Toxicity Problems Associated with the Grazing of Oak in Intermountain and Southwestern U.S.A.
Experimental evidence is good that tannins in excess of 5% by weight in forage do interfere with animal performance before symptoms of toxicity appear. J. W. Dollahite et al. demonstrated that calcium hydroxide added to the forage base in amounts equal to 10 to 15% by weight was adequate to forestall development of symptoms of toxicity. Since the oak species most frequently involved in incidents of poisoning in the Intermountain West are notoriously difficult to eliminate from rangelands, managers should develop programs that will minimize the probability of livestock poisoning. In the Intermountain and Southwestern regions most cases of toxicity involve cattle. Given the negative impacts of tannins on recovery of protein and energy from diets as reported by A. D. Nastis and J. C. Malechek, it seems inevitable that significant economic losses will occur any symptoms of poisoning appear.