No abstract

. 1990. Efficacy and stress of chemical vetsus surgical castration of cattle. Can. J. Anim. Illood rvas collected at 0, 3, 6, 12,24,36 and

1984-1985 and 1985-1986

of chemical castration and effects of agi at castration and implant regime on growth rate, testicular measurements and testosterone levels of beef calves. Can. J. Anim. Sci. 71: 1-11. In 1984-1986

Crossbred beef heifers received a 36-mg implant of zeranol at 60 d of age (R1; n = 35) or at both 60 and 197 d (weaning; R2; n = 32) or received no implants (C; n = 35). R2 heifers were heavier and had greater pelvic areas (P < 0.05 for both) at breeding compared with controls. There was no effect of treatment on the calving rates (78.1 vs. 80.0 vs. 74.3%) or on mean pelvic area at the time of calving (261.1 vs. 260.4 vs. 257.6 cm2) for R2, R1 and C heifers, respectively. We conclude that zeranol can be successfully used for growth enhancement from 60 d of age without detriment to subsequent reproductive performance. Key words: Zeranol, heifers, pregnancy rate, pelvic area