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Revista Brasileira de Zootecnia
On-line version ISSN 1806-9290
VAZ, Ricardo Zambarda and LOBATO, José Fernando Piva. Effects of the weaning age on the reproductive performance of beef heifers exposed to reproduction at 13/15 months old. R. Bras. Zootec. [online]. 2010, vol.39, n.1, pp. 142-150. ISSN 1806-9290. http://dx.doi.org/10.1590/S1516-35982010000100019.
The objective of the study was to evaluate, for two consecutive years, the weaning age effect on the reproductive performance of 121 Bradford heifers mated at 13/15 months old. Two weaning ages were assessed: at 77 days, early weaning (EW) or at 147 days, conventional weaning (CW). The heifers were born in 2004 (66) and 2005 (55). After weaning, heifers were kept initially on cultivated summer pasture (Pennisetum americanum, L.) and afterward on cultivated winter/spring pasture (Avena strigosa Schreb plus Lolium multiflorum Lam.). Live weight (LW), body condition (BC) and mean live weight gain (ADG) were evaluated during the mating period. Early weaning did not cause significant difference in weight at the beginning and end of the mating period. The heifers born in 2005 showed lower live weight during the mating than those born in 2004. The year influenced the body condition at the beginning and end of the mating that was, respectively, 4.16 and 4.29 points for heifers born in 2004, and 3.57 and 3.38 points for the ones born in 2005. Pregnancy rate was not affected by the heifer weaning age (55.5 and 70.7% for EW and CW heifers, respectively), nor by year (68.6 and 57.6% for heifers born in 2004 and 2005, respectively). Heifers that became pregnant had greater reproductive performance during the growing phase and mating period than those with negative diagnosis. The reproductive performance of the heifers was positively correlated with live weight and body condition at the beginning and end of the mating period. Early weaning did not affect the heifer reproductive performance at 13/15 months old.
Keywords : body condition; Bradford; early weaning; pregnancy; weight gain.