Effects of a Saccharomyces cerevisiae yeast on ruminal fermentation and fibre degradation of maize silages in cows

Effects of a Saccaromyces cerevisiae yeast (Levucell SC 10 ME; 1 × 1010 CFU/g (SC)) on ruminal fermentation and fibre degradation of maize silages was studied with 3 non-lactating fistulated cows fed maize silage, concentrate and meadow hay (48:42:10, DM basis) twice daily and supplemented with 0 (SC0), 0.3 (SC0.3) and 1 g (SC1.0) of SC/day. Maize silages, 40, were ruminally incubated in situ for 36 h to determine neutral detergent fibre degradation (NDFdeg). Silages were divided into two groups according to NDFdeg measured with the SC0 diet, being a low fibre degradation (LFD) group (NDFdeg: 0.20–0.30) and a high fibre degradation (HFD) group (NDFdeg: 0.35–0.45). Rumen fluid was collected on 2 non-consecutive days at 0, 2, 4 and 8 h post-feeding for determination of pH, ammonia N, volatile fatty acids (VFA) and lactate concentrations. The study was a 3 × 4 factorial design, with 3 replications, to examine effects on ruminal fermentation and in a 3 × 2 factorial design, with 3 replications, to examine effects on NDFdeg. Inclusion of SC increased (P<0.01) ruminal pH, decreased (P<0.01) lactate concentration and the acetate:propionate (P<0.01) ratio, but had no effect on ammonia N concentration. The SC addition at 1 g/day increased VFA concentration versus the control diet (P<0.01), further the reduced acetate:propionate ratio and increased fibrolytic activity of rumen bacteria as assessed by NDFdeg of silages. No effect on silage degradation occurred with the SC0.3 diet. Changes of rumen fermentation occurred from 0 to 8 h post-feeding, as expected, increasing (P<0.05) from 0 to 2 and/or 4 h after feeding followed by a decrease to 8 h. There was only an interaction (i.e., P<0.05) of diet × time post-feeding for ruminal pH and lactate concentration. Results show that this SC strain was effective in alleviating pH depression and lactate concentration after feeding of fistulated cows fed twice daily at close to the metabolizable energy maintenance requirements, irrespective of the level of YC inclusion. This suggests that this SC has the potential to reduce the risk of rumen acidosis in commercial cattle fed maize silage based diets and, if used at the highest level, could be of further benefit due to increased fibre degradation of low quality maize silages.