Lipogenic activity of intramuscular and subcutaneous adipose tissues from steers produced by different generations of angus sires.

Simmental and Hereford cows (n = 74) were inseminated with semen from purebred Angus bulls from the 1960s or with semen from purebred Angus bulls from the 1980s. The F1 calves provided the foundation for two investigations, one addressing growth and carcass characteristics, and another measuring the impact of sire generation on lipid metabolism and adiposity. Calves sired by the 1980s-type bulls had greater (P .05) in any measure of fatness between groups (adjusted fat thickness, kid- ney, pelvic, and heart fat, or marbling scores), but yield grade was higher numerically ( P < .l) for the 1980s steers. The second aspect of this research addressed the influence of different generations of Angus sires on specific carcass traits and adipose tissue metabolism. A subset of six steers for each generation type (from Simmental cows) were selected and samples were collected at slaughter for measure- ments in vitro. For both generation types, intramuscu- lar (i . m. adipocytes had lesser ( P < .05) cell volumes than subcutaneous (s.c. adipose tissue. Correspond- ingly, i.m. adipose tissue exhibited lower (P < .05) rates of 14C-labeled acetate incorporation into lipids as measured immediately after slaughter. Intramuscular and S.C. adipocytes from 1980s-type steers were smaller (P < .05) than those from the 1960s-types steers, with correspondingly more cells per gram of tissue. Thus, the newer generation-type steers required more adipocytes to achieve the same amounts of i.m. and S.C. fat. There was no difference between generation types in 14C-labeled acetate incor- poration into neutral lipids and, of the lipogenic enzyme activities measured, only 6-phosphogluconate dehydrogenase was significantly lower in adipose tissues of the 1980s-type steers. Thus, in spite of differences in sire generation and cellularity, carcass traits associated with fatness and in vitro measures of lipogenesis were not different between 1960s- and 1980s-type Angus crossbred steers.