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 F-1 calves provided the foundation for two i nvestigations, one addressing growth and carcass characteristics, and another measuring the impact of sire generation on lipid metabolism an d adiposity. Calves sired by the 1980s-type bulls had greater (P <.05) birth, weaning, and final live weights and carcass weights. They also had larger (P <.05) hip heights and hip widths at weaning and larger (P <.05) hip heights and lower (P <.05) body condition scores at slaug hter. There were no differences (P >.05) in any measure of fatness bet ween groups (adjusted fat thickness, kidney, pelvic, and heart fat, or marbling scores), but yield grade was higher numerically (P <.1) for the 1980s steers. The second aspect of this research addressed the inf luence of different generations of Angus sires on specific carcass tra its and adipose tissue metabolism. A subset of six steers for each gen eration type (from Simmental cows) were selected and samples were coll ected at slaughter for measurements in vitro. For both generation type s, intramuscular (i.m.) adipocytes had lesser (P <.05) cell volumes th an subcutaneous (s.c.) adipose tissue. Correspondingly, i.m. adipose t issue exhibited lower (P <.05) rates of C-14-labeled acetate incorpora tion into lipids as measured immediately after slaughter. Intramuscula r and s.c. adipocytes from 1980s-type steers smaller (P <.05) than tho se froth 1960s-types steers, with correspondingly more cells per gram of tissue. Thus, the newer generation-type steers required more adipoc ytes to achieve the same amounts of i.m. and s.c. fat. There was no di fference between generation types in C-14-labeled acetate incorporatio n into neutral lipids and, of the lipogenic Enzyme activities measured , only g-phosphogluconate dehydrogenase was significantly lower in adi pose tissues of the 1980s-type steers. Thus, in spite of differences i n sire generation and cellularity, carcass traits associated with fatn ess and in vitro measures of lipogenesis were not different between 19 60s- and 1980s-type Angus crossbred steers.