|Lay, Jr, Donald - Don|
Submitted to: Animal Reproduction Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/30/2006
Publication Date: 9/20/2007
Citation: Koch, J.M., Mortiz, J.S., Lay Jr, D.C., Wilson, M.E. 2007. Effects of melengestrol acetate as an alternative to induce molting in hens and on the expression of yolk proteins and turnover of oviductal epithelium. Animal Reproduction Sciences. 102:14-23.
Interpretive Summary: Inducing hens to molt increases egg quality, egg production, and extends the productive life of hens. We have demonstrated that Melangestrol Acetate (MGA), an orally active progestin, decreased hormonal support for the ovary. This caused the cessation of lay. The objective of this experiment was to determine the expression of yolk proteins and oviductal cell turn over, in response to a MGA induced molt. The results of the current experiment in which there was an observed increase in the number of cells committed to programmed cell death in the oviduct is similar to that observed previously. Thus far, current research has not examined the effects of induced rest on the epithelial cells of the oviduct. The current study reports an increase in cell proliferation of the ciliated cells in the oviduct of hens induced to molt by MGA, which is contradictory to the observed increase in programmed cell death of secretory cells. During an MGA induced rest, hens are maintained on a diet balanced to meet all nutrient requirement of the hen during production. It is proposed that a simple replacement of the exhausted cells may be all that is necessary to improve post-molt performance, and that major loss of the luminal cells as observed during a feed withdrawal induced rest may not be critical as previously speculated. The current criteria listed as necessary for improving post-molt performance may not be required, but instead an indicator of nutrient deprivation. Therefore, if rest is induced by utilizing a mechanism that disrupts the endocrine system while avoiding nutrient deprivation the cell turnover that occurs in the oviduct is different. The difference in oviduct epithelial cell turnover may explain the observed decrease in the time required from induced rest to 50 percent production, with improved egg quality, accomplished by an MGA induced molt. These data provide researchers with novel information that is important in developing alternatives to feed induced molt in hens.
Technical Abstract: Inducing hens to molt increases egg quality, egg production, and extends the productive life of hens. 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 and supports the oviductal epithelial cells. The objective of this experiment was to determine the expression of yolk proteins and oviductal epithelial cell turn over in response to a MGA induced molt. Hy-Line W-36 laying hens 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 36. Four birds per treatment on days 1, 8, 16, 28 and 36 were euthanized. The liver was then removed and snap frozen in liquid nitrogen until RNA was extracted. Expression of vitellogenin II and apolipoprotein II was determined using real-time RT-PCR. A portion of the magnum was removed to determine proliferation and programmed cell death for secretory and ciliated luminal epithelium. Vitellogenin II and apolipoprotein II expression was reduced 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. Proliferation was increased in the ciliated epithelial cells of the oviduct for those hens receiving 8 mg of MGA compared to those receiving 0 mg. However, programmed cell death was not different between controls and treated. Programmed cell death increased in the secretory epithelial cells in those hens receiving 8 mg of MGA compared to controls. However, there was no observed change in proliferation. Therefore, utilizing MGA as an alternative method to induce molt results in the similar changes in liver function and secretory epithelial cells that result from a feed withdrawal induced molt.