Effect of Epinephrine and Bromocriptine on Ovary Folliculogenesis and Productive Traits of Laying Hens

Egg production rate is a positive economical factor in commercial laying hens. In egg industry, the only source of income is the number and weight of eggs laid in a laying cycle, therefore, researchers have been trying to find approaches to increase the egg number in each laying cycle. In general, a hen lays eggs in clutches with a pause of one or a few days in between the clutches (pause days). The exact physiological mechanism involved in taking a pause between the sequences is not fully understood. In fact, it has been considered that increasing concentration of prolactin (PR) plays a role in the cessation of egg laying and broodiness during the active period of lay (Lea et al. 1981; Sharp et al. 1998). Li et al. (2011) indicated that immunization against PR slows down ovarian follicular development and reduced hen egg-laying performance, suggesting that PR plays a stimulatory role in ovarian follicular development in laying hens. Probably prolactin acts at all levels of the hypothalamus-hypophysis-gonadal axis and inhibits reproductive function (Camper and Burke, 1977). It has been suggested that an increase in plasma PR concentration during the incubation period may decrease luteinizing hormone (LH) secretion (Sharp et al. 1998).The secretion of PR from the anterior pituitary gland is regulated by dopamine. Dopamine inhibits the stimulatory action of vasoactive intestinal peptide (VIP), a PR releasing hormone, through receptors (D2), thereby decreasing the PR secretion to overcome broodiness in chicken (Sharp et al. 1989). Reddy et al. (2001) demonstrated that the use of bromocriptine, a dopamine agonist, during early life (from 17 to 36 weeks of age) of White Leghorn hens resulted in an An experiment was conducted to study the effect of Epinephrine (EP) and bromocriptine (BR) on productive traits of laying hens. Thirty White Leghorn hens, 50 weeks old, were divided into three equal treatments (with 10 hens for each treatment): control, physiological serum (0.5 mL/hen/week), EP (0.5 mL/hen/week) and BR (100 g/kg of body weight (BW); w/v in absolute alcohol). Hens were injected once a week for 10 weeks. At the end of the experimental period, all hens were killed by decapitation. Ovaries, oviducts and ovarian follicles were examined. Ovary folliculogenesis was affected (P<0.01) by EP and BR treatments. There were larger yellow follicle (LYF), smaller yellow follicle (SYF) and larger white follicle in EP and BR treated hens compared to control group respectively. EP and BR treatments shortened total pause length compared to control (P<0.01). Mean weekly egg production was higher (P<0.01) for treated hens with BR and EP compared to control group. Percentage of weekly egg production was higher (P<0.01) in treated birds compared to control group. It can be concluded that EP and BR may promote ovarian follicular development and stimulate ovulation in laying hens at the end of their reproductive cycle.