by Yadav Sharma Bajagai
Swine are particularly susceptible to increased environmental temperature because evaporative cooling by sweating is of limited value to them due to barely functional sweat glands. Impacts of thermal stress on pig due to increased ambient temperature are described here briefly.
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Impact of thermal/climatic stress in feed and water intake
It has been shown that pigs under thermal stress consume more feed during cool hours of the day (morning) than during hot hours (afternoon) and drink more water during hot hours (afternoon) than during cool hours (figure 1 and 2) . Overall consumption of feed is lower in the area of high temperature than in area of thermal comfort  and water consumption is higher in high temperature condition . Reduction in feed consumption may lead to weight loss and reduced reproductive performance .
Figure 1: Pattern of feed intake in pig kept with thermal stress (daily temperature fluctuation = 20 to 350C) – reproduced from Patience et al. .
Figure 2: Pattern of water intake in pig kept with thermal stress (daily temperature fluctuation = 20 to 350C) - reproduced from Patience et al. .
Physiological response of climate warming/heat stress
Respiration rate in pigs under thermal stress is up to seven times higher than that in pigs in thermal comfort (figure 3) [1, 3, 5, 6]. Similarly, rectal temperature and heat rate are higher in these heat stressed pigs [1, 3, 4, 5, 7]. Partial pressure of oxygen (pO2) in blood is also decreased during thermal stress .
Figure 3: Effects of heat stress on respiration rate in pigs at 19:00 o’clock - reproduced from Patience et al. 
Impacts on reproduction
Female swine exposed to thermal stress immediately after breeding have lower conception rate and higher embryonic death as compared to the animals in controlled environment [3, 4, 6, 7]. In contrast, heat stress during mid-pregnancy has less effect to the swine as compared to animals in early and late pregnancy . Heat stress during late pregnancy results in larger number of stillbirths and lower birth weight of new born piglets . Litter size in pig exposed to high ambient temperature is also smaller . Edwards and his colleagues  reported that length of estrus cycle is longer in the swine exposed to thermal stress. Reduced reproductive efficiency of swine during heat stress is attributable to alteration in endocrine function of the animals .
In addition, Quality of semen (motility and proportion of normal acrosome) has been found to be deteriorated by high ambient temperature .
Impacts on health
All animals under thermal stress die at rectal temperature of 430C and above . Similarly, Escherichia coli in the intestine of swine became more resistant to antimicrobial drug when exposed to thermal stress . Incidence of mycotoxicosis may increase in warm climate due to better growth of fungi in feed during warm climate [10, 11, 12]. In addition, climatic warming may establish new vectors of disease which can transmit diseases among animal populations .
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