Dietary effects on mixed function oxidase activity in the ruminant

The objectives of this research were to determine effects of age, heat-browned hay and protein intake on MFO activity in ruminants. A preliminary study determined that rats fed browned egg albumin had higher hepatic cytochrome P-450 concentrations than rats fed a similar diet, excluding the browned egg albumin. Holstein steer calves were then utilized in three experiments to determine the effects of age, heat-browned hay and protein level. MFO activity was assessed by measuring the rate of metabolism (disappearnce from blood plasma) of antipyrine, a compound extensively metabolized in the liver (Anderson et al., 1982). Calves were dosed with 18 mg/kg B.W. antipyrine via the jugular vein and blood samples were taken from the opposite vein at 0, 0.5, 1, 2, 3, 4 and 5 hr post dosing. Results indicated that antipyrine was metabolized faster at 1 mo of age than at either 2, 3 or 4 mo. Disappearance rates of antipyrine were 72.7, 45.8 and 60.7% faster (P < .05) at 1 mo than at 2, 3 or 4 mo, respectively. Heat-browned hay and protein content of the diet had no effect on MFO activity. In an experiment conducted on catherterized sheep in which blood flows and liver extraction ratios could be measured antipyrine clearance by the liver accounted for 10 to 20% of the initial dose. It was concluded that the remaining 80 to 90% was cleared via the saliva which carried antipyrine to the rumen where it was finally metabolized.