Relationship between fasting heat production, body composition and tissue distribution, in mature ewes from seven...

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 (HHP); 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.