Meeting Abstract

P2-15   -   Mate presence and exogenous testosterone treatment reduce rapid yolk deposition in laying hens Dean, CR*; Mendonça, MT; Navara, KJ; University of Georgia; Auburn University; University of Georgia Crd72388@uga.edu

Avian egg yolks provide key nutrients and energy reserves for a growing embryo. Once a follicle is selected into the ovulatory hierarchy, rings of yolk precursors are deposited daily until the yolk is large enough to ovulate. The composition of hen egg yolk and the mechanisms responsible for deposition in the ovarian follicle are well-studied. The factors that affect the rate of yolk deposition, and the number of days it takes for follicles to grow to the ideal size for ovulation, are less well known. There is evidence that growth rates of ovarian follicles differ greatly within and between species, and even between individuals, yet the reasons for this variation remain unknown. We hypothesized that social interactions surrounding the female, as well as the hormones that respond to those interactions, should influence the rate of follicle growth. We tested whether exposure to a potential mate influences rates of yolk deposition in eggs of laying hens. We placed groups of hens into mixed-sex or unisex pens for four hours a day for four days. We then collected eggs and measured egg and yolk weights, yolk diameters, and stained the yolks with potassium dichromate to quantify the number of days the follicle spent accumulating yolk. We also tested the influences of exogenous testosterone treatment by rubbing either 2.5% testosterone propionate cream or a control cream into hen combs daily for six days to increase plasma testosterone levels. Hens exposed to males grew their yolks more slowly (p>0.03), and exogenous testosterone treatment similarly decreased rates of yolk deposition (p>0.05). Testosterone and male presence also caused an increase in yolk weight but not yolk diameter. This means that, though took longer for a yolk to develop, more yolk material was being deposited. These denser yolks could indicate a larger investment in yolks after exposure to a potential mate.