Variations in Protein Deposition Might Be Associated with Insulin Resistance and Differences in Amino Acids Metabolism in Growing Gilts.

Abstract Pigs with similar body weight (BW), same genetic background and sex vary in terms of protein deposition (PD) overgrowth. Insulin stimulates protein synthesis, and differences in PD could be associated with the variation among pigs in postprandial insulin secretion. Therefore, this study aimed to investigate if changes in preprandial and postprandial amino acids (AA) response and insulin resistance differ between pigs having Low or High PD. Seventy gilts (33 kg BW, ± 3.6; Alphagène) were assigned to a randomized complete block (BW) design and housed in the same pen equipped with automatic feeders. Pigs were fed ad libitum with a diet balanced to maximize PD. Dual X-Ray estimated body protein (BP) and lipid (BL) masses on d 1 and 21, and by difference, PD was calculated. On d 23, pigs were grouped in Low (157 g/d) and High (219 g/d) PD. Eight pigs per PD group were canulated in a jugular vein, and after 48h recovery receiving feed at 90% of the measured feed intake, they were fasted for eight hours to study preprandial metabolism (-5, -1 min before the meal). In sequence, all pigs received a 300 g meal and blood samples were collected at 10, 15, 20, 30, 40, 50, 60, 75, 90, 120, 150, 178, 178 min, relative to the meal, to measure AA, insulin and glucose concentrations. In addition, insulin resistance (HOMA-IR) was calculated based on fasting glucose and insulin concentrations. The AA response was modeled for each PD group based on the average group response using differential equations derived from the Erlang equation. Thus, the basal concentration, area under the curve (AUC) and AA flux could be compared among groups using the parameters obtained by the non-linear model. An F-test was used to compare the difference in the indexes between Low and High PD pigs. The basal concentration of methionine, valine and leucine were similar, whereas AUC was greater for Low PD pigs with no difference in flux, with the exception of methionine (P < 0.10; Table 1). Conversely, lysine (15%) and threonine (10%) basal concentrations were less in Low PD pigs. Lysine AUC was greater (8%), whereas others AA AUC were on average 27% less for High PD than for Low PD pigs. Lysine maximal concentration was 11% greater for High PD pigs and occurred later than for Low PD (1.15h vs 1.03h). Such differences in AA postprandial metabolism might be partially due to metabolic differences in response to anabolic hormones such as insulin. For instance, HOMA-IR differed (P < 0.05) among PD categories, with Low PD showing a 44% lower index for insulin resistance than high PD pigs. High PD pigs are less insulin-resistant and show differences in pre- and postprandial AA metabolism.