The aim of the study was to conduct a basic evaluation of the in vitro effect of crude protein (CP) levels in concentrate and a saponin extract from Sesbania graniflora pods meal (SES) on the kinetics of gas, nutrient digestibility, ruminal fermentation, protein efficiency uses, and methane (CH4) mitigation. Eight treatments were formed according to a 2 × 4 factorial design in a completely randomized design (CRD). The first factor referred to the levels of CP at 14 and 16% on dry matter (DM) basis in the concentrate diet, and the second factor referred to the levels of SES supplementation at 0, 0.2, 0.4, and 0.6% of the total substrate on a DM basis. The results showed that S. graniflora pod meal contained 21.73% CP, 10.87% condensed tannins, and 16.20% crude saponins, respectively. Most kinetics of gas as well as cumulative gas were not influenced by the CP levels or SES addition (P > 0.05) except gas production from immediately soluble fraction (a) was significantly different by CP levels. Ammonia-nitrogen concentration of incubation at 4 h was significantly difference based on the CP levels and SES supplementation (P < 0.05). Increasing SES levels significantly (P < 0.05) decreased protozoal population. In vitro digestibility of DM and organic matter was not changed by CP levels or SES addition. Butyrate and acetate to propionate ration were decreased, and propionate was increased when increasing SES dose (P < 0.05), while CP levels did not change total volatile fatty acids and molar portions. The ruminal CH4 concentration was reduced by 44.12% when 0.6% SES was added after 8 h of incubation. Therefore, SES supplementation could enhance protein utilization and improve rumen fermentation particularly lowering CH4 production.
Keywords: Global warming; Methanogen; Plant secondary compound; Volatile fatty acids.