TISSUE DEVELOPMENT IN SWINE AS INFLUENCED BY LIVEWEIGHT, BREED, SEX AND RATION

Abstract

Carcasses of 73 pigs taken from an experiment which involved 144 barrows and gilts of Duroc × Yorkshire, Hampshire × Yorkshire and Yorkshire × Yorkshire breeding, fed either a high energy (HE) (3652 kcal DE/kg) or a low energy (LE) (2757 kcal DE/kg) ration, and slaughtered at 68, 91 and 114 kg liveweight, were dissected to study tissue development and carcass composition in pigs. To establish a starting point, an additional nine barrows and eight gilts of the same breed groups were slaughtered at 23 kg liveweight. A normal pattern of tissue growth was shown to occur, bone growth being relatively slow and muscle growth relatively fast. Fat deposition paralleled muscle growth from 68 to 91 kg liveweight, after which fat deposition exceeded muscle growth in absolute amount. Breed of sire tended to influence the carcass, muscle and fat weight per day of age as well as the proportions of lean and fat in the carcass. Gilts had more muscle per day of age and a greater percentage of muscle and less of fat than barrows. Barrows had a greater carcass weight and more fat per day of age than gilts. The LE ration resulted in higher percentage of muscle and lower percentage of fat in the carcass than did the HE ration. At all slaughter weights, the differences in the proportions of muscle, fat and bone between barrows and gilts were similar to the differences resulting from the HE and LE rations. Carcasses from gilts slaughtered at 114 kg liveweight were equal in composition to those from barrows slaughtered at 91 kilograms. Similarly, pigs fed the LE ration at 114 kg had equal carcass composition to HE-fed pigs at 91 kilograms. The data indicated that there may be some justification for extending the weight range in the Canadian grading system such that carcasses of superior composition outside the present weight range would be recognized on their merit. Some interactions occurred among breed, sex and ration groups reflecting differences in energy intake and partitioning of nutrients for tissue growth.