Influence of forage type in the diet of sheep on rumen microbiota and fermentation characteristics

Abstract

Four ruminally cannulated sheep were used in a cross-over design to assess the changes in rumen fluid microbial populations during the feeding cycle as affected by the type of forage (FOR) in the diet. The two experimental diets contained 70% of either alfalfa hay (AL) or grass hay (GR) as FOR and 30% of concentrate. Sheep were fed the diets twice daily and samples from rumen fluid were taken at 0, 4 and 8h after the morning feeding. Ruminal pH, lactate concentrations and xylanase activity were not affected (P>0.05) by FOR, but concentrations of NH3-N and total volatile fatty acid (VFA), and carboxymethylcellullase (CMCase) and amylase activities were greater (P<0.05) for AL compared with GR diet. Total protozoa numbers determined by microscopic counting were higher (P<0.05) in AL-fed sheep than in sheep fed the GR diet; in contrast, concentrations of protozoal DNA determined by quantitative real-time PCR tended (P=0.06) to be higher in GR-fed sheep, and no correlation (P>0.05) between protozoal numbers and total protozoal DNA concentrations was detected. Sheep fed GR had higher (P<0.001-0.05) relative abundance of Fibrobacter succinogenes, Ruminococcus flavefaciens and fungi than did AL-fed sheep, but bacterial DNA concentrations and relative abundance of Ruminococcus albus and methanogenic archaea were unaffected (P>0.05) by FOR. Postprandial changes of DNA concentrations of all determined microbial populations were similar for the two diets. Total bacterial and protozoal DNA concentrations decreased (P<0.05) at 4h post-feeding but recovered before-feeding values at 8h post-feeding. No correlations (P>0.05) were found between CMCase and xylanase activities and either the concentration of total bacterial DNA or the relative abundance of the three cellulolytic bacteria, but xylanase activity was positively correlated (P<0.05) with both protozoa numbers and protozoal DNA concentration. Although the postprandial evolution of fermentation parameters and microbes were similar for both forages, sheep fed the lower quality forage showed higher abundance of some cellulolytic bacteria and fungi, which could be interpreted as an adaptation to digest a more fibrous and complex forage.