Supplementation of Omnigen-AF Alters the Metabolic Response to a Glucose Tolerance Test in Beef Heifers

This study was designed to determine whether feeding OmniGen-AF to feedlot heifers would alter metabolic profiles in response to a glucose tolerance test. Heifer calves (n=184; 216±1 kg) were allocated into 2 treatment diets: 1) Control, fed a standard receiving ration, and 2) OmniGen-AF (OG), fed the Control diet supplemented with OmniGen-AF at 4.54 g/hd/d and were fed in a commercial feedlot for 42d. On d42, heifers (n=16/trt) were selected based on BW, phenotype, temperament, and treatment history and transported to Lubbock, TX (130 km). Upon arrival, heifers were housed in outdoor pens according to treatment and fed respective diets until fitted with indwelling jugular catheters and vaginal temperature recording devices and moved into individual stanchions in an enclosed barn. After cannulation, heifers were fed their treatment diets at 1400h. All orts were removed at 2000h to allow for a 12-h fast prior to first blood collection. The following day, heifers were administered 0.5 mL/kg BW of a 50% dextrose solution at 0900h (0h). Blood samples were collected and serum isolated at -60, -45, -30, -15, 0, 10, 20, 30, 45, 60, 90, 120, and 150min relative to bolus dextrose infusion immediately following the 0 min sample collection. Serum was stored at -80C until analyzed for cortisol, glucose, insulin, NEFA and serum urea nitrogen (SUN) concentrations. Data were analyzed using proc MIXED in SAS specific for repeated measures, with fixed effects of treatment, time and treatment x time. If main effects were significant, means were separated using the PDIFF option in SAS. Vaginal temperature was not affected by treatment (P = 0.80) but decreased post-infusion (P<0.01). There was a treatment x time interaction for cortisol (P<0.01) such that cortisol was greater in OG heifers than Control heifers from 10 to 45 min post-infusion. Glucose concentrations increased post-infusion (P<0.01) and were lesser in OG (146±3 mg/dL) compared to Control heifers (161±3 mg/dL; P<0.01). There was no treatment effect for serum insulin (P=0.61). Serum NEFA concentrations were reduced (P<0.01; 0.28 vs. 0.45±0.01 mmol/L) and SUN concentrations tended (P=0.06; 89 vs. 98±3 mg/dL) to be reduced in OG heifers compared to Control heifers. Insulin sensitivity, measured via RQUICKI, was greater (P<0.01) in OG heifers than Control heifers (0.36 vs. 0.35±0.002). These data suggest that OG heifers were more responsive to changes in glucose, perhaps affecting the storage and/or redistribution of energy deposits, and provide further evidence for altered metabolism in OmniGen-AF supplemented cattle.