Giving birth outdoors: Impact of thermal environment on sows parturition and piglet survival

Summary

About one-third of the piglets born in organic pig production die before weaning at 7 weeks of age. Studies report varying piglet mortalities across the year with increases during summer and winter.The temperature inside the farrowing hut during summer may exceed the upper critical temperature for parturient and lactating sows, which may result in sows experiencing hyperthermia. This condition has been related to prolonged parturitions and lowered lactation performance. Thereby, hyperthermia increases the risk of stillbirth and postnatal mortality. Low temperature may cause hypothermia in piglets if nest temperature is insufficient and hypothermia is a common cause of early liveborn mortality. Thus, the main aim of the current PhD project was to quantify the thermal conditions inside the farrowing hut and to obtain knowledge about how these impact the course of parturition, thermoregulation in lactating sows and early piglet mortality.Four studies were conducted. Study 1 was an observational study including data collection at five commercial organic pig-producing herds. At each herd, data loggers placed inside A-frame huts recorded and stored temperature and humidity, and farmers recorded production results.The study showed that piglet mortality varied across the year with a lower risk of stillbirth during winter (Dec, Jan, Feb; P=0.004) and lower risk of liveborn death until castration in spring (Mar, Apr, May; P=0.009). During winter, the risk of stillbirth increased with increasing temperature variation between day 1 pre-partum and the day of parturition (P=0.013).During the remaining part of the year, the risk of stillborn piglets increased at hut temperatures ≥27°C (P=0.002). Hut temperature had no significant effect on postnatal mortality. Hut humidity affected neither the risk of stillborn piglets nor postnatal mortality. Study 2 was an observational study conducted at an experimental farm. Eighty-seven parturitions were video filmed, and the time of birth of each piglet was recorded along with sow posture during parturition. The results showed that an increase in parturition duration increased the risk of having litters with stillborn piglets (P=0.003) and the odds of liveborn
piglets dying before day 4 postpartum (P=0.051). The median parturition lasted 4.3 hours.Posture changes during parturition did not affect liveborn mortality. Study 3 was also an observational study, and data were collected at an experimental herd and at a commercial organic pig-producing herd. Again, sow parturitions were video filmed, and information on time of birth of each piglet and sow posture was recorded. Furthermore, data loggers recorded and stored hut temperature, and on day 1 to 3 postpartum sow surface temperature and respiration frequency were recorded. The results of Study 3 showed that the level of thermoregulation, on day 1 postpartum increased with increasing hut temperature, reflected by an increase in maximum surface temperature (P<0.001) and respiration frequency (P<0.001). Neither the duration of parturition nor the hourly number of posture changes during parturition were significantly related to hut temperature. Study 4 was an experimental study conducted at a commercial herd where 57 sows had access to poplars in the farrowing field. Behavioural observations of sows’ use of the paddock(14 sows with access to poplars and 14 without access) and sows’ use of the area with poplar trees (57 sows with access) were conducted. During Study 4,access to poplars in interaction with hut temperature affected the sows’ use of the farrowing hut (P=0.001). Sows with access to poplars were observed less inside the hut when hut temperature increased, whereas this was not the case for sows without access to poplars. The odds of observing sows inside the poplar tree area were not significantly affected by hut temperature. On the contrary; when sows were inside the poplar area, the odds of sows lying increased with increasing hut temperature (P<0.001). Across the year, temperature inside insulated farrowing huts reached levels above the upper critical temperature of lactating sows and far below the lower critical temperature of neonatal piglets. High temperatures increased the risk of stillbirth, whereas no effect of high or low hut temperature could be shown for postnatal mortality. This could be due to 1) sows being able to thermoregulate through behaviour postpartum thereby avoiding potentially negative impacts of high temperature on lactation performance and 2) a sufficient microclimate in the nest reducing negative effects of low ambient temperature. A prolonged parturition increased the risk of piglet mortality. However, hut temperature did not significantly affect the course of parturition, which was likely due to the relatively low hut temperatures measured even during the warmest periods of the study. Increasing hut temperature resulted in increased level of physiological thermoregulation reflected as increased sow surface temperature and respiration frequency. At increasing temperature, sows inside the poplars were more often lying, suggesting they thermoregulated using behavior.In conclusion, high hut temperature contributed to piglet mortality by increasing the risk of stillborn piglets, whereas, with proper management, low temperature appeared to have no negative impact on piglet mortality.Thus,counteracting high temperatures during the warm part of the year seems essential for piglet survival.