RESUMEN
The present study is an attempt to shed more light on the role of epinephrine (EP) and norepinephrine (NE) in regulating ovarian follicular development, folliculogenesis and ovulation in laying hens. Sixty Egyptian local cross females (Mandarah), 50 weeks old, were individually housed and equally divided into three treatments: control (saline, 0.9% NaCl), EP (0.15 mg epinephrine/hen/day) and NE (0.75 mg norepinephrine/hen/day) (n=20). Animals were injected intramuscularly once a day for 15 successive days. At the end of the experimental period, 10 females from each treatment were randomly chosen, weighed and killed by decapitation. Ovaries and oviducts and ovarian follicles were examined. Plasma concentrations of estradiol-17beta, progesterone, zinc and triglyceride were determined. Results indicated that the ovaries of NE- and EP-treated hens were more developed than those of control hens being heavier and containing more yellow yolk-filled follicles. EP or NE significantly increased the ovulation rate and plasma concentrations of estradiol-17beta, progesterone, zinc and triglyceride compared with control treatment. It could be concluded that catecholamines may have a part in promoting ovarian follicular development and in stimulating ovulation in laying hens at the end of their reproductive lives.