BREED AND SEX EFFECTS ON THE DEVELOPMENT, DISTRIBUTION OF MUSCLE, FAT AND BONE, AND THE PARTITION OF FAT IN PIGS

Dissection data from 341 carcasses collected over a period of 7 years at the Institute of Food Research, Bristol (Large White, 138 entire males and 112 females; Pietrain, 41 entire males and 31 females; Iron Age (European Wild Pig .times. Tamworth), 8 entire males and 11 females) were used to examine the growth of muscle, fat and bone in joints relative to the corresponding total tissue in the side, and the growth of the fat depots relative to total side fat. The musculature of Iron Age pigs was early maturing, as indicated by a particularly slow growth of pelvic limb and fast growth of neck and thorax muscles relative to total side muscle. As a consequence, Iron Age pigs had a lower percentage of pelvic limb and a higher percentage of neck and thorax muscles than the other breeds. Pietrains had proportionately the heaviest pelvic limb muscles, a result which was apparently independent of the overriding effect of maturity. However, considering the large difference in body shape (conformation) between Pietrain and Iron Age pigs, the differences in muscle weight distribution were small. Entire males had faster growing and heavier neck and thorax muscles than females. This was considered to be due to the effects of sex hormones. Entire males had proportionately less muscle in the pelvic limb. Within carcass fat, the order of increasing growth rate relative to total side fat was intermuscular fat < subcutaneous fat < perirenal-retroperitoneal fat. Pietrain and Iron Age pigs had higher relative growth rates for subcutaneous fat and lower relative growth rates for intermuscular fat than Large Whites, an indication of earlier maturity in carcass fat development. This was reflected in Iron Age pigs, but not Pietrains, in a particularly heavy weight of subcutaneous fat and light weight of intermuscular fat . Within the subcutaneous and intermuscular fat depots, the highest allometric growth coefficients were generally observed in the forequarter. There were no consistent breed effects on the distribution of subcutaneous fat whereas, in the intermuscular fat depot, Iron Age pigs had less fat in the earlier-maturing thoracic limb, and lumbar and abdominal joint. At the same weight of total side fat (8.80 kg), entire male Pietrains and Large Whites had more intermuscular and less subcutaneous fat than females. There was no sex difference in fat partition in Iron Age pigs. In all breeds, bone in the pelvic limb had the slowest relative growth. Similarity, the femur and tibia-fibula were the two slowest growing bones of the four major limb bones examined. Otherwise there was no consistent pattern of relative growth throughout the skeleton. Breed effects on relative growth within the skeleton and on bone distribution were small and considered to be of little commercial significance. Pietrains had the highest muscle:bone ratio in each of the four anatomical joints. Entire males and females had a similar relative growth and distribution of bones. Females had consistently higher muscle:bone ratios.