SUMMARYThe digestibility of some fats (beef tallow, HEF, herring oil, soyabean oil and maize oil) were studied in balance trials with sheep which had been maintained on the diets for a 35 day period of acclimatization to establish ‘steady state’ conditions. Corrected digestibility coefficients for the individual fats were calculated from a knowledge of the intake and output of lipid on a low-fat basal ration. The difference between the intake of fat and the corrected lipid output (total lipid output minus lipid output on basal ration) expressed as a percentage gave the corrected digestibility coefficients.It was found that the corrected digestibility coefficients for beef tallow was 85%; HEF, 74%; herring oil, 84%; soyabean oil, 83%; and maize oil, 70%. The values for beef tallow and HEF were comparable to similar estimates in pigs. The digestibility of the highly unsaturated soyabean and maize oil were markedly lower in comparison with non-ruminant species. Extensive hydrogenation of dietary unsaturated fatty acids was confirmed. For soyabean and maize oil the corrected output of stearic acid exceeded the dietary intake.

The effect of fatty acid chain length and unsaturation on digestibility in sheep were examined using partially purified samples of lauric, myristic, palmitic, stearic, oleic and linoleic acids. The digestibility of the fatty acids was relatively constant with only a very slight decrease on increasing chain length. There was an extensive hydrogenation of the unsaturated fatty acids.The corrected digestibility coefficients for lauric acid was 91%, myristic 86%, palmitic 87 % and stearic acid 81-83 % whereas the corrected digestibility coefficients for oleic and linoleic acids were calculated at 87 and 93 % respectively. The digestibility coefficients for the saturated fatty acids are higher than similar estimates that have been reported for non-ruminants. It is suggested that the ruminant is better able to utilize saturated fatty acids than the non-ruminant.The efficient formulation of high energy diets containing fat for ruminant animals presupposes a knowledge of the relative merits of different types of fatty materials. Since fats in a diet serve essentially as sources of energy, a quantitative evaluation of fats in this respect can be made in terms of units of digestible energy.It was reported by Andrews & Lewis, 1970, that beef tallow, HEF, herring oil, soyabean and maize oil were well digested by sheep, and furthermore that corrected digestibility coefficients for these products covered a relatively narrow range. This is in marked contrast to the situation with respect to non-ruminant animals in which plant and marine oils have an appreciably higher digestibility than fats of animal origin, and suggests that those factors which are instrumental in determining the digestibility of a fat by such species are of less significance in the ruminant. One important factor in this respect is fatty acid chainlength. Studies with nonruminants have clearly demonstrated that the digestibility of a fat decreases as the mean molecular weight of its component fatty acids increases.In respect of unsaturation, it is now well established that the predominant factors affecting the digestibility of a fat by non-ruminant animals include the degree of unsaturation of the fat and its content of unesterified fatty acids. Since dietary fats ingested by these species arrive in the small * Present address:

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