EFFECTS OF OAK (QUERCUS-ILEX) TANNINS ON DIGESTION AND NITROGEN-BALANCE IN SHEEP AND GOATS

Sheep and goats exhibited different levels of tolerance to the effects of tannins extracted from oak leaves (Quercus ilex). Feed intake, N b alance, and rumen ammonia concentrations decreased by 8%, 159% and 50% , respectively, in sheep infused intraruminally with tannins (P < 0.05 ). Similar measurements were not depressed (P > 0.05) in goats althoug h mean rumen ammonia content was 39% less. In vivo DM digestibility wa s not significantly different for either sheep or goats. Averaged in v itro fermentation capacity was depressed 10% by tannin (8-12% concentr ation) in the rumen fluid from non-infused sheep given the same diet, but was improved by 9% for goats. Finally, tannin-infused goats lost i n urine only 17% of the N ingested, while tannin-infused sheep excrete d as much as 44%. The superiority of oats in dealing with tannin might result from the greater ability of their microbial population to degr ade tannins, and/or their higher urea recycling and salivary secretion capabilities. Results derived from this study indicate that goats may be more suitable for grazing in oak woodland, especially during the s eason when alternative forage availability is scarce.