Evaluation of dam parity and internal biosecurity practices in influenza infections in piglets prior to weaning

This week we are sharing a recent publication from the Torremorell lab in the Preventive Veterinary Medicine journal, looking at the impact of internal biosecurity measures such as cross-fostering and sow parity on influenza infections in piglets.


  • Three influenza-positive breeding herds from the Midwest
  • 360 litters (half with parity< or =3 sows and half with P>3) in 30 farrowing rooms total
  • Treatment rooms: no cross-fostering after processing, no nurse sows, change of gloves between litters and use of plastic booties to enter the crates
  • Udder wipes and environmental samples were tested for influenza by PCR at day 2, 8, 13 and 18 of the piglet’s age.
  • One piglet per litter was tested at weaning with PCR on nasal swab and ELISA on serum.


Proportion of influenza positive litters by treatment group and day of sampling
  • More litters tested positive in the control group compared to the treatment group on day 8 and 13 of the piglets’ age (see figure above).
  • Average Ct-values decreased from 35 at day 8 to around 27 at day 18.
  • No significant difference in the overall percentage of positive litters between young and older parity sows at any of the sampling points.
  • Influenza antibodies were detected in pigs from all three farms but no significant difference in the ELISA results between the experimental groups.
  • Piglets from older parity sows had a higher quantity of influenza antibodies than piglets from younger sows.
  • Additionally, environmental samples were more often influenza PCR positive in the control group compared to the treatment group (70.8% vs 54.1%).
  • 46% of tools samples and 58.6% of farmworkers’ hand samples tested PCR positive as well.

Visit the journal’s website for the full publication, available in open-access.


Influenza is an important respiratory disease of pigs and humans. Controlling influenza in pigs is challenging due to the substantial genetic diversity of influenza A virus (IAV). In this study, we assessed the impact of internal biosecurity practices directed at limiting exposure of piglets to IAV before weaning; evaluated the association of sow parity with IAV prevalence in piglets and the levels of maternally derived antibodies (MDA), and documented the frequency of detection of IAV on farmworkers’ hands and the instruments used when handling pigs. The control group included litters in rooms where no specific changes were made to standard farm procedures. The treatment group included litters in rooms where no cross-fostering or nurse sows use was allowed, and where farmworkers were required to change gloves between litters when handling pigs. Both, younger (≤ Parity 3) and older parity sows (>Parity 3) were represented in all rooms included in the study. Overall, litters in the treatment group had lower IAV prevalence (29.9 %) than litters in the control group (44.2 %) (p < 0.001), and at day 8 of age the litters from the control group had 7.5 times higher IAV prevalence than the litters from the treatment group. However, at weaning differences were not found (77.2 % vs. 81 % for treatment vs. control, respectively, p = 0.41). There were no differences in IAV detection between parity groups at any of the sampling points (p = 0.86) and incidence of detection in sows from farrowing to weaning was 29 %. Piglets that tested ELISA negative were 1.3 times more likely to test IAV positive than piglets that were ELISA positive for IAV antibody test, suggesting that effective colostrum intake may reduce the likelihood of infection. IAV was detected on 46 % of the instruments used when handling piglets and on 58 % of farmworkers’ hands, indicating the potential risk for mechanical transmission of IAV in pigs. Overall, we showed that the implementation of internal biosecurity practices that limit IAV exposure to newborn piglets helped delay IAV infections but were not sufficient to reduce the prevalence of IAV infection in litters at weaning.

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