Sub-acute ruminal acidosis: Understanding the pathophysiology and management with exogenous buffers

Abstract

Sub-acute ruminal acidosis (SARA) is an economically important clinical condition and contributes to loss of farm returns, second only to mastitis. It is more prominent in cows in their early and mid-lactation, having peak milk yield and considerably high dry matter intake. SARA detection in a dairy farm is difficult as it does not present any pathognomonic symptoms, and the manifestation of clinical signs is delayed. SARA's characteristic feature is the occurrence of daily fluctuations of pH when the pH drops to the range of 5.2 to 6 for a considerable period due to the accumulation of volatile fatty acids in the rumen. Grain-based diets, which have higher proportions of non-structural carbohydrates, high-quality fermentable forages like legumes, and lack of physically adequate dietary fibre (peNDF), are the significant causes of SARA. SARA consequences include the inflammation of rumen mucosa and several other organs and long-term health and economic losses like reduced feed intake reduced fibre degradability, drop in milk yield and milk fat, damage to the gastrointestinal tract, laminitis, liver dysfunctions, and lameness. SARA can be prevented and treated by the right combination and judicious use of exogenous dietary buffers like sodium bicarbonate, magnesium oxide, and direct-fed microbial like yeast. This review aims to provide a gist of the recent literature available on the pathophysiological aspects, indicators, detection techniques, prevalence, and preventive measures for SARA, including the mechanism of action and utility of the commonly used dietary buffers and direct-fed microbials.