Seasonal variation of the climatic environment is known to adversely affect reproductive performance in sows. This study was designed to identify the period within the reproductive cycle when elevated ambient temperature has the greatest effect on the farrowing rate (FR) and to implement empirical relationships between temperature and FR according to the parity number of reproductive sows. The data consisted of 2,120,000 records on 497,541 sows from 780 commercial farms in mainland France and the island of Réunion collected from 2002 and 2012. Climatic parameters were provided by public meteorological stations located at proximity from pig farms (less than 10 km). Heat stress on a given day was measured in term of maximal temperature (Tmax). Pearson correlation coefficients were calculated between Tmax and FR for each day of the reproductive cycle and each sow. The pattern of the correlation coefficients during the reproductive cycle was fitted with a polynomial function. Consecutives days with greatest negative correlation between Tmax and FR were considered as the period for which Tmax has maximum effect on FR. Our results indicated that increasing Tmax between 26 and 5 days before the first insemination had largest impact on FR for primiparous sows. For multiparous sows, heat stress during 20 and 5 days before inseminations had largest effect on FR. The average of Tmax over these periods was then used to calculate polynomial relationships between heat load and average FR. In primiparous and multiparous sows, the relationship were as followed: FR (%) = 84.05 + 0.376×Tmax – 0.015×Tmax2 (adjusted R2=0.85) and FR (%) = 87.66 + 0.506×Tmax – 0.020×Tmax2 (adjusted R2=0.96), respectively. In multiparous sows, the second parity sows seemed to be more susceptible to heat stress than sows in later parities. These empirical equations could represent an interesting tool for predicting the consequence of warming climate of reproductive performance of sows.