Summer Stress Management in Livestock
Dr. Nutan Chauhan
PhD scholar
National Dairy research institute, Karnal, Haryana
nutanc03@gmail.com
Introduction
Heat stress is a form of hyperthermia in which, the physiological systems of the body fail to regulate the body temperature within a normal range. It is combined effect of environmental temperature and relative humidity. The aftermath of heat stroke may lead to severe damages in terms of general health, immunity and productivity of farm animals e.g. poultry, dairy and meat animals; pets e.g. dogs, cats, rabbits etc. and work animals e.g. equines, camels, draught animals, etc. Many factors can affect livestock production. Climatic environment is one of the main limiting factors of production efficiency in these regions The increasing concerns on production losses because of high ambient temperature. Heat stress is an occasional problem during the 2 to 3 summer months (June and July). So, there has been a great deal to overcome the heat stress in animals.
Causes of Heat Stress
Animals may be prone to heat stress due to higher environmental Temperature-Humidity Index (THI), solar radiation and lower wind speed in summer season. Environmental factors like:
- Recent rainfall and subsequent rise in humidity leading to decreased sweating and breathing for heat dissipation
- A high solar radiation level due to absence of natural cloud cover may predispose animals to heat stroke
- High environmental humidity
- Warm cloudy nights might also increase the risk of heat stroke
- A sudden shift to adverse climatic conditions might also predispose animals to heat stress
- Husbandry practices and farm layout may sometimes facilitate the onset of heat stress in animals
Some characteristics of animals might put the individual to a greater risk of heat stroke. Following attributes might be responsible for higher incidence of heat stroke in conjunction with some environmental factors:
- Breed: Indigenous breeds (Bos indicus e.g. Sahiwal) are more heat tolerant than exotic breeds (Bos Taurus e.g. Ayrshire). Similarly, Brachycephalic anatomy (flat-faced breeds) such as Pugs, English bulldogs, French bulldogs, Persian and Himalayan cats are among other breeds which are not heat tolerant.
- Genetic variation: Variations attributable to the phenotypes of individual animal breeds.
- Coat color and type: Animals with lighter coat color (e.g. cattle vs buffalo) tend to be more tolerant of heat. Animals having coarse hair type as coat may be more prone to heat stress (e.g. sheep vs goat).
- Body condition: Obese and emaciated animals tend to be more susceptible to heat stroke.
- Age: Animals that are recently weaned or aged animals are more prone to heat stress.
- Adaptation: Indigenous animals might adapt to local climatic conditions, provided the temperature change is gradual.
- Disease: Animals having ailment of any etiology might not be able to adapt to changes in the weather.
- Physiological State: Lactating animals or peri-parturient animals might be at higher risks of getting affected by temperature or humidity rise due to their hormonal profiles.
- Vector Density: Some flies and mosquitoes might cause nuisance to animals, leading to overcrowding/ huddling towards vector free areas. Symptoms of Heat Stress
Effect of heat stress on animals
Heat stress is one of the most important stressors especially in hot regions of the world. Adaptation to heat stress requires the physiological integration of many organs and systems viz. endocrine, cardiorespiratory and immune system. Increased breathing, heart and sweating rates may be recorded. Initially, symptoms like increased panting, vomiting and diarrhea might be noticeable. There are some common effects –
- Effect on Behaviour
Seeking shade, crowding towards shady areas, orientation avoiding contact with solar radiation, standing in or next to water source might be observed in animals having onset of heat stroke.
- Effect on productivity and fertility
Productivity parameters like milk production, egg production, weight gain, FCR (feed conversion rate), milk and meat composition (decline in protein and fat contents) might show abrupt changes in heat stressed animals. Heat stress reduces libido, fertility and embryonic survival in animals. Primary effect of environmental stress in neonates is increased disease incidence associated with reduced immunoglobulin content in plasma. Heat stress in late gestation reduces fetal growth.
- Effect on feeding
Drop in routine feed consumption and sudden increase in water intake might signal the onset of heat stress.
- Effect on health
The later stages of heat stressed animals might exhibit symptoms like dry and hyper congested mucosal surfaces, listlessness/lethargy, staggered gait, general weakness and electrolyte loss from the body. Neurological symptoms might include irritability, delusions, hallucinations, seizures and coma.
Changes during heat stress
Metabolic changes
High ambient temperature can adversely affect the structure and physiology of cells causing impaired transcription, RNA processing, translation, oxidative metabolism, membrane structure and function. Heat stress increased lipid peroxidation which was associated with production of large number of free radicals which are capable of initiating peroxidation of polyunsaturated fatty acids. Heat stress in lactating animals results in dramatic reduction in roughage intake, gut motility and rumination which in turn contribute to decreased volatile fatty acid production and may contribute to alteration in acetate: propionate ratio. Rumen pH also declines during thermal stress. Electrolyte concentrations, in particular Na+ and K+ are reduced in rumen fluid of heat stressed cattle. The decrease in Na+ and K+ are related to increase in loss of urinary Na+ and loss of skin K+ as well as decline in plasma aldosterone and increase in plasma prolactin. Enhanced heat dissipation during heat stress may also lead to electrolyte losses through sweat, saliva and urine. Heat stressed animal, particularly a lactating cow, might experience metabolic ketosis.
Hormonal changes
There is increase in plasma concentration of cortisol and corticosterone and less frequently an increase in plasma epinephrine and nor epinephrine concentration in heat stressed animals. During heat stress there were significant reduction in concentrations of T3 and thyroxine (T4) in plasma and in milk of lactating cows.
Immunological changes
Since stressors have been associated with increased circulatory concentration of glucocorticoids, they also have been linked with decreased functioning of the cells of the immune system. Lymphocyte proliferative responses were reduced. High ambient temperature causes functional and metabolic alterations in cells and tissues including cells of immune system. In such conditions, the administration of antioxidants has proved useful for improvement of several immune functions.
Prevention of Heat Stress
The incidence of heat stress in animals might be reduced largely if there is a beforehand management of cases. The following approaches might be helpful in preventing heat stroke cases in dairy, meat, working, pets and zoo animals: –
- Physical modification of the environment
- Genetic development of heat tolerant breeds
- Improved nutritional management practices
- Physical modification of the environment
Housing management
Management of heat stress on the part of building and infrastructure is very crucial. The principle of construction should allow maximum air flow throughout the farm avoiding direct exposure to solar radiation during day time. With the help of management, it is possible to modify the microenvironment to enhance heat dissipation mechanism to relieve heat stress. Sheds if constructed scientifically, provide comfortable environment to animals. There is no doubt that shading is one of the cheapest ways to modify an animal’s environment during hot weather. Although shade reduces heat accumulation, there is no effect on air temperature or relative humidity and additional cooling is necessary for farm animals in a hot humid climate. Major design considerations must be taken into account for shade structures (orientation, space, height and roof construction). The most effective in terms of reducing heat load is a reflective roof such as a white galvanized or aluminium roof.
Environmental modifications
Heat can be minimized by adopting simple and basic rules for designing animal facilities (shape, orientation, thermo-physical properties of construction materials, ventilation, opening facilities, etc.). For outdoors animals, the provision of shade (natural or artificial) is one of the simplest and cost-effective methods to minimize heat from solar radiations. Trees are very effective and natural shading materials providing shade to the animals combined with beneficial cooling as moisture evaporates from the leaves. Air temperature can be lowered by air conditioning. Fogging systems use very fine droplets of water in order to increase the water surface in contact with the air. The water is evaporated into the air causing a reduction in Temperature. So, the adequate shades/shelters on farm, the use of fans, sprinklers, misters, foggers and coolers might be helpful in preventing the higher incidence of heat stroke animals in hot and humid months of the year.
Methods for enhancing animal heat losses
Air movement is an important factor in the relief of heat stress, as it affects both convective and evaporative heat losses. Natural ventilation rate can be maximized using a well-oriented semi-opened building with high and well isolated roof. One of the most common and effective methods to promote heat losses involves the addition of water to the skin with or without supplemental airflow to increase the rate of evaporation of additional water. The water can be provided to the air coat with drippers or sprinkler equipment. Avoid physical exercise on part of the animal during the hottest hours of the day, especially in the summer months. Try to utilize early morning and evening hours in case of draught animals.
- Genetic modification
There is genetic variation among animals for cooling capability, which suggests that more heat tolerant animals can be selected genetically. Cross breeding offers another opportunity. However, extensive crossbreeding studies have shown little heterosis for heat tolerance. Improved nutritional management practices
Among all nutritional interventions could be one of the easiest and most promising options for minimizing the effect of heat stress. Therefore, nutritional interventions should be attempting to improve the following attributes in a coordinated way–
- Maintenance of modified nutrition requirement
Water
Dietary fibre
Protein
Dietary Fat
Maintaining the mineral balance
- Maintenance of the oxidative stress and healthy rumen
Maintenance of modified nutrition requirement
Water
Water is an essential nutrient for livestock animals, especially during a thermal stress. In hot conditions, water losses increase (evaporation by panting and sweating) and water ingested in feed and generated by metabolism is reduced. Dietary plans may be changed in case of farmed animals (like cattle, buffalo, equines, poultry, etc. to ensure that maximum possible water content is present in the fodder/ feed of animals. Consequently, drinking water consumption has to increase to cover the requirements of a heat-stressed animal. Chilled water can provide sufficient cooling to allow the lactating sows to increase their feed intake and milk production during heat stress. The cow may drink up to 50% more water when the temperature/humidity value is greater than 80%. Place water in a shady area to prevent evaporative loss.
Fibre
High fibre diets can increase heat production. Acetate metabolism (associated with a high-fibre diet) produces more endogenous heat than propionate heat (associated with a high-concentration diet). Consequently, the increased intake of dietary fibre can increase the thermal load and then thermal stress occur. In dairy cattle, some of the milk output lost (35-50%) during HS could be recovered through nutritional management. In ruminants, diets formulated for low metabolic heat increments can help to improve feed intake and performance under HS conditions.
Protein
The increase in protein content with the help of highly degradable materials seems to increase the thermal load. The excess nitrogen supplied by the proteins must be detoxified into liver urea via a metabolic pathway, which is a very high energy demand (1 g urea = 7.3 Kcal). Protein content and feed degradation cause a reduction in feed consumption, resulting in a reduction in milk production. Essential nutritional amino acids may help prevent the risk of HS. During HS, transcription and translation of RNA are inhibited, with a decrease in milk protein synthesis. Methionine is one of the most important limiting amino acids for dairy cattle. Methionine supplementation enhances milk production and antioxidant capacity, decreases lymphocytic apoptosis.
Fat
Fat supplementation increases the net energy input of dairy cow subject to thermal stresses due to its higher energy density and lower metabolic heat compared to fibre or starch. The high fat content has led to a measurable decrease in heat generation also under thermos-neutral conditions. The best alternative in ruminant is the use of processed fats, which bypass the intact rumen environment, not affecting the microbial growth of the rumen.
Maintaining the mineral balance
The negative effects heat stresses are associated with changes in mineral metabolism.
There are some minerals –
- Sodium& Potassium
- Mineral electrolytes, sodium and potassium are important for maintaining the water balance, ion balance and acid base of heat-exposed cows. Urinary excretion in a hot environment compared to excrete in a cooler environment can increase by as much as 80% and 18%, respectively. Alkaline diets are more preferable. Thus, sodium bicarbonate and magnesium oxide were found to be very effective in relieving heat stress. A diet with high chloride content depressed DMI and was associated with low blood pH and reduced blood buffering.
- Dietary cation-anion difference (DCAD)
DCAD =(Na++k+) – (Cl–+SO4-) meq/100g DM
An increase in DCAD in the diet was observed to increase DMI in heat-stressed cows. The calculation of Na+, K+, and Cl concentrations has a significant impact on productivity and health status by influencing the equilibrium of the acid base. A higher DCAD also reduced blood urea nitrogen in heat stressed Holstein dairy cows, suggesting the possibility that it enhanced microbial ammonia utilization for protein synthesis and ruminal N metabolism or utilization. A DCAD of +25 to +30 mEq/100 g DM is considered to be optimal for milk production in heat-stressed cows.
- Manganese
Manganese minimized oxidative stress during heat stress. Manganese acts as an antioxidant in the body to be part of the enzyme manganese superoxide dismutase (MnSOD) which is a major antioxidant enzyme found in mitochondria. MnSOD catalyses the conversion of superoxide radicals into hydrogen peroxide that can be further reduced to a non-toxic product, water, by other antioxidant enzymes like catalase.
- Zinc
Zinc plays major biological roles in the living system, which includes cell growth, development, differentiation, homeostasis, connective tissue growth and maintenance, DNA synthesis, RNA transcription, cell division, cell activation and the immune system. Carbon dioxide and carboxypeptidase are the two important examples of zinc-containing enzymes, which are crucial to the regulation of carbon dioxide (CO2) and protein digestion, respectively, in the animal organism. Zinc is considered essential to sexual maturity, reproductive effectiveness, regulation and the development of oestrus.
- Copper
Cu also acts as a part of enzyme superoxide dismutase for protecting cells against the toxic effects of superoxide radical by converting them to hydrogen peroxide in the cytosol. Deficiency of copper may be the cause of delayed onset of puberty, repeat breeding, low conception, early embryonic mortality and increased incidence of retention of placenta.
- Chromium
Chromium is a trace element that facilitates the effect of insulin on glucose, lipid and protein metabolism. Chromium supplements have the potential to reduce the negative effects of heat stress. Dairy cows in early lactation supplemented with chromium under hot conditions have shown a reduction of weight loss, an improvement of milk production, a reduction of plasma NEFA concentrations, and an improvement of breeding rates.
- Selenium
Among the trace minerals, Se is probably the most interesting to support the antioxidant defence of heat stress. Selenium is involved in the structure of the enzyme glutathione peroxydase. The biochemical function of glutathione peroxidase is to reduce lipid hydroperoxides to their corresponding alcohols and to reduce free hydrogen peroxide to water inhibiting the formation of other highly reactive oxygen free radical and protecting cell membrane against lipid peroxidation or oxidative damage. With vitamin E, it plays an important role in the immunity and health of the mammary glands, particularly under stressful conditions.
Management of the oxidative stress and maintenance of healthy rumen
Feed additives
- Buffers
Na- bicarbonate is the most prevalent and important ruminal buffer used to prevent acidosis, which is common during summers due to higher intake of concentrates.
- Niacine
Niacin is a subcutaneous vasodilator in many species and has been studied to achieve a decrease in body temperature. However, niacin is rapidly metabolized in the rumen, leading to poorly administered niacin in the small intestine. Niacin helps mitigate HS(Heat stress) by increasing heat loss by evaporating the body and reducing heat effects at the cellular level. Amongst the vitamins, the role of niacin in lipid metabolism has been studied.
- Antioxidant
To reduce the negative impacts of environmental stress, vitamins A, C and E are generally used due to their anti-stress effects. Antioxidants diminish cortisol secretion and oxidative stress. Supplementation of Vit C and vitamin E have a negative effect on cortisol level during heat stress. L-Ascorbic acid and B- complex vitamin can be synthesized by ruminants and a supplementation in the diet is not required under normal conditions. Vitamin E plays an important role in maintaining the integrity of the membrane in nearly all cells of the body against oxygen free radical’s toxic against their per oxidation. Vitamin A and vitamin E play an important role in the immunity and health of the mammary gland, particularly under stressful conditions.
Conclusion
Heat stress negatively impacts the animal performance. The severity of heat-stress issue will become an increasing problem in the future as global warming. Major advances in environmental management including improved housing and cooling systems and changes in feeding strategy can attenuate the effect of thermal stress on performances. The efficiency of these solutions depends on many factors related to the animal (species, physiological stage and breed) and the livestock production system (confined systems v. Extensive systems). Maximizing the production level and the efficiency of livestock enterprises is important; however economic considerations largely determine the level of environmental manipulation selected for livestock systems. In terms of research needs, additional works are required to better predict adequately the effect of heat stress on animal productivity in practical conditions.
