Ratios of rumen inoculum from Tibetan and Small-tailed Han sheep influenced in vitro fermentation and digestibility

Tibetan sheep are well adapted to harsh environmental conditions and poor-quality forage and are known to produce less methane (CH₄) gas than lowland sheep. In this study, rumen inocula from Tibetan sheep (TBI) and from Small-tailed Han sheep (HSI) were incubated in in vitro batch cultures in five ratios (TBI: HSI): 0:100, 25:75, 50:50, 75:25 or 100:0 for 72 h. With an increasing proportion of TBI, there was a linear decrease (P < 0.001) in gas and CH₄ production on a degraded dry matter (DM) basis at 12, 24, 48 and 72 h. In addition, increasing the proportion of TBI increased the digestibility of DM (P < 0.05), neutral detergent fiber and acid detergent fiber and total and individual volatile fatty acids (VFA) concentrations at almost all time points. An increase in the TBI: HSI ratio resulted in less metabolic hydrogen ([2H]) incorporated into CH₄ and more into propionate. The recovery of [2H] consistently decreased with an increase in the TBI: HSI ratio, indicating the existence of unaccounted [2H] in TBI. It would be important to study the rumen microbiome in Tibetan sheep with the use of classical microbiology and modern –omics techniques to identify [2H] sinks alternative to CH₄, which could perhaps be stimulated in other domestic ruminants.