Food intake, growth and body composition in Australian Merino sheep selected for high and low weaning weight 5. Adipocyte volume and number in the dissected fat partitions

Abstract

ABSTRACTThe cellular characteristics of dissected carcass (subcutaneous and intermuscular fat) and non-carcass (kidney fat, omental and mesenteric fat) fat partitions were examined at maturity in a total of 34 rams and ewes from flocks of Peppin Merino sheep selected for high (weight-plus) or low (weight-minus) weaning weight and from a randomly bred control flock. Strain and sex effects on the rate of change in adipocyte volume in each fat partition relative to the change in chemical-fat weight in that partition, were examined in 60 immature animals.Selection for high or low weaning weight had no effect on adipocyte volume in the mature animals, with the increased weight of fat in the weight-plus animals due to an increased number of adipocytes in the dissected fat partitions. Consequently, hyperplasia had a greater contribution to increases in chemical-fat weight in the weight-plus, compared with the weight-minus animals.Mature ewes had larger and fewer adipocytes in the subcutaneous and intermuscular partitions than the mature rams, whereas there was no difference between the sexes in adipocyte volume in the kidney, omental and mesenteric fat partitions. Mature ewes had fewer adipocytes than the mature rams in the subcutaneous, intermuscular, omental and mesenteric fat partitions. With the exception of the kidney fat partition, there was no sex effect on the relative contribution of hypertrophy to increases in chemical-fat weight of the dissected carcass and non-carcass fat partitions.