| In tropical countries, perennial grasses are the key feed resources for ruminants; grasses having high nutritional characteristics are important for maintaining the productivity and health of animals. In this study, the nutrient composition and in vitro ruminal degradation characteristics as well as the short-chain fatty acid (SCFA) production of 7 grasses grown over short cutting intervals were compared with those of corn and rice straw. Grasses were harvested at 35 -39 days after regrowth in the wet season in Laguna, Philippines. Crude protein (CP) contents were not remarkably different among the grasses (from 9 to 11% in a dry matter (DM) basis, p>0.05). Neutral detergent fiber (NDF) contents varied from 63% to 73% DM (p<0.05); the lowest was found in Napier grass (Pennisetum purpureum) and the highest in Para grass (Brachiaria mutica). Non-fiber carbohydrate (NFC) content was the highest in corn, followed by Jarra grass (Digitaria milanjiana) and Gamba grass (Andropogon gayanus) (p<0.05). The in vitro NDF degradability was also the highest in corn, followed by that in Jarra grass and Guinea grass (Panicum maximum) (p<0.05). SCFA production and gas production was the highest in corn, followed by Jarra grass, Guinea grass, and Signal grass (Brachiaria decumbens), and the lowest in rice straw (p<0.05). These findings suggested that the nutritional characteristics, particularly NFC and NDF contents, and rumen degradation varied across grasses harvested at short cutting intervals. Among the grasses investigated in this study, Jarra grass and Guinea grass contained potentially high nutritive value due to the highest rumen fermentation characteristics. Keywords

Two experiments, namely the situ nylon bag technique and the in vitro gas production technique, were carried out to determine the correlations between the in situ ruminal degradability and the in vitro gas production of different forages, and to predict the ruminal degradability of the forages using the gas production parameters. Forage samples from Napier grass (Pennisetum purpureum), Guinea grass (Panicum maximum), Para grass (Brachiaria mutica), Leucaena (Leucaena leucocephala), Rain tree (Samanea saman), and Gliricidia (Gliricidia sepium) were incubated in the rumen of three rumen-cannulated buffaloes using the in situ nylon bag technique for 3, 6, 12, 24, 48, and 72 h. The six forage samples were also subjected to the in vitro gas production analysis following the modified methods developed by Menke & Steingass (1988), along with 30 other commonly used forages in the Philippines. Both experiments followed a randomized complete block design. Their dry matter (DM), organic matter (OM), neutral detergent fiber (NDF), and crude protein (CP) degradation kinetics and effective degradability (ED) as well as the gas production parameters were then estimated. Results revealed that the ED of each nutrient was found to be moderately to strongly correlated with some of the gas production times and estimated gas parameters. The predictor models generated using the gas production parameters for the ED of DM, OM, and NDF were sufficiently strong (R 2 = 0.740, p value= 0.0002; R 2 = 0.659, p value= 0.0009; and R 2 = 0.813, p value < 0.0001, respectively) while that of CP was only moderate (R 2 = 0.500, p value= 0.0055). It was concluded that the relationship between the two techniques is sufficiently strong and therefore the gas production parameters can be used to predict the in situ ruminal nutrient degradability of forages.