On March 26, 2025, a joint team from Hyovet Research in Denmark, the University of Copenhagen, and the Danish Pig Research Center published a significant study in the renowned journal *BMC Veterinary Research*, providing the first field assessment in Europe of the impact of different weaning strategies on the spread of porcine reproductive and respiratory syndrome virus (PRRSV) in nursery areas.
This study was conducted in six PRRSV-positive pig farms, comparing "all-in, all-out" and "mixed weaning" management models. The results showed that farms using mixed weaning had an 8.4 times higher risk of PRRSV detection during the nursery stage compared to "all-in, all-out" farms, highlighting the crucial role of weaning management in controlling virus transmission.
Research Highlights
• First field study in Europe investigating the impact of weaning strategies on PRRSV transmission
• Mixed weaning (MIX) increased the risk of PRRSV detection in nursery areas by 8 times
• Good concordance between oral fluid and tongue tip samples (Kappa=0.44)
• Proposed "all-in, all-out" management strategy to effectively reduce virus transmission
This study was conducted in six PRRSV-positive pig farms, comparing the "All-In, All-Out" (AIAO) and "Mixed Weaning" (MIX) strategies. In the MIX strategy, underweight piglets were held for two weeks before being mixed with newly weaned piglets, while AIAO strictly enforced batch- and age-matched management. The study tracked virus and antibody dynamics by collecting oral fluid and tongue tip samples to reveal the key impact of weaning management on virus transmission.
The study assessed the PRRSV transmission risk under different weaning strategies using RT-qPCR and ELISA detection of oral fluid and tongue tip samples (TSS).
Results
1. Significant difference in virus detection rate:
41 oral fluid samples from the MIX farms were PRRSV positive, compared to only 5 from the AIAO farms.
Table 1. Number of positive oral fluid PRRSV RT-qPCR samples detected in three MIX herds and one AIAO herd;
Herd D. No positive samples were detected in AIAO herds E and F.
Figure 1. Percentage of PRRSV-positive (RT-qPCR) oral fluid samples at weaning and mean S/P ratio of PRRSV ELISA (collected at 5, 8 and 11 weeks of age, respectively).
Figure 2. Percentage of PRRSV-positive (RT-qPCR) oral fluid samples and mean PRRSV ELISA S/P ratio collected at 5, 8, and 11 weeks of age during AIAO after weaning.
3. Consistent antibody dynamics:
Antibody levels increased with age in MIX farms, while they generally decreased in AIAO farms, consistent with virus detection.
Table 2. Comparison of PRRSV detection results (RT-qPCR) in different batches of pigs infected with MIX at weaning using OF and TTS. Bold results indicate batches showing differences in oral fluid and tongue examination results.
Table 3. Comparison of PRRSV detection results (RT-qPCR) between different batches in AIAO-infected weaned piglets using OF and TTS methods. Bold results indicate batches with discrepancies between oral fluid and tongue examination results.
4. Feasibility of Tongue Tip Samples:
Tongue tip samples showed good consistency with oral fluid detection results and can be used as an auxiliary monitoring method.
Conclusion
This study clearly demonstrates that the "all-in, all-out" weaning strategy can significantly reduce the risk of PRRSV transmission during the nursery stage. Mixing pigs of different ages significantly increases the chance of cross-infection, especially during the nursery period. Pig farms should prioritize AIAO management and combine it with oral fluid and tongue tip sample monitoring for more precise PRRSV control.
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