THE ENERGY COSTS OF INGESTION OF NATURALLY-OCCURRING NONTANNIN PLANT PHENOLICS BY SHEEP

We examined the energetic consequences to a ruminant herbivore of inge stion and absorption of low-molecular-weight phenolics, which commonly occur in ericaceous plant species. The first experiment simulated the entrance of absorbable xenobiotics into the general circulation as mi ght occur if the detoxification capacity of the animal were exceeded. Orcinol was administered intravenously to six sheep for 10 d at a low rate equivalent to about 5% of the total nontannin phenolics likely to be ingested by free-ranging sheep. This led to a 5% increase in energ y expenditure (P < 0.05), measured by indirect calorimetry In a furthe r experiment orcinol and quinol were continuously infused into the rum en of five ewes, at a rare equivalent to the likely, dietary intake of nontannin phenolics. When administered via this normal oral route, wi thin the normal physiological range, the phenolics had no detectable e ffect on energy expenditure but led to a reduction in the intake of di gestible energy (P < 0.05) and an increase in urinary energy excretion (P < 0.01). These experiments suggest that the effectiveness of the d etoxification system is crucial to permit use of toxin-containing plan ts by herbivores, and it should be strongly associated with their fora ging strategies.