By Dr. Sanket WakchaureNutritionist, Trouw Nutrition South Asia
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
- Decreased milkcomponent.
- Leaky Gut
- 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.
Table. 1: THI as an indicator of heat stress
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, as shown in Fig. 1.
Fig. 1- Effect of Betaine in Dairy Cows during Heat Stress
- 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, as shown in Fig. 2.
Fig. 2- Antioxidants attack free radicles if they can reach them.
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.
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