Metabolic adaptation to increased glucose demand in ruminants

Four Dorset wethers were utilized in a 4 × 4 Latin square design and injected subcutaneously with 0, 0.5, 1.0, and 2.0 g/d of phlorizin to determine if the phlorizin-treated wether is a suitable model to study metabolic adaptation to perturbed glucose metabolism. Total collection of urine and feces and repeated blood sampling were conducted during each 72-h treatment period. Urinary glucose excretion averaged 0, 72.7, 97.9, and 98.5 g/d for the four treatments, respectively. Plasma glucose concentrations were decreased after the first injection in phlorizin-treated wethers compared with the excipient (TRT X TIME, P < 0.06), but were similar for all treatments by 32 h after the first injection. Plasma urea N concentrations were similar for all treatments during the first 20 h of the treatment period, but were increased by 32 h for wethers treated with 1.0 and 2.0 g/d of phlorizin compared with 0 and 0.5 g/d (TRT X TIME, P < 0.01). Plasma nonesterified fatty acid concentrations were similar for all treatments during the first 20 h of the treatment period, but were increased by 24 h for the wethers treated with 1.0 and 2.0 g/d of phlorizin compared with 0 and 0.5 g/d (TRT X TIME, P < 0.10). Differences in digestibilities of energy and N were not significant. Increased urinary energy loss accompanied phlorizin injection (TRT X TIME, P < 0.04) and reflected urinary glucose excretion. These data suggest that phlorizin-treated wethers adapted to increased glucose demand by 32 h of treatment and should be useful for investigations of metabolic adaptations associated with situations where glucose demand in ruminants is increased suddenly.