Energy and protein evaluation of tropical feedstuffs for whole tract and ruminal digestion by chemical analyses and rumen inoculum studies in vitro

A range of tropical feedstuffs used in feeding ruminants were analysed for metabolisable energy (ME) and nitrogen fractions. The ME content was predicted from the extent of fermentation in in-vitro incubation with rumen inoculum and N was evaluated based on solubility in borate-phosphate buffer, protease enzyme and acid detergent solution. The range in predicted ME content and the rate of organic matter fermentation for grains, byproduct feeds, cultivated fodders and nonlegume straw were respectively, 11.8–13.9 and 0.05–0.11; 6.0–13.7 and 0.05–0.15; 7.1–9.4 and 0.05–0.13; 5.7–7.7 and 0.02–0.04. Potentially digestible N was more than 90% for most feedstuffs with the exception of finger millet grains (73.9%), rice bran (88.0%), napier grass (79.3%), spear grass (82.6%) and nonlegume straw (66.0–88.6%). N insolubility in protease enzyme (PIN) was maximum in rice bran, solvent extracted (s.e.) (56.6%) and minimum in sesame meal (3.3%), with cottonseed meal and rapeseed meal > sunflower meal, coconut meal, groundnut meal, s.e. > groundnut meal, expeller (exp). However, the buffer insoluble N soluble in protease enzyme (considered as slowly degraded N) was found to be maximum in sesame meal (90.6%), followed by coconut meal (60.2%), cottonseed meal (50.6, 61.6%), sunflower meal (45.7%), groundnut meal, s.e (45.1%) and groundnut cake, exp. (22.7%). In situ N undegradability reported in the literature for similar feedstuffs indicated too wide a range making it difficult to take these values as standards for comparison with any of the N fractions obtained from the laboratory analysis.