Indices of energy metabolism and insulin sensitivity in the indigenous, crossbred, and pure-bred heifers in subtropical climate.

As breed is known to influence metabolic traits, we compared the energy indices in the heifers of milch (Holstein Frisian, Jersey and their crosses) and draught (Amrut mahal, Hallikar, and Khillari) breeds (n = 6/breed) maintained under a subtropical production system. Intravenous insulin tolerance test and glucose tolerance test were done to the heifers and serial blood samples were collected to determine the concentration of glucose (glc), insulin, and surrogate indices of insulin sensitivity. Further, the relative expression of glucose transporters (GLUT) in the skeletal muscle, udder, and peripheral blood mononuclear cells were determined by qRT-PCR. The results revealed that the indigenous draught breeds had significantly higher glc and insulin concentrations, glycated hemoglobin, and plasma fructosamine. In contrast, exotic and crossbred dairy breeds had higher serum non-esterified fatty acid and β-hydroxybutyrate concentrations (P < 0.05). Further, the indigenous draught breeds showed a significantly higher slope and intercept of the glc curve, insulin stimulated higher blood glc reduction and elimination rate of glc than the pure and crossbred dairy breeds (P < 0.05). Insulin-stimulated glc uptake was higher in indigenous breeds, as evident from higher (P < 0.05) slope and intercept of the glc curve, glc clearance rate, and lower (P < 0.05) T_1/2 of glc during intravenous glc tolerance tests. The expression of GLUT 4 was upregulated (P < 0.05) in the skeletal muscles of indigenous breeds, while GLUT 1 expression was upregulated (P < 0.05) in the udder of dairy breeds. The increased peripheral insulin sensitivity was partly due to upregulation of GLUT4 in the skeletal muscle of the indigenous draught breeds.