|Lay, jr, Donald - Don|
Submitted to: Journal of Animal Science
Publication Type: Abstract only
Publication Acceptance Date: 5/15/2004
Publication Date: 7/25/2004
Citation: Koch, J.M., Moritz, J.S., Lay, Jr., D.C., Wilson, M.E. 2004. MGA as an alternative molting method for hens [abstract]. Journal of Animal Science. 82:152. Interpretive Summary:
Technical Abstract: Inducing hens to molt increases egg quality, egg production and extends the productive life of hens. Molting is normally accomplished by feed withdrawal, which has received criticism, and alternatives described thus far have resulted in poor post-molt performance. The process of molting leads to cessation of lay, regression of large yellow follicles (LYF) and results in loss of steroidogenic support for the oviduct. MGA, an orally active progestin, may decrease gonadotropic support for the ovary and cessation of lay. Hyline W-36 laying hens (n=104) at 40 wk-of-age were fed either 0 or 8 mg/d MGA for 28 d in a balanced diet and then returned to a normal diet. Four birds on d 0 and 4 birds/treatment on d 1, 2, 4, 8, 12, 16, 20, 24, 28, 32, 36, 40 and 44 were euthanized. The wt (g) of ovary with LYF, magnum, isthmus, shell gland and the length (cm) and wt of the intact oviduct were determined. By d 19, egg production in the MGA treated hens (M) had decreased to 24% where it remained until d 28 compared to 88% in the controls (C). The wt of the ovary with LYF, the oviduct and the magnum decreased (p<.05) by day 8 in M compared to C (33±15 vs. 62±7, 39±10 vs. 71±1 and 19±6 vs. 41±2). Furthermore, oviduct length, isthmus and shell gland wt decreased (p<.05) by d 20 in M compared to C (54±7 vs. 78±3, 1.2±0.5 vs. 3.3±0.3 and 11±3 vs. 23±2). From d 28 to 40, egg production in M increased until similar to C at 83%. Oviduct length, isthmus wt and LYF recrudescence in 3 out of 4 M was similar (p>.05) to C by d 32 (59±10 vs. 70±3, 2.0±0.5 vs. 2.8±0.4, 36±12 vs. 54±5). By d 36 the shell gland wt in M was similar (p>.10) to C and 4 out of 4 hens had recrudescence of LYF (14±2 vs. 21±1, 47±8 vs. 40±10); however, it was not until d 40 that the wt of the oviduct and magnum in M was similar (p>.05) to C (61±8 vs. 64±1, 33±5 vs. 37±1). MGA, when fed to hens in a balanced layer diet, can cause regression of LYF on the ovary, leading to loss of steroidogenic support for the oviduct. Removal of MGA led to recrudescence of LYF, leading to steroidogenic support for the oviduct and return to lay.