Impact of PRRSV on Digestibility and Endogenous Losses in Pigs Fed High or Low Soybean Meal Diets

Porcine reproductive and respiratory syndrome virus (PRRSV) is a significant pathogen that antagonizes pig performance. Increasing dietary soybean meal during disease challenges may improve performance. Our objectives were to determine the impact of soybean meal level on apparent total tract (ATTD) and apparent ileal digestibility (AID) during PRRSV infection and to determine ileal and total tract basal endogenous losses during PRRSV infection. Forty PRRSV naïve pigs (~40 kg BW), were surgically fitted with a T-cannula in the distal ileum. Treatments were arranged as a 2x2 factorial (HSBM, 29% vs LSBM, 10%) with and without PRRSV (n=6/treatment group). The remaining 16 pigs (n=8/PRRSV status) were fed a nitrogen-free diet. Chromic oxide was used as an indigestible marker. On days post inoculation (dpi) 0, 20 pigs were inoculated with live PRRSV (strain 1-3-4); control pigs were sham inoculated. Infection was confirmed by serum PCR and seroconversion in all inoculated pigs. Feces were collected at dpi 5-6 and 16-17 and ileal digesta was collected at dpi 7-8 and 18-19. Feed, feces, and digesta were analyzed for DM, OM, N, and energy. Digesta and feed were also analyzed for amino acids. Data were analyzed in a 2x2 design to determine diet and PRRSV main effects and interactions. Control pigs remained PRRSV negative throughout the study. There was no main effect of PRRSV or diet by PRRSV interaction for AID values at either time point. There was no diet by PRRSV interaction for ileal amino acid digestibility. The HSBM diet decreased DM AID at dpi 7-8 (72.52 vs 77.87%, P<0.01) and tended to decrease DM AID at 18-19 dpi (70.16 vs 77.56%, P=0.09). There was an interaction for energy ATTD at dpi 16-17 (P=0.04), where PRRSV decreased energy ATTD in HSBM (86.42 vs 83.82%), while energy ATTD remained unchanged in LSBM (84.95 vs 84.97%) due to PRRSV. Similar results were observed for N ATTD; however, this was only a tendency (P=0.06). There was an effect of PRRSV to reduce DM ATTD (P=0.04) at dpi 16-17 regardless of diet. Interestingly, total tract endogenous loss of crude protein (Nx6.25) was increased due to PRRSV at dpi 5-6 (10.91 vs 4.90 g CP/kg DMI) and 16-17 (17.58 vs 10.78 g CP/kg DMI) in pigs fed a nitrogen-free diet. In summary, energy and DM ATTD were influenced differently by diet during PRRSV challenge, while AID remained unaffected. Endogenous loss of total tract N was increased due to PRRSV.