SUMMER STRESS MANAGEMENT IN LIVESTOCK

SUMMER STRESS MANAGEMENT IN LIVESTOCK

Dr. DEEP NARAYAN SINGH

Assistant Professor (LPM)

College of Veterinary Science & Animal Husbandry, DUVASU, Mathura

Abstract

The livestock growth, productivity and reproductive capabilities are very much susceptible for the variation in microclimatic variables viz. environmental temperature, humidity, radiation and wind velocity etc. Due to unfavorable climatic variables animals comes under stressful condition and ultimately the performance of livestock will be severely affected. The stressful condition during extreme heat load or summer is termed as heat stress condition. Heat stress results from the animal’s inability to dissipate sufficient heat to maintain homoeothermic condition, which is caused primarily by high air temperature but can be intensified with high humidity, solar radiation, wind velocity & by metabolic heat production. As the environmental temperature increases, the difference between the temperatures of the animal’s surrounding & their body decreases & reliance on evaporative cooling mechanisms (sweating & panting) to dissipate body heat will be increases in livestock. The number of sweat glands plays a very significant role in maintaining the body temperature. Among the livestock exotic & cross bred cattle and buffalo faces severe stresses than sheep & goat during summer season. To ameliorate the summer stress various management interventions viz. housing, cooling, curtaining, nutritional manipulations have a very significant role to improve dry matter intake, growth, milk production, wool production & meat production and reproductive parameters.

Key words: Dry matter Intake, heat stress, microclimate, silent heat, panting, Thermoneutral zone.

 Introduction

India’s milk production is growing by 35.61% during the last six years to 198.4 million tons in 2019-20, says the Economic Survey. Milk production in the country has increased from 146.3 million tons in 2014-15 to 198.4 million tons in 2019-20. Animal environment is affected by climatic factors that include temperature, humidity, radiation and wind movement. Extreme climatic conditions can alter energy transfer between the animal and its environment and might have deleterious effect on growth, production and reproduction in dairy animals. One of the major contributors of milk in India is buffalo and crossbred cattle, but they are highly susceptible to hot, humid and cold climate.

Environmental temperature below or above the thermo neutral range or zone (TNZ) for livestock especially dairy animals, alter the dry matter intake and metabolic activity leads to the stressful conditions. TNZ is the range of environmental temperatures from lower critical temperature (LCT) to upper critical temperature (UCT) where normal body temperature is maintained and heat production is at the basal level. Thermoneutral zone depends on the age, breed, feed intake, diet composition, previous state of temperature acclimatization, production, housing and stall conditions, tissue (fat, skin) insulation and external (coat) insulation and the behavior of the animal. The bovine thermal comfort zone is -13ºC to 25ºC. Within this temperature range, the animal comfort is optimal, with a body temperature between 38.4ºC and 39.1ºC. To ameliorate the effect of environmental summer stress, the mechanism of thermoregulation takes place within the animal body which might result in reduced milk production, milk fat content, impaired reproductive performance and making the animal more susceptible to various health problems.

In India, the summer temperature goes beyond 45°C which is 180°C above the upper critical temperature of dairy animal. Humidity also plays a significant role in heat stress or summer stress condition. The most common index of heat stress (Temperature Humidity Index or THI) is calculated from the temperature and relative humidity (RH).

THI =0.8*T + RH*(T-14.4) + 46.4

Signs of heat stress

            During heat stress the animals usually show the following signs.

• Restlessness
• Lethargy
• Decreased activity
• Crowding under shade
• More crowding around the water tanks
• Usually more animals remain standing rather than lying down
• Increased respiration rate (gasping): More than 70-80 breaths/ min.
• 80 to 120 breaths per minute moderate heat stress
• 120 to 160 breaths per minute strong heat stress
• Over 160 breaths per minute severe heat stress
• Panting
• Increased salivation
• Rise of rectal temperature
• Reduction in heart rate
• Increased sweating
• Maintenance requirement may increase by 20-30% in animals under heat stress.
• Blood flow to the skin is increased while blood flow to the internal organs and digestive tract is decreased
• Reduction in weight gain
• Urine volume generally increases.

Mechanisms of heat dissipation:

Basically there are four methods of heat loss or dissipation conduction, convection, radiation and evaporation. Among which evaporative cooling mechanism plays a significant role in heat dissipation mechanism. The number and location of seat gland is the major contributory factor for the evaporative cooling mechanism.

Our Indigenous cattle are very less affected with summer stress due to presence more quantity of sweat gland (1696/cm²) and superficially located especially at dewlap region, while in Holstein Friesian cattle there is only 1120/ cm² number of sweat glands and it is deeply located. Hence, Holstein Friesian (HF) is comparatively more affected with summer stress or heat stress condition in terms of growth, production & reproduction. The buffaloes are also very much susceptible for heat stress condition due to very less number of sweat gland and its black coat colour. Hence buffaloes prefer wallowing during to get rid of

Adverse effect of summer or heat Stress:

1. Dry Matter intake: At the temperatures of more than 27ºC to 30ºC feed intake in dairy animal begins to decline and drops more rapidly above 35ºC, in case of dairy animals. At 40ºC, dietary intake may decline by as much as 40%. Heat stress in high producing lactating dairy cows results in considerable reduction in appetite, roughage intake and rumination. Heat stress affects rumen fermentation adversely and the total volatile fatty acid (VFA) production is decreased even when the feed intake is same. During heat stress, DMI (dry matter intake) or nutrient intake declines whereas nutrient requirement for maintenance and active cooling processes like panting increases. Therefore, offering more forage to animals will cause more heat production in animal’s body, adding on to the heat stress problem. On the other side blood flow to internal organs like the mammary gland is reduced delivering fewer nutrients to these organs for metabolism. Thus, fewer nutrients are available for milk production during heat stress. In case of dry cows, off-feed or decrease in DMI during the heat stress can lead to more health problems at parturition and potentially reduce milk production during the subsequent lactation. Dry matter intake starts to drop (8-12%) and milk production losses of 20-30%. Dry cows whose last 3 months of gestation occurred during hot weather had calves with smaller birth weights and more metabolic problems after calving with 12% less milk production in the next lactation.

Besides these the following impacts of heat stress on feed intake or digestion have been observed

• Increased feed refusals
• Increased feed sorting
• Reduced natural buffering capacity due to reduced saliva production and increased carbon dioxide expiration
• Increased loss of minerals due to sweating, panting, and urination
• Increased metabolic disorders (acidosis)
• Metabolism is reduced due to reduction in thyroid hormone secretion, plasma growth hormone concentration and secretion rate, ruminal pH and gut motility in heat stressed cattle. Major changes in dietary electrolyte balance (Na⁺, K⁺, CL^¯ and the buffer HCO₃^¯) and acid/base balance associated with heat stress takes place.

2. Water intake: The total body water is estimated to range between 75 and 81% of the body weight for lactating dairy cows. Milk contains 87% water and large concentrations of the electrolytes Na, K, and Cl. Water and macro-mineral need increases heavily under heat conditions to maintain homeostasis and homeothermy. Under thermal stress cows tend to have increased water content in the rumen as a result of an accelerated water turnover rate. Moreover, there is need to compensate additional evaporative water loss. Heat stress increases water consumption by at least five times than normal level in temperate weather and three times more in tropical weather.
3. Milk production: It has been established that reduction in milk yield during heat stress is mainly, due to less feed intake on one hand and increased maintenance requirement, which reduce feed efficiency on the other hand. Milk yield usually reduce 10-15% or more during this period. The lactating cows are affected more with heat load due to increased metabolically derived heat associated with milk production, increased rate of respiration and rectal temperature leads to hyperthermia and milk production is reduced proportionately. This may also be explained by the negative effect of heat stress on the secretary function of the udder. There is reduction in daily output, lactation peaks, milk fat production, casein composition, milk component levels and increase in SCC levels. Similarly, higher environmental temperature during last three months of gestation alters blood flow and prolonged hyperthermia interferes with normal placental growth and endocrine function, which results in lower calf birth weight and hormonal alterations affect mammary development and lactogenesis. Reduced hormonal activity particularly thyroxin hormone during pregnancy affects metabolic state of the dam at parturition and thus reduce mammary development prior to the initiation of lactation which ultimately leads to poor milk production.
4. Effect on reproductive efficiency: Adverse effects of heat stress on reproduction include reduction in estrous activity, estrous duration, heat detection, follicular development, oocyte quality, semen quality, conception rate, pregnancy rate, uterine function, multiple ovulations and twinning, suppressed intensity of estrus, a reduction in the strength of the preovulatory LH surge, a decreased secretion of progesterone, altered follicular development, decreased embryo development as well as fetal growth and reduced fertility. Conception rate declined from 61 to 45% when rectal temperature 12 h post breeding increased 1°C.

Besides these some other impacts of heat stress on reproduction has been observed

• Decreased uterine blood flow
• Increased embryonic death
• Reduced placental mass
• Reduced fetal tissue growth
• Reduced mammary tissue growth
• Early calvings
• Light, weak or dead calves
• Lower colostrum immunoglobulin (IgG)
• Lower colostrum protein, fat, and lactose
• Lower calf blood protein levels
• More “quiet heats”
• Unsynchronized ovulations
• Fertility failure
• Decreased growth, size and development of ovarian follicles
• Abortion and retained placenta cases are more for cows calving during the summer.
• Cows calving during hot months show longer calving to conception intervals, more services per conception
• Heat stress during the dry period may alter the development of the placenta.

5. Oxidative stress: Heat stress generally increases the production of free radicals, leading to oxidative stress. In dairy cows, oxidative stress has a negative impact on immune and reproductive functions viz. increased mastitis frequency and higher somatic cells counts in milk, decreased fertility, increased embryo mortality, post-partum retained placenta and early calving, with consequences on the calves live weight, mortality and health.
6. Effect on Health of Dairy cows: During hot and humid weather conditions, the animals become more vulnerable to diseases. There is an increase in the somatic cell counts (SCC) and a higher incidence of mastitis and increase in number of flies during summer aggravates the situation.

Heat stress can result in sick cows, which require prolonged care. It is associated with difficult births, heat exhaustion, fatty liver in fresh cows. Heat stress can contribute to lameness, perhaps due to acidosis or increased output of bicarbonate. As ambient temperatures rise, the respiratory rate increases with panting progressing to open-mouth breathing. A consequence is respiratory alkalosis resulting from a rapid loss of carbon dioxide. The cow compensates by increasing urinary output of bicarbonate, and rumen buffering is affected by decreased salivary bicarbonate pool.

Ameliorative measures to reduce summer stress or heat

To prevent the effects of heat stress, economically feasible heat stress relief techniques can be used which include the use of fans, shades, foggers, misters, desert coolers, air conditioners, water bathing and adequate air circulation. Modifications in feeding strategies by either dietary fiber adjustment or the use of high-quality forage, supplemental protected fat and feeding at cool hours can greatly help in reducing the negative effect of heat stress on productive and reproductive performance.

1. Physical protection: Trees are an excellent natural source of shade on the pasture and cools the surrounding air. Solar radiation is a major factor in heat stress can be blocked by use of properly constructed shade structures alone increases milk production remarkably.

Besides these some of the protective measures are

• Avoid overcrowding
• Do not keep the animals in the holding area for long time. The holding area is a very crowded and poorly cooled area in many farms.

• The air flow over the cow housing area should be 4-5 mph.

2. Environmental temperature reduction measures

Air temperature of micro-environment can be lowered by air conditioning or cooler, fogger, misters and fan etc. but the expenses of such types of air cooling make these impractical. The evaporative cooling pad and a fan system which uses the energy of air to evaporate water is a more economically feasible method to cool the micro-environment.

3. Nutritional dietary manipulation: Evaporative heat loss through sweating, frequent urination and panting is the primary mechanism for heat loss at high environmental temperatures. Besides this following manipulations in feed and feeding system can help to reduce the heat stress

• Increasing the amount of feed available during the cooler period of the day, early morning or late evening. Feeding 60 to 70 percent of the ration between 8 p.m. and 8 a.m. has successfully increased milk production during hot weather.
• Feeding of bypass protein.
• Increase the amount of concentrate by adding an energy-rich feedstuff such as maize, or other cereal, and reduce the amount of fiber in the diet.
• Allow for grazing during cool hours only.
• Minimize drastic change in ration.
• During heat stress rumen degradable protein should not exceed 61% of Crude Protein (CP).
• Management of the dietary electrolyte balance is based on adding essential body salts and electrolytes to the drinking water and feed.
• Adding water to diets may help DMI during summer months. Water will soften fiber feeds and reduce dustiness and dryness of the diet increasing palatability and DMI. A three to five percent addition of water is recommended
• To reduce rumen acidosis high energy, more palatable diets, with high quality, highly palatable forages should be provided. On the other hand feeding of live yeast Saccharomyces cerevisiae CNCM I- 1077, improves rumen pH as a result reduce acidosis risk, improve fiber digestion and nitrogen utilization, increased feed efficacy, help in rumen microflora stabilization and helps in milk production.
• A well balanced (Total mixed ration) TMR will allow diets to be formulated at minimum fiber levels encouraging DMI and minimizing rumen fermentation fluctuations and pH declines.
• Use of anti-oxidants such as selenium enriched yeast help reducing the impact of heat stress on the oxidative balance, resulting in improved milk quality, immune and reproductive functions, prevention of retained placenta and reduced somatic cells
• Vitamin A, Vitamin E, niacin and selenium should be supplemented in diet during this period. Sometimes zinc and biotin may also play important role.
• Provision of fresh and cooled water all the time is most important. Water tanks should be located close to the feeding area to encourage both DMI and frequent drinking.
• An increase in the levels of deficient nutrients sodium (0.4 to 0.5%, Sodium bicarb or Sodium sesquicarbonate), potassium (1.5%, potassium carbonate, potassium sulfate/ magnesium sulfate and potassium chloride) and magnesium (0.3 to 0.35%, magnesium oxide, magnesium sulfate) and decrease in chloride (go down to .25-.30 % in heat) may be helpful.

Besides the importance of providing shade, cooling measures and nutritional modification the following measures should also be taken into consideration as ameliorative measures.

• Reduce parlor walking distance.
• Reduce time in holding area.
• Improve ventilation.
• In areas of extreme heat, it is even more important for cows to give birth in good body condition because after parturition their dry matter intake will be lowered by heat stress, as well as the usual low intake immediately after calving.
• Fly control.
• Under these conditions dairy farmers must go for artificial insemination rather than using natural service of heat stressed bulls.
• Teat dipping with germicidal dips is recommended.
• Handling cattle can elevate their body temperature by as much as 3.5^O Therefore avoid handling during intense heat.

4. Reproductive management: Anoestrus and silent heat is the common problem in buffaloes leads to summer infertility during summer season by which the calving interval and conception interval may be exceed more than 1.5 years. So, always try to keep the buffaloes under good environmental condition and detection of heat by the teasure should be recommended and artificial or natural insemination can be provided during cool environmental condition.
5. Development of heat tolerant breeds: Government and scientist should emphasize the identification and development of heat tolerant breed to reduce the risk hazards against heat stress condition. So, identification of gene responsible for heat tolerancy can be identify and incorporate such genes to a particular species and breed to combat the adverse effects of summer stress condition by genetic engineering method.

Conclusion: Heat stress is an inevitable part of life during the summer for livestock especially dairy animals in India. The livestock growth, productivity and reproductive efficiencies are very much affected with extreme of environmental variables. Summer stress severally affects the performance of dairy animals in terms of growth, production and reproduction and ultimately the farmer’s bears a huge loss from their animals. Hence we should convey the importance of summer stress management to our livestock farmers by adopting ameliorative measures in terms of physical protection, environmental protection, dietary manipulations, health management, reproductive management and development of heat tolerant breed to achieve the maximum profit, so that the farming community can achieve maximum profit from dairy enterprises and improves their socio-economic conditions.

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