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Holstein cows fed concentrate:hay diets also were fed for 14 days supplements of soybean oil plus casein, soybean oil protected from ruminal hydrogenation by encapsulation in a casein-formaldehyde matrix, cottonseed oil plus casein, or cottonseed oil protected with casein formaldehyde. The supplements were fed at rates to give a linoleic acid (18:2) intake of 225 g/day. Yields of milk and milk protein were not affected by treatment. Milk 18:2 was not increased by the unprotected soybean oil or cottonseed oil but was increased by protected soybean and cottonseed oil from a control of 2.3 to 5.7% of total milk fat. Milk 18:0 and 18:1 also increased. Compensatory declines were observed in milk 16:0 and 14:0 acids. In fecal fatty acids during the treatment periods, percentage of 18:2 of the total fat decreased and 18:0 markedly increased. These results indicate hydrogenation of the dietary oils in the alimentary tract or a differential absorption. Fecal 16:0 and 14:0 decreased.

Four groups of eight 4 wk-old Holstein bull calves were fed calf starter diets containing either no additive (control) or added ingredients: 1% cholesterol, 5% tallow, or 1% cholesterol plus 5% tallow. Body weight and size were reduced, and average daily gain was lowered by added 5% tallow. The added dietary tallow and cholesterol increased lipids and cholesterol of plasma by 35 to 40%. The increased intake of fat due to feeding tallow caused both increased fat metabolism and fat excretion as based on chromic oxide estimates of digestibility. Fat digestibility was lowest in animals receiving cholesterol with no added tallow. Organ weights and composition of meat at slaughter at 21 wk of age were not different.

The influence of dietary fats on in vitro lipid absorption by bovine intestine was studied in 14 calves. Holstein bull calves were fed for 16 wk five liquid diets containing skim milk plus either 3.5% milk fat, 3.5% tallow, 3.5% tallow and .2% cholesterol, 7.0% tallow, or 7.0% tallow and .2% cholesterol. Uptake of oleic acid or triolein by everted jejunal or ileal sacs was measured after incubation for 30 min at 37 degrees C in pH 7.4 micellar solutions containing tritium-labeled oleic acid or tritium-labeled triolein. Lipids were extracted from homogenates of sacs and separated into lipid classes by thin layer chromatography. Equal amounts of oleic acid were taken up by jejunal or ileal sacs. Triolein uptake was less than oleic acid uptake, but uptakes by jejunal or ileal sacs did not differ. Oleic acid incorporation into triglyceride was three to four times greater in intestinal sacs from milk fat-fed calves than in sacs from calves fed either 3.5 or 7% tallow. Oleic acid incorporation in intestinal sacs from calves fed cholesterol as well as tallow was equal to that in milk fat-fed calves. Intestinal uptake and metabolism of oleic acid proceeded faster when calves were fed milk fat than when fed tallow. The lower intestinal incorporation with tallow increased if cholesterol was fed, suggesting that cholesterol either stimulated absorption or increased esterification.