Selenomonas ruminantium strains were isolated from sheep rumen, and their significance for fiber digestion was evaluated. Based on the phylogenetic classification, two clades of S. ruminantium (clades I and II) were proposed. Clade II is newly found, as it comprised only new isolates that were phylogenetically distant from the type strain, while all of the known isolates were grouped in the major clade I. More than half of clade I isolates displayed CMCase activity with no relation to the degree of bacterial adherence to fibers. Although none of the isolates digested fiber in monoculture, they stimulated fiber digestion when co-cultured with Fibrobacter succinogenes, and there was an enhancement of propionate production. The extent of such synergy depended on the clade, with higher digestion observed by co-culture of clade I isolates with F. succinogenes than by co-culture with clade II isolates. Quantitative PCR analysis showed that bacterial abundance in the rumen was higher for clade I than for clade II. These results suggest that S. ruminantium, in particular the major clade I, is involved in rumen fiber digestion by cooperating with F. succinogenes.

To investigate the rumen bacterial interaction between cellulolytic Ruminococcus flavefaciens and non‐cellulolytic Selenomonas ruminantium, fiber digestibility and fermentation products were determined in defined cultures consisting of these two species. Avicel, orchardgrass hay, rice straw and alfalfa hay were used as substrates for 72 h incubation to monitor digestibility, volatile fatty acids, succinate, lactate and bacterial number. In monoculture, R. flavefaciens digested the fiber sources at 21–32%, while S. ruminantium strains did not. When R. flavefaciens was cocultured with one of three different strains (GA192, S137 and S150) of S. ruminantium, fiber digestion exceeded the value recorded by R. flavefaciens alone. In particular, cocultures with S. ruminantium S137 showed significantly higher digestibility for all the fiber sources than R. flavefaciens alone (P < 0.05). Propionate production and growth of S. ruminantium was notable in all cocultures but not in monocultures. Succinate was accumulated in monoculture of R. flavefaciens, while the accumulation was not observed in cocultures. These results indicate that R. flavefaciens provides fiber hydrolysis products to S. ruminantium as growth substrates. In addition, S. ruminantium could activate R. flavefaciens by rapidly consuming the products. Such cross‐feeding between cellulolytic and non‐cellulolytic bacteria could enhance fiber digestion, although the extent of the enhancement may depend on strain combinations.

No abstract

This experiment was conducted to determine the effects of pineapple stem by-product silage as a feed source in total replacement of Napier or corn silages on growth performance, feed intake and feed efficiency, ruminal fermentation, carcass characteristics and meat quality of Holstein crossbred steers. Forty-eight steers with an average age of 18 months (448.6 ± 51.5 kg) were randomly allocated to three groups (one diet per group) in a completely randomized design. Steers were fed total mixed ration (TMR) containing a roughage-to-concentrate ratio of 20 : 80. The TMR diets contained Napier grass silage (nTMR), whole corn silage (cTMR) or pineapple stem silage (pTMR) and were offered ad libitum for six months. The results revealed that pTMR and cTMR diets resulted in a significantly higher weight gain than nTMR. These results were observed because pTMR and cTMR diets provided more N-free extract (NFE) total digestible nutrients (TDN) than nTMR diet, and the feed conversion efficiencies for pTMR and cTMR diets were higher than those of nTMR. Ruminal pH, ammonia-nitrogen and volatile fatty acid concentrations were not significantly different among dietary treatments. The carcass characteristics of steers fed cTMR and pTMR diets included significantly larger rib eye areas than steers fed nTMR, whereas meat quality was not affected by treatment. Additionally, the current research showed that pTMR diet provided the lowest feed cost per gain. The results suggest that pineapple stem by-product could be regarded as a potential feed source for reducing costs in cattle feedlots.

No abstract