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Methionine Hydroxy Analog for Lactating Dairy Cows^1,2,

Department of Animal Sciences, New Hampshire Agricultural Experiment Station Durham 03824

ABSTRACT

Fourteen lactating Holstein cows were paired according to expected solids-corrected milk production and randomly assigned to Control or methionine hydroxy analog treatments. Hay, corn silage (treated with .5% urea) and pelleted concentrate (containing .5% urea), either with or without the analog (.357%), were fed. Treatment continued from 2 weeks prepartum to 24 weeks postpartum. During the sixth and tenth week postpartum six pairs of cows were subjected to digestibility and energy (indirect respiration calorimetry) and nitrogen balance trials.

Cows supplemented with methionine hydroxy analog produced more milk fat (P < .05), particularly during Weeks 1 to 12, while feed consumption and yields of milk (actual) and solids-not-fat were not significantly affected. Methionine hydroxy analog increased digestibility of fiber and fat (P < .01) but not protein, increased urinary N loss (P < .01), reduced dietary N retention (P < .05), and increased methane energy loss (P < .01). Proportion of dietary gross energy and total N secreted in milk was not affected by treatment. Evidence is presented for higher maintenance energy requirement and higher efficiency of conversion of metabolizable energy to milk when methionine was included in the diet. The data are consistent with enhanced rumen microbial activity, but the specific mechanism by which methionine increases milk fat yield needs further clarification.

¹ Published with the approval of the Director of the New Hampshire Agricultural Experiment Station as Scientific Contribution 584.

² Research was partially supported by a grant from Agway, Inc., Syracuse, N.Y. Technical assistance of H. H. Hayes in gratefully acknowledged.

³ Present address: Department of Animal Science, Rutgers University, The State University of New Jersey, New Brunswick 08903.