95.3; 77.3 e 73.4%. Conception rates were 47.9% in the initial third and 40.8% in the second third versus 11.3% in the final third of the breeding season. Heifer average age at conception was 438 and 434 days for early weaning and conventional weaning. Pregnancy rates and production efficiency estimates at calving and calf weaning were not affected by heifer weaning age. Heifer early weaning did not affect their subsequent performance until the end of the second breeding season, at 22/24 months of age.
Highlights
Reproductive efficiency is essential in breeding-tofattening systems or cow-calf systems, where cows are Fagundes et al, 2003)
Pregnancy rates and production efficiency estimates at calving and calf weaning were not affected by heifer weaning age
Simeone (1995) quoted by Lobato (1997), obtained 71.3% average pregnancy rates in cows submitted to early weaning, and 28.3% in cows whose calves were weaned at 7 months of age
Summary
The use of management practices, such as early weaning, is required to improve reproductive efficiency (Simeone & Lobato, 1996; Restle et al, 2001; Almeida et al, 2002). Simeone (1995) quoted by Lobato (1997), obtained 71.3% average pregnancy rates in cows submitted to early weaning, and 28.3% in cows whose calves were weaned at 7 months of age. Early weaning is an alternative to improve body condition and pregnancy rates of cows in beef systems with high stocking rates or to attenuate annual weather effects, which are frequent in pasture systems, as it eliminates the nutritional cost of lactation, decreasing beef cow nutritional requirements (Lobato et al, 2000; Restle et al, 2001). Considering the need to intensify production systems and to obtain higher productivity in kg of weaned calf per female bred, this study was carried out to evaluate the reproductive and productive performance of primiparous cows weaned, on average, at 90 days or 156 days of age
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