332. Association of Glucose Metabolism with Residual Feed Intake in Beef Bulls.

Abstract In the beef industry, improving feed efficiency provides economic and environmental benefits. Residual feed intake (RFI) has been widely used to identify animals that maintain performance with reduced feed intake, yet the biological mechanisms underlying RFI variation remain unclear. The objective of this experiment was to determine the association of glucose metabolism with RFI. After a 21 d adaptation period, Brangus and Simbrah bulls (n = 120; initial BW 373 ± 39 kg) underwent a 70 d feed efficiency trial. Body weight was measured every 2 weeks, and dry matter intake (DMI) was calculated from as-fed intake recorded using an automated feeding system (GrowSafe, Vytelle SENSE). A blood sample was collected for DNA extraction to estimate the percentage of Bos indicus influence on each bull. RFI was calculated, and bulls were ranked by RFI status. The 30 most (low RFI < 2.5 SD from the mean) and the 30 least efficient (high RFI > 2.5 SD from the mean) bulls were subjected to an intravenous glucose tolerance test after 16-h of fasting. Glucose was infused at 1 g glucose/kg BW^0.75 via a jugular catheter, and blood samples were collected at -15, -5, 0, 5, 10, 15, 20, 30, 45, 60, 90, and 120 minutes relative to glucose infusion to determine plasma glucose concentration. The area under the curve (AUC; mg/dL), baseline glucose concentration (mg/dL), peak glucose concentration (mg/dL), glucose clearance at 30, 60, 90, and 120 minutes (%), glucose nadir (mg/dL) and time to glucose nadir (min) were calculated. Data was analyzed with a mixed model analysis using the MIXED procedure of SAS. The model included the percentage of Bos Indicus influence as a covariate and breed as a random effect. To evaluate the effect of RFI, time of sample collection, and their interaction on glucose concentration, a mixed model with a repeated measures statement was used. Data was transformed, and outliers were removed when necessary. There was a significant effect of RFI (P = 0.04) and sampling time (P = < .0001) on glucose concentration, with low RFI bulls maintaining higher glucose concentrations over time than high RFI bulls. Consistent with this pattern, Glucose AUC (P = 0.05) and nadir (P = 0.03). were greater in low RFI. In contrast, high RFI exhibited faster Glucose clearance at 30, 60, 90, and 120 minutes. Baseline glucose, peak glucose concentration, and time to glucose nadir were not affected by RFI (P > 0.10). These results indicate that low RFI bulls maintain higher glucose concentrations for a longer period following a glucose infusion, suggesting differences in glucose utilization dynamics between RFI groups. Further research is needed to clarify the physiological mechanisms underlying these metabolic differences. For image description, please refer to the figure legend and surrounding text.