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Influence of Amount and Degree of Saturation of Dietary Fat on Yield and Quality of Milk¹

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

ABSTRACT

Four rumen-fistulated Holstein cows were used in a Latin square design experiment over 20 weeks to compare effects of a standard diet, basal low-fat, basal + hydrogenated tallow, and basal + soybean oil diets on voluntary feed intake, rumen fermentation, and on yield and composition of milk. In a second trial, six Holstein cows fed similar basal and fat supplemented diets were used in a 3 x 6 Latin rectangle to compare milk production and composition under a system of restricted feed intake.

Voluntary feed intake was not affected by fat or oil supplementation although intake was highest on the standard diet. There were no significant differences in yields of milk, fat, or lactose. Milk fat test was lowest and protein content highest on the standard ration, presumably reflecting high grain intake. Tallow supplementation did not affect milk composition. Addition of soybean oil to the basal diet lowered milk fat percentages (P < .05), 3.06 versus 3.92 and 3.42 versus 3.74 in Trials 1 and 2. Soybean oil also reduced protein content of milk.

Ruminal acetic and butyric acids were lowered in favor of higher propionic acid on the standard diet whereas percentages of acetic and propionic acids were not affected by tallow or soybean oil feeding and butyric acid decreased on the soybean oil diet. There were no significant treatment effects on rumen ammonia or pH. Blood glucose levels were not significantly different but means tended to be low (33 to 38 mg/100 ml).

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

² Present address: Jamaica School of Agriculture, Twichenham Park, Spanish Town, Jamaica, West Indies.