Staigmiller R B, Brownson R M, Kartchner R J, Williams J H
J Anim Sci. 1985 Feb;60(2):342-51. doi: 10.2527/jas1985.602342x.
Two trials were conducted to study the effect of zeranol implants on growth and sexual development of bull calves. Trial 1 compared the effects of implanting with 72 mg of zeranol at 48 d of age (branding), at 215 d of age, or at both times with nonimplanted control bulls. Implanting at branding resulted in decreased scrotal circumference, testicle weight and proportion of bulls that could produce an ejaculate at 14 mo of age (P less than .01). Implanting at 215 d of age had no effect on any of these traits. Growth rate was not increased by implanting at either time but was decreased (P less than .02) in animals implanted at both times when compared with control bulls. In trial 2, both bulls and steers were implanted with zeranol and compared with nonimplanted control bulls and steers. Thirty-six-milligram implants were given at 21, 103, 260 and 343 d of age. Scrotal circumference, testicle weight and serum testosterone concentrations decreased (P less than .01) and the occurrence of penis abnormalities increased (P less than .01) in implanted bulls compared with control bulls. By the time of slaughter, however, testosterone concentrations were equal in control and implanted bulls; and the difference in scrotal circumference was diminishing. This is interpreted as evidence that as the bulls get older, they can overcome the effect of the implants. Carcass weights were heavier in implanted steers than in control steers but were lighter in implanted bulls than in control bulls (P less than .02). Carcasses of implanted bulls had higher quality scores and more marbling than control bulls, but carcasses of implanted steers had lower quality scores and less marbling than control steers (both interactions, P less than .01). Implanting bulls with zeranol at an early age resulted in restricted sexual development but not in total sterility. Repeated zeranol implants throughout the growing and finishing phase enhanced carcass quality in bulls slaughtered at 14 to 16 mo of age.
进行了两项试验以研究玉米赤霉醇植入剂对公牛犊生长和性发育的影响。试验1比较了在48日龄（烙印期）、215日龄或两个时间点均植入72毫克玉米赤霉醇与未植入的对照公牛的效果。在烙印期植入导致阴囊周长、睾丸重量以及14月龄时能射精的公牛比例降低（P < 0.01）。在215日龄植入对这些性状均无影响。在任何一个时间点植入均未提高生长速度，但与对照公牛相比，在两个时间点均植入的动物生长速度降低（P < 0.02）。在试验2中，公牛和阉牛均植入玉米赤霉醇，并与未植入的对照公牛和阉牛进行比较。在21、103、260和343日龄给予36毫克的植入剂。与对照公牛相比，植入的公牛阴囊周长、睾丸重量和血清睾酮浓度降低（P < 0.01），阴茎异常的发生率增加（P < 0.01）。然而，到屠宰时，对照公牛和植入公牛的睾酮浓度相等；阴囊周长的差异正在减小。这被解释为随着公牛年龄增长，它们能够克服植入剂影响的证据。植入的阉牛胴体重量比对照阉牛重，但植入的公牛胴体重量比对照公牛轻（P < 0.02）。植入公牛的胴体质量评分和大理石花纹比对照公牛高，但植入阉牛的胴体质量评分和大理石花纹比对照阉牛低（两者的交互作用，P < 0.01）。早期给公牛植入玉米赤霉醇会导致性发育受限，但不会导致完全不育。在生长育肥阶段反复植入玉米赤霉醇可提高14至16月龄屠宰公牛的胴体质量。
