Influences of climatic parameters on piglet preweaning mortality in Thailand.

The objective of the present study was to determine the influences of temperature, humidity, and temperature-humidity index (THI) on piglet preweaning mortality in a conventional open-housing system commercial swine herd in Thailand. The analyzed data included 11,157 litters from 3574 Landrace × Yorkshire crossbred sows. The daily temperature, humidity, and THI data were collected from a meteorological station near the herd. The associations between temperature, humidity, and THI for periods before and after farrowings and piglet preweaning mortality were analyzed. Piglet preweaning mortality (log transformation) and the proportion of litters with piglet preweaning mortality greater than 20% were analyzed by using general linear mixed models and generalized linear mixed models (GLIMMIX), respectively. On average, the piglet preweaning mortality and the proportion of litters with piglet preweaning mortality greater than 20% were 14.5% (14.2 to 14.8% CI) and 26.4% (25.5 to 27.2% CI), respectively. Piglet preweaning mortality was positively correlated with the mean temperature (r = 0.028, P = 0.003), humidity (r = 0.038, P < 0.001), and THI (r = 0.036, P < 0.001) during 0-7 days postpartum. In primiparous sows, piglet preweaning mortality increased from 12.1 to 18.5% (+ 6.4%, P < 0.001) when the mean temperature during 0-7 days postpartum increased from < 25.0 to ≥ 29 °C. However, the influence of the temperature during 0-7 days postpartum was insignificant in multiparous sows (P = 0.569, P = 0.593, and P = 0.539 in sows parity numbers 2, 3-5, and 6-9, respectively). Likewise, piglet preweaning mortality increased from 10.7 to 16.7% (+ 6.0%, P = 0.012) when humidity during 0-7 days postpartum increased from < 60 to ≥ 80% in primiparous sows but it was insignificant in sows parity numbers 3-5 (P = 0.095) and 6-9 (P = 0.219). Moreover, the proportion of the litters with piglet preweaning mortality greater than 20% in primiparous sows increased from 18.3 to 32.4% (+ 14.1%, P = 0.017) when the THI during 0-7 days postpartum increased from < 73 to ≥ 81. In conclusion, the negative influences of temperature, humidity, and THI on piglet preweaning mortality were more evident in primiparous than multiparous sows. These findings implied that strategies to reduce temperature for postpartum sows in the open-housing system in Thailand are inadequate, and the proper management of postpartum primiparous sows should be emphasized.