Impact of Dietary Protein on Yield and Composition of Sow Milk

The aim of the current study was to determine the effect of increased dietary protein for lactating sows on yield (MY) and composition of milk. A total of 594 sows (parity 1 to 5) were randomly allocated to one of six diets with standardized ileal digestible (SID) CP of 96, 110, 119, 128, 137, and 152 g/kg. The dietary contents of SID Lys, Met+Cys, Thr, and Trp fulfilled Danish recommendations by including crystalline amino acids. The proportion of dietary Leu, Ile, His, Phe, Tyr, and Val relative to Lys increased with dietary CP because of a greater inclusion of soy bean meal. The study was initiated at litter standardization (14 piglets; d 3 postpartum) and was completed at weaning (d 26) when the litter weight was recorded. The ADG of the litter and the average litter size were used to estimate the MY (Hansen et al., 2012). On a subsample of 12 sows per dietary group, milk samples were obtained at day 4, 11, 18, and 25 postpartum. Milk samples were analyzed for lactose, fat, and protein. Milk gross energy (GE) was estimated, using the equation after (Chwalibog, 2008): GE (MJ/100 g) = 39.8 x milk fat + 23.8 x milk protein + 16.5 x lactose, in which milk constituents appear in percentage. The experimental design was a complete block design and in the statistical analysis, the individual dietary SID CP concentration of each sow was used. Linear or curvilinear responses were determined for the milk constituents, and estimated MY was analyzed, using linear and linear broken-line models. Litter size at weaning (13.1 ± 0.05; P = 0.62) was not affected by the treatment. Estimated MY was affected by parity (12.7 vs. 13.2 kg/day for first vs. multiparous sows; P<0.001), however the maximum was reached at the equal breakpoint (126 g dietary SID protein/kg). Lactose was not affected by treatment (P = 0.16), having an average on 5.2 ± 0.01%. Milk protein increased linearly with expanding dietary CP from 4.1% in group 1 to 5.1% in group 6 (P < 0.001). Milk fat peaked at 110 g dietary SID protein/kg (P <0.05), and milk GE peaked at 120 g dietary SID protein/kg (P <0.05). In conclusion, a dietary content between 110 and 126 g dietary SID protein/kg was required for maximizing sow MY and milk contents of fat and energy, whereas milk protein increased without reaching a plateau.