Effects of supplementing a Saccharomyces cerevisiae fermentation product during the transition period on rumen fermentation of dairy cows fed fresh diets differing in starch content.

 Discipline: supplementation; Key words: calving transition, dietary starch, Saccharomyces cerevisiae fermentation product, rumen fermentation.

Dairy cows often experience negative energy balance in early lactation because the energy intake is insufficient to meet the sudden increase in demand for milk production. Therefore, high-starch diets are usually fed to early-lactation dairy cows to reduce the energy deficit. However, high-starch diets during the first several weeks after calving may decrease rumen pH and further increases the risk of sub-acute ruminal acidosis (SARA). The occurrence of SARA is associated with variable feed intake, production losses and impaired animal health and thus may exacerbate the negative energy balance. Nutritional management should aim to reduce the duration and severity of SARA without compromising energy intake. One way of dealing with this is utilization of additives such as Saccharomyces cerevisiae, the fermentation products (SCFP) of which have been used to increase production performance and stabilize the rumen environment. The beneficial effects of SCFP on rumen fermentation include contribution to greater fibre digestion, reduced lactate concentration of rumen fluid, increased microbial protein synthesis and reduced duration of pH below 5.6 (SARA level). The interaction effects of dietary starch content and SCFP supplementation on rumen fermentation have however as yet not been extensively studied, particularly for the immediate post-calving period. Therefore, the objective of the study by Dr W. Shi and co-workers was to evaluate the effects of SCFP supplementation during the immediate pre-calving period on rumen pH, VFA profile, and the mRNA abundance of genes associated with rumen epithelial growth, VFA transporters, and VFA metabolism in the rumen epithelium in fresh cows fed diets differing in starch content. They hypothesized that feeding low-starch diets during the fresh period and supplementing SCFP during the immediate pre-calving period would reduce the decrease in rumen pH after calving and that the benefits of SCFP supplementation would be greater for dairy cows fed high-starch diets. The results of their study were published in the Journal of Dairy Science, Volume 102 of 2019, page 9943 to 9955, the title being: Effects of supplementing a Saccharomyces cerevisiae fermentation product during the transition period on rumen fermentation of dairy cows fed fresh diets differing in starch content.

The SCFP was supplemented during the transition period (day −28 to +23 relative to calving) and the effects studied on rumen fermentation and mRNA abundance of genes in the rumen epithelium of fresh cows (day 1 to 23 after calving) fed diets differing in starch content. Eighteen ruminally cannulated multi-lactation Holstein cows were fed diets with either SCFP or without (CON) throughout the experiment. Within each treatment (CON or SCFP) cows were fed either a low-starch (LS; 22.1% starch) or a high-starch (HS; 28.3% starch) diet during the fresh period. Rumen pH was measured continuously for 72 hours starting on day −10, −3, +1, +7, and +21 relative to calving date. Rumen papillae were collected on day −10 and +21 relative to calving.

Supplementation of SCFP had no effect on rumen pH during day −10 to −8, but mean rumen pH tended to be higher (6.64 versus 6.49) for SCFP cows than for CON cows during days −3 to −1. Feeding SCFP decreased the range of rumen pH variation compared with CON within the HS group during both days 7 to 9 (1.08 versus 1.38) and days 21 to 23 (1.03 versus 1.30) after calving. In addition, nadir rumen pH tended to be higher (5.64 versus 5.44) and duration of pH below 5.6 tended to be shorter (116 versus 323 minutes per day) for the SCFP group than for the CON group during days 21 to 23 after calving. Supplementation of SCFP increased the mRNA abundance of insulin-like growth factor-6 (1.10 versus 0.69) before calving and decreased the mRNA abundance of putative anion transporter iso-form 1 (1.12 versus 2.27) after calving. Nadir rumen pH tended to be higher during days 1 to 3 (5.63 versu. 5.41) for LS cows than for HS cows, but rumen pH was not affected by dietary starch content during other time periods. Dietary starch content had no effect on mRNA abundance of genes in the rumen epithelium after calving.

These results suggest that supplementation of SCFP may reduce the range of variation in rumen pH in fresh cows fed HS diets and the duration of sub-acute ruminal acidosis by the end of the fresh period regardless of dietary starch content and that decreasing dietary starch content during the fresh period may reduce the decrease in rumen pH immediately after parturition.