The partition of body fat in British Friesian and Jersey steers

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Abstract
Ninety-two British Friesians and 62 Jersey castrated male cattle were slaughtered serially in five age groups at 13, 89, 170, 339 and 507 days, and dissected fully into lean, bone, intermuscular fat, subcutaneous fat, perirenal-retroperitoneal fat (kidney knob and channel fat), omental fat and mesenteric fat. The aim was to investigate the partition of body fat in these dairy breeds and the role of the partition of fat in determining carcass value. Relative to live weight, Friesians had more lean, subcutaneous fat and carcass fat (subcutaneous and intermuscular) at most ages, and Jerseys had more kidney knob and channel fat, and intra-abdominal fat. Friesians had a higher killing-out proportion and lean:bone ratio, and thicker subcutaneous fat. The order of increasing relative growth of fat depots with total body fat as the independent variable was, for Friesians: intermuscular < mesenteric < kidney knob and channel fat < subcutaneous < omental. In Jerseys the order was: intermuscular < mesenteric < subcutaneous < kidney knob and channel fat < omental. There were only small breed differences in the distribution of subcutaneous fat between eight regions. t I is suggested that, between breeds, there is a physiological link between the capacity for milk-fat production and the partition of fat within the body, with relatively high milk-fat producers depositing proportionately more fat intra-abdominally. Since the timing of slaughter is often determined by level of external finish in beef production, the breed difference in the partition of fat, which caused Jerseys to have a higher proportion of kidney knob and channel fat, and intermuscular fat, at the same proportion of subcutaneous fat, would reduce carcass value in Jerseys compared with Friesians.