Some observations on the effectiveness of anabolic agents in increasing the growth rate of poultry

This paper will discuss data obtained on the growth promoting effects of metabolically active agents for avian species generally used for food production. The compounds to be considered are those with estrogenic, androgenic, or thyroid hormone activity. Estrogens have been studied most extensively with poultry. At physiologically active levels, estrogens markedly stimulate food intake and at times, weight gain. There is a marked increase in fattening in chickens fed estrogenic compounds and generally a decrease in nitrogen retention. There seems to be a particular stimulation of lipogenesis of estrogenic compounds to the extent that protein synthesis is depressed. Generally high levels of estrogenic compounds are required for metabolic effects. Estrogens have marked effects on circulating nutrient levels and also decrease the choline requirement of growing chicks. Thyroid active substances have been extensively studied. Iodinated casein has been shown to stimulate early growth especially in growing ducks. Efficiency of feed utilization is depressed by feeding iodinated casein and body fat content is reduced. Feathering may be improved by thyroid hormone and in species where feathers are economically imported, it is sometimes advantageous to use these compounds. Methyltestosterone has been shown to be growth stimulating for female chickens and turkeys but relatively ineffective for males. In general, androgens seem to be somewhat less effective in stimulating growth rate and nitrogen retention in domestic birds compared to effects observed in mammals. The role of growth hormone as an anabolic agent in birds is somewhat obscure. Mammalian growth hormone preparations seem ineffective in poultry. The anabolic agents that will be considered in this paper are the hormone active substances with estrogenic, androgenic, or thyroid activity. These will be considered primarily as they affect growth and carcass composition of various species of poultry and not in their normal physiological roles. When considering the role of these compounds in production of human food through their effects on animals, the effects on growth rate, feed efficiency, and carcass composition are primary traits of concern and many other interesting aspects of the physiological effects of these compounds cannot be considered. The paper will not be an exhaustive review of the literature but will attempt to document the effects of these agents on the productive characteristics of poultry.