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Weight Gains, Carcass Fat Characteristics and Ration Digestibility in Steers as Affected by Dietary Rapeseed Oil, Sunflowerseed Oil and Animal Tallow¹

University of Manitoba,² Winnipeg, Canada

Abstract

Twenty-four steers were group fed the following rations during a 133-day feeding trial: basal, basal + 5% crude rapeseed oil, basal + 5% crude sunflowerseed oil and basal + 5% prime animal tallow. Average daily gains, dressing percent and percent separable fat of the 9–11th rib cuts from each animal were not significantly affected by treatment. Steers receiving sunflowerseed oil consumed about 7% more concentrate and were more efficient in feed conversion than steers receiving the other rations.

Fatty acid analyses by gas-liquid chromatography of perirenal fat from steers receiving the experimental rations showed significantly (P<.01) more palmitic acid in perirenal fat of steers receiving the control and animal tallow rations than in steers receiving the rapeseed or sunflowerseed oil rations. The percent stearic and oleic acids in perirenal fat were not significantly affected by treatment. The ether extract of the rapeseed oil ration contained 8.1% eicosenoic and 14.4% erucic acids, whereas the perirenal fat of steers which received this ration contained 3.5% eicosenoic and 3.2% erucic acids. This illustrates that a portion of these two fatty acids was not chemically altered in the rumen and was available for absorption and subsequent direct deposition within the animal.

Apparent digestibility of the various ration components was determined in a separate digestibility study. Dry matter and energy digestibilities were not significantly affected by treatment. However, ether extract digestibility of the basal ration was significantly (P<.01) less than that of the other rations. Crude fat digestion, which considers fecal soap excretion, was determined and digestibility values were in all cases less than comparable ether extract values. Furthermore, the fecal crude fat excretion of steers receiving sunflowerseed oil was significantly (P<.01) higher than that of steers receiving the other rations, and crude fat digestibility of the sunflowerseed oil ration was significantly (P<.01) less than that of the rapeseed oil or animal tallow rations. These data strongly suggest that fecal soap excretion should be considered when fat digestibility in cattle is determined.

¹ Appreciation is expressed to Co-op Vegetable Oils, Ltd., Altona, Manitoba, for supplying the rapeseed oil used in this study.

² Department of Animal Science.