Effect of dietary protein for gestating sows on re-establishment of body reserves and impact on reproductive performance

This study aimed to investigate the effect of increasing dietary protein during gestation on sows’ ability to re-establish body reserves and evaluate the impact on reproductive performance of multiparous sows. The experiment was carried out in a commercial Danish herd and 431 sows were included and allotted to one of five dietary treatments. The treatment period extended from the time of service until the sows were moved to the farrowing section, approximately 5 d before expected farrowing. Experimental diets were isoenergetic and contained increasing concentrations of dietary protein (standardized ileal digestible SID lysine Lys; 3.37 to 6.39 g/kg). Sow body weight (BW) and backfat (BF) were recorded at service, on d 28 and 84 of gestation, and one to three days post-farrowing. Live and stillborn piglets and piglet birth weight were recorded. Sow body protein and fat were estimated; however, body fat estimations were considered inaccurate. Moreover, the feed and Lys to BW gain ratios were calculated. In early gestation, the BW and body protein gain of parity 2 to 3 sows increased linearly with increasing SID Lys (P < 0.001), while in mid-gestation BW gain had a polynomic response to SID Lys (P < 0.001), showing that BW gain was maximized at 5.0 g SID Lys/kg diet. Above the maximal BW gain sows’ body protein gain reached a plateau (P < 0.001) and Lys to BW gain ratio increased (P < 0.001), indicating oxidation of excess protein. In contrast, sow BW and body protein gain of parity 4 to 5 did not change with increasing SID Lys in most gestation stages, indicating that maternal growth was limited by energy intake. Sow BF gain did not change with increasing SID Lys, even though increasing SID Lys presumably increased the energy costs for protein retention or oxidation. Sow reproductive performances were not affected by dietary treatment, showing that fetuses are highly prioritized. In conclusion, sows of parity 2 to 3 re-established more BW and body protein than parity 4 to 5, when fed increasing dietary protein (SID Lys) during gestation. The dietary concentration of SID Lys did not affect sow reproduction in terms of litter size and average piglet birth weight; thus, SID Lys should be kept low during gestation until approximately one week prior to farrowing, and yet allow sows to re-establish sufficient body reserves for mobilization in the following lactation.