PSIV-16 - Production impacts of a wild-type 1-7-4 lineage 1A porcine reproductive and respiratory syndrome virus introduction on a naïve batch farrow sow herd

Abstract: Porcine reproductive and respiratory syndrome virus (PRRS) is one of the costliest diseases in swine, with an estimated 1.2B USD impact to the US swine industry each year (Holtkamp et al., 2024). Clinical signs often include abortions, reduced vitality and livability, poorer reproductive performance in sows, and increased mortality and respiratory distress in post-weaning pigs. In December 2023, a 1,000 head research sow farm experienced a wild-type 1-7-4 lineage 1A PRRS introduction. The sow farm operates as a batch farrow system with 216 farrowings per batch every 5 weeks. Gilt development is onsite with incoming gilts arriving at weaning. All sows and piglets are tagged with an RFID tag used to monitor and record individual pig lifetime production. Cross-fostering is carried out within 24 hours of birth and standardized to teat count. Farrowing rooms are equipped with an electronic feed system that allows for individual sow feed deliveries and intake measurements. Piglets are weighed individually at birth and weaning. Onset of clinical symptoms associated with PRRS occurred approximately 14 days post-farrowing and included reduced sow lactation ADFI and increased abortions in gestation. Tilmicosin was added to gestation and lactation feeds and tulathromycin administered to all pigs at processing and weaning following introduction. Live virus inoculation was completed within 4 weeks of disease onset at the veterinarian’s recommendation. Circulation of PRRS virus was detected in processing fluids and due-to-wean pig serum for approximately 5-6 months. Farm baseline production data were retrospectively compared to the 5 months after PRRS break to determine the impact of PRRS break on production metrics. Total born was reduced 0.9 pigs/litter while born alive was reduced 4.4 pigs (29.1%; P = 0.02), stillborn percentage increased 50% (8.4% to 12.6%; P = 0.02), and incidence of mummies increased from 1.9% to 20.5%, an 18.6% unit increase (P < 0.001). Pre-wean mortality increased (P = 0.002) from 15.0% to 28.2% average, with the greatest increase being in the January 2024 farrowing (57.6% PWM). Average wean weight was reduced for two groups before recovering to above baseline values, largely due to reduced competition from reduced pig numbers. Pigs weighing less than 3.63 kgs at weaning was also increased (P = 0.02) for two farrowing groups after break. Sow heat by day 5 was reduced (P = 0.02) by 5.7% units and resulting conception rate was reduced (P < 0.001) by 9.2% compared to baseline. Furthermore, downstream nursery mortality was increased (P = 0.002) from 4.8% to 12.4% for the pre- and post-PRRS break periods. The farm had significant production impacts from the wild-type PRRS introduction, but clean biosecurity breaks and the batch farrow flow allowed much of the production interruption to be largely limited to the initial 2-3 batches post-break.