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RELATIONSHIPS AMONG DIET, METABOLIZABLE ENERGY UTILIZATION AND NET ENERGY VALUES OF FEEDSTUFFS W. N. Garrett University of California 1 Davis 95616 Summary A comparative slaughter experiment was conducted with beef steers to determine the energy utilization of six specific mixtures of a roughage basal and a concentrate basal diet. Of special interest were comparisons of relation- ships among metabolizable energy (ME) utiliza- tion, net energy values and diet composition. ME (kcal/g) was linearly related to proportion of roughage in the diet (r = -.96) and to mean net energy values determined for the diets (r = -.99 for NE m and r = -.97 for NEg). None of these regressions had significant curvilinear components. Since the efficiency of ME utiliza- tion for maintenance (km) or for gain (kg) is the product of the reciprocal of ME and NEm or NEg, a curvilinear relationship could be expected between the proportion of roughage in the diet and km or kg. However, these relationships were also linear (r = .96 and -.93, respectively). These findings along with some observations made from the literature form the basis for the suggestion that experimental variability (tech- nical and animal) together with the model chosen to present the results of a particular trial may be responsible for some reports of the associative effects of feeds. (Key Words: Net Energy, Metabolizable Energy, Energy Utilization, Associative Effects.) Introduction The early work of Forbes et al. (1931, 1933) led Kriss (1943) to conclude that net energy values of individual feeds are fundamentally variable in the sense that their value depends on the combination in which they are fed with other feeding stuffs. Blaxter and Wainman (1964) reported, "Our results agree with the t Dept. of Animal Science. statement by Kriss in that the energy retained by an animal depends on the amount and composition of its ration as a whole, and that net energy values can only be applied to single foods when they are given as the sole food." These statements deal with "associative effects" and by implication suggest that a system of feed evaluation based on assigning a specific net energy value to each feedstuff (Lofgreen and Garrett, 1968) may not be appropriate. Vance et al. (1972) and Byers (1976) also attributed the variability they have observed in net energy values of corn and corn silage mixtures to associative effects. The objective of this investigation was to determine the energy utilization of specific combinations of roughage and concentrate by beef steers giving special consideration to the relationships among diet composition, net energy values and the efficiency of metaboliz- able energy utilization. Experimental Methods This experiment used the comparative slaughter technique to estimate energy reten- tion in beef steers fed diets differing in propor- tion of roughage and concentrate. Initial and final empty body composition was determined from carcass density (Garrett and Hinman, 1969). The 86 experimental animals, purchased from commercial sources, were of Hereford and Angus parentage (initial empty body weight 234 kg). Six steers were halter broken for use in
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This note was uploaded on 09/19/2011 for the course ANS 5446 taught by Professor Brown during the Spring '08 term at University of Florida.

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