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Effects of Sex, Diet and Stage of Growth upon Energy Utilization by Lambs^{1 ,2,}

U.S. Department of Agriculture^,5, Clay Center, NE 68933 and and University of Wyoming, Laramie 82071

Abstract

Ram (72) and ewe (72) lambs were stratified by weight within sex and assigned to one of three diets containing 2.18 (L), 2.39(M), or 2.80(H) Meal of metabolizable energy (ME)/-kilogram dry matter or to an initial slaughter group. Twelve lambs of each sex were slaughtered initially. About one-fourth of the lambs of each sex within each diet were slaughtered when the respective mean weights of ram lambs were 32, 42, 54 or 66 kilograms. Carcass weight and composition were determined at slaughter, and empty body weight and composition were estimated. Comparative slaughter procedures were used to estimate empty body gains. Rams were heavier at slaughter and contained more water and protein but less fat than ewes. Rams and ewes contained similar amounts of energy at slaughter. Daily ME intake/W^3/4 did not differ due to sex, but daily ME required for maintenance (MEM) tended to be greater in rams than in ewes (112 vs 109 kcal/W^3/4). Daily ME available for gain (MEA) was similar in rams and ewes (175 vs 176 kcal/W^3/4), but energy gain (EG) by rams was less (54 vs 63 kcal/W^3/4). Daily ME intakes were 274, 290 and 292 kcal/W^3/4 on L, M and H diets, respectively. Daily MEM's were 114, 109 and 107 kcal/W^3/4 and MEA's were 161, 181 and 186 kcal/W^3/4 on L, M and H diets, respectively. Daily EG's were 48, 59 and 68 kcal/W^3/4 on these diets. Relationships between body protein and heat production at maintenance and multiple linear relationships between body protein, fat and heat production at maintenance, suggested that maintenance of body protein was responsible for a high proportion (85%) maintenance energy expenditures. Multiple regression analysis also indicated energy costs of protein and fat gain to be 45 and 14 kcal/g, respectively.

¹ Wyoming Paper No. 976.

² Cooperation of the Nebraska Agr. Exp. Sta. Univ. of Nebraska, Lincoln is acknowledged.

³ Roman L. Hruska US Meat Animal Research Center, Agricultural Research, SEA, Clay Center, NE 68933.

⁴ Division of Animal Science, Univ. of Wyoming.

⁵ Mention of a trade name, proprietary product or specific equipment does not constitute a guarantee or warranty of the product by the U.S. Department of Agriculture and does not imply its approval to the exclusion of other products that may also be suitable.