title: Melengestrol acetate as an effective alternative to induce a decline in egg production and reversible regression of the reproductive tract in laying hens. II. Effects on postmolt egg quality.
abstract: Induced molting increases egg quality and egg production and extends the productive life of hens. Molting is accomplished by feed withdrawal, which has received criticism, and alternatives described thus far result in poor postmolt performance. Melengestrol acetate at a dosage of 4 or 8 mg/d, in a balanced diet, leads to reversible regression of the reproductive tract. However, this alternative must also increase egg quality after rest to be considered an adequate method by the industry. Hy-Line W-36 (n = 497) laying hens were assigned randomly to a diet containing 0 mg of melengestrol acetate (MGA; control) throughout the experiment or 4 or 8 mg of MGA/d for 2, 4, or 6 wk. Upon reaching 50 and 70% lay, after MGA removal, eggs were collected for measurements of egg quality, including Haugh units (i.e., internal egg quality), shell thickness, and breaking strength (i.e., external egg quality). Haugh units were greater (P < 0.05) for eggs laid by hens molted with a diet containing 8 mg of MGA for all durations compared with controls. Shell thickness was greater (P < 0.05) when hens were treated with 4 mg of MGA for 6 wk and 8 mg of MGA for 4 and 6 wk compared with control. Egg breaking strength was greater (P < 0.05) than controls for all hens fed MGA, regardless of dosage or duration of feeding. A subset of hens was fed 8 mg of MGA per hen/d for 2 wk, and eggs were collected for 3 wk. Seven days after MGA was removed from the diet, the amount of MGA in the yolk was below the level of detection of the assay, and the concentration found in the eggs at all time points was 3 orders of magnitude below the Food and Drug Administration's tolerance for MGA in edible tissue. When used as an alterative method to induce a rest, MGA leads to an increase in the internal and external egg quality of hens compared with nonmolted hens.
authors.affiliation: Division of Animal and Veterinary Science, Davis College of Agriculture, Forestry and Consumer Sciences, West Virginia University Morgantown, West Virginia 26506, USA.
authors.forename: J M
authors.initials: JM
authors.lastname: Koch
authors.forename: J S
authors.initials: JS
authors.lastname: Moritz
authors.forename: D L
authors.initials: DL
authors.lastname: Smith
authors.forename: D C
authors.initials: DC
authors.lastname: Lay
authors.forename: M E
authors.initials: ME
authors.lastname: Wilson
mesh_terms: D000375:Aging; D000821:Animal Feed; D000818:Animals; D002645:Chickens / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004334:Drug Administration Schedule; D004528:Egg Shell / Q000187:drug effects; D005260:Female; D005836:Genitalia, Female / Q000187:drug effects / Q000502:physiology / Q000503:physiopathology; D005938:Glucocorticoids / Q000494:pharmacology; D008552:Melengestrol Acetate / Q000494:pharmacology*; D010058:Oviposition / Q000187:drug effects* / Q000502:physiology; D010063:Ovum / Q000187:drug effects* / Q000502:physiology*
chemical_list: D005938:Glucocorticoids; D008552:Melengestrol Acetate