Metabolic regulation of cattle adiposity in different breed types using two disparate diets

Fifteen steers were used to evaluate the difference of diets (corn-based for 8 mo or hay-based for 12 mo) and breeds (Angus; n = 7 or Wagyu; n = 8) in a completely randomized design with 2 x 2 factorial arrangement of treatments to test the hypothesis that there are differences in fatty acid metabolism and cellularity in subcutaneous (s.c.) and intramuscular (i.m.) adipose tissue between these breeds types. Fat thickness, carcass weight, overall maturity, and yield grade of Angus steers were higher than those of Wagyu steers fed either corn (34%, 22%, 3%, and 8% higher, respectively) or hay diets (20%, 8%, 10%, and 8% higher, respectively) (P < 0.03). Moreover, marbling scores tended (P = 0.70) to be greater in Angus steers than in Wagyu steers fed either diet. Lipogenesis from acetate in both s.c and i.m. adipose tissue was higher in Wagyu steers (212.82 and 86.23 nmol/(105 cells per 2 h)) than in the Angus steers (86.23 and 29.66 nmol/(105 cells per 2 h)). Also, acetate incorporation into fatty acids was greater in s.c. adipose tissue than in i.m. adipose tissue (P < 0.05). Subcutaneous adipose tissue stearoyl-CoA desaturase (SCD) activity was significantly greater in corn-fed steers and than in hay-fed steers (P < 0.05), but there was no difference in SCD activity between Angus and Wagyu steers (P > 0.05). Adipocyte cellularity data demonstrated that both breeds have more cells per gram adipose tissue and smaller cell volumes in i.m. adipose tissue than in s.c. adipose tissue. In s.c. adipose tissue, saturated fatty acids tended to be lower in corn-fed Angus and Wagyu steers than in hay-fed steers (P < 0.06). Similarly, monounsaturated fatty acids were higher in corn-fed Wagyu and Angus steers than in hay-fed Wagyu and Angus steers (P < 0.01). Slip point was positively correlated with percentage stearic acid in corn-fed and hay-fed steers, and there was a negative correlation between slip point and the SCD index. These data demonstrated that corn-based diets provide not only increased contents of monounsaturated fatty acid in Angus and Wagyu adipose tissue but also increased lipogenic activity.