Rumen fermentation patterns in sheep receiving silages of different chemical composition supplemented with concentrates rich in starch or in digestible fibre

Abstract

SUMMARYIn each of two experiments, eight silages supplemented with concentrates containing a high proportion of either starch or digestible fibre were given to rumen-cannulated sheep. The silages constituted c. 65% of the total dry matter and differed widely in chemical composition, reflecting differences in the extent of fermentation in the silo.Rumen pH was lower (P < 0·01 and P < 0·001 for Expts 1 and 2 respectively) and the concentration of total volatile fatty acids (VFA) in the rumen was higher (P < 0·001 for Expt 2) for the starchy concentrate. Silages differed in their effects on ruminal proportions of acetate (P < 0·001 and P < 0·01 for Expts 1 and 2 respectively) and, inversely, of propionate (P < 0·001 for Expt 1). There was evidence of a strong relationship between the molar proportion of propionate in the rumen and the concentration of lactic acid in the silage. The results indicate that the production of propionate during the metabolism of silage lactic acid by the rumen microbial population was the predominant influence on rumen fermentation pattern.It is suggested that this relationship is the basis of some of the differences in milk production reported for silages showing restricted as opposed to extensive fermentation.