Different Types of Heat Tolerance Indices Used in Dairy Production

Abstract

Livestock production is affected by several factors such as environmental factors, physiological adaptations and physical characteristics of livestock. Environmental factors include temperature, humidity, solar radiation and speed of the wind. Physiological adaptations mainly concern the ability of livestock to resist environmental extremes by the means of vital parameters of the body such as rectal temperature, heartrate, and respiration rate. Physical characteristics involve body surface area, the density of sweat glands and bodycoat. The climate of a particular region mainly influences animal production and performance. In tropical areas due to high temperature and sunlight, heat tolerance indices are key in livestock production and management. Major indicators of heat stress in animals are variations in body temperature, respiration rate and heart rate. Consequently, changes in blood parameters also occur due to heat stress in form of loss of water and ion. The respiratory, circulatory, excretory, endocrine and nervous system coordinate in such a way that heat stress can be resisted which inturn may be called heat tolerance. Heat tolerance is the ability to neutralize the effect of heat stress on the body. Information regarding heat tolerance is very essential in selecting breeds for a specific region and inturn, contributes better to the production aspect of livestock. Several indices were developed to determine of heat tolerance of animals keeping in view the accuracy of measurement and changing environmental conditions.