Analysis of lactation feed intakes for sows including data on environmental temperatures and humidity

Daily feed intakes (DFI) of 565 lactation records were evaluated for sows of 2 genetic lines, PIC C-22 and L-42. Sows were fed ad libitum during the entire 21-d lactation period with a diet supplemented with either 0 or 0.3% betaine-HCl. Sows were fed corn-soybean based diets (3.32 Mcal of ME/kg). The DFI data were fitted to generalized Michaelis-Menten functions of day of lactation. The generalized Michaelis-Menten function {DFIi, t (kg/d) = DFI0 + (DFIA − DFI0)(t/K)C/[1 + (t/K)C]} with 2 random effects for DFI (dfiAi) and intercept (dfi0i) with K as a linear function of dfi0i provided the best fit to the DFI data (R2 = 0.474). The addition of a single covariate including daily degree-hours above 24°C (DGH24), daily maximum temperature (MaxT), or daily mean temperature (MeanT) of the current day were considerable (P < 0.001). Furthermore, the addition of either a second covariate as the prior day DGH24 or MaxT to the single covariate models with current day DGH24 or MaxT was significant (P < 0.001). No genetic line differences were found for the random effects dfi0i and dfiAi. Betaine-supplemented sows had a 0.27 kg/d greater mean for dfiAi (P = 0.004). Substantially greater DFI was found at the end of lactation in betaine-supplemented parity 1 and parity 2 sows (P = 0.012 and 0.005, respectively). Parity was important for both random effects (P < 0.001). Parity × treatment and genetic × parity interactions were found for dfiAi (P = 0.006 and 0.049, respectively).