In recent decades, remarkable increases in milk yield have created challenges to managing nutrition in dairy herds. More aggressive feeding systems designed to meet the energy requirements of high producing cows often lead to unbalanced diets with regards to types of carbohydrates and effective (long) fiber content. Rumen pH is a critical factor for good rumen health, and feeding these diets can cause pH to drop below a critical threshold, leading to subacute ruminal acidosis (SARA). Animal production and health can be severely affected due to impaired feed digestion and animal susceptibility to digestive and metabolic diseases such as displaced abomasum, laminitis, and mycotoxicosis.
For the rumen to function correctly and efficiently with an ideal pH (6.4 - 7.0), a steady and balanced supply of fermentable carbohydrates and degradable protein is required. To minimize the risk of acidosis while maximizing energy intake, amounts and sources of non-fiber carbohydrates must be balanced. Excessive intake of rapidly fermentable carbohydrates will produce excessive amounts of acids that drive pH below 6.0, which is detrimental to fiber-digesting bacteria. If low pH prevails for extended periods, clinical acidosis occurs, resulting in rapid declines in milk components, milk production, and health.
Fibrous feedstuffs such as grass and hay are necessary to stimulate rumen mixing, rumination, and saliva production for buffering. Inadequate ruminal adaptation to highly fermentable diets such as in early lactation can also lead to SARA. Transition diets should provide adequate forage fiber while progressively introducing grains three weeks before and after calving to allow for proper adaption to highly fermentable diets. To ensure the effectiveness of a well balanced total mixed ration, management practices that promote rumen stability and minimize the risk of acidosis should be maintained. These include proper processing and mixing of the TMR to ensure adequate particle size and effective fiber, maintaining consistent feed delivery times, minimizing sorting at the feed bunk, allowing adequate bunk space to avoid slug feeding and ensuring animal comfort.
Feeding yeast cultures based on Sacchromyces Cervisiae is another way to stabilize rumen pH. Yeast supplementation before calving and in combination with buffers post-calving is an effective strategy to reduce the risk of ruminal acidosis in transition cows. Addition of yeast increases ruminal bacterial count, initial rate of fiber digestion in the rumen, and flow of microbial protein from the rumen. This results in increased feed intake and improved feed efficiency. Supplementation causes rumen pH to increase, resulting in more favorable conditions for growth and activity of the anaerobic rumen microflora. Strain, number and viability of cells, and scientifically proven activity in the rumen should be considered when choosing a yeast supplement.