Responsiveness of swine divergently selected for feed efficiency to exogenous adrenocorticotropic hormone and glucose...

Increasing the feed efficiency of lean tissue gains is an important goal for improving sustainable pork production and profitability for swine producers. To study feed efficiency, genetic selection based on residual feed intake (RFI) was used to create two divergent lines. Low-RFI pigs consume less feed for equal weight gain compared with their less-efficient, high-RFI counterparts. As cortisol and insulin are important energy control and growth regulators, our objective was to evaluate the role of the adrenocorticotropic hormone (ACTH)-cortisol and the glucose-insulin axes in pigs divergently selected for RFI. Adrenocorticotropic hormone (0.2 IU/kg BW)-stimulated cortisol and non-esterified fatty acids (NEFA) concentrations and intravenous glucose tolerance test (IVGTT; 0.25 g/kg BW)-stimulated glucose, insulin, and NEFA concentrations were assessed in six low-RFI and six high-RFI gilts (68 ± 5.2 kg). Before the ACTH challenge, low-RFI gilts tended to have less baseline plasma cortisol (P = 0.08) but no difference in NEFA concentrations (P = 0.63) compared with high-RFI gilts. After the ACTH challenge, low-RFI gilts had less cortisol (P = 0.04) and NEFA concentrations (P = 0.05) compared with high-RFI gilts. Glucose, insulin, and NEFA concentrations did not differ between genetic lines before the IVGTT. After glucose infusion, low-RFI gilts had greater insulin concentrations (P = 0.003) but did not differ in glucose or NEFA concentrations compared with high-RFI gilts. These results indicate that genetic selection for reduced RFI (improved feed efficiency) resulted in less stress responsiveness and an increase in insulin after glucose infusion. These data have implications for identifying and selecting more feed efficient pigs and for understanding the physiological mechanisms underlying feed efficiency.