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Metabolism of Fatty Acids by Mammary Glands of Cows Fed Normal, Restricted Roughage, or Magnesium Oxide Supplemented Rations^1,2,

Dairy Department, Michigan State University, East Lansing 48823

ABSTRACT

Lactating Holstein cows were fed restricted roughage-high grain and normal rations in a sequential manner to study the effect of ration on mammary gland lipid metabolism. Biopsy samples of mammary tissue were analyzed for lipoprotein lipase and glyceride synthetase activities and long chain fatty acid composition. Cows fed restricted roughage-high grain rations exhibited a lower milk fat test than cows fed normal rations but had no difference in lipoprotein lipase and glyceride synthetase activities. Decreased milk fat per cent from feeding restricted roughagehigh grain rations was accompanied by decreased proportions of saturated and increased proportions of unsaturated fatty acids in mammary tissue. Decreases in milk fat per cent were related to increases in weight per cent of linoleic and oleic acids and to decreases in stearic and palmitic acids in the milk fat (r = –0.79,–0.94, 0.75 and 0.58, respectively). A qualitative alteration of long-chain fatty acids presented to the mammary gland when cows are fed restricted roughage-high grain rations may be in part responsible for reduced production of milk fat.

¹ Published with the approval of the Agricultural Experiment Station as Journal Article 5258.

² Partially supported by NIH Training Grant GMO 1818 and Research Grant AM13177.

³ Data presented are taken from a thesis submitted by the senior author to the graduate school of Michigan State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy. Present address: United States Army Medical Research and Nutrition Laboratory, Fitzsimons General Hospital, Denver, Colorado 80240.

⁴ Present address: Letterman Army Institute of Research, Letterman General Hospital, San Francisco, California.