Pearson correlations between farrowing rate of gilts (sows from parity 1) and daily temperature variables. Farrowing rate was corrected for the systematic effects of herd, year of insemination, the interaction between herd and year of insemination and service sire. Day zero was the day of first insemination in a parity. Vertical bars in a) and b) show SE of the correlations. Heat load in c) was estimated as deviation from the upper critical temperature (UCT) considering 3 levels of UCT (i.e., 15°C, 19.2°C, and 25°C). A sixth degree polynomial function was fitted to the correlations.