Thermal Neutral Zone in Animals

Objective:

The purpose of this model is to characterize the thermoneutral zone and thermal stress.

Body:

Every animal has a unique thermoneutral zone. This zone is the range of ambient temperatures in which an animal will not experience stress. The thermoneutral zone is different for every animal because it varies based on external and internal conditions, such as how humid the day is, and whether or not an animal is lactating. It is these same conditions that can therefore lead to thermal stress, or when the ambient temperature is higher or lower than the limits at either side of the thermoneutral zone.

There are several factors that can cause a change in the range thermoneutral zone and lead to thermal stress. Some of these factors are species, breed, age, diet, housing, temperature acclimation, ambient humidity, and insulation in the from fat and fur thickness. For instance, cows are much bigger and have a greater fat thickness than calves. Thus, they consequently have a lesser lower critical temperature because of the fat thickness and a higher upper critical temperature because they have more surface area for evaporative cooling. In sheep, however, the thickness of their wool layer means that lambs can actually withstand a higher upper critical temperature before becoming stressed because they do not have all of the wool to insulate them.

Once animals begin to have thermal stress, they must work to create or dissipate heat, depending upon which limit is being exceeded. If the upper limit is breached, there are three passive ways to dissipate the heat. These there mechanisms are conduction, convection, and radiation. Out of the three, convection is the most important in agriculture because it is the easiest to manipulate. Animals can also actively participate in heat dissipation via evaporation by panting and sweating. In both methods, water is whisked away from the body after blood flow was increase to the extremities to create a cooling effect. In...