Lower farrowing rate in female pigs associated with higher outdoor temperatures in humid subtropical and continental climate zones in Japan

Abstract

The aim of this study was to examine the respective associations between farrowing rate and either environmental or production factors in female pigs in commercial herds. We analyzed 264,057 records of females serviced in 101 Japanese herds located either in humid subtropical or humid continental climate zones. Outside environment data were obtained from 21 weather stations located close to the respective herds. Mean daily average temperatures (Tavg) and relative humidity for the 21-day pre-service periods for each female were coordinated with that female’s performance data. Generalized linear models were applied to the data for each parity. Overall average farrowing rate (± SE) was 85.2 ± 0.07%, and the mean daily average temperature (range) and relative humidity were 15.0 (−8.1 to 32.7)°C and 68.1 (19-99)%, respectively. Higher Tavg was associated with lower farrowing rate in all parity groups (P < 0.05). Farrowing rates of females in all parities decreased non-linearly as pre-service Tavg increased from 15 to 30°C (P < 0.05). Decreases ranged from 83.1-71.3% in parity 1 to 85.1% to 80.0% in parity 5. Also, delayed gilt age at first-mating, re-servicing, and a weaning-to-first-mating interval of 7 days or longer were associated with lower farrowing rate in either gilts or sows, or both (P < 0.05). However, there were no associations between farrowing rate and either pre-service humidity (P ≥ 0.09) or lactation length (P ≥ 0.06) in any parity. Therefore, we recommend that producers pay particular attention to females at risk of having reproductive failure, and apply cooling systems to prevent a decrease in farrowing rate for heat-stressed female.