Heat Stress as menace to the Dairy industry : Strategies to reduce the adverse effect of heat stress in Dairy animals

Heat Stress as menace to the Dairy industry : Strategies to reduce the adverse effect of heat stress in Dairy animals

Heat stress will cost the global dairy sector an estimated $5 billion a year in 2050 (Wankar et al., 2021).To reduce the costs for both the farmer and animal, a more integrated approach regarding production, health and welfare is needed. The key lies in prediction tools in combination with target nutritional solutions.

Heat stress management in farm animals is on the industry’s radar for many years, but is more topical than ever for multiple reasons. With the increased global demand for dairy production, we see an increase in the number of dairy cows in hot and new dairy regions like the Middle East and Asia. At the same time, we thrive to make these systems in these challenging conditions as efficient as possible with high milk outputs and high feed efficiency.

We can all bring up the image of a very hot subtropical desert, where the temperature sometimes exceeds 40°C (104°F). In the meantime, it is getting hotter in other parts of the world as well, due to global warming. According to data from NOAA (National Centers for Environmental Information, 2020), the earth’s temperature has risen by 0.08°C (0.14°F) per decade since 1880, and the rate of warming over the past 40 years is more than twice that: 0.18°C (0.32°F) per decade since 1981. In farming, climate changes could increase thermal stress for animals and thereby reduce their production and profitability by lowering feed efficiency, growth rates, reproduction rates and welfare. Heat stress might be an old problem, but it requires new effective and integrated solutions to deal with this better and more sustainably in the future.

The dairy sector is a business that is dedicated to the collection or processing (or both) of animal milk for human use, typically from cows or buffaloes, but occasionally from goats, sheep, horses, or camels. A dairy is usually found on a dedicated dairy farm or in a sector of a multi-purpose farm (mixed farm) that is dedicated to milk production. India is the world’s largest producer of milk.

While a variety of environmental conditions can influence a dairy animal’s immunological status and productivity of milk, heat stress is the most common cause of animal health problems around the world. Heat stress potential is increasing as global temperatures rise, both in absolute terms and in terms of duration. Heat stress is caused by a number of factors, the most important of which are high ambient temperature and high humidity.

India is the world’s largest producer of milk, generating more than 200 million tons every year. The country possesses about 300 million bovines (nearly 200 million cattle and 100 million buffaloes). Nearly half of the milk production comes from buffaloes and a little over a quarter from crossbred cattle. Indian dairy industry, which relies on 80 million farmers across the country, most with small herds, has grown steadily and now accounts for nearly 5 percent of India’s economy.
Environmental heat stress is obviously the problem faced by animals located in hotter (tropical) regions of the world, including India. 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. 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 as well, primarily due to an increase in somatic cell count (SCC) and incidence of mastitis, which also results in increased health care costs.
Climatic Stress on animals, especially due to heat stress, is one of the big challenges faced by dairy animals in India, including their owners, which may reduce the milk yield of cows and buffaloes substantially. The reduction in milk yield of cows and buffalos results in an increase in both feed costs as well as milk prices. Thus, apart from affecting dairy farmers, extreme heat is proving crucial to the dairy industry as a whole.
In view of the chronic shortage of green fodder, which gets further compounded during hotter months, farmers have to depend more on straws and stovers to give bulk feed to their animals. This year, due to erratic rains and hot spells, the yield of even wheat crops too dropped, causing a shortage of wheat straw as well, with their prices also shooting up. However, these bulky fibrous straws are only low-quality feeds, being low in energy, protein as well as in minerals. Fortunately, the ruminant animals possess the mechanism in their rumen by which part of these bulky (cellulosic) feeds are partly fermented through a large number of microbiota present in the rumen, and the end product is volatile fatty acids, mainly acetate, which serves as precursors for long chain fatty acids in the liver. Starchy diets produce Propionic acid in the rumen and serve as a precursor for glucose synthesis in the liver. Glucose ultimately serves as a precursor for lactose synthesis in the mammary gland and regulates milk volume. This is because Lactose maintains the osmotic pressure of milk.
But even then, due to the shortage of green fodder and its replacement by straw feeding, the animals have to be fed more of concentrate feed in order to meet their requirement of nutrients fully. So, naturally, the demand for feed also increases, and so is the increase in feed cost.
To overcome the challenge of environmental heat stress in tropical countries on dairy animals, some management, as well as nutritional strategies, have been worked out by several researchers, which may help, but only partially.
Adaptations of animals to hot and hot & humid climate
Camel is bestowed with a big hump, which helps the animal to use the stored energy during the period of its limited nutrient supply and thus fight heat stress. But compared to camels, Bos indicus have a smaller hump, so they do not possess as efficient an adaptive mechanism to fight heat stress as camels possess. However, Bos indicus animals are still in a better position to dissipate heat during the hot season, unlike Bos taurus, like crossbred cows, which are devoid of any hump.
The hot humid conditions are the most stressful for the animals. The best-adapted animal for the humid tropics is the buffalo. Although its sweat glands are far less active than the zebu cattle, however, wallowing in ponds helps it a lot to get rid of the body heat and causes thermo-regulation. Temperature -Humidity Index (THI) is a better predictor of whether or not the cows are “stressed”. THI < 72 is the point at which a dairy cow starts to decrease productivity.

Heat stress is defined as an increase in core body temperature above its normal range. This is especially the case for high producing cows that generate more heat because of the higher feed intake and related raised metabolic heat increment. The comfort zone or thermoneutral zone for a dairy cow is wide varying from around -15°C to +25°C. Dairy cows are therefore mostly farmed in mild and somewhat colder ambient temperatures that are ideal for both grass production and the animal’s preferences. But also humidity (in %) plays a role. In livestock we therefore speak about a Temperature Humidity Index (THI), a combination of temperature and humidity, as a threshold for heat stress.

When the THI unit is over 68 (22°C, 50% Humidity), dairy cows start to show moderate heat stress related symptoms. When it goes over 80 and 90, we speak about high and severe heat stress respectively, with more dramatic effects on performance, animal health and animal welfare (Figure 1). In a 2-year study conducted under field conditions, Bernabucci et al. (2010) found a decrease of 0.27 kg of milk per THI unit when Holstein cows were exposed to a THI higher than 68. The effects of heat stress can be seen on cow level (changes in behaviour), on blood and hormone level, at metabolic level and at cell level.

Heat stress is a major challenge in dairy production, especially during the scorching summer months in which daytime temperatures can reach as high as 45°C, while nighttime temperatures typically remain around 30°C. Additionally, the photoperiod during this season can last between 12 to 14 hours. Dairy animals can maintain a constant body temperature, making them homeothermic. Heat stress is a condition that arises when dairy animals are subjected to elevated environmental temperatures, humidity, solar radiation, and heat waves, which can disrupt the animals’ homeorthermic responses. If the animals are unable to dissipate the excess metabolic heat via various mechanisms like conduction, convection, radiation, and evaporative cooling, they may experience heat stress.Heat stress can adversely impact the health, productivity, and profitability of dairy animals, it is essential to implement both managemental and nutritional strategies to alleviate this condition.

Impact of heat stress on dairy animals

• Decreases dry matter intake
• Rumen acidosis
• Laminitis
• Decreased milkcomponent.
• Leaky Gut
•  Inflammation
• Reduced Milk production
• Poor Reproductive performance
• Decreased oestrus intensity and length
• Decreased Ovarian follicle growth
• Impaired fetal growth
• Decreased fertility rate
• Early embryonic death
• Impaired immune function.

Visible signs of Heat Stress in dairy animals

• Animals seek out shaded areas to lessen the impact of solar heat.
• To regulate their body temperature, animals increase their water intake while decreasing their feed intake.
• The animal prefers standing rather than lying down.
• Increased respiration rate
• Increased body temperature
• Increased production of saliva
• Open mouthbreathing and panting with extended neck.
• Animals experiencing heat stress exhibit decreased activity levels.
• Sweating and excessive drooling

Impact of heat stress on milk production

All cellular processes produce heat energy that needs to be released or stored based on the environmental condition. Lactating cattle can use up to 31% of their total energy as heat for metabolic functions. Exposure to elevated temperatures and humidity can increase their energy expenditure by 20%, causing heat load. High yielding cattle are more susceptible to heat stress due to low thermotolerance, inability to return to normalproduction levels, and lack of acclimatization to adverse weather conditions.

Lactating cattle easily enter negative energy balance due to reduced feed intake, milk production pressure, and increased energy expenditure. During heat stress in cattle, thermoregulation at the cost of production (energy) is the primary cause of decreased milk production. Reduced feed intake, feed quality, nutrient assimilation, utilization, and rumen functions are some other factors, affecting milk production. Heat stress affects lactation by altering endocrine and metabolic functions and reducing the supply of essential nutrient like glucose, non-esterified fatty acid etc.to the mammary gland. This decreases milk yield and can lead to mastitis.

Temperature Humidity index

The degree of heat stress and its impact on the animal is dependent on multiple factors including the maximum temperature to which the animal was exposed, the duration of high temperatures, the rate of temperature change, and the relative humidity of the air.Many methods and models have been constructed to assess the heat stress impact on animals. Temperature humidity index (THI) is the simplest, effective, and most commonly used technique, which can be utilized as a means of measuring the joint impact of both temperature and humidity to estimate the level of heat stress cows will experience based on environmental conditions.

Mitigation strategies for managing heat stress in Dairy Animals.

1. Managemental strategies

• Provide shed to heat stressed animal, especially over feeding areas without love crowding of animal to reduce solar heat load and increase feed intake.
• Barns and pole sheds with adequate ventilation are good option for providing shed. Keep cows inside during the day if it is cooler for them.

• Cows are cooled by exchanging the air between the inside and outside of the barn through ventilation. Ventilation can occur naturally or by using mechanical methods.
• Provide extra air movement by installing fan in stall barns and holding areas.
• Using sprinklers and misters can help cows dissipate excess body heat. Sprinklers wet the cow’s skin, which allows the liquid water on the skin to evaporate using the cow’s body heat. Meanwhile, misting systems cool the air by evaporating water droplets with the heat in the air. Although both methods increase the air’s relative humidity, proper ventilation in the barn should prevent excessive humidity levels.
• Sprinklers and misters are more effective in dry, low dew-point weather, and they should be used periodically to allow for water evaporation.
• Water can be run over a shade or roof to facilitate evaporative cooling.
• It is crucial to maintain a continuous supply of  clean and hygienic water.
• Sanitation should be increased due to the higher risk of mastitis and other infections caused by environmental microorganisms. This requires more cleaning, bedding, and disease control measures.

2. Nutritional strategies

• During heat stress, feed intake is often reduced. To combat this, a popular approach is to raise the energy and nutrient densities of the diet by adding more concentrates and supplemental fat. It is believed that reducing the fiber content of the diet can also enhance the cow’s thermal balance and lower its body temperature, in addition to regulating energy. Nevertheless, caution must be exercised when increasing the amount of concentrate in the diet, as heat-stressed cows are particularly susceptible to rumen acidosis.
• Use of buffers like sodium bicarbonate, sodium sesquicarbonate and magnesium oxide are useful to neutralize excess acid within the animal’s digestive system and maintain normal rumen environment.
• To mitigate the negative effects of heat stress on fibre digestibility, it is recommended to feed forages with the highest digestibility during this time to minimize the risk of acidosis.
• Maintain adequatefibre levels while slightly reducing the amount of ADF and NDF in the ration. To maintain production and a reasonably normal fat test, ensure that the total ration dry matter contains at least 28% to 30% neutral detergent fiber (NDF) level.
• Supplementation of additional fat in ration to maintain energy balance but it should not be exceeded 5 % of total ration dry matter. The use of rumen protected fats in the diet can substantially lower heat increment.
• Balance the protein levels in the ration to minimize excess soluble and rumen degradable protein, which require the animal to expend energy to excrete from the body.
• As heat stress reduces feed intake, it becomes necessary to increase the protein content of the ration with rumen un-degradable protein (bypass protein).
• Adequate amounts of trace minerals and vitamins should be provided to dairy cows experiencing heat stress.
• Betaine helps to water retention, increases anabolic activity, maintain integrity of cells during heat stress condition. Additionally, betaine enhances production performance by supplying methyl group. Betaine increases feed intake, milk yield, milk lactose and milk protein when supplied for 8 weeks in dairy cattle during heat stress condition.
• Chromium supplementation which is essential for glucose metabolism may improve thermal tolerance or production in heat-stressed animals.
• Supplementing with niacin is known to enhance milk production in dairy cattle by increasing sweat gland activity through peripheral vasodilation.
• Maintaining a DCAD level of 200 to 300 mEq/kg DM is beneficial for healthy lactation during the warm summer months.
• Adjust increased requirement of K+ in diet which is primary osmotic regulator of water secretion from sweat glands. Increase dietary levels of Na+ and Mg+ as they compete with K+ for intestinal absorption.
• Selko® IntelliBond ® Zinc usage shows slightly higher milk fat production and reduced systemic inflammation in heat stress condition.
• Rumen Fermentation Modifiers like Monensin (an ionophore) and live yeast cultures (Saccharomyces cerevisiae) are useful in heat stressed animals.
• Optimal level of Natural and synthetic antioxidants in the feed helps to reduce heat stress. (e.g., SelkoAOmix, Vitamin E, Vitamin C, etc.). antioxidant’s effectiveness is dependent on its water vs. fat solubility, which can vary widely. The solubility is what determines where antioxidants are distributed in the body. Vitamin E, for instance, mainly delivers its antioxidant effect at the cell membrane, and has less impact on the internal or external cell environment.

3. Feeding Management

• To minimize heat production during high temperatures, provide most of the ration during cooler periods of the day since the peak of heat production from feed intake occurs 4-6 hours after feeding. (Morning 4 am to 6 am and evening 9 pm to 11 pm)
• To enhance feeding efficiency, increase feeding frequency to 4-6 times per day, with the largest proportion given at late evening or during nighttime.
• All cows are fed at the same time and offered a total mixed ration as per feasibility.
• If dry matter intake (DMI) significantly decreases, extra water should be added to the TMR, silage, or haylage. This can significantly increase DMI in some cases.
• Ensure that the ration for dry cows and springing heifers is balanced to minimize the risk of infectious and metabolic diseases.
• Increase the proportion of green fodder in the diet of heat stressed animal.

Signs of heat Stress:-

Common symptoms of heat-stressed animal include,

• Animal moves to shade
• Water intake enhanced while feed intake reduced
• Prefers standing than lying down
• Increased respiration rate, body temperature
• Increased production of saliva
• Open-mouth panting
• Incidences of silent heat increase during heat stress

Heat Stress Reduces Feed Intake and the quantity of Milk Produced

Unabated heat stress can decrease feed intake by more than 35%. However, even in well-cooled dairies decrease in feed intake due to heat stress may be between 15-20 %. In noncooled management systems, milk yield can decrease by 40-50 % during severe conditions. Reduction in feed intake due to heat stress reduces consequently nutrient intake, resulting in decreased milk synthesis in the mammary gland. However, the overall reduction in milk production is not just due to a reduction in feed intake only, but also due to heat stress itself. Because, the animal has to spend part of its energy intake on panting, to get rid of its excess heat, just the way an air conditioner requires electric energy to cause a cooling effect.

Strategies to reduce the adverse effect of heat stress in Dairy animals

It has been proved through research that only the 40 % of the decrease in milk production is due to reduced DM intake, the rest of the 60 % reduction in milk production can be explained by heat-stressed induced other biochemical changes. However, the adverse effect of heat stress on the overall health and productivity of dairy animals can be overcome to some extent by improving the microenvironment and feed management. Following the approaches may help.
Providing Shelter/ Cooling System: The decline in old heat mitigation mechanisms such as the shared village ponds and rivers helped these animals, especially buffaloes to cool off. These village water bodies have vanished and the rivers are polluted. Under Indian conditions, the heat stress can now be reduced somewhat by providing proper shelter, controlling air moments, and causing a cooling effect inside with the combination of mist cooling and fan in sheds. This is being adopted by many big dairy farmers in India. Of course, the effect of heat stress on milk production can only be partially reduced.
At NDRI Karnal, some experiment is being performed on music therapy, as a way of reducing heat stress on dairy animals. They have reported that 40 to 60 decibels of sounds may be the best to reduce heat stress to some extent.
Reducing the quantity of fibrous diets and increasing concentrate: It is a known fact that fibrous diets generate more heat during rumen fermentation, called heat of fermentation. By reducing the quantity of highly fibrous feeds in the diet, the animal’s heat load can be slightly reduced. Instead, the animals may be offered succulent green fodders to meet their fiber requirement. In the absence of sufficient green fodder, the quantity of concentrate must be increased to meet the animal’s nutrient requirements.
Bypass Nutrient feeding: Bypass nutrients, instead of being degraded in the rumen, are protected against ruminal enzymes. Thus, proteins are not attacked by proteolytic enzymes and fats are not attacked by lipolytic and hydrolyzing enzymes of microbes. These nutrients are passed on to the lower tract where they are digested and subsequently absorbed from the intestines.
1. Feeding of bypass protein: Since rumen-protected proteins (bypass proteins) are not degraded in the rumen, these are digested in the abomasum (true stomach, or 4th compartment) and then absorbed from the intestines. After absorption, amino acids are then converted to glucose in the liver, to serve partly as an energy source and partly used as a precursor for lactose synthesis in the mammary gland. Apart from the generation of less heat in the rumen, feeding of bypass protein increase the efficiency of nutrient utilization, and thus, try to maintain milk production to some extent.
2. Feeding of bypass fat: The inclusion of Bypass fat in the diet of ruminants, increases the energy density of the ration. Accordingly, it compensates for lower feed intake, by providing energy for maintenance and productive purpose in a more concentrated form. In fact, in high-yielding animals, the inclusion of bypass fat as a dietary supplement is very essential, especially during hotter months, in order to maintain cow’s milk production.
Use of Feed Additives like Antioxidants: Heat stress generally increases the production of free radicals in the body, which then leads to oxidative stress as well. Oxidative stress has a negative impact on immune and reproductive functions. This may lead to increased frequency of mastitis, higher somatic cell counts in milk, decreased fertility, increased embryo mortality, post-partum retained placenta, and early calving. Glutathione peroxidases family of anti-oxidative enzymes, containing selenium incorporated within an amino acid (organic/chelated form), plays a major role in maintaining the anti-oxidative balance, protecting the cells from damage against heat stress. If given along with Vit E, which too is an antioxidant, the result is twofold.
Supplementing the diet with other feed additives like buffers (Sod. Bicarbonate), Niacin and Yeast also has a beneficial effect on the rumen environment and has an overall positive effect on milk production and stress reduction.

Reproductive and Productive challenges:- Heat stress challenges the production and reproduction performances of dairy animals. Milk composition, such as milk fat percentage and SNF percentage, is also affected. Follicular development and the estrous cycle are both negatively affected by heat stress.

Strategies to combat the negative effects of heat stress:- There are certain mitigation strategies to alleviate the detrimental effects imposed on dairy animals due to high ambient temperature.

Breeding Management

As cows express lesser heat symptoms during heat stress zones as compared to thermal comfort periods, it is necessary to approve or adopt a good heat detection program to detect cows with marginal heat symptoms. It is always advisable to continue breeding with the help of Artificial Insemination technique instead of using bulls because in natural breeding both bull and cows suffers infertility due to summer stress or heat stress. Genetic selection of heat tolerant animals and inclusion of heat tolerance as a trait in selection programme will be a boon to the dairy farmers.

Animal Housing Management

There must be a cooling system in farms/animal houses to combat heat stress. The greatest cooling solution is to use fans in combination with a water sprinkling or water fogging system. This must be exercised in case of buffalo farming as they are more prone to heat stress in comparison to other dairy animals. Excessive sprinkling should never be done because it can result in moist bedding, which can lead to mastitis and other problems in the animals. The farm should be adequately ventilated. The long axis of animal houses must be in east-west direction for provision of a cooler environment inside the shed. The color of roof and outside walls should be painted with white color that cause a reflection of sunlight upto 75 %. Houses should be made up of a thick isolating material that does not give access to the sunlight inside animal houses.

Nutritional Management

Heat-stressed animals are more likely to perform faultily in terms of reproduction and productivity. In heat stress, feed intake decreases. Hence, the demand of energy and nutrient densities increases. High-quality forages and balanced meals will alleviate some of the impacts of heat stress and improve animal performance. The following are some nutritional management suggestions for dealing with heat stress:

• Provide high quality feeds like total mixed rations
• Increase the frequency of feedings
• Feed during cooler times of the day and graze the animals in night time
• Keep feed fresh as much as possible
• Provide high-quality forage
• Decrease fibre content of the diet
• More fat and concentrates should be given to make feed more dense in energy
• Use of by–pass proteins can enhance the milk yield and protein content.
• Animals should be given more minerals (zinc, chromium and selenium) and vitamins A, C, E along with the diets to reduce oxidative stress and enhance their immunity.
• Rumen fermentation modifiers such as monensin and live yeast culture should also be incorporated in animal diets to improve glucose status, nutrient utilization and increase feed intake.
• Intake of sufficient cool water is probably the most important strategy for animals to undertake during heat stress. At least 10% of the herd should be capable of drinking simultaneously from, preferably, large open water troughs that are easily accessible.

Providing natural or artificial surface area

Plantation surrounding the farm will help to reduce the animals’ heat load. However, it is not always feasible in today’s commercial dairy business. As a result, providing artificial shade in the form of a shade cloth or a naturally ventilated structure with open sidewalls can keep the animals away from exposure of direct sunlight up to 30%.

Selection of heat tolerant animals

Genetic Selection of animals based on specific molecular genetic markers (HSP and ATP1B2 gene) for heat tolerance will definitely be a boon to alleviate heat stress in cattle and buffaloes by identifying the heat tolerant animals. It has been proven that animals with shorter hairs, greater diameter and lighter coat are more heat tolerant in comparison to animals with longer hairs and darker color coat. Therefore, selection of such animals will also be fruitful to dairy farmers.

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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