Growth and Sexual Characteristics of Suckling Beef Calves as Influenced by Age at Castration and Growth Implants

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Abstract
A 2-yr study using crossbred male calves (n = 228) evaluated castrating at birth or at 4 mo of age and use of anabolic growth implants (none, zeranol or estradiol-17β). Angus, Hereford and Brahman crossbred calves produced in seven cow-calf units that varied by breed component, stocking rate and calving season were allotted to treatment at birth in a 2 × 3 factorial arrangement. Growth implants decreased (P < .01) testicular weight and expression (P < .05) of male secondary sex characteristics in suckling bull calves at 4 mo. Implanted calves were shorter (P < .05) at the hips and had shorter front legs (P < .01) at both 4 mo and at weaning. Cannon bone circumference at weaning was increased (P < .05) by growth implants. Age at castration did not affect (P > .05) calf performance or body characteristics. Calves given growth implants had higher (P < .05) rates of gain from birth to 4 mo than did nonimplanted calves (.75 vs .71 kg/d). Implanted calves were heavier (P < .01) at weaning and had higher (P < .01) ADG from 4 mo to weaning than did nonimplanted calves. These data indicate no benefit from delaying age at castration, but implanting increased weaning weight an average of 8.2 kg. Copyright © 1989. American Society of Animal Science . Copyright 1989 by American Society of Animal Science