Interactive Effects of Nypa fruticans Fruit Pellets and Dietary Protein Levels on Rumen Fermentation, Gas Kinetics, and Methane Production In Vitro

This study evaluated the effects of Nypa fruticans fruit pellet supplementation combined with different CP levels on rumen fermentation characteristics and CH4 production using an in vitro gas production technique. A 3 × 4 factorial arrangement was used, consisting of three CP levels (12, 14, and 16%) and four levels of Nypa fruticans fruit pellet supplementation (0, 0.5, 1.0, and 1.5% of substrate dry matter), with incubation run included as a random effect in the statistical model. Rumen fluid from Thai native beef cattle was incubated under anaerobic conditions. Gas production kinetics, ruminal pH, ammonia–nitrogen (NH3–N), protozoal populations, digestibility, volatile fatty acids (VFA), and CH4 production were determined. Significant interactions between CP level and Nypa fruticans fruit pellet supplementation were observed for gas production kinetics. Ruminal pH was influenced by CP level at 24 h, while NH3–N increased with higher CP levels but decreased with increasing supplementation. Protozoal populations were reduced by Nypa fruticans fruit pellets. Methane production was affected by CP level, Nypa fruticans fruit pellet supplementation, and their interaction. A clearer reduction was observed at 24 h, particularly at higher supplementation levels. At 24 h of incubation, total VFA, propionate, and butyrate concentrations increased with supplementation, whereas no clear effects were observed at 12 h. In vitro dry matter digestibility was affected at 24 h (p < 0.05), but no effect was observed at 48 h, while organic matter digestibility remained unchanged. In conclusion, Nypa fruticans fruit pellets, in combination with CP level, modified rumen fermentation patterns and were associated with lower CH4 production under in vitro conditions, without negatively affecting digestibility. These findings suggest potential for further in vivo evaluation.