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 (P0.05) between protozoal numbers and total protozoal DNA concentrations was detected. Sheep fed GR had higher (P0.05) 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 (P0.05) 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.

Funding was provided by the Spanish C.I.C.Y.T. (AGL2011-22628 and AGL2008-04707-C02-02). M.L.Tejido gratefully acknowledges a postdoctoral contract from Spanish CSIC (JAE-docprogram).

8 páginas, 4 tablas.

Peer Reviewed