Heat Stress in Buffaloes under Tropical and Subtropical Climate: Part II
A.K.Wankar*,S.N.Rindhe1 and M.F.M.F. Sidddiqui2
* Assistant Professor, Department of Veterinary Physiology, College of Veterinary & Animal Sciences [MAFSU], Parbhani, Maharashtra, India
1 Assistant Professor, Livestock Product Technology Department, College of Veterinary & Animal Sciences [MAFSU], Parbhani Maharashtra, India
2 Assistant Professor, Department of Veterinary Medicine, College of Veterinary & Animal Sciences [MAFSU], Parbhani Maharashtra, India
*Corresponding author: Assistant Professor, Department of Veterinary Physiology, College of Veterinary & Animal Sciences [MAFSU], Parbhani, Maharashtra, India
Email ID: wankaralok@covaspbn.co.in, wankaralok@gmail.com
Continued from part I…..
ACCLIMATION TO ACCLIMATIZATION PHASE
Adaptation to a single stressor is comparatively easier than multiple stressors. In natural conditions single stressors are seldom present but animals are subjected to multitude of harsh conditions like high temperatures and humidity (THI), solar radiations, heat waves or lack of wind which makes them susceptible to heat stress. These multiple stressors challenge heat dissipation in animals, activating thermoregulation mechanisms.
Immediate effect of heat stress is increase in respiration rates, water consumption and depression in feed intake. Simultaneously, there are several alterations like in physical activity, standing and lying behaviours. Thereafter if heat loss by normal (conduction, convection, radiation) and unconventional means (evaporative cooling) are not adequate, heat load increases and core body temperature rises. Activation of nervous and endocrine systems enable acclimation during acute and chronic stress period and there is shift in energy metabolism, cellular mechanisms and molecular pathways. Expression of heat shock proteins (HSPS) finally complete the cellular acclimatization and there are dynamic alterations in molecular, enzymatic pathways and DNA and RNA functions (Collier et al., 2019). The severity of stress response is dependent on many factors like, duration and magnitude of heat stress and animal breed, species and general health. Although our native breeds are well adapted to harsh tropical summer, every year the intensity and duration of adverse climate is extending, making adaptation difficult. Also, there are sudden events like heat waves or solar flares, which compromise the homeothermy, subjecting livestock to heat stress.
PHYSIO-BEHAVIOURAL RESPONSES IN BUFFALOES DURING HEAT STRESS
The first sign of heat stress in animals is increasing in standing behaviour and elevated respiratory frequencies. When normal modes of heat loss are compromised, evaporative cooling is activated to ward off the excess heat. Panting is major heat loss mechanism in buffaloes accounting 90 % of total heat loss. Standing increases the available surface area and facilitates heat loss. As evaporative cooling utilizes copious volumes of water, slowly there is fall in total body water, leading to osmoconcentration and activation of thirst centre and increased water consumption.
Activation of panting for evaporative cooling also increases the maintenance energy and heat generation, therefore cannot be continued for extended bouts. This leads to gradual increase in core body temperature and also activates profuse salivation and sweating. Sweating is another form of evaporative cooling, although a minor one in buffaloes, accounting for less than 10 % of heat loss. In cattle sweating is major heat dissipation pathway (80-90 %). The gradual increase in core body temperature culminates into depressed feed intake, mainly due to cahnges in feeding patterns, rumen temperature, function, rumino-reticular motility, fermentation pathways, gut filling etc. There are essential cardiovascular changes and blood is diverted to peripheries for evaporative heat loss. Initially there is an increase in heart rate during acute stress, but gradually it normalizes or lowers, as seen during sustained heat stress. At this stage the metabolism is rewired, assisted by nervous and endocrine system. Alternate energy sources like fats and proteins are mobilized, cellular pathways, antioxidant and enzymatic machinery is modified, mediated by catecholamine’s, neurotransmitters and glucocorticoids hormones. Molecular stress chaperons like HSPS are expressed, mobilized and mediate cellular adaptation to stress (Mishra, 2021).
Physiological indices like increase in respiration rate, rectal temperature are considered good stress indicators, while heart rates can vary. Decreased feeding and reduction in eating frequencies, forage portions, ruminating, lying with higher water intake and continuous standing are important animal behaviours which confirm the severity of heat stress. Other metabolic and molecular markers including variety of metabolites, enzymes or proteins can be used as diagnostic tools to assess the stress and acclimatization levels in buffaloes, cattle and other livestock alike (Mishra, 2021).
NEGATIVE EFFECT OF HEAT STRESS ON PRODUCTION
During heat stress the animals priority is maintenance of thermoregulation and survival, so most of the energy is expended on it, leaving the animal in negative energy balance (NEBAL). The heat stressed animals have reduced growth, both prenatal and postnatal growth. These animals attain puberty late as compared to animals raised under ambient climate. Similarly the sexual maturity and production of gametes is also delayed. It is well documented that heat stress modulates the endocrine axes and reproductive functions are compromised in both sexes.
In bulls seasonal infertility in summers is very common and total spermatozoa’s count, sperm maturation and functions decreases significantly. While, the total morphological abnormal spermatozoa’s with suboptimum potential increases. Also, heat stress reduces the circulating concentration of testosterone, essential for male libido and sexual activity, influencing the sexual behaviour in bulls (Marai and Haeeb, 2010).
In females the follicular growth and dynamics is altered and seasonal anestrus is very common in buffaloes during summers. Suboptimum follicular growth, reduced production of estrogen leads to extended estrus cycle length. Another common observation is poor estrus expression in buffaloes during heat stress, mainly attributed to altered endocrine axes and behavioural changes. Also, the estrus is displayed in cooler night time making timely artificial insemination during heat stress or summer season nearly impossible. Other significant problems in buffaloes are failure of fertilization, implantation, abortions and poor fetal growth during heat stress (Marai and Haeeb, 2010).
The animals subjected to high environmental temperatures, radiations, humidity and THI, as an acclimatization response naturally decrease milk and meat production. Heat stress severity depends on the stage of lactation and especially early lactating cows are more susceptible. There is decline in total milk yield, herd milk yield and alterations in milk components like fat, protein, lactose and solid not fats (SNF). Generally, buffaloes produce milk with significantly lower fat, protein, sugar and SNF % during hot conditions (Wankar et al., 2021). Similar decrease in both meat production and meat quality is also evident in livestock during stressful period.
CONCLUSION
The buffalo is an important multipurpose animal in Asia and Africa, mainly reared for its valuable products and services. It is adapted to climatic conditions of the region, but natural phenotypic traits make it gain heat more quickly than cattle and subject it easily to thermal stress. Animals suffering from heat stress have compromised welfare, growth, reproduction and production. To obtain optimum production form the buffalo, under harsh tropical conditions, application of simple mamagemental practices like; allowing it to wallow regularly, use of shade, fans, coolers, foggers, sprinklers etc or environmentally controlled sheds is essential. With the climate change and global warming in recent years, it becomes pertinent to maintain our livestock under manageable conditions, which will ensure animal welfare and sustained food supply to humans.
REFERENCES
Collier, R.J., Baumgard, L. H., Zimbelman, R. B. and Xiao. Y. (2019). Heat stress: physiology of acclimation and adaptation. Animal Frontiers, 9(1): 1-19.
Marai, I.F.M. and Haeeb A.A.M. (2010). Buffalo’s biological functions as affected by heat stress — A review. Livestock Science, 127: 89–109.
Mishra. S.R. (2021). Thermoregulatory responses in riverine buffaloes against heat stress: An updated review. Journal of Thermal Biology, 96. 102844. https://doi.org/10.1016/j.jtherbio.2021.102844.
Wankar, A.K., Rindhe, S.N. and Doijad, N.S. (2021). Review-Heat stress in dairy animals and current milk production trends, economics, and future perspectives: the global scenario. Tropical Animal Health and Production, 53:70. DOI:10.1007/s11250-020-02541-x.
