Heat Stress in Pigs and its Management

Heat stress in Pigs and its management

Abstract: Heat stress highly affects the pork industry. Specifically losses induced by heat stress results from poor sow performance, reduced growth, lowered carcass quality, mortality, morbidity difficulty in processing caused by less rigid fat tissue also known as flimsy adipose tissue. When environmental conditions exceeds the pigs thermal natural zone and results in  less supply of nutrient to the foetus, less milk production, less body muscle gain thereby compromising the efficiency. Genetic selection for high litter size and lean meat type leads to decrease in tolerance to heat. Advances in cooling system management have partially elevated the negative impacts of heat stress but productivity continues to decline during the warm summer months. The detrimental effects of heat stress on animal welfare and production will likely become more of an issue in regions most affected by continued climate change. Therefore, heat stress is likely one of the primary factors limiting profitable animal protein production and will certainly continue to compromise food security and pork production in developed countries. Thus there is an urgent need to have a better understanding of how heat stress reduces animal productivity.

Key words: Homoeothermic, stocking densities, endotoximiea, lipopolysacchride, farrowing, polydipsia, polyurea.

Introduction

Animal husbandry and livestock sectors are critical for rural livelihood and economic development of the country. Among the livestock species pig finds an important place as it being reared by socioeconomically weaker section of the society. Pig as compared to other livestock species has a great potential to contribute to faster economic return to the farmers, because of certain inherent traits like better feed conversion efficiency, early maturity and short gestation interval. Pig farming also requires small investment on buildings and equipments. It has eminence potential to ensure nutritional and economic security for the weaker section of the society.

As we all know that the climate of India is changing. The period of heat stress will increase in frequency and in length hence causing production losses by causing weakness, diarrhoea etc. pigs are homoeothermic animals ie they are unable to maintain internal body temperature of 39ºc as compared with other animals. The pig is less tolerant to hot and humid weather conditions due to inability to sweat. Heat stress can occur in all classes of pigs under a wide range of production system during periods of high ambient temperatures. Adult pigs and sows are more sensitive to heat stress as compare to younger pigs (sucklers and weaners). Heat stress not only causes unnecessary suffering to animals and even death but also reduces productivity and consequently profitability.

Heat stress occurs in temperate states of India like Punjab, Haryana, Uttar Pradesh, and Madhya Pradesh, Delhi etc. during summer months and in tropical states like Gujarat and Rajasthan during the whole year.

Causes of heat stress

Most animals can transfer internal heat to the outside of the body by sweating and panting , these are two most important tools for the maintenance of body temperature and from their inbuilt evaporative cooling system .However, pigs do not sweat and have relatively small lungs. Due to these physiological limitations and their relatively thick subcutaneous fat, pigs are prone to heat stress.

• Temperature: In pigs the zone of thermal comfort is simply the range of temperature in which the animal (pig) is not cold or hot (18-25℃), which is very difficult to maintain in field conditions, when environmental temperature is 35-40℃. Zone of thermal temperature also depends on humidity and animal weight .pigs over 75 kg body weight is more sensitive to heat stress. Table showing body weight v/s ideal temperature of the pig sheds

• High humidity: Pigs generally develop heat stress at much lower temperature when humidity is high.
• Exposure to direct sunlight: when the animals are exposed to direct sun light accidently or due to faulty sheds the respiratory rate, distress, rectal temperature rises to 43℃. This effect all ages of pigs.
• Poor ventilation in indoor houses: This happens due to poor management of animals, when the cooling devices/natural ventilation system fails to create the required temperature zoon in the animal pens.
• Shortage of water: Inadequate supply of water and hot water results in heat stress.
• Composition of feed: Feed play important role in heat stress. Dry feed, feed having high fibre and high protein is not good in summer season.

Clinical signs of heat stress

When internal body temperature of animal increases and it reaches a point where it can no longer increase moisture loss via high respiration rate, this state of animal is called as “heat stress emergency” point. The lungs of pigs are very small as compare to other animals. The animal may pant fast but without any relief, this can lead to death of the animal.

• Panting
• Increased morbidity and mortality rates
• Increased risk of endotoxemia: Hot and humid weather increases the chance of mycotoxin contamination on the feed and under storage conditions. The major organ first affected by heat stress is GIT due to redistribution of blood to the extremities to support heat loss (et.al 2002). As a result intestinal function and integrity are reduced and this can increase the risk of acute endotoximiea within 2-6 hours of heat stress exposure in pigs (Pearce.et.al 2012-13). Enodotoxins are also known as lypopolysacchrides and in pigs LPS is potent immune stimulator that induces inflammation and antagonize protein synthesis (Webbel. et.al 1997).
• Reduced growth rate
• Reduced feed efficiency
• Changes in carcass composition and quality
• Delayed time to oestrus: Heat stress produces seasonal infertility in sows and decreases reproductive efficiency and increases weaning to estrus interval, further resulting in anoestrus.
• Reduced pregnancy rates: This condition is due to poor semen quality of boar.
• Reduced farrowing rates
• Lethargy when moving
• Reduction in feed intake
• Retarded growth in grower pigs
• Less milk production in farrowing sows
• Diarrhoea
• Increase in water intake ( Polydipsia)
• Increase in urine output ( Polyurea )
• Prolonged reduction in semen quality: The health and good quality semen directly related to conception and litter size. Sperm production occur at 2-4ºc below body temperature however as one third of boar testicles are inside the body, they are less effective at temperature regulation then other mammals with fully suspended scrotum. Heat stress related boar infertility can last up to 8 weeks following a period of hot weather. The testis operates as a production line with sperm at all stages of development being present at all times. If anything happens to the boar to damage this system it can take up to 8 weeks for new normal mature sperm to be produced.
• Effect of heat stress on sows : The effect of heat stress in sows include higher rectal temperature in sows post partum, higher respiration rates and prolonged farrowing, all leading to poor sow welfare. The effect in the first 5 days post insemination has been shown to significantly reduce the number of viable embryos.
• Piglets born from heat stressed sows have higher level of back fat in the grower phase. Effect of heat stress on lactating sows are reduced feed intake result in low milk production result in higher pre weaning mortality and reduced piglet weaning weight. This may also result in increase in weaning to service interval.

Management of heat stress in pigs

• Indoor housing and ventilation: Check all indoor ventilation units are working correctly to maintain the temperature near to comfort zone i.e. 20-25℃ and make ensure that any issue are corrected immediately. Stocking densities are reduced during periods of extreme heat if ventilation cannot be improved. Protect the pigs from direct sun light by applying shades or planting trees. Insulate the inner walls of pig houses and paint them with light paint colours

   Indoor house with ceiling exhaust fan

Clean the manure and urine properly from sheds because it releases heat and moisture during composition. Use water sprinklers, exhaust fans and ceiling fans to lower down the body temperature of animals as well as sheds.

     Water sprinklers in indoor housing

• Outdoor housing: In case of outdoor housing provide plenty of shade, artificial by applying canopies or natural by planting trees. Thatch roof are best for providing shades in outdoor housing. We can use sprinkler system around the house and create wallows.

         Outdoor housing

• Feed management: Distribute the feed into smaller meals, sufficient supply of fresh and clean water. Distribute the feed early in the morning and late in the evening. Provide wet feed instead of dry feed. When using dry feed; provide it in the form of pellets.

      Pelleted feed

• Use less fibre: Higher the fibre content in feed, the worse is digestibility. Undigested fibre goes to large intestine where it stimulates the growth of micro organisms that will generate heat in fermentation process.
• Lower the crude protein level: Less protein in feed and use more synthetic amino acids.
• Replace starch with fat as an energy source: Use more fat and less starch as energy source. Fats are excellent of energy for swine to compensate for lower feed intake. Fat is also a more digestible ingredient that generates less metabolic heat.
• Maintain the right electrolyte balance: as temperature increases, an animal breathing tension increases. Faster respiration takes more carbon dioxide out of the blood stream which is then exhaled. This changes the ph level in the blood leading to metabolic acidosis and lower feed intake. Blood buffer such as sodium bicarbonate restores the electrolytic balance and support feed intake.
• Water management: Provide plenty of clean and cold water in hottest hours of days. Allow pigs to use water to facilitate evaporative cooling by setting up water drip line or sprinklers to let pigs get wet. Be sure to also have space in the pen to allow them to dry. Without drying evaporation does not work to cool the pigs.

           Supply of fresh and clean drinking water (adlib)

• Provide shade: For pigs raised outdoors, shade provides a retreat from the sun, the primary source of heat, and minimises the possibility of sun burn for breeds with white hair and skin. Check your ventilation.
• Take care when handling animals: Animal handling should be fast because high temperature causes stress to animal. Handle the animal early in the morning or late at night will minimise added stress. Pig appetite should return in cooler temperatures use this to your advantage when transporting pigs.
• Management of boar and sow in summer season: The same measures must be taken for the boars and for sows during period of high temperature i.e provision of wallows and shades. Space is a critical factor that must be taken care i.e provide for ample space for lying. Reduce the amount of bedding used; this will insulate the boars from the cooling effect of lying directly on the ground. Record periods of hot weather on a calendar and remember to check semen quality for up to 8 weeks after the last period of heat stress.

We can help the sow to cope with heat stress challenges by genetic changes, environmental changes and nutritional strategies.

Reference

• Contents of this essay are practical experience of pig farming in Punjab. Images used in this article are taken from various pig farms in Punjab.
• J. and Kirkwood Scientific article, Seasonal infertility in gilts and sows: Aetiology, clinical implications and treatment 2017.

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