Composition of the whole body and component fractions in mature ewes from seven breeds

In a sheep production system, effects of body composition on nutrient requirements for maintenance, tissue deposition and lean meat production may be important. Composition of body fractions differing in expected metabolic activity was measured for 12 nonpregnant, nonlactating, 3- to 4-yr-old ewes from each of seven breeds representing diverse body size and performance characteristics. Half the ewes in each breed had ad libitum access to feed and half were fed at maintenance levels for an average of 41 d. Ewes were slaughtered after a 72-h fast. Empty bodies were divided into visceral organs and blood (ORB); gastrointestinal tract and internal fat (GIF); head, hooves and pelt (HHP); and carcass (CAR). Water, fat, ash and the remaining fat-free dry organic matter (FFDOM) contents were determined for each fraction. Mean empty body weight (EBW) was 60.8 kg and mean composition was 47.6% water, 34.1% fat, 14.8% FFDOM and 3.5% ash. Among breeds, larger mature size generally was associated with a higher percentage of fat and a lower percentage of water (P less than .01), in agreement with carcass composition. Ewes with ad libitum access to feed had more fat and less water in their EBW than did those fed at maintenance levels, especially in the GIF fraction. Distribution of EBW averaged 58.1%, CAR, 19.0%, GIF, 15.4% HHP and 7.5% ORB. The larger, faster growing breeds had the highest proportion of the EBW and of each chemical component located in the carcass. The smaller, more prolific breeds had the highest percentages of EBW in the ORB and GIF fractions. Effects of these large genetic differences in body composition and tissue distribution on production efficiency need to be evaluated.