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Net Energy of Fat and Molasses for Beef Heifers with Observations on the Method for Net Energy Determination¹

University of California, Davis²

Abstract

The response of growing-finishing beef heifers to rations containing yellow grease, bleachable tallow or acidulated cottonseed foots at levels of 2.5, 5.0, 7.5 and 10.0% of the ration has been determined. Animals receiving the tallow consumed less feed and gained less than those on the other two fats. When adjusted to equal energy gain by covariance analysis, however, feed intake did not differ, indicating the same efficiency of energy utilization among the three fats. The NE_p for all fats at all levels was 2.59 megcal. per kg., when barley fed as a reference standard contained 1.06 megcal. per kg. There were no significant differences in the performance of animals fed the various fat levels except for the decrease in feed required per unit of gain as fat level increased. Animals receiving levels of molasses of 5, 10, 15 and 20% of the ration performed similarly, although those receiving the 20% molasses level required more feed than other groups when adjusted to equal energy gain. The NE_p of molasses at 5, 10 and 15% of the ration was 0.78 megcal. per kg. and declined to 0.70 megcal. per kg. when increased to 20% of the ration. Fat had a NE_p value of approximately 2.4 times that of barley, while molasses fed up to 15% of the ration had a value of approximately 0.74 times that of barley. A method is presented for the measurement of NE_m and NE_p by the difference trial procedure involving the determination of the heat production of animals on an ad libitum intake and using the heat produced at zero feed intake as the base level. The method provides a saving in number of animals required, since a restricted group is not necessary. The validity of the method is dependent upon the accuracy of the estimation of the heat production at zero feed intake.

¹ This study was supported in part by grants from Baker Commodities, Inc., Los Angeles, R. S. Wilson Company, Los Angeles, and Pacific Molasses Company, San Francisco.

² Department of Animal Husbandry.