|Lay, Jr, Donald - Don|
Submitted to: Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/13/2005
Publication Date: 10/18/2005
Citation: Koch, J.M., Mortiz, J.S., Smith, D.L., Lay, Jr., D.C., Wilson, M.E. 2005. 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 post molt egg quality. Poultry Science. 84:1757-1762. Interpretive Summary: Inducing hens to molt by incorporating melengestrol acetate into a balanced layer diet at a level of 4 or 8 mg per hen per day resulted in an improvement in egg quality. Breaking strength, a measure of external egg quality, was improved with all melengestrol acetate amounts and durations. The greatest improvement was observed in the eggs laid by hens that had been receiving 8 mg of melengestrol acetate for either two, four or six weeks. This improvement was similar to the improvement seen from those eggs laid by hens receiving 4 mg of melengestrol acetate, but only for four or six weeks. Shell thickness, another measure of external egg quality, increased as the duration of melengestrol acetate feeding increased in both treatment groups. The greatest improvement in egg quality was observed in the hens receiving 4 or 8 mg of melengestrol acetate for six weeks. Melengestrol acetate at a level of 8 mg per hen per day, at all durations resulted in the greatest internal egg quality. The key to increasing post molt performance is inducing a molt that leads to reversible regression of the reproductive tract. The alternative method that is the most successful at causing reversible regression, results in an increased post molt performance, and addresses hen well-being, will be the most desired alternative method. Without meeting these criteria, an alternative will not be implemented because it is not cost effective for producers. When utilized as an alternative method to induce molt, melengestrol acetate leads to an increase in both the internal and external egg quality compared to non-molted hens. Establishing a molting practice which does not cause hunger, will increase the well-being of millions of hens.
Technical Abstract: Inducing hens to molt increases egg quality, egg production and extends the productive life of the hens. Molting is normally accomplished by feed withdrawal, which has received criticism, and alternatives described thus far have resulted in poor post-molt performance. Previous studies have shown that MGA at a dosage of 4 or 8 mg per day, when incorporated into a balanced layer diet, leads to reversible regression of the reproductive tract. However, this alternative must also result in an increase in egg quality post-molt to be considered an adequate method by the industry. Hy-Line W-36 (n=72) laying hens at 67 weeks of age were randomly assigned to receive either a diet containing 0 mg MGA (control) throughout the experiment, or 4 or 8 mg MGA per day for 2, 4 or 6 weeks. Eggs were collected daily to determine percent lay throughout the experiment. Upon reaching 50 and 70 percent lay, following removal of MGA, eggs were collected for four days and measurements of egg quality, including haugh units (i.e., internal egg quality), as well as shell thickness and breaking strength (i.e., measures of external egg quality) were determined. Egg quality measured by haugh units was greater (P < 0.05) for those eggs laid by hens molted with a diet containing 8 mg of MGA for four or six weeks compared to controls (81.2 +/- 0.7 vs. 78.4 +/- 0.5). Following MGA induced molt, shell thickness was greater (P < 0.05) when hens were treated with 4 mg for six weeks and 8 mg MGA for four and six weeks compared to control (0.341 +/- 0.004, 0.334 +/- 0.005, 0.358 +/- 0.004 vs. 0.320 +/- 0.002 mm). Egg breaking strength was greater (P < 0.05) than controls for all hens fed MGA regardless of dosage or duration of feeding (4.48 +/- 0.06 vs. 3.88 +/- 0.04 kg). To address concerns about the amount of MGA remaining in the egg a subset of hens was fed 8 mg of MGA per hen per day for two weeks and egg were collected for three weeks starting with last egg laid while the hens were on treatment. 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 that the concentration found in the eggs at all time points was three orders of magnitude below the FDA tolerance for MGA in edible tissue. When utilized as an alterative method to induce molt, MGA leads to an increase in both the internal (i.e., haugh units) and external (i.e., shell thickness and breaking strength) egg quality compared to non-molted hens.