Efeito do dietilestilbestrol sobre o comportamento de novilhos da raça zebu, alimentados em pastagens

The results of ten comparisons of stilbestrol-treated steers and untreated steers are reported. All steers were on pasture during the trial period, and some steers received various kinds and amounte of supplemental feeds. In each experiment, a part of the steers in each pasture or treatment were implanted with stilbestrol, with the remainder left as untreated controls. A total of 1086 steers of Zebu breeds were included in the ten experiments, and the trials were from 224 to 364 days in length. Various kinds of supplements including ground ear corn, molasses, molasses-urea, and low-protein concentrates, and feed additives had no effect upon the response to stilbestrol (P>0.25) The implantation of stilbestrol increased the average daily gain by 111 g, which represented a 22% increase over the control steers. The increase in average daily gain for the winter-dry season was 100 g and for the summer-wet season 121 g, indicating that the response to stilbestrol with respect to increasing growth rate was not greatly different for the two seasons of the year. Even though the average daily gains of the steers during the severe winter-dry season of 1961 were very low, the increase for stilbestrol averaged 96 g per steer per day (Experiments 2, 4, 5, 0, 7, 8, 10). The production of liveweight gain per ha as influenced by stilbestrol was found to increase as the productivity and carrying capacity of the pasture increased. On a Colonial Guinea grass pasture with a carrying capacity of 1.2 steers per ha, the increase in live weight gain per hectare was 33 kg for the stilbestrol-treated steers. On a similar pasture fertilized with 200 kg of nitrogen per ha with a carrying capacity of 3.0 steers, the increase for the stilbestrol-treated steers was 117 kg of liveweight increase per hectare. In Brazil, the widespread use of stilbestrol on steers could increase the production of beef by 20%, reduce the amount of feed required to produce a kilogram of beef, shorten the period required to produce a slaughter animal and reduce the cost of production. At present prices, less than the price of 2 kg of live weight of beef is required to pay for the stilbestrol which will give an additional 40 kg of liveweight increase.Em dez experimentos separados, num total de 1.086 novilhos, o estilbestrol produziu um aumento na média de ganho de peso diário de 111 g e um aumento de 22% sobre os animais-de-controle que não receberam tratamento. O aumento na média de ganho de peso diário, durante o inverno seco, foi de 100 g por novilho e por dia e durante o verão úmido, de 121 g por novilho. Isto indica que o estilbestrol é quase tão eficaz durante os períodos de carência nutricional, como nas ocasiões em que as pastagens apresentam-se em boas condições. Uma vez que a lotação das pastagens aumentou de 1,2 a 3,0 novilhos, por hectare, como resultado da adubação nitrogenada, os novilhos tratados com estilbestrol produziram um ganho de peso vivo adicional de 33 kg/ha, quando não foi feita nenhuma aplicação de nitrogênio às pastagens, apresentando os mesmos um ganho de 117 kg/ha quando 200 kg desse elemento foram aplicados. O uso difundido do estilbestrol em novilhos destinados ao abate, no Brasil, poderia aumentar a produção de carne bovina em cerca de 20%, reduziria a quantidade de alimento necessário para produzir um quilograma de carne, abreviaria o período exigido para o abate e diminuiria o custo a produção. Aos preços atuais, um valor menor que o de 2 kg de peso vivo cobriria as despesas com o estilbestrol, o qual proporcionaria um aumento adicional de 40 kg de peso vivo por novilho