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Arquivo Brasileiro de Medicina Veterinária e Zootecnia

Print version ISSN 0102-0935On-line version ISSN 1678-4162


MACHADO, P.F.A.; BERGMANN, J.A.G.; PEREIRA, J.C.C.  and  SILVA, M.A.. Prediction of pregnancy rate of Nellore heifers mated at yearling age. Arq. Bras. Med. Vet. Zootec. [online]. 2001, vol.53, n.2, pp.1-10. ISSN 0102-0935.

The objectives of this experiment were to quantify the relationships among variables observed before the breeding season and fertility of 321 Nelore heifers and to use these variables to fit prediction equations for heifers fertility, using logistic regression methodology. Variables analysed were: birth weight, weaning weight, yearling weight and birth-weaning, birth-yearling and weaning-yearling average daily gains and relative growth rates, age of heifer at breeding and age of cow at calving. Heifers conceiving in the breeding season were 18 days older at the beginning of the breeding season than those failing to conceive. Pregnant heifers in the breeding season were 1.1kg lighter at birth than not pregnant heifer. Heifers conceiving in the breeding season had, on the average, 0.01% more preweaning and birth-yearling relative growth rates than those that failed to conceive and they were daughters of younger cows at calving. The full model accounted for 26.6% of the total variation in heifers fertility. Fitted model including linear effect of age of heifer at the beginning of the breeding season and birth-yearling relative growth rate was the best model to predict heifers fertility.

Keywords : Heifer; Nellore; fertility; sexual precocity; pregnancy rate.

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