The impact of elevated temperatures on quality of dairy feed
Fresh TMR for dairy cows contains yeasts, moulds and bacteria that can reduce the quality of the dairy ration. Growth of these micro-organisms leads to heating and fermentation, which reduces both the palatability and the feeding value of the ration. Particularly the easily fermentable proteins, carbohydrates and starch are fermented into water and CO2 (see Figure 1) reducing the dry matter and therefore nutritional value of the dairy feed.
Growth of micro-organisms and fermentation in TMR of dairy cows starts once the ingredients have been exposed to oxygen in the air and results in an increase of the temperature of the TMR. On a warm day in the summer, increases of more than 20°C are not uncommon. Once environmental temperatures start rising, performance of the dairy herd is under pressure for two reasons. Firstly, dairy cows could potentially suffer from heat stress resulting in a decrease of dry matter intake. Secondly, the reduction of palatability and feeding value resulting from heating of the TMR will lead to a further reduction of dry matter intake of dairy cattle.