Factors affecting fat content and distribution of fat in cattle and carcasses Stephen B. Smith, Texas A&M University, USA
Like most animals, beef cattle are highly efficient in depositing fat. Estimates of efficiency rates for fat and protein deposition are approximately 0.75 and 0.25, respectively. Growth promotants such as b-adrenergic agonists can partition energy from fat growth to lean growth, but do not reduce the efficiency of the biochemical processes involved in fatty acid and triacylglycerol biosynthesis. Any ingested energy not used for maintenance and growth of lean tissues ultimately is deposited as carcass fat (adipose tissue). It has been known for decades that the various fat depots in cattle are deposited in a specific order. Abdominal (kidney, pelvic and heart) fat is deposited during the third trimester of gestation. This is followed by seam (intermuscular) fat, which is laid down between individual muscle groups, which is in turn followed by subcutaneous fat. The last fat depot to develop, and paradoxically the economically most important in many countries, is marbling (intramuscular, interfascicular) fat. Subcutaneous and seam fats also are of high value in the United States and in many other countries, because they are used extensively in the production of ground beef (mince), sausages and other processed meats. Excess fat trim is shipped to rendering facilities, where the extracted lipid is used to produce beef tallow.