Effect of melengestrol acetate as an alternative to induce molting in hens on the expression of yolk proteins and turnover of oviductal epithelium

Abstract

Inducing hens to molt increases egg quality, egg production and extends the productive life of hens. It has been previously demonstrated that melengestrol acetate (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. Estradiol produced by the theca cells of small follicles stimulates the production of the yolk proteins vitellogenin II and apolipoprotein II by the liver and supports the oviductal epithelial cells. The objective of the present experiment was to determine gene expression for 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 standard layer ration until day 36. Four birds per treatment on days 1, 8, 16, 28 and 36 were euthanized and the liver was removed and snap frozen in liquid nitrogen until RNA was extracted. Expression of vitellogenin II and apolipoprotein II genes 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 gene expression was reduced in hens fed 8 mg MGA compared to those fed 0 mg MGA. There was no effect of day on gene expression of either yolk protein. Cell proliferation was increased in the ciliated epithelial cells of the oviduct in hens receiving 8 mg MGA compared to those receiving 0 mg. However, programmed cell death of the ciliated epithelial cells was not different between controls and MGA treatment. Programmed cell death and proliferation increased in the secretory epithelial cells in hens receiving 8 mg MGA compared to controls. Therefore, utilizing MGA as an alternative method to induce molt results in some, but not all, of the physiological changes previously described for hens molted by feed withdrawal. These findings lead us to suggest that some of the observed physiological changes resulting from feed withdrawal are required to increase egg quality and egg production following molt and other changes are not necessary, but are just a result of nutrient deprivation.