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Influence of Dietary Fat on Rumen Fatty Acids, Plasma Lipid and Milk Fat Composition in the Cow¹

Department of Animal and Poultry Science, University of Guelph, Guelph, Ontario

ABSTRACT

The influence of amount and type of dietary fat on fatty acid composition of rumen fluids, plasma lipids, and milk fat was studied with the ten rumen fistulated Holstein cows in two Latin square design experiments. The fatty acid composition of AM and PM milk from uneven milking intervals was also studied. The diets received were "standard" dairy ration, low-fat basal diet, basal + hydrogenated tallow, and basal + soybean oil.

Feeding the low-fat basal diet resulted in normal fat test and high concentrations of short chain fatty acids. The addition of hydrogenated tallow to the basal diet had no effect on proportions or yields of fatty acids in milk whereas inclusion of soybean oil increased proportions and yields of C18:0 and C18:1 acids and decreased concentration of shorter chain fatty acids in milk. Reduced polyunsaturated fatty acids in rumen fluid and very low levels in milk fat provided evidence of hydrogenation in the rumen of cows fed oil-rich diets. Protozoa counts in rumen fluid were variable but normal. Implications of these findings are discussed.

Addition of hydrogenated tallow or soybean oil to the basal diet increased plasma lipid fractions compared to the basal diet. Diets containing high concentrations of unsaturated fat resulted in higher triglycerides, cholesterol, and phospholipids than the saturated fat.

Milk produced at uneven milking intervals was similar in fatty acid composition but was markedly different in fat test.

¹ This research was supported in part by the Ontario Department of Agriculture and Food and by a grant from the National Research Council of Canada.

² Present address: Jamaica School of Agriculture, Twickenham Park, Spanish Town, Jamaica, W.T.