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RELATIONSHIPS AMONG FEED INTAKE, BODY COMPOSITION AND FASTING HEAT PRODUCTION IN MATURE EWES (SHEEP, BREEDING, ENERGY METABOLISM)
Abstract
Modeling the effects of genetic changes in production potentials on input/output efficiency of lamb and wool production requires quantitative knowledge of sheep production biology. A major portion of the input costs are required for body maintenance. Genetic and environmental factors affecting maintenance and above maintenance costs were examined to validate equations in a sheep production model. A total of 84 non-lactating, non-pregnant, 3 to 4-year-old ewes was selected from 7 biological types: Rambouillet (R), Dorset (D), Finn (F), Suffolk (S) and three composites: 1/2 F, 1/4 R and 1/4 D (I); 1/2 F, 1/4 S and 1/4 Targhee (II) and 1/2 Columbia, 1/4 S and 1/4 Hampshire (III). A pelleted alfalfa diet was fed at either ad libitum or maintenance levels of 6 ewes/breed for about 40 days. Fasting heat production (FHP), after shearing and a 56 hour fast, was measured in indirect calorimeters over 16 hours. Ewes then were slaughtered and chemical water, fat, ash and protein, by difference, were obtained on four metabolically different body fractions: carcass, head and pelt, organs and blood, and gastrointestinal tract and internal fat. Activity adjusted FHP averaged 72.6 kcal/kg WT('.75). The F, I and II ewes, with higher reproductive rates, were less fat and had a greater proportion of their lean and fat in the metabolically more active internal fractions than the faster gaining S and III ewes. Ewe FHP was closely associated with lean body mass, particularly visceral, and independent of fat. Predicting FHP from ST('.75) does not account for body composition differences. Maintenance requirement estimates were high, 186 kcal/kg WT('.75). Costs of deposition above maintenance were 38.3 kcal/g for protein and 12.3 kcal/g for fat. Corresponding efficiencies of energy utilization were: maintenance (k(,m) = .39), protein gain (k(,p) = .15) and fat gain (k(,f) = .76). Genetically increasing lean would increase maintenance and dry matter gain costs, but decrease lean gain costs, the magnitude depended on the deposition site. Increasing lean in market lambs yield would be increase efficiency of lamb production only if breeding ewe changes are minimized.
Subject Area
Livestock
Recommended Citation
OLTHOFF, JOHN CRAIG, "RELATIONSHIPS AMONG FEED INTAKE, BODY COMPOSITION AND FASTING HEAT PRODUCTION IN MATURE EWES (SHEEP, BREEDING, ENERGY METABOLISM)" (1985). ETD collection for University of Nebraska-Lincoln. AAI8521470.
https://digitalcommons.unl.edu/dissertations/AAI8521470