Development and Application of a Model of Heat Production for Lactating Sows

The objectives of this research were to develop a model of heat production for lactating sows to estimate differences due to genetics, parity, and day of lactation; and to estimate the magnitude of daily sow to sow variation. The model was developed using NRC (2012). Sow body weight (BW), mean daily litter weight gain (Cabezón et al., 2016a), and daily feed intake (DFI) data (Cabezón et al., 2016b) from 317 sows of 2 genetic lines C-22 (n = 164) and L-42 (n = 153) were used to predict the heat production (watts) for each day of lactation. The data were sorted in 4 parity groups, parity 1 (n = 80, P1), parity 2 (n = 57, P2), parities 3 to 5 (n = 142, P3-5) and parity 6 and greater sows (n = 38, P6+). The variance of the predicted mean daily heat production (PMHP, watts, d 1 to d 21 of lactation) was calculated using the partial regression coefficients and variances for sow BW, mean daily litter weight gain and DFI. A two-sample t-test was performed to test for significant differences for PMHP between genetic lines and parities. Parity group differences were similar for the genetic lines (P > 0.05). No differences were observed for PMHP between genetic lines (P > 0.05). The PMHP were 459.2, 507.3, 541.3 and 554.7 watts for P1, P2, P3-5 and P6+ sows, respectively. Parity 1 sows had less PMHP than all greater parity sows (P < 0.05). Parity 2 sows had less PMHP than P3-5 and P6+ sows (P < 0.05). No difference was found in the PMHP between P3-5 and P6+ sows (P > 0.05). The coefficients of variation were 18.4, 17.6, 17.1 and 15.5% for P1, P2, P3-5 and P6+ sows, respectively. Within a parity, variation in DFI accounted for approximately 95% of the variation in PMHP. The model was also applied to older data (Shurson et al., 1986; Noblet and Etienne, 1987) with lower sow productivity. The model estimated that the current sows produce approximately 24 to 39% more heat than past sows. Heat production increases with parity and there is substantial variation for PMHP within sows of the same parity. Strategies to remove the excess heat production of lactating sows in high environmental temperatures should try to account for sources of variation in heat production.