Response of swine divergently selected for feed efficiency to a glucose tolerance test

Abstract Text: Pigs divergently selected for residual feed intake (RFI) differ in allele frequencies for SNPs near genes that regulate insulin release and function. As insulin is important for energy control and animal growth, insulin sensitivity and glucose clearance may help define feed efficiency differences in growing swine. Therefore, our objective was to evaluate insulin sensitivity and glucose clearance via an intravenous glucose tolerance test (IVGTT) in pigs divergently selected for RFI. Six high- (defined as less feed efficient) and six low-RFI (defined as more feed efficient) gilts (68 ± 5.3 kg) from the 8^th generation of the ISU Yorkshire RFI selection project were fitted with non-surgical jugular catheters. Three days later, following an overnight fast, all gilts were subjected to IVGTT (0.25 g glucose/kg BW). Serial blood samples were collected at -60, -30, -15, -1, 2, 5, 10, 15, 20, 30, 45, and 60 min relative to the IVGTT. Plasma glucose and insulin concentrations and the glucose to insulin ratio (G:I) were determined; baseline, peak, and area under the curve (AUC) from baseline to 60 min post-IVGTT data were calculated and analyzed using the Mixed procedure of SAS. The average baseline (-60 to -1 min) glucose and insulin concentrations and G:I did not differ between line (P≥0.32). As expected, both lines responded to the IVGTT by increasing plasma glucose and insulin over time (P<0.01). Plasma glucose and insulin concentrations peaked 2 and 10 min post-IVGTT, respectively. Lines did not differ in peak glucose concentration or G:I (P≥0.32); however, low-RFI gilts had a larger peak insulin concentration compared to high-RFI gilts (614 vs. 437 pmol/L, P=0.03). Similarly, glucose and G:I AUC did not differ between lines; however, low-RFI gilts had a 19% larger AUC compared to high-RFI gilts (P<0.01). Plasma glucose concentrations took longer to return to baseline post-IVGTT in low-RFI gilts than in high-RFI gilts (30 vs. 20 min, P≥0.16); however, regardless of line, plasma insulin concentrations returned to baseline 30 min post-IVGTT (P≥0.55). In conclusion, divergent selection for RFI has resulted in altered post-IVGTT induced insulin responses in gilts. Plasma glucose concentrations took longer to return to baseline in the low-RFI gilts, with more insulin following the IVGTT compared to the high-RFI gilts, suggesting some level of insulin resistance in the more feed efficient line. Therefore, glucose sensitivity may be related to RFI and feed efficiency in swine.

Keywords: Swine; Feed efficiency; Glucose tolerance test