Respiratory diseases represent a major challenge due to pig flow, sourcing, transport, numbers of pigs per site, sow herd age and care, and the emergence of PRRS porcine circovirus, and new subtypes of influenza.
Although a standard program for respiratory disease control is not practical or cost-effective, a well-designed program for individual farms is a reasonable goal.
Diagnostic and monitoring tools must change as technology and information advance.
At a recent farm visit, a producer asked why veterinarians do fewer slaughter checks. There are multiple reasons, including less cases of atrophic rhinitis, lack of sensitivity for early Mycoplasmal pneumonia infections, line speeds at packing plants and the development of new serology and diagnostic tools. Serology has replaced them as a more routine tool.
With growing segmentation of production systems, one challenge is coordinating sow herd respiratory programs with the downstream pig flow, especially with a change of ownership. Diagnostics of sow herds is complicated by vaccination and the tendency for bacterial and viral organisms to be subclinical in older animals.
Therefore, nursery problems may occur that require a sow program to help in deterring the problem, as depicted in this first case report.
Case Study No. 1
A 2,400-sow herd sells 1,000 weaners/week to the owner of a nursery in central Indiana. Monitoring serology in October '02, April '03 and January '04 showed no evidence of significant hemagglutination inhibition flu titers for either H1N1 or H3N2. Flu serology will not detect all subtypes.
In August '04, coughing pigs were checked and H1N2 flu was isolated. The sow herd was being vaccinated for flu, but there is no commercial vaccine specifically for H1N2. Some vaccines have shown efficacy against some H1N2 subtypes, however. Clinical signs dissipated and no further changes were made.
In January '05, two pigs on monitoring serology showed low titers to H3N2, not unusual for a vaccinated sow herd. This spring, a low-grade cough became persistent at two weeks postweaning. An occasional pig was observed thumping, but mortality didn't significantly increase. Nasal swabs were collected and flu virus was isolated. Polymerase chain reaction testing identified H3N2 flu. Extra water and injectable antibiotics were used to prevent bacterial problems.
Because problems persisted, the sow herd veterinarian ordered mass-vaccination with a different flu vaccine. Plans were to continue with this vaccine pre-farrowing, emphasizing the vaccine was being administered properly.
As the nursery veterinarian, the quick response by the sow herd was appreciated.
Four lessons learned:
In segmented production, develop good communication between purchaser and supplier.
Flu in nurseries, especially from vaccinated sow herds, may be very subtle, lacking acute signs typically seen in naïve pigs.
Monitoring programs may help predict when flu becomes more active and/or help design finisher respiratory programs.
Virus subtyping helps the nursery and sow herd. Sequencing may show relationship of viruses in the herd(s) if conventional vaccine programs are ineffective.
Case Study No. 2
This case involves control of mycoplasma in a 5,000-sow, farrow-to-finish system in four sow herds. Pigs are commingled, weaned to off-site nurseries and later moved to contract finishers.
Because mycoplasma was diagnosed in finishers several years ago, a one-dose mycoplasma vaccination has been used. Initially this helped, but eventually more clinical signs appeared.
Vaccine timing was changed, but coughing in finishers persisted in a high percentage of contract barns at 2-4 weeks post-arrival. A dry, non-productive cough was observed.
Mycoplasma was suspected and pigs were bled at 6, 10, 14, 18 and 22 weeks of age. The 6- and 10-week-old pigs were negative for mycoplasma. Five of 20 pigs were positive at 14 weeks of age and nine of 20 pigs at 18 weeks of age. By 22 weeks, 17 of 20 pigs tested positive for mycoplasma. All samples were negative for porcine reproductive and respiratory syndrome, two different H1N1 flu subtypes and H3N2 flu.
When testing pigs vaccinated with a one-dose product, don't expect all pigs to seroconvert to positive status. If there is field exposure to mycoplasma, seroconversion will occur. This was the diagnosis in this case.
Mycoplasma vaccination was changed to a two-dose regimen at 6 and 8 weeks of age. Some groups were even boostered as they were moved to the finisher.