Heat Stress in Fattening Pigs: Which Indicators Can Reveal Reduced Welfare?

Fattening pigs suffer when it is hot. Timely provision of cooling measures increases both animal welfare and success in pig fattening. Researchers at Agroscope examined which indicators reliably indicate heat stress in fattening pigs.  

Prolonged heat periods can compromise the welfare of pigs. Furthermore, heat stress has negative effects on performance and thus on the profitability of production. Pigs are especially sensitive to heat because they have no functional sweat glands and can only release heat by panting. Therefore, heat can quickly become critical for the animals. To avoid an increase in body temperature due to digestive heat production, pigs limit their activity and feed intake. Another effective strategy is to avoid body contact with their pen mates if enough space is available. To dissipate heat, pigs seek cool, humid floor surfaces and increase the area of contact between body and floor by optimizing their lying position, that is, by lying on their side with stretched-out legs instead of lying in sternal recumbency.

Heat stress is especially problematic in the finishing stage

Pigs in the finishing stage are especially affected by heat stress because they have a fast metabolism due to the high daily weight gain and can dissipate heat poorly owing to the less favourable ratio of body surface to body volume. Heat-stressed fattening pigs try to increase heat release via their skin.

Indicators of heat stress in pigs

Farmers should be able to detect heat stress at an early stage and respond by providing cooling measures. The study examined several behavioural and physiological parameters in 72 fattening pigs of three weight classes (40–100 kg) during one month in summer. The core body temperature, measured with a vaginal temperature logger, showed high variability between individuals and did not increase with increasing ambient temperature. The respiration rate was highly variable and increased only in the heaviest pigs. By contrast, the body surface temperature, measured via thermal imaging, increased in all weight classes with increasing ambient temperature. The assessed behaviour was mostly independent of the ambient temperature. The percentage of pigs lying in sternal recumbency increased with increasing ambient temperature.

Respiration rate, skin temperature and lying position indicate heat stress

In summary, the results of the study suggest that respiration rate, skin surface temperature and lying position are reliable indicators of heat stress in fattening pigs.