Polyunsaturated fatty acids are normally hydrogenated by microorganisms in the rumen. Because of this hydrogenation ruminant triglycerides contain very low proportions of polyunsaturated fatty acids. A new process is described whereby polyunsaturated oil droplets are protected from ruminal hydrogenation by encapsulation with formaldehyde-treated protein. The formaldehyde-treated protein resists breakdown in the rumen thereby protecting the fatty acids against microbial hydrogenation. When these protected oils are fed to ruminants the formaldehydeprotein complex is hydrolyzed in the acidic conditions of the abomasum and the fatty acids are absorbed from the small intestine. This results in substantial changes in the triglycerides of plasma, milk and depot fats, in which the proportion of polyunsaturated fatty acids is increased from 2-5% to 20-30%. These effects are observed in the plasma and milk within 24-48 hr of feeding while a longer period is necessary to alter the composition of sheep depot fat. The implications of these findings are discussed in relation to human and ruminant nutrition.

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Steers were given diets containing formaldehyde‐treated casein‐safflower oil supplements, in which the constituent 18∶2 was protected from ruminal hydrogenation. A similar group was given unsupplemented diets. The fatty acid compositions of plasma, liver, muscle and adipose tissue lipids were determined in both groups of cattle after 0, 2, 4 and 8 weeks of experimentation. The proportion of 18∶2 in the triglycerides was markedly increased on feeding the supplement and the rate of incorporation into the plasma triglycerides was higher than that in the triglycerides of muscle and adipose tissue. Associated with this increase there were compensatory decreases in the proportions of 16∶0 and 18∶1 but no consistent change in the proportion of 18∶0. The proportion of 18∶2 in the plasma phospholipids and cholesteryl esters was initially much higher than in the triglycerides and this was further increased by feeding the safflower oil supplement. A linear relationship existed between the proportion of 18∶2 in the phospholipids and cholesteryl esters of plasma. The supplement also caused substantial increases in the proportion of 18∶2, both in phospholipids from liver and muscle and in cholesteryl esters from liver, and there were compensatory decreases in the proportions of other unsaturated fatty acids, e.g., 18∶1, 18∶3, 22∶6. These studies demonstrate that when ruminal hydrogenation was circumvented by feeding formaldehyde‐treated casein‐safflower oil particles, the linoleic acid was absorbed and the pattern of incorporation into plasma and tissue lipids was similar to that in nonruminants.

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I. Thirty-three cross-bred lambs were given reconstituted dried whole cow's milk from I week of age at different levels of intake and at different frequencies of feeding. 2.Feeding frequency had no effect on live-weight gain, N retention or total body composition.3. Lambs given two feeds daily had significantly heavier abomasums than pair-fed lambs given six feeds daily. 4.The weights of fat, protein (N x 6 2 5 ) and water in the body were closely related to empty body weight; body composition (% of empty body) was not significantly affected by the level of milk intake or by the rate of growth.5 . Live-weight gain was closely related to energy intake (r = +o.gg) and to N retention (r = +o*g7). A live-weight gain of IOO g was associated with an intake of 51 I kcal and a N retention of 2.28 g N.Lambs and calves when reared with their dams are known to suckle at more frequent intervals than is usually practicable when they are hand-reared (Munro, 1955 ;. There is at present no evidence that feeding frequency has any marked effect on the growth rate or utilization of energy and nitrogen by the preruminant lamb or calf (Voelker & Jacobson, 1953), though studies with other animals suggest that both protein and fat metabolism may be affected (Cohn, 1962;Mochrie, 1964).The present paper describes three experiments, with milk-fed lambs, in which the effect of frequency of feeding over a wide range of energy and N intakes was studied. In the first experiment, lambs were bottle-fed two, three or six times daily, the intakes of energy being similar but controlled throughout. In the second experiment, lambs which were allowed to feed ad lib. twice daily were compared with pair-fed lambs given the same amount of milk in six feeds. In the third experiment, lambs were allowed to self-feed to appetite. The effect of feeding frequency on live-weight gain, N balance and total body composition was measured. EXPERIMENTALExperimental design Expt I . Comparison of two, three and six feeds daily. Fifteen male lambs were allotted at random to the dietary treatments. The experimental period of 4 weeks was divided into two equal periods (periods I and 2). The diet was given for a preliminary period of I week followed by a collection period of I week. The intake of feed was determined by the live weight of the lamb at the beginning of each preliminary period, and was * Paper no. 4 : Br.