Summer Heat Stress in Dairy Cattle and Their Management for Optimum Productivity
Kuldeep Singh
Ph.D. Research Scholar, SKNAU, Jobner, Rajasthan, 303328
Email: kuldeeptamana4@gmail.com
ABSTRACT
India is first in milk production in the world production, with 78 million metric ton of milk from 57 million cows and 39 million buffaloes. This was possible only due to large scale crossbreeding of local breeds and non descript breeds of cattle. Now crossbred cows are emerging as in important dairy animals. Nearly 9 to 11% of all the cows in milk are crossbred. Heat stress in dairy animals is one of the leading causes of decreased production and fertility during summer months. In India, the summer temperature goes beyond 450 C which is 180 C above the upper critical temperature of dairy cattle. When the temperature exceeds 270 even with low humidity, the temperature is above the comfort zone for the high producing dairy cows. Humidity plays significant role in heat stress. The most common index of heat stress (temperature- humidity index or THI) is calculated from the temperature and relative humidity (RH). During summer the milk production is reduced to the extent of 50%. The crossbred / exotic animals are more prone to the heat stress losses as compared to indigenous cattle.
https://www.pashudhanpraharee.com/heat-stress-management-an-essential-tool-in-livestock-rearing/
KEY WORD: Milk, cows, crossbred, heat stress, humidity
Armstrong (1994) reported following responses in animals during heat stress.
- Reduced feed intake
- Increase water intake
- Change in the metabolic rate / maintenance
- Increased evaporative loss
This productivity loss during summer can be reduced substantially by adopting the following heat stress management coupled with good health management.
- Proper summer oriented housing
- Animal cooling system
- Development of breeds tolerant to heat stress
- High energy
Armstrong (1994) reported that by evaporative cooling, the cow produced 7.5 kg extra milk per day when the ambient temperature was about 40.5° C (RH less than 30%). Igono (1986) observed that cows cooled with spray and fans under shade produced 2 kg / cow / day more milk compared to the cows in shade alone. Blackshow and Blackshow (1994) recorded that no shed environment caused depression in milk production to the tune of 3.3 kg / day/ cow in predominantly black cows.
Table- 1: Body response to the temperature
| Response to cold temperature | Response to high temperature | |
| Respiration | Decrease | Increase |
| Pulse Rate | Decrease | Increase |
| Body temperature | Normal | More than normal |
| Superficial blood vessels | Constrict | Dilate |
| Muscle tone Increase with | Shivering | Seating |
| Appetite | Increase | Decrease |
| Water from circulatory blood | Is removed | Is added |
Source: (Belsare., 2018)
How to reduce heat stress:
Methods to reduce heat stress are managing mental practices and nutritional correction. Under manages mental practices, emphasis should be given on proper water supply, proper animal housing to reduce or to manage heat stress. Dairy animals need to increase water intake during time of heat stress to dissipate heat through respiration and sweating. Water consumption increases by as much as 50% as the environmental temperature rises. Water should be fresh, clean at 70- 86 F. It should be close to shed with enough water space. Minimum of 3 inches of depth of waterer are necessary to accommodate cattle muzzle. Provide at least two water locations per group. Proper animal housing the cow sheds in Indian conditions should be designed to reduce the heat load because heat stress cause more damage to animals compared to winter. Animal can tolerate winter condition up to 150° C without any difficulty. But the temperature above 300° C result in drop in milk production and breeding efficiency. Therefore our cattle’s especially crossbreds must be provided with proper housing. Theoretically speaking, the best type of animal shelter is a one where the micro environment temperature remains within 15 to 250° C and humidity level around 10-12 mm Hg. Shades of trees provides an ideal protection from radiant heat, but do not fit because of other reasons. Principles for creating an optimum microenvironment within an around the sheds are directed to reduce heat gain and promote heat losses from structure of animals house by radiation & condition. The point needs to be considered are:
- Orientation
Shed with its long axis running East – West provides a cooler environment than one with a North-South orientation (Kelly et al, 1950). In the East- West oriented shelters animals get more opportunity for radiation exchange with cooler north sky. The shelter is shaded for a greater part of the day resulting into lower floor temperature. Thus this orientation favors heat loss from animal body to environment both by radiation and
- Shelter design
Open type of sheds has advantage over closed type shed. Mean temperature and minimum temperature in close shed was significantly higher than those of open type shed. The close type shed significantly contributed to higher ambient temperature during both hot dry and hot humid months i.e. from April to September. The mean vapor pressure in close type shed have been reported to be higher than open type shed.
- Width and size of shelter
Slightly more shaded area than the minimum recommended floor space required for different species of livestock should be provided in hot dry climate. Floor space requirement for calf is 1.5 to 2 m2, Adult male 7.0 m2 and for adult female is 4.0-5.0 m2. Optimum width of the shelter is 5.0-6.0 m. although wide shelter results in lower ground temperature underneath it and thus the amount of radiation from ground to animal body is reduced. Yet is simultaneously restricts the radiation from animals to cooler sky during night. Length of shelter depends on requirements. Ensure minimum cow stand of 5.5 x 9.0 feet with Pacca and well drained floor. Shaded resting area of about 30-40 square feet/ animal.
- Height of shelter
Minimum roof height should be 10.0 feet to reduce heat load. The height of shelter in hot climate should be between 3.0 – 5.0 m. A height less than 3.0 m interferes with proper ventilation resulting into reduced convective heat loss from animals. The shadow size is not affected by height since higher the shade the faster the shadow more. The impedance of the total sun and sky radiation at 3.5 m height is 61% against 64% at 2.2 m height. A too high shelter without providing any significant additional benefit involves high cost of construction.
- Shape and type of roof
The shape of the roof can be either flat, slopped or “A” shaped. “A” shaped roof is definitely better than a flat roof in hot climate. One side of “A” shaped roof saves the other half form direct solar radiation by casting its shadow. This helps in cutting down heat gain from roof. Roof – may be either single or double with both the roofs of same or different materials.
Feeding and nutritional management
Points to be consider while feeding animals during hot weather, as feeding frequency, (extra feeding) time of feeding, (cooler time of a day, adequate feeding space and plenty of cool water. Modification in ration can help to minimize the drop in milk production, decreasing forage to concentrate ratio, result in more digestible rations. Feeding buffers such as sodium bicarbonate and magnesium oxide allow higher concentrate rations and can help in low fat milk syndrome also. Hot weather increases the need of certain minerals. Do not overfeed highly degradable protein during hot weather it should be 18% or less. Supplemental fat can be added in ration to increase energy in take. Also avoid feeding excess fat, over feeding causes problem with rumen function supplementing extra vitamins during summer has no added advantage.
Animal cooling system
Rise in ambient temperature activates sweat glands to produce sweat. Each gram of sweat evaporated from skin utilises 590 calories from skin surface (Latent heat of evaporation of water). This process of evaporation causes cooling of skin. A part form sweating animals increase their respiration rate (induced evaporation of moisture from mouth/ lungs). Breathing of animals at a much faster rate to combat heat stress leads to panting. To reduce the metabolic heat load, animals reject feed and fodder.
Zero energy cooling
Cows having access to sheds with evaporated coolers had marked higher breeding efficiency than cows having access to only conventional sheds. The milk production is group maintained under cooled shed was 1.8 kg more per head than in conventionally shaded group.
The NDDB, Anand has developed a cooling with an estimated cost of Rs. 5000/- per set suitable for 6-8 milch animals. The results of the same system used for cooling Holstein cows are presented in table. It required a power of Rs. 400/- per summer which comes to about Rs. 50/- per animal which results in increase in milk production of about 1 to 1.5 kg per animal per day.
Shelter surroundings
Surface around shelter are very important in view of radiation exchange between different surfaces and the shelter. The temperature of different surfaces varies significantly at same air temperature. It is clear that green surface do not heat up as much as other surfaces like gravel or loose loam. It is difficult to maintain green vegetation adjacent to animal shelters. It may be possible to increase animal comfort by selection of proper type of unvegetated ground surface. These vary significantly in view of the difference in reflectivity, thermal conductivity and density etc.
REFERENCES
Armstrong, D. V. (1994). Heat stress interaction with shade and cooling J. Dairy Sci. 77: 2044-2050.
Belsare, V.P. and Pandey, V. (2008). Management of heat stress in dairy cattle and buffaloes for optimum productivity. Journal of Agrometerology, 2: 365-368
Blackshow, J. K., Blackshow, A. W. and Kusano, T. (1994). Heat stress in cattle and effect of shed on production behavior: a review. Australian J. Exp. Agric., 34: 285-95
Igono, M. O. (1986). Effect of humid temperate climate and environmental modifications with shed, spray and fan. on milk production, thermal balance and hormone functions of dairy cows. Dissertation Abstracts. International J. (Sciences & Engineering) 46: 3645
Kelly, C.F., Bond, T.E, and Ittner N. R. (1950). Thermal design livestock sheds. Agric. Engg., 36, 173- 80.
