Sub-Acute Ruminal Acidosis in Dairy Cows: Its Causes, Consequences and Preventive Measures

Current feeding programs for cattle prescribe concentrate rich diets to meet their ever increasing demands for high levels of milk production. These diets, however, can impair rumen health and thus cattle production, milk yield and welfare. High energy diets are rapidly fermented in the rumen because they are high in fermentable starch, low in NDF and contain finely chopped digestible forages. Feeding rapidly fermentable diet to the cows predominantly adapted to digest and metabolize forage based total mixed ration (TMR) substantially increases short term milk yield, but the risk of sub- acute ruminal acidosis (SARA) increases. Additionally, too high concentrate to forage ratio, too fast a switch from high forage to high concentrate, diet composed of highly fermented feeds, improperly mixed TMR and mycotoxins in feed also increases the incidence of SARA in dairy herds. SARA causes depressed feed intake, cycling feeding, reduced cud chewing, poor fibre digestion, rumenitis, mastitis, metritis, dehydration, diarrhoea, abomasal displacement, pulmonary bacterial emboli, systemic inflammation, liver abscesses, low milk fat, low milk protein, sore hooves, laminitis and low fertility. Therefore, SARA is a major challenge for animal health, productivity, economic efficiency and welfare issue even in well managed dairy herds. Feeding higher amounts of forages, supplying adequate peNDF, processing grains less thoroughly, reducing fermentability of the carbohydrate fraction and adapting rumen to the dietary changes are the key factors to be considered for preventing SARA. Continued research for accurate quantification of peNDF in diet, grain processing, optimization of meal size, dietary cation-anion balance, narrowspectrum rumen modifier, inoculation of lactate utilizing microbes, inhibition of lactate producing microbes and innovation of the unique fermentability characteristics of feed ingredients to promote sufficient buffering and rapid absorption of VFA from rumen will explore new horizon for reducing incidence of SARA in future.