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Summer Stress Management in Dairy AnimalsDairy cattle produce milk most efficiently in environments where they can maintain their body

temperature at around 101.3-102.8 F (rectal). Relatively small increases in body temperature of at

least 1C result in detectable, deleterious effects on metabolism and tissue integrity, in particular, the

breakdown of body protein and a significant depression in production.

Milk production potential of dairy animals not only depends on balanced feeding, breeding, good

housing and management but also on the environment. Extremely high temperature can have

negative impact on the production and performance of animals.

Dairy cows are more prone to heat stress than other animals due to the genetic selection for

high milk production. The main limitation with crossbred dairy cattle in India is its susceptibility to

diseases and not adjusting with hot and humid climate resulting in the reduced milk production to

even much less than the half of their potential. Research findings have shown that exotic and

crossbred cows have less tolerance to summer stress than indigenous cows and buffaloes. The

environmental temperature and the relative humidity in months of May-June sometimes exceed 45

degrees centigrade and 60% respectively. The continuous high temperatures in summer make animal

body less resistant to fight against external infections. All dairy operations must be well planned with

regards to comfort of animals in summer.

Heat Stress

Heat stress is a result of an imbalance between heat gain and heat dissipation in an animal

and when the heat load of a cow is greater than her capacity to lose heat. The cows heat load is

determined by her own body heat production plus environmental heat that includes air temperature

and humidity and both are combined into a temperature humidity index (THI). The THI above 72 is

usually considered the point at which stress occurs.

The primary sources of heat gain from the environment are solar radiation and elevated

ambient air temperature. Atmospheric temperature and heat produced internally from basal nutrient

metabolism are the two sources of heat stress. As milk production and feed intake increases more

heat from nutrient metabolism is produced thus aggravating any heat stress incurred from

environmental sources. As the result, higher producing cows will experience more heat stress than

lower producing or dry cows. Humidity plays a significant role in heat stress.

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