Strategies for Managing Heat Stress in Dairy Animals
Livestock contributes significantly to worlds economy. India is the largest producer of milk which account 26.67% share of total milk produced globally. Extensive crossbreeding between regional breeds and unremarkable breeds of cattle made such a larger contribution possible. A dairy industry generally revolves around collection and processing of cattle and buffalo milk for human use.
While a number of environmental factors can affect a dairy animal’s immunological status and milk production, heat stress is the most frequent contributor to animal health issues globally. As temperatures rise around the world, there is a greater possibility for heat stress. Summers in India are very harsh as the environmental temperature rises upto 45 degree Celsius. Ambient temperature of dairy animal is 18-23 degree Celsius. The consequences of climate change not only affect crop output; but they also have an impact on animal production, such as decreased milk yields and quality as well as affect animal fertility.
Environmental heat stress is obviously the problem faced by the animals located in hotter (tropical) regions of the world. Heat stress not only reduces milk yield in cows and buffaloes but also affects several other economic parameters viz. animal health and animal reproduction, resulting in a significant economic impact on the dairy owners in these countries. The most obvious effect of heat stress is the reduction in feed intake, leading to a decrease in milk yield. But apart from that, there are several other metabolic implications that also contribute to the reduction in milk yield. In addition to that, there is a decrease in milk quality, primarily due to an increase in somatic cell count (SCC) and incidence in mastitis, increased health care cost, and reduced growth in heifers. However, to overcome the challenge of environmental heat stress in tropical countries on dairy animals, some management and nutritional strategies have been worked out by several researchers, which may help, but only partially.
India is first in milk production in the world production, with 20 crore tons of milk from 20 cr. cows 10Cr.Buffaloes during the period of 2020-2021.This was possible only due to large scale crossbreeding of local breeds and non-descript breeds of cattle. Livestock plays an important role in the global economy. Among the environmental variables affecting animals, heat stress is one of the factors making animal production challenging in many parts of the world. Climate change effects are not only limited to crop production, but also affect livestock production, for example reduced milk yields and milk quality and reduced fertility.
Heat stress is one of the greatest challenges faced by dairy farmers in many regions of the world. The crossbred animals are more susceptible to heat stress. 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 46°C which is 19°C above the upper critical temperature of dairy cattle. When the temperature exceeds 27 °C even with low humidity, the temperature is above the comfort zone for the high producing dairy cows. Humidity plays significant role in heat stress.
Signs of heat Stress: –
- Increased salivation.
- Open-mouth panting.
- The animal moves to the shade.
- The animal drinks more water while eating less.
- The animal prefers to stand up rather than lie down.
- The animal’s body temperature rises (often to 106-108°F).
- Dehydration-related dry gums and mucosal membranes.
- Animals may show sunken eyes and a faster heartbeat as their dehydration gets worse.
- The “skin-pinch” test is an additional technique for determining dehydration.
- Pinch or “tent” a fold of skin near the calf’s neck to conduct the maneuver, then time how long it takes for the fold to flatten.
- In typical animals, it takes less than two seconds for it to resume its natural posture.
- The animal may be up to 8% dehydrated if flattening takes up to four seconds. If it takes longer than that, dehydration has advanced to a more dangerous and potentially fatal stage.
- There is an increase in incidence of silent heat.
As dehydration becomes more severe, animals also may exhibit sunken eyes and an increased pulse rate. The “skin-pinch” test is another method to evaluate dehydration. To perform it, pinch or “tent” a fold of skin at the calf’s neck and observe how many seconds it takes to flatten. In normal animals, it will return to its regular position in less than two seconds. A flattening time of up to four seconds indicates the animal is up to 8% dehydrated. If it takes longer than that, even more serious, and potentially life-threatening, dehydration has set in.
Effects on milk production
Annual total milk loss due to thermal stress at the all-India level was 0.18 crore tones or approximately 2% of the total milk production of the country amounting to a whopping Rs. 2661.62 crores per year Upadhyay et al. The negative impact of global warming on total milk production in India is also estimated to about 1.5 crore tones by 2050.The decline in milk production due to Heat stress was 14% in early lactation and 35% in mid-lactation. Indeed, up to 10% of the variability in milk production has been attributed to the effect of climatic factors such as temperature.
According to scientists at the National Dairy Research Institute (NDRI), a pioneer institute in the field of dairy research, heat stress and poor maintenance of milch animals in the summer, particularly in May and June, leads to a decline of around 15 per cent to 20 per cent in milk production in crossbred cows and around 10 per cent to 15 per cent in buffaloes. In the humid months of July and August, it falls further to around 20 per cent to 25 per cent in crossbred cows and 20 per cent in buffaloes.
Haryana, Punjab, UP and Rajasthan are major contributors to milk production, but during summer, these states have temperature in excess of 44 degrees Celsius, which leads to reduction of milk yield
Effects on reproductive performance
Heat stress reduces the length and intensity of estrus besides increases incidence of anestrous and silent heat in farm animals. Heat stress affects the fertility and reproductive livestock performance by compromising the physiology reproductive tract, through hormonal imbalance, decreased oocyte quality and poor semen quality, and decreased embryo development and survival. In general, the percentage of conception rate was found to be reduced by 4.6% for each unit increase in temperature humidity index (THI) above 70, and heat stress during pregnancy further slows down the growth of the foetus and results in lower birth weight.
STRATEGIES TO MITIGATE THE HARMFUL EFFECTS OF HEAT STRESS:
- Breeding Management
It is important to install a good heat detection programme to identify cows with minimal heat symptoms since they display less symptoms during heat stress condition compared to thermal comfort periods. Instead of employing bulls to continue breeding, it is usually advised to utilize artificial insemination since in natural breeding, both bulls and cows have infertility due to summer stress or heat stress. The dairy farmers will benefit from genetic selection of heat-tolerant animals and inclusion of heat tolerance traits in selection programmes
- Animal Housing Management
In order to prevent heat stress, farms and animal housing must have a cooling system. Combining fans with a water sprinkling or water fogging system is the best cooling method. While raising buffaloes special care must be taken as they are more susceptible to heat stress than cattle. Sprinkling too much water is never a good idea since it might cause the animals’ bedding to become too damp, which can cause mastitis and other issues. Farm should have sufficient ventilation. Animal hutches must have an east-west long axis in order to provide a cooler atmosphere inside. White paint should be used on the roof and exterior walls to reflect up to 75% of the sun’s rays.Animal housing should be constructed of a heavy, insulating material that prevents access to sunlight.
- Nutritional Management
Animals under heat stress are more likely to have poor reproductive and productive outcomes. Feed intake decreases during heat stress. Thus, there is an increase in the need for energy and nutrient densities. High-quality forages and nutritious meals will help animals work better and lessen the effects of heat stress.
Here are some tips for managing your diet to prevent and treat heat exhaustion:
- Offer premium feeds, such as total mixed rations.
- Increase feeding frequency, feed during cooler hours of the day, let animals to graze at night, keep feed as fresh as possible, provide high-quality forage, and reduce the diet’s fibre level.
- To increase the energy density of the feed, provide more fat and concentrates.
- The milk yield and protein content can be improved by using bypass proteins.
- To lower oxidative stress and to boost immunity, animals should receive extra minerals (zinc, chromium, and selenium) and vitamins A, C, and E in their diets.
- To enhance glucose status, nutrient utilization, and increase feed intake, animal diets should also include rumen fermentation modifiers like monensin and live yeast culture.
- The most crucial action that animals may take to combat heat stress is to drink enough cool water. At least 10% of the herd should be able to drink at once from readily available, huge open water troughs.
- As the THI gets closer to 80, water consumption rises by up to 50%.
- Refilling electrolyte losses with providing electrolytes.
- Supplying a surface, natural or manufactured
The farm’s surrounding plantations will aid in lowering the heat stress on the animals. In the modern commercial dairy industry, it is not always practical. Therefore, providing artificial shade in the form of a shade cloth or a naturally ventilated building with open sidewalls can prevent the animals from being exposed to direct sunlight by up to 30%.
- Selection of animals tolerant of heat
To reduce heat stress in cattle and buffaloes, genetic selection of animals based on specific molecular genetic markers (HSP and ATP1B2 gene) for heat tolerance will undoubtedly be beneficial. Animals with shorter hairs, larger diameter, and lighter coats are known to be more heat-tolerant than those with longer hairs and darker coats. Therefore, dairy farmers will benefit from the choice of such animals.
Conclusion:
The key to maintaining animal health and performance during heat stress is to support the rumen and gut barrier function and ensure proper liver function. Producers should consider feed additives that support intestinal barrier function, neutralise endotoxins in the intestine, improve digestibility and promote feed intake. Finding the right solution may require a combination of additives tailored to a farm’s specific requirement. An integrated solution should be applied to minimize production and profitability losses associated with the effects of heat stress in dairy animals. This should include animal comfort, by providing animals with a comfortable environment and access to water, adjusted feeding management and necessary diet modifications. Feed additives like Levabon® and Digestarom® can be valuable tools that help to support DMI, increase digestibility and gastrointestinal comfort, thus minimizing the negative effects associated with hot and humid environmental conditions. Heat stress in dairy animals can challenge the reproductive and production potential of the animals. Implementing proper breeding programs, cooling strategies at farm with better feeding programs can help to minimize some of the negative effects of heat stress.
The body temperature and feed intake of dairy cows are affected by rising ambient temperature and humidity, which in turn affect milk production and reproduction.Mineral losses via sweating (primarily K) and changes in blood acid-base chemistry resulting from hyperventilation reduce blood bicarbonate and blood buffering capacity and increase urinary excretion of electrolytes. If animals are severely dehydrated due to heat stress, then animal should rehydrate with oral electrolytes.
Compiled & Shared by- This paper is a compilation of group work provided by the Team, LITD (Livestock Institute of Training & Development)
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Reference-On Request
