Low fertility in aging roosters is related to a high plasma concentration of insulin and low testicular contents of ACTH and lactate.

Fertility in roosters peaks between 30 and 40 weeks of age and declines rapidly from about 50 weeks of age. Low-fertility, aging roosters have a higher density of elongated spermatids attached to Sertoli cells than do high-fertility roosters, but display normal spermatogenesis and ejaculated spermatozoa. Plasma levels of insulin and lactate and testicular contents of ACTH and lactate were compared in Cornish roosters aged 27 weeks (early state of sexual maturity), 37 weeks (high fertility), 67 weeks (reduced fertility), and 72 weeks (low fertility). Insulin may act as an endocrine regulator of Sertoli cell function, and ACTH as an autocrine regulator of Leydig cells for androgen production and as a paracrine regulator of Sertoli cells by amplifying FSH response. Lactate is the primary energy substrate of spermatocytes and spermatids in the adluminal compartment. Roosters aged 67 and 72 weeks had higher (P < 0.05) plasma insulin levels but lower (P < 0.05) testicular lactate content than roosters aged 27 and 37 weeks. The lower lactate content in testes of low-fertility roosters may reflect an increased consumption of lactate due to the higher density of elongated spermatids. Furthermore, the content of testicular ACTH was lower in low-fertility roosters than in 27-week-old roosters. These results suggest that ACTH may be involved indirectly in the mechanism responsible for the high density of spermatids in the tubuli and the lower spermatozoa concentration in the ejaculate of low-fertility roosters, as was reported in previous studies, since this hormone may serve as a paracrine regulator of Sertoli cell function.