Dr. A. Samad
April heralds the onset of intense summer in most parts of India. Lot of myths about heat stress in animals are prevalent, and this post hopes to separate the facts from fiction.
Let us consider first the temperature comfort zone for cattle?
From numerous investigations, it has emerged that it is not only ambient temperature, but the combined effect of humidity and temperature that affects animals’ physiology.
The term THI (temperature humidity index) was developed for animals reared in temperate climate. One of the limitations of THI is that it does not take into consideration solar radiation (radiant temperature), wind velocity and vapour pressure. Studies in tropical climate have shown that THI index is good only for animals reared in temperate climate whereas for tropical climate two indices have been proposed: (a) Heat Load Index (HLI) and (b) Equivalent Temperature Index (ETI). Considering the physiological responses of cattle to heat stress following alerts has been proposed:
Caution 30-34 89-92
Extreme Caution 34-35 92-95
Danger > 35 > 95
Consequences of heat stress:
Increased breathing rate
Increased water intake.
Decreased feed intake.
Decreased milk production.
Change in milk composition, e.g. fat % and protein % declines.
Change in blood hormone concentration, e.g. increased prolactin
Heat Stress Mitigation Strategies:
Provide covered shelter to reduce effect of direct solar radiation. Natural shade of trees like Neem and Mango works best. Plant trees outside in the periphery of the fence / wall. For temporary period shadow net of different grades depending upon the solar radiation intensity in the area can also be installed. These are quite cheap and easy to put up. In summer the wind blows upwards from the ground and might damage the roof net. Punching small holes in the net will prevent this from happening. You can find suppliers of such nets on www.indiancattle.com
- Thatched roof with sufficient straw insulation is another cheap option. These are quite common and can be put up by local artisans.
- Heat stress can cause losses in production and reproduction of up to 25-30% during the summer season. For example if a farmer having five milking animals and is producing 75 liters milk per day the loss due to production in summer months would be around Rs. 42,000; and the loss due to extended open period by half of the summer days @ Rs 100 per day would be Rs. 45,000. It therefore makes economic sense to invest Rs. 20 to 25 thousand on heat stress mitigation. The heat stress effect on crossbred cows especially could be irreversible. Hence depending upon you location you must consider providing shaded area to animals.
- Use of metallic roofs or asbestos is more harmful to animals as these absorb and reflect radiation in the day as well as at night. Height of the shed roof is also important. In rural India roofs are built just over the animal height. As per the length and type of shed material being used farmers should try to provide maximum roof height.
- Give cold water? in case of loose animals and 4-5 times a day in case of tied animals: Apart from access, the temperature of water is also important. It is wise to invest in providing water troughs there are insulated. For this there are two options; while purchasing overhead water tank ask for insulated multi-layered plastic tank which are now available in Indian market. For details of the suppliers please visit indiancattle.com
- Provision of cooling systems: A number of research reports have documented beneficial effects of using cooling systems in cow shed. These range from simple fan to foggers and misting fans.
The choice would depend on type of climate that is dry heat, humidity and natural air circulation. In India a number of systems are available ranging from simple stand-fans to industrial mist fans.