Heat stress in lactating dairy cows leads to physiological responses that affect their well-being and performance. The peculiarity of their digestive system leads to increased heat increment, which further compounds with external environmental warm temperatures.
To cope with this heat overload, cows rely on two main mechanisms. One internal, which is to reduce feed intake and thus heat production, the second external which is to look for cooler spots in the barn or the field. The heat overload affects several aspects of the animal’s physiology, ranging from reductions in productivity, reproductive losses, all the may to increased incidence of digestive upsets.
Dairy farmers in warmer climates tackle this problem with a few different approaches targeting both internal and external sources of heat. One frequent approach (external) is to cool-off cow’s through water sprinklers, forced air through fans or a combination of both. Another approach (internal) is to increase the nutrient density of the diet to account for reduced feed intake. Despite all these efforts there is still always a sensible reduction in intake, which results in a negative energy balance.
A negative energy balance causes hormonal changes such as a reduction in leptin and an increment in ghrelin
This disparity between energy intake and its requirements for production leads to hormonal changes responsible for further drops in intake. One such change is the reduction in leptin and an increase in ghrelin. Leptin synthesized in the adipose tissue has important bearing in eating behavior, energy expenditure, and body weight. It signals the hypothalamus of the adequacy of the energy status in the body, and the need to reduce intake.