When porcine circovirus-associated disease (PCVAD) struck the 130,000-sow Pipestone System, their swine veterinary team made adjustments until more vaccine became available.
In 2005, PCVAD was little more than a passing concern for the Pipestone System. By the spring/summer of 2006, all that had changed as the virus began to consistently impact grow-finish pig flows.
Finishing mortality jumped from 2-5% to 6-10% or more in pigs averaging 12-18 weeks of age, recounts Joel Nerem, Pipestone veterinarian. Many cases were in herds with other health challenges.
But a few high-health herds were also struck by the porcine circovirus type 2 (PCV2) virus. Those herds were mostly negative for porcine reproductive and respiratory syndrome (PRRS), Mycoplasmal pneumonia and Actinobacillus pleuropneumonia.
Outlining the Problem
The Pipestone Veterinary Clinic quickly found most pigs were unresponsive to antibiotic and other treatment therapies. Further, demand for the three commercially available circovirus vaccines were quickly outstripping limited supplies.
Plus, the shareholders in the Pipestone System's farrow-to-wean operations that receive weaned pigs to finish out on their farms were quickly becoming disenchanted and demanding some answers.
Nerem, the newest of seven swine veterinarians at the Minnesota clinic, was assigned the dubious task of controlling the allocation of limited supplies of the three circovirus vaccines.
“It was kind of hard to be friends with new customers when you are the guy controlling the ‘circo’ vaccine,” he recalls.
Meeting the Challenge
As the scope of the disease widened during 2006, and more and more producer customers were impacted, the calls for vaccine grew more intense, Nerem relates. Problems were popping up in all of the Pipestone System locations: southwest Minnesota, eastern South Dakota, Nebraska and northern Iowa.
In their practice area, wasting was the most common tipoff PCVAD was present, along with the respiratory form of the disease. Enlarged lymph nodes were typical. Lesions were less commonly reported than they were by some veterinary clinics.
“At our clinic, it became very frustrating because we knew what the problem was. We knew that vaccination was the answer, but we couldn't give our producers the solution,” he declares.
“The Pipestone clinic was forced to develop criteria for allocating PCV2 vaccine to clients,” says Nerem, “with the goal of utilizing vaccine in a way that was ‘fair’ and that would have the biggest impact on pig health.”
Their position statement featured three criteria for determining which finishing flows would receive vaccine:
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Confirmed diagnosis of PCVAD by a Pipestone veterinarian. Diagnosis requirements included clinical signs consistent with PCVAD and doubling of historical finishing mortality; gross lesions consistent with PCVAD; and, microscopic lesions consistent with PCVAD, including presence of PCV2 in lesions.
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Severity of historical PCVAD from the source farm or site.
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Age of pigs at the time of vaccine eligibility. Eligible pigs were 6 weeks of age or less.
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New Vaccine Strategies
Nerem and colleagues also devised a number of plans to stretch tight vaccine supplies to see what might work.
But first, the clinic decided it had to protect the overall integrity of the Pipestone System. That meant reserving a small quantity of full-dose vaccine for incoming breeding stock, particularly the 21-day-old replacement gilts purchased, and for limited use in sows as a pre-farrowing vaccine trial.
“We did a limited trial in sows because we knew there was a product that was labeled for use in sows in Europe (Merial), and we wanted to see if it could make a difference in maximizing use of the vaccine,” Nerem explains.
PCV2 vaccine was administered to about 18,000 sows from November 2006 through January 2007. No measurable changes were observed in sow and litter performance as measured by standard PigChamp data analysis. Most pigs from vaccinated sows were vaccinated in the nursery, so offspring performance from vaccinated sows could not be measured. Another confounding factor was an outbreak of PRRS that struck some sow units in January 2007, he notes.
The bulk of limited vaccine supplies went to commercial wean-to-finish systems using three guidelines:
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Vaccinate affected flows or sites only;
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Vaccinate pigs 3-6 weeks of age; and
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Vaccinate pigs with ½ dose of commercial vaccine.
By the spring of 2007, vaccine demand had drastically outpaced supply. The Pipestone clinic implemented a focused plan to make the most of vaccine supplies:
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Vaccinate affected flows or sites only;
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Vaccinate pigs at weaning at the sow farm; and
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Vaccinate pigs with ¼ dose of commercial vaccine.
As vaccine supplies increased this summer, but were still not enough to use full-dose vaccine throughout the Pipestone System, the strategy became:
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Vaccinate affected flows or sites only;
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Vaccinate pigs at processing and at weaning on the sow farm using the two-dose product; and
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Vaccinate pigs with ½ dose of commercial vaccine.
Nerem told the crowd at the Leman Swine Conference in St. Paul, MN, that he understands those vaccine strategies didn't follow the label guidelines developed by the manufacturers.
“I am in no way advocating that kind of use. We had a very tough decision to make. We made a decision that there might be another way to reduce shareholders' risk, and prevent disease in young pigs, by using less than a full dose of vaccine,” he explains.
Trial Conclusions
The main objective of the partial- dosing protocols was to maximize the number of pigs getting at least some protection, Nerem emphasizes. He summarized those results:
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Pigs given ½ dose of circovirus vaccine from 3-6 weeks postweaning performed very well. On several occasions, vaccinated and unvaccinated pigs from the same source were placed on the same finishing sites. For roughly 10,000 pigs compared, vaccinated pig groups closed out with 2.7-5.0% mortality, while unvaccinated counterparts finished with 11.4-23.7% mortality. He says clinical signs in most vaccinated groups were minimal to non-existent.
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Pigs given ¼ dose of circovirus vaccine at weaning were closing out at the time of his presentation in mid-September. But Nerem says preliminary data clearly indicates that most groups getting ¼ dose of vaccine lacked complete protection, with mortality and prevalence of clinically affected pigs both running higher.
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In another limited trial, pigs were given ½ dose of commercial vaccine twice preweaning. Results were not available at presstime.
Overall, using ½ dose of vaccine has provided acceptable results when given to pigs at the appropriate age (under 6 weeks of age), says Nerem.
Current Program
Now that it appears sufficient quantities of PCV2 vaccine are available, the Pipestone clinic will use vaccine at the full dose recommended by the manufacturers on the label.
Nerem observes: “Our shareholders now expect to get vaccinated pigs when they receive them from the sow farm. So we have implemented a program of delivering vaccine to the sow farm for use at piglet processing and at weaning (two-dose program). We are seeing good results from that strategy, and those pigs are just coming to market now.”
He stresses again, even though it is not the manufacturers' recommendations, the Pipestone clinic has been able to immunize pigs prior to weaning and get protection to market. Circovirus vaccines are federally licensed for use in pigs at 3 weeks of age and older.
Finally, the clinic is conducting an experiment to investigate the return to growth performance from vaccinating pigs with a full dose vs. a half dose of vaccine.
“Certainly, the mortality data would indicate that the results are very similar with both dose regimens, but there are probably some advantages to a full dose of vaccine, and we are seeking to verify those claims,” Nerem points out.
The jury is also still out on sow vaccination. He admits more work needs to be done to determine the impact on maternal antibody as well as the piglet vaccination program.
