Effects of Dietary Chromium on the Egg Yield and Reproductive Hormone Secretion of Laying Hens

Seventy two laying hens, 25 weeks of age, were randomly allocated into 3 groups and fed with diets containing 5.09,10.09,55.09 mg/kg chromium respectively for 4 months. Egg yield was observed. Estrodiol(E 2), progesterone(P) and luteinizing hormone(LH) were determined by radioimmunoassay ( RIA).Follicular cells were cultured with pituitary cells or hypothalamus extracts. Different dosages of chromium were added to the culture medium to observe the influence of chromium on concentrations of E 2 or P secreted by in vitro cultured follicular cell F 3 and F 1 respectively. The results showed that the rations containing 10.09 mg/kg chromium suited the hens better and enhanced egg productive ratio so as to prolong the laying peak period (>90%) . Proper concentration of chromium could directly affect the secretion of E 2 by follicular cells to a significant extent ( P <0.01) .The mechanisms concerning how chromium affected the endocrine activity of laying hens as well as the association with the metabolism of glucose and lipids were also discussed.