Thermostasis is the process by which animals attempt to keep body temperature constant despite changes in environmental temperatures. Heat stress occurs when cows are incapable of dissipating enough heat to maintain their core body temperature. This increase in body temperature results from the combination of heat from the environment and heat increment produced internally during rumen fermentation and nutrient metabolism. In addition, heat stress increases respiratory frequency (panting) to enhance heat dissipation.
Heat increment is greater at higher feed intakes and milk production, which is why high-producing cows are more sensitive to heat stress than their lower-producing counterparts. While there has been extensive research analyzing these effects in mature cows, comparatively little has been done addressing the potential negative consequences on future productivity, health, and reproduction, of their offspring.
Long-term consequences of suffering heat stress in utero and immediately after birth
Aside for shade, pre-weaned calves are not usually considered a priority when heat abatement strategies are implemented in the farm. The main reasons are that they have a larger surface/mass ratio, and not highly significant heat increment, smaller heat loads, when compared to mature cows. However, heat stress in heifer calves both in utero as well as immediately after birth, can have long-term consequences on their future productivity in the herd.