Effects of soybean meal concentration in lactating sow diets on sow and litter performance and blood criteria

A total of 131 sows (Line 241; DNA, Columbus, NE) were used in a study to evaluate the effect of increasing soybean meal concentration in lactating sow diets on sow and litter performance. Sows were blocked by body weight (BW) within parity on day 112 of gestation and allotted to one of three treatments of increasing dietary soybean meal (25%, 30%, or 35% of the total diet). Diets were formulated to 1.05% standardized ileal digestible lysine (Lys) with L-Lys HCl decreasing as soybean meal increased. All other amino acids and nutrients were formulated to meet nutrient requirement recommendations. Diets were fed from day 112 of gestation until weaning (day 20 ± 2). Litters were cross-fostered up to 48 h after farrowing to equalize litter size. Increasing soybean meal concentration increased (linear, P = 0.017) sow BW loss and tended to increase (quadratic, P = 0.052) sow backfat loss from farrowing to weaning. Sow average daily feed intake (ADFI) from day 0 to 7 was similar (P > 0.10) across dietary treatments. However, from day 7 to 14, 14 to weaning, and overall, ADFI decreased (linear, P = 0.01) as soybean meal concentration increased. Despite the linear response in ADFI, the greatest decrease was observed as soybean meal concentration increased from 30% to 35% of the diet. There was no evidence for difference (P > 0.10) in wean-to-estrus interval, litter size, litter weight, or litter weight gain between dietary treatments. Sow serum urea nitrogen concentrations taken on day 14 of lactation increased (linear, P = 0.001) as soybean meal concentration increased. There was no difference (P > 0.05) for sow creatinine concentration, regardless of dietary treatment, suggesting that the increased urea nitrogen was a reflection of the increased dietary crude protein as opposed to increased protein catabolism. In summary, sow feed intake decreased and weight loss increased as soybean meal concentration of the diet increased, with the greatest decrease observed at 35% of the total diet. Although there were no differences in litter performance, it appeared that 35% soybean meal in the lactation diet negatively affected feed intake.