Adipocyte characteristics of calf- and yearling-fed cloned Brangus steers

Abstract

Two parallel experiments were conducted to evaluate the impact of calf-versus yearling-feeding on differentiation of subcutaneous and intramuscular adipocytes from nuclear transfer cloned Brangus steers. The cloned steers were used to eliminate genetic variation. In Experiment 1, Brangus steers were fed as weanling calves (CF; n = 4) or as yearlings (YF; n = 4) to a constant age endpoint of 16 mo. In Experiment 2, Brangus steers were fed as weanling calves (CF; n = 5) or yearlings (YF; n = 4) to a constant live weight of 530 kg. Adjusted fat thickness, USDA marbling scores, and quality grades were lower in steers slaughtered at a constant age than those that were slaughtered at a constant weight. In addition, postmortem cellularity data showed that there were more cells per g of tissue, and smaller cell diameters and volumes from steers slaughtered at a constant age than those slaughtered at a constant weight. Lipogenic rates and 3H-thymidine incorporation rates were higher in the s.c. and i.m. adipocytes of constant age steers, further demonstrating the lack of maturity these cells. These data also confirmed that i.m. adipose tissue was a later-developing depot. Intramuscular adipocytes possessed more cells per g tissue, and smaller cell diameters and volumes than their s.c. counterparts. Lipogenic rates and DNA replication rates also demonstrated this. Postculture data demonstrated that there were more cells per g tissue, smaller cell diameters, and smaller cell volumes when compared to postmortem values for all groups except calf-fed steers that were slaughtered at a constant weight. The adipocytes from the CF constant weight treatment group also retained their ability to synthesize lipid and replicate. The stromal vascular portion retained a greater amount of 3H-thymidine, suggesting that the adipocytes from these steers may be replicating. The steers from this group were younger than any of the other treatment groups, indicating that age is a predominant factor in deteriming the ability of the adipocyte to replicate. Diet was shown to have the greater influence on overall fatness. Calf-feeding resulted in higher dressing percentages. However, yearling-feeding resulted in more desirable carcass grades. The ability to replicate DNA was highest in CF steers slaughtered at a constant weight.