Feed intake of lactation diets by sows during extended lactation periods

The objectives of this research were to quantify and model daily feed intakes (DFI) of lactation diets to 28 d of lactation in modern sows. A total of 4,512 DFI records were collected for 156 Hypor sows from February 2015 to March 2016. The mean lactation length was 27.9 ± 2.0 d, overall mean = 7.31 kg/d). Data included 9 parity 1, 33 parity 2 and 114 parity 3+ sows. Data were collected using a computerized feeding system (Gestal Solo, JYGA Technologies, Quebec, Canada). The feeding system was used to set an upper limit to DFI for the first 7 d of lactation. Overall, the least-squares means of a model including the random effect of sow indicated that DFI’s continued to slowly increase to 28 d of lactation. The DFI data were fitted to Generalized Michaelis-Menten (GMM) and polynomial functions of day of lactation (t). The GMM function [DFI_i,t (kg/d) = DFI₀ + (DFI_A – DFI₀)(t/K)^C/[1 + (t/K)^C]] was fitted with 2 random effects for DFI (dfi_Ai) and intercept (dfi_0i) using the NLMIXED procedure in SAS^®. The polynomial function DFI_i,t (kg/d) = [B_o + B₁ t + B₂ t² +B₃ t³ + B₄ t⁴] was fitted with three random effects for B_o, B_1, and B₂ using the MIXED procedure in SAS^®. Fixed effects models of the two functions had similar Akaike’s Information Criteria (AIC) values and predicted DFI’s. The polynomial function with 3 random effects provided a better fit to the data based on R² (0.81 versus 0.79), AIC (14,709 versus 15,158) and RSD (1.204 versus 1.321) values than the GMM function with two random effects. The random effect for B₂ allowed for the fitting of the function to lactation records that had decreased DFI after 15 d of lactation. The random effects were used to sort the lactation records into three groups based on the derivative of the polynomial function at 21 d of lactation. Lactation records of the three groups had similar DFI the first two weeks of lactation (P > 0.40). The three groups of sows had substantially different DFI’s after 21 d of lactation (10.7, 9.1 and 6.9 kg/d, P < 0.001). The differences in actual and predicted DFI’s between the three groups increased with each day of lactation to day 28 (P < 0.001). Mixed model polynomial functions can be used to identify sows with different patterns of DFI after 15 d of lactation.