Performance and health of early lactating dairy cows under long-term environmental heat stress
Dairy cows are susceptible to thermal stress due to their level of milk production and feed intake. The present study sought to determine the impact of dietary inclusion of Loprotin on early lactation high producing dairy cows' production performance, metabolic responses and health status during a period of long-term environmental heat stress.
High genetic merit modern dairy cows undergo thermal stress starting at an average temperature-humidity index (THI) of 68, whereas at THI > 72 significant losses in milk production have been observed. Under heat stress, dry matter intake typically decreases i.e., cows will be subjected to an unfavourable energy status. Consequently, milk production and reproductive indices would be impaired. Feeding amino acid (AA) deficient diets resulted in heat production elevation in the animals, due to the increase of tissue protein turnover. Optimising post-ruminal levels of rate-limiting AA such as methionine (Met), i.e., metabolisable Met concentration, might alleviate the negative consequences of heat stress. Recent studies indicated that feeding rumen-protected Met could increase milk protein yield.
Zinc (Zn), one of the most essential trace minerals for animals, is incorporated into a variety of proteins and enzymes that are involved in a wide range of physiological processes. It was shown that feed intake and both Zn digestibility and deposition in dairy cows increased linearly with increasing Zn-Met supplementation. Organic form of Zn supplementation could enhance milk production and decrease somatic cell scores in lactating cows.
