Rumen acidosis results from an excessive acid load in the rumen not neutralised by salivary or feed buffers. Changes in physiology, metabolism, and behaviour of heat stressed cows increase their susceptibility to both sub-acute (SARA) and acute acidosis.
Researchers from University of Missouri observed lower rumen pH (6.1 vs. 6.4) when cows were fed 65% forage diets under warm, humid conditions (29.4°C – 85% relative humidity; RH) compared to cooler, drier conditions (18.3°C – 50% HR). When forage in the diet was reduced to 35%, the differences in ruminal pH were higher (5.6 vs. 6.1 for warmer and cooler conditions, respectively). The main herd problems observed with SARA during warm weather are a reduction in milk fat and an increase in lameness.
As feed fermentation in the rumen generates heat, to maintain constant body temperature during hot weather, one of the strategies employed by the cow is to reduce feed intake. Additionally, other mechanisms (i.e. panting) that operate to dissipate heat increases the maintenance energy requirements, making it necessary for the diet to have a higher energy density.
In general, nutritionists accomplish this by increasing concentrates and reducing forages in the diets. This is a sound approach, however sufficient effective fiber should be maintained in the diet to stimulate cud chewing and rumination, thereby maintaining adequate rumen pH.
Continue reading this article published in International Dairy Topics.
