Postmortem Shrinkage of Lamb Carcasses

Abstract

E XPERIMENTS involving 1,000 lamb carcasses were conducted to identify those factors which affect postmortem shrinkage. During the first 36 hr. postmortem, 92% of the 72-hr. weight loss occurred. Postmortem shrinkage results from evaporation and drip loss of wash water and from loss of moisture by the carcass components. Increases in confor-mation score, U.S.D.A. grade, completeness of fat cover, subcutaneous fat thickness and carcass weight were associated (P(.01) with decreases in lamb carcass shrinkage either through decreases in surface area (total area exposed and/or amount of lean exposed) or because of increased amounts of subcutaneous fat. Increased fatness may reduce shrinkage by serving as a barrier against moisture loss (preventing evaporation from the lean) or may act by reducing the total moisture content in the carcass (because adipose tissue contains less water than does muscle tissue). Data suggest that a fat covering of 2.5 mm (at the 12th rib) will prevent excessive postmortem shrinkage during chilling and transit. Increased fat thickness (above 2.5 ram) was associated with decreased weight loss, but within the approximate range of 2.5 to 9.1 mm the advantage was usually small and not significant. Increases in conformation score or final grade beyond High Choice, in carcass weight beyond approximately 22.5 kg and in fat cover completeness beyond that level described as slightly completely covered with subcutane-ous fat, though possibly effective in further reducing postmortem shrinkage, would probably not be feasible since all of these factors are indicative of increased fatness. The monetary return which would result from reducing shrinkage by encouraging additional fatness would not compensate for the decrease in car