Determining the appropriate soybean meal inclusion level in lactation diets for sows endemically infected with porcine reproductive and respiratory syndrome virus (PRRSv) (2025)

Soybean meal (SBM) contains many bioactive compounds, such as isoflavones, which possess anti-inflammatory and anti-oxidative properties that may provide nutritional intervention to pigs infected with porcine reproductive and respiratory syndrome virus (PRRSv). The disease results in abortions, stillborn piglets, and overall impairs reproductive success in sows. Today, there are no data available on feeding SBM to sows infected with PRRSv to mitigate the negative impacts of PRRSv on sow and litter performance. A total of 960 sows were used for this study at an endemically PRRSv-infected farm. There were 4 dietary treatments with 20%, 25%, 30%, or 35% SBM inclusion in the lactation diet. All dietary treatments were formulated to target 65g of standardized ileal digestibility (SID) Lys and 24.1 Mcal of metabolizable energy (ME) intake per day regardless of SBM inclusion. Daily feed intakes of sows were recorded prior to farrowing and throughout lactation. The total number of pigs born, pigs born alive, stillbirths, and mummies were recorded for each litter within 24h of farrowing. The individual body weight of each piglet was collected at birth and again at weaning. Pig mortalities were recorded for the entire lactation period. Body condition score (BCS) of sows at entry into farrowing room was not different (P = 0.32) among treatments, however BCS at weaning was at least 0.09 units greater (P ≤ 0.03) in sows fed 20% SBM compared to all other treatments. Sows fed 20% SBM in the diet consumed at least 1.74g/d more (P ≤ 0.05) SID lysine and 0.57 Mcal/kg more (P ≤ 0.05) metabolizable energy compared to all other treatments. The number and percentage of pigs born alive were not different (P ≥ 0.37) among treatments. The number of pigs weaned was not different (P = 0.71) among treatments. The coefficient of variation (CV) of the weight of total pigs born per litter was not different (P = 0.54) among treatments. Average starting weight, average weaning weight, and weaning weights CV were not different (P ≥ 0.19) among treatments. Average daily piglet gain was not different (P = 0.49) among treatments. Feed efficiency improved with higher SBM inclusion because of reduced feed intake, which significantly reduced BCS at weaning. As a result, sows fed the lowest SBM level (20%) ate more, maintained better BCS, and may be better positioned for future performance and longevity.