Graduate Thesis Or Dissertation
 

Some effects of diethylstilbestrol on sexual maturation and growth of male calves

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  • Six experiments were conducted to determine the effects of DES implantation on preweaning performance and sexual maturation of male calves when implanted at various stages of development and different sites. Calves receiving DES implants in Experiments I and II were implanted at birth, at birth and at about three months of age, or at about three months of age. Some of the calves in Experiment I were left intact until slaughter, while the remainder of the calves in the first two trials were castrated two weeks prior to weaning. Statistical analysis of data from the first trial showed that calves implanted (12 mg.) at birth gained significantly (P < .05) faster to three months of age than did non-implanted calves and held a slight advantage to weaning. An advantage in preweaning performance was not observed for implanted calves in Experiment II. However, there was a significant (P < .01) reduction in the average external diameter of seminiferous tubules in calves receiving two preweaning implants. In both trials, DES treatment caused a delay in development of secondary sex characteristics, such as crest, increased shoulder development and curly hair about the head. In Experiment IIIa there were no differences in preweaning performance and sexual maturation between bull calves implanted at birth and at three months of age and those implanted at three months of age. In yearling bulls with the same treatments (Experiment IIIb) there was a delay in the onset of semen production. Bull calves in Experiment IV received implants at birth, at three months of age, at weaning and after 110 days in the feedlot; the same treatment without the birth implant; or no DES implants. There was a trend toward increased average daily gain with increasing levels of DES. The testes weight was significantly (P < .01) decreased by DES treatment. Furthermore, testes weights of the two DES treatments were significantly (P < .05) different. There was a significant (P < .01) reduction in average external seminiferous tubule diameter with each increase in DES level. Two levels of scrotal DES implants at birth plus ear implants at three months of age were compared to two levels of ear implants at birth plus ear implants at three months of age. In this experiment (Experiment V) scrotal implants did not cause an increase in gain to three months, but there was an advantage over the controls to weaning. Gains were similar for scrotal and ear implants to weaning. At weaning there was a significant (P < .01) reduction in testes weight and average external seminiferous tubule diameter with DES treatment. Experiment VI dealt with bull and steer calves implanted with DES at three different stages of development prior to weaning. At slaughter the inside diameters of the urethras were measured at four locations. Urethra diameter was significantly (P < .01) reduced by castration. DES implants caused a significant (P < .01) increase in the inside diameter of the urethras of steers, but had no effect in bulls.
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