We thank the producers and practicing veterinarians who have enrolled herds in POMP.
POMP is the largest structured, longitudinal PRRS outbreak dataset linking viral genetics, immunologic response, and whole-herd productivity outcomes in the US, enabling evidence-based decision-making during outbreaks. Thanks to our sponsors, we offer, at no cost to participants, financial support for diagnostic monitoring (i.e., PCRs and WGS sequencing) and help monitor the recovery of viral activity and productivity.
This virutal newsletter provides weekly benchmarks for key production indicators affected by outbreak-associated PRRSV lineages in breeding herds and whole-herd metrics (time to stability and piglet losses per 1,000 sows) with associated interventions used to manage the PRRS outbreaks derived from multivariable models.
To standardize events and metrics associated with the onset of PRRSV outbreaks in breeding herds enrolled in POMP, this newsletter uses the following definitions:
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Unit of analysis: herd-outbreak
POMP data including survey, diagnostic, production, PRRSV genotype, and recovery metrics data will be captured and organized into herd-outbreak, reflecting all metadata related to a particular outbreak of a given breeding herd. This means the same breeding herd can be enrolled in multiple instances over time – one for each distinct PRRSV outbreak.
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PRRSV outbreak date and Week 0 reference
The PRRSV outbreak date, designated as Week 0 for all analyses, is defined as a) the date provided by herd veterinarian, (b) the date of the first wild-type PRRSV-positive PCR result, or (c) when the first deviation in key productivity indicators such as abortions or pre-weaning mortality is detected – whichever happens first. PRRSV ORF5 sequences are used to determine lineage and variant for each herd-outbreak, and whether the outbreak is a new viral introduction or re-break.
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POMP metrics
- Time to Baseline Production (TTBP): Number of weeks from the PRRSV outbreak until recovering the pre-outbreak volume of weekly piglet production.
- Piglet Losses per 1,000 sows: Cumulative sum of piglets that were not weaned until TTBP standardized by 1,000 sows. Thus, herds differing in sizes can be compared.
- Time to Stability (TTS): Number of weeks from the outbreak until the first PCR-negative result followed by 3 months or 13 weeks of consistently producing PRRSV PCR-negative piglets.
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PRRSV herd status before the outbreak
The PRRSV status of each breeding herd before the outbreak date is classified according to the American Association of Swine Veterinarians (AASV) PRRSV herd-status classification system, as summarized in Table 1.
Table 1. Adapted from the American Association of Swine Veterinarians classification of PRRSV status in breeding herds
Adapted from: Holtkamp DJ et al. J Swine Health and Prod. 2021;29(5):261–270. doi:10.54846/jshap/1218 AASV Category Herd Status Practical Description I-A High Prevalence Positive Unstable PRRSV RNA is consistently detected by RT-PCR. Herds with an unknown PRRSV status are classified as I-A by default. I-B Low Prevalence Positive Unstable PRRSV RNA is detected on ≤ 25% of the routine samples tested. II Positive Stable Demonstration of 13 weeks of consistently RT-PCR-negative results in piglet sampling. Still ELISA-positive. II-vx Positive Stable with Vaccination Ongoing MLV use in gilts or sows. Demonstration of 13 weeks of consistently RT-PCR-negative results in piglet sampling. Two-weeks grace for testing given after breeding-herd vaccination. ELISA-positive. III Provisional Negative PRRSV-naïve replacement animals have been introduced and remain PCR and ELISA-negative. The older sows will still test ELISA-positive, piglets are expected to be weaned PCR-negative. IV Naïve The breeding herd is PCR and ELISA-negative and thus free of PRRSV infection.
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All Definitions together into one figure:
Understanding PRRSV outbreak recovery in a breeding herd. The red curve represents PRRSV shedding after the outbreak, while the blue area represents the temporary reduction in piglet production. The colored squares summarize weekly PRRSV PCR results: red squares indicate PCR-positive results and green squares indicate PCR-negative results. Time to baseline production (TTBP) is the time required for piglet production to return to the herd’s expected pre-outbreak level. Time to stability (TTS) is the time required to meet the PRRSV stability criteria based on consecutive negative PCR results. The top bars illustrate the progression of the herd through the AASV PRRS status categories, from unstable to stable.
15 outbreaks in 2026: The majority of the outbreaks enrolled thus far in 2026 were 1C.5.32. Unstable herds have been the most affected in the 2026 POMP database.
| Lineage | % all breaks | AASV status at the time of outbreak | % within lineages |
|---|---|---|---|
| L1C.5 (1C.5.32 variant) |
87% | IA or IB II or II-VX III or IV |
39% 52% 8% |
| L1H (1.H.9.51 variant) |
7% | IA or IB | 100% |
| L1A (1A-unclassified) |
6% | III or IV | 100% |
POMP benchmarks: Expected weeks to recover selected production KPIs among reference herds — AASV-negative or AASV-stable herds that pursued PRRSV elimination from the suckling piglet population and achieved both time to baseline production and time to stability within 52 weeks.
| Weekly KPI | 25th | Median | 75th |
|---|---|---|---|
| Aborts/1K sows (recover to ≤ 2 aborts/1K sows) | 4 | 6 | 9 |
| Dead Sows/1K sows (to recover 2 deaths/1K sows) | 0 | 0 | 3 |
| Dead Sows/1K sows (to fully recover the pre-break baseline) | 4 | 7 | 13 |
| % Stillborn (recover to ≤ 10% of total born) | 2 | 7 | 11 |
| % Stillborn (to fully recover the pre-break baseline or ≤ 7%) | 4 | 9 | 13 |
| % Mummies (recover to ≤ 7% of total born) | 2 | 16 | 20 |
| % Mummies (to fully recover the pre-break baseline or ≤ 4%) | 7 | 20 | 22 |
| % Pre-wean Mortality (recover to ≤ 12.5%) | 11 | 13 | 17 |
| % Pre-wean Mortality (to fully recover the pre-break baseline) | 15 | 18 | 20 |
| Time to Baseline Production (TTBP)1 | 22 | 26 | 28 |
| Time to Stability (TTS)2 | 34 | 42 | 47 |
1 Time to Baseline Production (TTBP): Number of weeks from the PRRSV outbreak until recovering the pre-outbreak volume of weekly piglet production. 2 Time to Stability (TTS): Number of weeks from the outbreak until the first PCR-negative result followed by 3 months of consistently producing PRRSV PCR-negative piglets.
For more information, please visit fieldepi.org/pomp/pomp-technical-info/
Note: Results reflect estimations from a smoothing regression model controlling for AASV status at break, swine system, and year. Results should be interpreted as directional indicators and not as true means.
Insights from the plot
- Outbreaks with the 1C.5.32 variant had the highest production losses. Abortions increased by ↑ ~30 aborts/1,000 sows in the peak week of losses. Sow losses also increased, reaching ↑ ~17 dead sows/1,000 sows above the pre-outbreak level, with approximately 50% of farms recovering by week 3. Farrowing rate dropped substantially by ↓ ~35 percentage points. Stillborn increased by ↑ ~14 percentage points, with approximately 50% of farms recovering by week 9. Mummies increased by ↑ ~18 percentage points, with recovery extending to approximately week 20. Pigs weaned also showed major losses, declining by ↓ ~400 pigs/1,000 sows in the peak week of losses, with approximately 50% of farms recovering by week 24. Pre-weaning mortality increased by ↑ ~30 percentage points, with approximately 50% of farms recovering by week 13.
- All other L1C.5 variants were also associated with high production impact. Abortions increased by ↑ ~18 aborts/1,000 sows and sow losses by ↑ ~18 dead sows/1,000 sows above the pre-outbreak level. Farrowing rate dropped by ↓ ~20 percentage points, while pigs weaned declined by ↓ ~370 pigs/1,000 sows. Stillborn increased by ↑ ~9 percentage points, mummies increased by ↑ ~25 percentage points, and pre-weaning mortality increased by ↑ ~35 percentage points.
- L1C.2 was also associated with a high production impact. Abortions increased by ↑ ~17 aborts/1,000 sows and sow losses by ↑ ~8 dead sows/1,000 sows above the pre-outbreak level. Farrowing rate dropped by ↓ ~20 percentage points, while pigs weaned declined by ↓ ~320 pigs/1,000 sows. Stillborn increased by ↑ ~10 percentage points, mummies increased by ↑ ~15 percentage points, and pre-weaning mortality increased by ↑ ~25 percentage points.
- Outbreaks with L1A and L1H had a moderate production impact. Abortions increased by ↑ ~8–10 aborts/1,000 sows and sow losses by ↑ ~5–8 dead sows/1,000 sows above the pre-outbreak level. Farrowing rate dropped by ↓ ~10–15 percentage points, while pigs weaned declined by ↓ ~200–250 pigs/1,000 sows. Stillborn increased by ↑ ~6–8 percentage points, mummies increased by ↑ ~7–10 percentage points, and pre-weaning mortality increased by ↑ ~15–20 percentage points.
Note: Piglet losses data reflect estimations from an adjusted regression model. Time to stability plots reflect non-adjusted medians, and bullet points considerations derived from adjusted regression models. Results should be interpreted as directional indicators and not as true means.
- Total Piglet Losses and Time to Stability varied significantly by lineage, indicating the importance of genotyping the virus and understanding PRRSV status to align expectations on the magnitude of each outbreak.
- Outbreaks with Lineage L1C.5 had substantially higher piglet losses and longer time to stability compared to other lineages, reinforcing the need for aggressive stabilization strategies for outbreaks with L1C’s.
Note: Piglet losses data reflect estimations from an adjusted regression model. Time to stability plots reflect non-adjusted medians, and bullet points considerations derived from adjusted regression models. Results should be interpreted as directional indicators and not as true means.
- Outbreaks managed with LVI had substantially higher losses than those with MLV only. Outbreaks where both LVI and MLV were implemented had results in between MLV only or LVI only.
Note: Piglet losses data reflect estimations from an adjusted regression model. Time to stability plots reflect non-adjusted medians, and bullet points considerations derived from adjusted regression models. Results should be interpreted as directional indicators and not as true means.
- Negative herds (AASV III or IV) showed the highest median piglet losses, likely reflecting lower herd immunity at the time of exposure. However, these herds were associated with faster time to stability.
- A preliminary analysis comparing different herd closure protocols in stable and negative herds pursuing stability showed that time to stability was statistically shortest (31.7 weeks) when the herd was closed (gilt entry was ceased) within two weeks after the outbreak date. In the plot, different letters by adjusted TTS means represent statistically significant differences.