EFFECT OF GONADAL-STEROIDS ON BONE AND OTHER PHYSIOLOGICAL-PARAMETERSOF MALE BROILER-CHICKENS

Comparative studies of the effects of estradiol, progesterone, testost erone, cholesterol, and megestrol on juvenile chickens were carried ou t to determine their effects on bone and other physiological parameter s. The chickens were implanted at 6 wk of age with ethylene-vinyl acet ate copolymers containing steroids equivalent to a weekly dose of 10 m g/kg body weight for 3 consecutive wk. Estradiol caused a gain in body weight and relative liver weight but suppressed the growth of comb an d testis. It also increased several serum variables, including triglyc erides, cholesterol, calcium, phosphorus, and iron, and reduced testos terone levels. Testosterone produced an increase in comb weight and de creased both testicular and bursal weights. Growths of testis and comb were suppressed in progesterone-implanted chickens, as was the level of serum testosterone. Megestrol stimulated liver growth and increased serum testosterone levels. The lengths, relative weights, diaphyseal diameters, and ash percentages of both femur and tibia did not change significantly due to any treatment except that estradiol reduced tibia l weight. Both progesterone and megestrol increased fibular growth pla te alkaline and tartarate-resistant acid phosphatase activities. Other steroids did not affect these or the levels of calcium and of phospho rus of the fibular growth plate. Only testosterone caused a marked inc rease in the breaking strengths of both femur and tibia in all three p arameters, i.e., load at yield, Young's modulus, and stress at yield r esponses. These findings suggest that the effects of steroids on bone in juvenile chickens may be limited.