Influence of Diet on Glucose Turnover and Rates of Gluconeogenesis, Oxidation and Turnover of D-(-)-Lactate in the Bovine

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Abstract
D-(-)-Lactate metabolism as influenced by the level of roughage in the diet was examined in eight Hereford heifers (306 kg) fed ad libitum an alfalfa hay diet (R) (2.02 Mcal ME/kg) (ME, metabolizable energy) or a 90% concentrate diet (C) (2.95 Mcal ME/kg) for 18 days. Animals were adjusted to negative pressure hoods (188 liter/minute airflow) and fitted with jugular and urinary catheters. Animals received 32.2 and 71.4 µCi of D-[U-14C]lactate and 435.7 and 233.3 µCi of 2-[3H]glucose for the primer dose and hourly infusion rates, respectively. Blood, expired CO2 and urine samples were taken at 30-minute intervals for 6 hours with CO2 and urine samples taken for an additional 24 and 42 hours, respectively. ME intakes were not different between diets (P > 0.05) for the day of infusion. Glucose turnover rates were 143.3 and 154.3 mmol/hour, whereas, D-(-)-lactate turnover was 0.67 and 0.57 mmol/hour for R and C, respectively. Rates of oxidation and gluconeogenesis were 0.61 and 0.22 mmol/hour for R and 0.55 and 0.16 mmol/hour for C. Recovery of 14C in urine and expired air accounted for 3.73 and 44.3% of the infused dose for R and 2.13 and 43.5% of the infused dose for C. Oxidation was the major route of D-(-)-lactate elimination but the potential for D-(-)-lactate elimination from the bovine under high D-(-)-lactate loads is as yet undetermined.