|Lay Jr, Donald|
Submitted to: Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/13/2005
Publication Date: 10/18/2005
Citation: Koch, J.M., Moritz, J.S., Lay, Jr., D.C., Wilson, M.E. 2005. Melengestrol acetate in experimental diets as an effective alternative to induce a decline in egg production and reversible regression of the reproductive tract in laying hens I. Determining an effective concentration of MGA. Poultry Science. 84:1750-1756.
Interpretive Summary: Incorporating melengestrol acetate, an orally active progestin, into a balanced layer diet at a dosage of 4 or 8 mg per hen per day for four weeks led to reversible regression of the reproductive tract. These treatments led to a regression of the large yellow follicles on the ovary and a decrease in size and weight of the oviduct resulting in a dramatic decrease in egg production, without a reduction in hen weight. In the current experiment 4 or 8 mg per day of MGA resulted in a rapid decline in egg production. There was no observed decrease in total hen body weight between the control hens and those receiving MGA treatment even though there was an observed decrease in oviduct weight of those receiving 4 or 8 mg of MGA per hen per day compared to those receiving 0, 0.1 and 1.0 mg of MGA. This may due to the fact that hens are maintained on a balanced layer diet throughout the experiment and that during molting the nutrients required per hen decline as production declines. Establishing a molting practice which does not cause hunger will increase the well-being of millions of hens.
Technical Abstract: Induced molting is practiced to increase egg quality, egg production, and to extend the productive life of the hen. Traditionally, molting is accomplished by an extended period of feed withdrawal accompanied by a decrease in lighting. The traditional method to induce molt has been criticized for not addressing hen well-being and current alternatives described thus far have resulted in poor post-molt performance. The process of molting leads to regression of large yellow follicles on the ovary which result in the loss of steroidogenic support for the oviduct, ultimately leading to cessation of lay. Melengestrol acetate (MGA), an orally active progestin, may have the ability to decrease gonadotropic support for the ovary, resulting in loss of steroidogenic support for the oviduct while hens are maintained on a balanced layer diet. Hyline W-36 laying hens at 40 weeks of age were fed 0, 0.1, 1, 4 or 8 mg MGA per hen per day in a balanced diet for 28 days and then returned to a normal diet. Four birds per treatment on days 1, 2, 4, 8, 12, 16, 20, 24, 28, 32, 36, 40 and 44 were euthanized. The weight of the ovary with large yellow follicles, magnum, shell gland and the length and weight of the intact oviduct were determined. A decrease in egg production was observed in those groups receiving 4 and 8 mg of MGA, until removal of MGA from the diet at day 28. After day 28, egg production increased to the production level of hens fed either 0, 0.1 or 1 mg MGA had maintained throughout the experiment. The weight of the ovary with large yellow follicles, the oviduct, the magnum, the shell gland and the length of the oviduct were unchanged throughout the experiment in the 0, 0.1 and 1 mg MGA groups. However, the 4 and 8 mg of MGA groups had a dramatic decrease (P < 0.05) in the weight of the ovary with large yellow follicles, the oviduct, the magnum, the shell gland and the length of the oviduct until day 28. Recrudescence of the large yellow follicles as well as rejuvenation of the oviduct and its major components the magnum and shell gland in the 4 and 8 mg MGA groups occurred by the end of the experiment. Melengestrol acetate, when fed to hens in a balanced layer diet, caused regression of large yellow follicles, leading to loss of steroidogenic support for the oviduct. Removal of MGA led to recrudescence of large yellow follicles, leading to a return of the steroidogenic support for the oviduct and return to lay.