Lactation and Reproductive Performance of Sows Fed Heightened SID Lys or Vitamin C During Late Gestation

Abstract It is plausible that decades of genetic improvement for litter size have resulted in greater maternal and fetal metabolic demand requiring sows to consume more nutrients during late gestation. Recent research has indicated that primiparous sows may require 20 g SID Lys/d during late gestation. It has historically been accepted that vitamin C is a nonessential nutrient for pigs; however, recent research has indicated that it may improve birth and wean weights. Therefore, we investigated whether daily sow amino acid supply or supplemental Vitamin C would influence sow and litter performance during lactation and subsequent sow reproductive performance on a commercial farm. A total of 1,527 multiparous (average parity 2.4 considering mated gilts as parity 0) DNA 241 sows were blocked by breed group and parity within breed group and then randomly allotted to three dietary treatments: 1) Control (12.7 g SID Lys/sow/d), 2) once daily top-dress of 363 g/d soybean meal (CP 46.4%) to achieve 22 g SID Lys/sow/d, 3) once daily top-dress premix delivering 900 mg/d vitamin C. Sows were individually top-dressed from d 88 of gestation until moved to farrowing at approximately d 114 of gestation. Sows were weighed at entry and exit from farrowing, live piglets (N = 21,733) were weighed at birth and wean, sow and piglet mortality recorded, and a subset of farrowing duration (n = 422/treatment) and blood hemoglobin status change (n = 28/treatment) was measured. The experiment was conducted June to August 2025. Experimental treatment did not affect total born, live born, stillborn, mummies, piglet birthweight, farrowing duration, sow lactation weight change, nor piglet pre-wean ADG. However, pigs born to sows fed 22 g SID Lys/sow/d died at a greater (P 0.0001; 13.68%) rate than pigs born to sows fed Control (10.68%) or vitamin C (11.21%) resulting in 0.52 more pigs weaned/litter in Control fed sows versus 22 g SID Lys/sow/d sows (12.67 vs 12.15, respectively, P 0.0001). Sows fed 22 g SID Lys/sow/d also had greater (P 0.05) wean-to-estrus interval than Control sows. These results indicate that the late gestation SID Lys requirement is less than 22 g SID Lys/sow/d and that dietary vitamin C has no positive effects on sow or litter performance. Additionally, these data indicate that overfeeding protein during late gestation may negatively affect pre-wean mortality and wean-to-estrus interval.