|Lay, Jr, Donald - Don|
Submitted to: Poultry Science Association Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 5/18/2005
Publication Date: 10/14/2005
Citation: Koch, J.M., Moritz, J.S., Lay Jr, D.C., Wilson, M.E. 2005. Effect of melengestrol acetate (MGA) on the production of yolk proteins by the liver. Poultry Science Association Meeting Abstract. 84(1):44.
Technical Abstract: Inducing hens to molt increases egg quality, egg production and extends the productive life of hens. Recently, we have demonstrated that MGA, an orally active progestin, decreased gonadotropic support for the ovary, which decreased the steroidogenic support for the oviduct and resulted in the cessation of lay. Estrogen produced by the large yellow follicles stimulates the production of the yolk proteins vitellogenin II and apolipoprotein II. The objective of this experiment was do determine the expression of yolk proteins in response to a MGA induced molt. Hy-Line W-36 laying hens (n=48) at 40 weeks of age were fed either 0 or 8 mg MGA per day for 28 days in a balanced diet and then returned to a normal diet until day 44. Four birds per treatment on days 1, 8, 16, 28, 36 and 44 were euthanized and the liver was removed and snap frozen in liquid nitrogen until RNA was extracted. Expression of vitellogenin II and apolipoprotein II, relative to actin, was determined using real-time RT-PCR. Data for relative expression of the two genes were analyzed by defining regression models with day as a continuous variable and treatment as a categorical variable. Following the regression analysis, T-tests were used to make pair-wise comparisons of the resultant slope coefficients. Vitellogenin II expression was reduced (P < 0.05) in hens fed 8 mg of MGA compared to those fed 0 mg of MGA. Expression of vitellogenin increased after removal of MGA from the diet. There was no difference (P > 0.10) in the expression of apolipoprotein II between the two groups throughout the experiment. One potential reason for the lack of similarity in the pattern of expression of these two yolk proteins may be that vitellogenin II is used only as a yolk protein and therefore depends on the follicular estrogen; however, apolipoprotein II is a component of the very-low-density lipoprotein particle and its synthesis may not be as dependent on follicular estrogen. Therefore, utilizing MGA as an alternative method to induce molt results in the similar changes in liver function that result from a feed withdrawal induced molt.