Effect on feed intake, digestibility, N retention and methane emissions in goats of supplementing foliages of cassava (Manihot esculenta Crantz) and Tithonia diversifolia with water spinach (Ipomoea aquatica)

Four growing male goats (Bach Thao breed) with body weight in the range from 10 to 13.5 kg and about 4-6 months of age were fed basal diets of sweet cassava foliage or Tithonia diversifolia without or with supplementation with fresh water spinach. Appparent DM digestibility was higher by 30% for diets based on Tithonia than on cassava foliage and was improved slightly (about 3%) when water spinach was also fed. There was a 21% increase in N retention when cassava was the main foliage rather than Tithonia, but the apparent benefits from giving water spinach were less (about 8%). Methane emissions in eructed gas were reduced by 50% when cassava rather than Tithonia was the main foliage in the diet, and were increased when water spinach was also fed. It is postulated that on such feeds the balance of feed fermented in the cecum/large intestine relative to the rumen is increased. As disposal of hydrogen in fermentation degradation in the cecum-colon appears to be dominated by acetogenesis, this would account for decreased methane production on such diets.