Submitted to: Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 28, 1995
Publication Date: N/A
Interpretive Summary: One of the major leg problems in poultry is the persistence of a plug of nonviable cartilage that extends from growth plate into the marrow space of tibial bone making the bone susceptible to breakage. This is a common occurrence in juvenile poultry when the growth rate is maximum and tends to dissipate automatically around the time of puberty. Since sex hormones are known to play a profound role in the process of growth as well as in mineralization and maintenance of skeletal tissues, we investigated the effects of exogenous steroids on growth and metabolism of bones as well as other physiological parameters of juvenile chickens. Six wk-old chickens were implanted with different sex steroids, a synthetic anabolic steroid megestrol, as well as their parent compound cholesterol, embedded in slow release polymer implants for following three consecutive wks. Both male and female sex steroids (testosterone, estrogen and progesterone) caused selective stimulation or suppression of growth of several target organs such as the comb, testis, bursa, and liver and changes in serum chemistry. There were no significant changes in the growth and mineralization of bones by any steroid. The androgen, testosterone, caused consistent increase in the strengths of both femur and tibia. It appears that while steroid hormones are capable of causing significant changes in several physiological parameters, the effect on bone is limited in juvenile poultry.
Technical Abstract: Comparative studies of the effects of estradiol, progesterone, testosterone, cholesterol, and megestrol on juvenile chickens were carried out to find their effects on bone and other physiological parameters. The chickens were implanted at 6 wk of age with ethylene-vinyl acetate copolymers containing steroids equivalent to a weekly dose of 10 mg/kg body weight for 3 consecutive weeks. Estradiol caused a gain in bod weight and relative liver weight but suppressed the growth of comb and testis. It also increased several serum variables including triglycerides, cholesterol, calcium, phosphorus, and iron while reducing testosterone levels. Testosterone produced an increase in comb weight and decreased the 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 ask percentages o both femur and tibia did not change significantly due to any treatment except that estradiol reduced tibial weight. Both progesterone and megestrol increased fibular growth plate alkaline and tartarate-resistant acid phosphorus activities. Other steroids did not affect these or the levels of calcium, and phosphorus of fibular growth plate. Only testosterone caused a marked increase in the breaking strengths of both femur and tibia in all three parameters; i.e., load at yield, Young's modulus, and stress at yield responses. These findings suggest that the effects of steroids on bone in juvenile chickens may be limited.