HEAT STRESS ▶▶▶


Heat stress is not only an environmental issue


The challenge of heat stress is a complex one, and the best way to tackle it is to seek a range of solutions rather than just one. That is why an approach revolving around animal and environmental management should be supplemented by a nutritional strategy.


BY FRANCESC PAYOLA AND MORGANE PIRIOU, WISIUM P


10 15 20 25 30 35 40


0 Weaning


igs are sensitive to heat stress as they are homeo- thermic animals and have few sweat glands and small lungs. In addition, the focus in genetics for many years has been on increasing performance


instead of animals’ resistance and adaptation to different stresses. To adapt to heat stress, pigs first increase their heat dissipation and then reduce heat production. The first step induces heat loss by conduction and evapora- tion. The reduction in blood flow to the digestive tract can re- sult in intestinal damage and reduced barrier function, result- ing in gut inflammation and reduced nutrient absorption. The second step, reducing heat production, is brought about through reduced physical activity but also lower feed and water intake. The thermoneutral zone of pigs, illustrated in Figure 1, extends from the lower critical temperature to the point where metabolic rate is actively reduced by heat stress – slightly below the upper critical temperature. The


Figure 1 - Thermoneutral zone of pigs. Hyperthermia zone


thermoneutral zone is also linked to the humidity level, expressed by the Temperature–Humidity Index (THI). The THI is still the best, simplest and most practical parameter for the measurement of environmental warmth that causes heat stress to animals.


Focus on heat stress impacts in sows In the US alone, heat stress is estimated to cost $ 900 million per year in swine production, and only half of that loss comes from decreased performance in the grower/finisher phase. The other half comes from impaired performance in the breeding stock, including phases of infertility and de- creased milk production. A number of studies have summa- rised the impacts of heat stress for sows, with identical con- clusions. The most challenging time is during the lactation period, when the ideal situation would be to have, in the same pen, two distinct climate zones: a cooler one for the sow to ensure her welfare and thermoneutrality and a warmer one for the piglets. Even in countries that are not considered hot, sows are suf- fering from the consequences of heat stress. These sows re- duce their feed intake during the lactation period, which can lead to a negative energy balance, a loss of body condi- tion and associated reproductive problems. They are very sensitive to heat stress and use various mechanisms to adapt, which have direct consequences for their own health status but also for that of their piglets. Reduced milk production can impact the weight of piglets at weaning. According to researchers Dr Nathalie Quiniou and Dr Jean Noblet in 1999, a decrease of 55 g/day in pig- lets’ average daily gain was observed when comparing pig- lets from sows that were in rooms at 18°C with the ones in rooms at 29°C.


Thermoneutral zone Hypothermia zone 10 20 Adapted from Baumgard et al., 2021 14 30 40 50


Live weight (kg) 70


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Solutions to deal with heat stress Nowadays, various solutions are available on the market to reduce heat stress risks, from nutritional solutions to environ- mental management. In that context, an R&D trial was con- ducted in a Brazilian commercial farm in São Paulo state in 2020 on two batches of sows for 2.5 months. Two experimental groups (40 sows per group, weaning at 26 days) were compared over the whole lactation period, re- ceiving either a conventional lactating diet or a nutritional


▶ PIG PROGRESS | Volume 37, No. 5/6, 2021


Ambient temperature (°C)


PHOTO: VINCENT TER BEEK


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