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LIVE YEAST AS A SUPPLEMENT TO COWS ON LOW AND HIGH CONCENTRATE: ROUGHAGE DIETS.

Efficient and optimal feeding for milk production remains a major challenge in dairy nutrition. Feeding high concentrate diets is of course necessary to supply dairy cows with sufficient amounts of nutrients for high milk yields. However, efficiency of rumen function and fermentation is usually the point of departure and therefore from time to time new products come on the market to assist in this quest. Live yeast is such a product. It alters ruminal fermentation but its effects can be dictated by different conditions, one being the  concentrate: roughage ratio of the diet. This was the topic of the study referenced below. 

The objective of the authors was to evaluate the effects of dietary concentrate level and live yeast supplementation on milk yield, milk composition and rumen fermentation parameters of early lactating dairy cows. Four multi-lactation Holstein cows were used immediately after calving with all cows receiving all diets according to a specific pre-determined design. They were fed in 11‐day periods, of which seven days were used for adaption and four for data collection. The four experimental treatments were: (1) a low concentrate (C)(40%): roughage (R)(60%) ratio diet with no added live yeast (LY): (2) a low C:R diet with LY; (3) a high C(60%):R(40%) diet with no added LY; and (4) a high C:R diet with LY. The diets were analysed for organic matter, ether extract, calcium, potassium, magnesium, phosphorous, ADF, NDF and OM. In a laboratory study rumen liquor was collected from a Holstein rumen-fistulated cow. Treatments were the same as for (1) to (4) above. 

Cows fed the low C:R diet supplemented with LY had lower dry matter intakes (DMI) and lower milk yield, but greater feed efficiency compared to cows in all other groups. Milk fat yield was lower in cows fed the low C:R diet supplemented with LY compared to cows fed the high C:R diet with no LY. These cows had also lower protein yields compared to all other groups. No differences in milk fat %, milk lactose (% and kg per day), MUN, SCC and energy corrected milk were observed between groups. The total volatile fatty acids (VFA’s) were higher in the supplemented group fed the high C:R compared to the un-supplemented cows fed the high C:R diet. The interaction between LY and C:R for the volatile fatty acids propionate, iso‐valerate and the acetate:propionate ratio showed that propionate was increased by LY on the low C:R diet, but decreased on high C:R diet. Feeding LY at 40:60 C:R resulted in better feed efficiency, which suggested that LYs effect was better pronounced at the low C:R diet compared to the high C:R diet. This result was supported in the laboratory trial where addition of LY at 40:60 C:R decreased ruminal ammonia concentrations and increased total VFA’s. The effects of LY were better pronounced on most parameters at the low C:R diet.

The authors recommended that: (a) LY should rather be added to low C:R diets in order to increase the production potential of cows, since LY at low C:R diets increased feed efficiency, decreased ruminal ammonia and increased total VFA concentration; (b) future studies should focus on the dosage level of LY at low C:R in order to find the optimum.

Reference: 

N.P. Shabangu, M.C. Muya & J.J. Baloyi, 2016. Milk yield and quality, nitrogen metabolism and rumen fermentation parameters in dairy cows fed different levels of dietary concentrate and live yeast. Proc. of the 49th Annual SASAS Congress, 3-6 July 2016, Stellenbosch. Abstract 76.