Effects of supplementing galacto-oligosaccharides, Yucca schidigera or nisin on rumen methanogenesis, nitrogen and energy metabolism in sheep

The effects of galacto-oligosaccharides (GOS), Yucca schidigera (YS) or nisin (NS), as additives to a basal diet of grass silage and concentrate, on rumen methanogenesis, nitrogen and energy metabolism were conducted using four rumen cannulated wethers in a 4×4 Latin square design. Four treatments comprised basal diet (control), basal diet+20 g GOS, basal diet+120 ppm YS, basal diet+3 mg/kg BW^0.75 of NS. Apparent digestibility of DM, OM, CP, NDF and ADF were similar in all treatment diets. Animals fed YS had lower N losses in urine and total N losses resulting in a higher retained N. Ruminal pH values ranged from 6.33 to 6.47 and was significantly (P<0.05) altered by treatment. Sheep given YS had the lowest NH₃-N concentration, moderate in control and GOS, and the highest in NS. The GOS supplemented sheep had lower (P<0.01) proportion of acetic acid and higher (P<0.01) proportion of propionic acid compared to those fed the control diet. Microbial nitrogen supply was higher (P<0.05) in GOS supplemented sheep than those given control, YS and NS diets. Relative to control, YS and NS treatments, GOS reduced (P<0.05) methane production (l/kg BW^0.75). These results indicated that natural products have the potential to be used as manipulators of rumen fermentation.