Parvovirus is one of those “old” diseases that seems to have gone away, right? Well, maybe not. Swine parvovirus causes fetal mortality and mummified fetuses when naïve animals are infected during gestation. The virus infects fetal tissue and causes fetal death at most stages of gestation. Typically, parvovirus cases produce mummies of various sizes within litters.
A farm that was positive for porcine reproductive and respiratory syndrome (PRRS), and also needed to make a genetic change, decided that a complete depopulation-repopulation was the best way to meet all of their goals.
The farm stopped breeding, started to sell sows at weaning and initiated an off-site breeding project five weeks after the owners stopped breeding at the main farm. They had always raised their own gilts. But given the desire to change genetics and maintain a high-health herd, staff chose to source new gilts from a genetic multiplier herd that was PRRS- and Mycoplasma pneumonia-free.
A dedicated crew was placed at the site. The breeding project was going along really well. Gilts cycled on time. Breeding targets were met and conception rates were above target levels. Cleanup was completed on schedule and gilts were moved back to the main farm one week prior to farrowing.
Litters produced the first week were okay, but not great. The total number of pigs born per litter was two pigs below expectations, and mummies averaged about 5%.
Week 2 was a train wreck. Total born fell by five pigs, and mummies were 20%. Staff started to panic, thinking the herd had PRRS and all the work was now just a mess.
Diagnostics were submitted, and lo and behold — parvovirus was detected. Good old parvovirus wreaked havoc. The mummies and low total born pigs per litter continued unabated for the next 20 weeks, ending up costing the farm about 40% of its expected output.
This case is a reminder of what can happen when old diseases raise their ugly heads. Remember that disease due to parvovirus only happens when naïve dams are infected in gestation.
Why were they naïve and how did they get infected?
For starters, most herds are infected with parvovirus. It is common for transmission (infection) to occur when gilts are between 150-200 days of age. This is partially a function of when maternally derived immunity declines and animals are susceptible to infection.
In addition, parvovirus is very stable in the environment and is resistant to disinfection.
In this case, the barn used for the breeding project had served as the gilt developer. Gilts raised there previously had been infected with parvovirus, and the barns were heavily contaminated.
Recall that the gilts for the repopulation project were from a brand-new herd, that had been raised in a brand-new barn prior to breeding. In the desire to get “high-health” animals, the farm ended up purchasing gilts without knowing if they were negative for parvovirus. In placing parvovirus-negative gilts into a contaminated barn, it was not surprising that they became infected.
What was surprising was that they were not vaccinated prior to delivery to the new breeding barn.
In checking the orders for what was shipped to the breeding project, it was learned that no parvovirus vaccine had been shipped. The farm was using a combination of a swine influenza virus and parvovirus, erysipelas and five serovar leptospira bacterin/vaccine (PLE).
What Really Happened?
This is one of those case studies where the following series of small missteps led to a major disaster:
• Unknown status of gilts for an important disease at entry to the project (veterinarian);
• Not ordering vaccine (barn crew); and
• Lack of process monitoring (management).
Take Home Lessons
There are more diseases than just PRRS and Mycoplasma pneumonia that we need to understand when we introduce gilts into breeding herds.
Knowing that we did what we actually said we were going to do is really important.
There are reasons that we still use interventions for old diseases, and not forgetting about those diseases can be critically important.