The effect of testosterone or estradiol on the development of TOCP-induced delayed neurotoxicity in immature broiler-breed cockerels

Immature cockerels were susceptible to OPIDN when dosed with TOCP. Using 30 broiler-breed cockerels, 6 w old, 10 birds each received 28 daily im injections of either 50 mg estradiol, 100 mg testosterone or 0.1 ml of vehicle. At 7 w of age, 5 birds in each of the 3 groups received a single oral dose of 500 mg TOCP/kg body weight, while the remaining 5 birds/groups were given corn oil. The birds were observed daily for 14 d beginning on day 8 post-TOCP exposure for the development of clinical signs characteristic of OPIDN. At 21 d post-TOCP, all birds were killed and the adrenal gland and testes were prepared for histopathology of the birds that received TOCP, 1 of 5 that were given testosterone and 2 of 5 that received estradiol had signs typical of OPIDN. All of the 5 birds that received TOCP alone showed OPIDN signs. The testes of the TOCP-exposed birds that showed clinical signs had reductions in the size of the seminiferous tubules and no evidence of spermatogenic activity. This study demonstrated that sex hormones can modulate the clinical effects of TOCP in immature cockerels through unknown mechanisms that are similar to those reported for corticosterone in adult chickens.