The circovirus disease complex manifests itself in many different ways.
The disease complex called PCVAD or porcine circovirus-associated disease includes many disease syndromes involving type 2 porcine circovirus (PCV2). These other viral and bacterial pathogens manifest themselves differently in each pig affected. All North American swine herds are believed infected, but this doesn’t mean all pigs become sick.
A diagnosis of PCVAD requires an increase in mortality, demonstration of PCV2 in affected tissues and microscopic confirmation of specific cellular changes.
For most veterinarians and producers, the circovirus vaccines have been a marvel of modern swine veterinary medicine necessary to maintaining a healthy herd.
However, PCV2 vaccines are expensive and compel some producers to experiment with dosage(s). Vaccine timing is critical to pig protection, and may be complicated by vaccine strategies used for other diseases, like mycoplasma, swine influenza and PRRS (porcine reproductive and respiratory syndrome).
Case Study No. 1
The owner of a two-barn, wean-to-finish site purchased weaner pigs from a sow farm that was PRRS-virus positive but stable for the last two years. Last winter, the sow farm became exposed to another strain of PRRS virus that caused significant losses. Testing illustrated most pigs were not viremic with PRRS virus but 10% were positive. All buyers were advised to protect incoming weaner pigs upon arrival against PRRS virus, using modified-live-virus vaccine. The owner of the finishing barns followed those recommendations, but to reduce stress on the pigs, delayed PCV2 vaccination until 3-4 weeks later.
Mortality was 8% in the first barn filled with the PRRS-vaccinated pigs at 8-10 weeks post-placement, which the producer attributed to the PRRS virus brought in with the pigs. After the second barn was filled, the pigs started to experience similar problems as the first barn. At this point, the producer became frustrated with pig health and called me out to walk through both barns and collect tissues for diagnostics. A few unthrifty pigs from each barn were selected for euthanasia and sampling.
The results indicated pigs in both barns were positive for PCVAD and PRRS virus in serum. We concluded death loss was due to PCVAD from poor PCV2 vaccine timing. I recommended PCV2 vaccine be given to the pigs upon arrival, and the PRRS vaccine be delayed one week after arrival. This new vaccine schedule improved performance.
Case Study No. 2
An 1,800-sow, farrow-to-finish farm schedules quarterly visits to the sow unit and walk-throughs of all finishers. This farm is PRRS-virus negative and vaccinates the weaned pigs with a two-dose program for circovirus and mycoplasma. In reviewing a finisher closeout report, the producer expressed concerns about the gains and feed conversion of all finishing sites. All of the finishing spaces were contract finishers fed by his feedmill. Recently, he had pulled the distiller’s dried grains with solubles (DDGS) from the diets, thinking this was impacting the performance.
After visiting all of the finishing barns, we observed that finishing pigs in the 10- to 16-week age groups were stalling out. An analysis of tissue samples from the diagnostic lab indicated a mixed bacterial infection found in the lungs with PCV2 virus also present. Histopathology (tissue) exam did not confirm PCVAD, but only that PCV2 virus was present. The current vaccine schedule and procedures were reviewed. The farm was giving a half dose of a commercial PCV2 vaccine at weaning and again three weeks later. I suggested that he try using a full dose of the vaccine instead. This program has always worked well to stop the high mortality in the finishers.
We reviewed some finisher closeout reports for pigs vaccinated with the new dosing schedule. The average daily gain had improved by 8% and the feed conversion decreased by 5%. The producer was particularly stunned that a subtle change in vaccine protocols would have such a significant impact on performance.
Summary
The impact of PCV2 vaccines on the U.S. pork industry has been profound. Initially, when the vaccines were released, the availability was limited and producers tried to stretch the vaccine by cutting dosage rates so that more pigs could be vaccinated. Also, the industry has discovered that timing of PCV2 vaccines are fundamental for a successful response by the pig.
Other disease pressures are important to consider when developing a vaccination program. Consult with your veterinarian to establish an effective vaccination program for improving performance on your farm.