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Relationship between Fasting Heat Production, Body Composition and Tissue Distribution, in Mature Ewes from Seven Breeds¹

University of Nebraska and U.S. Department of Agriculture, Lincoln 68583-0908

Abstract

To evaluate the relationship between measures of maintenance and body composition, data were collected on 12 mature, nonpregnant, nonlactating ewes from each of seven breeds following 6 wk of ad libitum (AL) or maintenance (MN) feeding (six per breed-level). After fasting 56 h, fasting heat production (FHP) was measured for each of 42 pairs of ewes over a 16-h period. Ewes then were slaughtered and the empty body divided into visceral organs and blood (ORB); gastrointestinal tract and internal fat (GIF); head, hooves and pelt (HUP); and carcass (CAR). Each fraction was chemically analyzed for water, fat, ash and (by difference) fat-free dry organic matter (FFDOM or protein). Correlations with FHP/d were highest (.86 to .87) for weights of empty body and body water or lean (FFDOM + water) and were lower (.77) for weight of empty body fat. Best nonlinear LWT predictors of FHP/d were LWT^.63 and water^.71 or lean^.71 (R² = .76). Correlations of metabolic FHP (kcal/kg^.75) with percentage lean and fat, respectively, were .53 and –.55 for the empty body and .60 and -.60 for the GIF fraction. For AL ewes, the better predictors of FHP/d were weights of lean in GIF + ORB (R² = .88, ESD = 106), live weight (LWT) plus fat and lean in GIF fraction (R² .88, ESD = 112) or LWT plus fat in HHP and GIF fractions (R² = .90, ESD = 103). For MN ewes, LWT alone was as accurate (R² = .80, ESD = 123) as any combination of components. Breed mean daily FHP was predicted very accurately (R² = .94) from total weight of empty body lean plus the proportion of total body lean located in the GIF fractions.

¹ Published as Paper No 8713, Journal Ser., Agric. Res. Div., Univ. of Nebraska, Lincoln. Partial publication of the Ph.D. Dissertation of the senior author.

² Present address: Agric. Dept., Dordt College, Sioux Center, IA 51250.

³ Roman L. Hruska U.S. Meat Anim. Res. Center, ARS, USDA, A218 AnS, Univ. of Nebraska Lincoln 68583-0908.