Relative development of subcutaneous, intermuscular, and kidney fat in growing pigs with different body compositions

A total of 94 pigs from seven groups considered as lean (boars from a synthetic line and the Pietrain breed), conventional (boars, gilts, and barrows from the Large White breed), fat (barrows from the Meishan x Large White cross), or obese (Meishan barrows) were serially slaughtered between 12 and 110 kg BW. Carcasses were dissected into muscle, bone, skin, and fat, which was further separated into subcutaneous, intermuscular, and kidney fats. Subcutaneous fat accounted for 60 to 70% of body fat and intermuscular fat for 20 to 35% of body fat. Relative to total fat, intermuscular fat grew more slowly (allometric growth coefficients generally < 1), subcutaneous fat at the same rate (b close to 1), and kidney fat more rapidly (1.12 < b < 1.33). The leaner the animals genetically, the higher the proportion of intermuscular fat in total fat. The ratio of intermuscular to subcutaneous fat varied from .31 in Meishan barrows to .66 in Pietrain boars. Overall, the ratio of intermuscular fat to muscle weight or body weight was positively related to the development of total fat. However, Pietrain pigs were unique in having a high development of intermuscular fat. The present results suggest that 1) the genetic controls of the development of intermuscular and subcutaneous fat are partially independent and 2) the development of intermuscular fat may be determined at an early stage, before 20 kg BW.