EFFECT OF BIRTH WEIGHT, WEANING WEIGHT AND PREWEANING WEIGHT GAIN ON FERTILITY OF HOLSTEIN HEIFERS UNDER HOT MEXICAN CONDITIONS

摘要

Holstein calves(n= 767)from a commercial herd were used to determine the effect of birthweight(BW), weaning weight (WW) and preweaning average daily gain (ADG) on subsequent reproductive performance of heifers inseminated with sex-sorted semen in a hot environment (25 degrees N; mean annual temperature 23.7 degrees C). BW were divided into three groups: 36, 36-39 and 39 kg. WW were classified as 66, 66-74 and 74 kg. ADG was categorized as 450, 450-520 and 520 g. Of the heifers initially bred, 7.8% failed to conceive with services. Services/pregnancy were higher (p0.01) in heifers with low BW (2.42 +/- 1.39) than heifers with medium (2.13 +/- 1.38) and high BW (2.05 +/- 1.34). The proportion of heifers conceiving to the first service was lowest (27.9%; p0.01) in heifers with the lowest BW compared to heifers weighing 36-39 kg (36.3%) and 39 kg at birth (40.3%). However, neither BW, WW, nor ADG significantly affected (p0.10) all-service conception rate. Categories for BW, WW and ADG did not influence abortion rate (3.5% for all pregnant heifers). It was concluded that the heavier the Holstein calves are at birth and weaning, the shorter the age at calving under the present conditions, but low birth and weaning weight did not hamper all-service conception rate.