What timing should you follow for PCV2 sow vaccination?

Friday, June 7, 2013

The answer depends on whether your primary concern is PCV2-associated reproductive failure or development of PCVAD in younger nursery pigs   

by ERNEST SANFORD

Requests for information on PCV2 sow vaccination has grown dramatically over the last two to three years. Interest has been instigated primarily because of occurrences in two areas: reproductive failures attributable to PCV2 infection and development of Porcine Circovirus Associated Disease (PCVAD) in younger (nursery) pigs in PCV2-vaccinated herds

PCV2-associated reproductive failure
PCV2-associated reproductive failure results in increased numbers of non-viable piglets at birth. Abortion, mummified, stillborn and weakborn piglets are all possible results of PCV2 infection of the pregnant sow, but the most common outcome is the delivery of increased numbers of mummified and stillborn piglets at parturition.

Reproductive failure is most common in naïve gilts and sows in startup herds, but is also known to occur in mature sows and sow herds previously exposed to PCV and which should therefore have immunity to PCV2.

For the eight-year period from 2003 to 2010, the Iowa State University Diagnostic Laboratory reported 501 cases of reproductive failure caused by infectious agents in swine. Of these, 12 per cent (58 of 501) had PCV2 involvement, indicating that it is not a rare event.

Pathogenesis and diagnosis. Sows become viremic after PCV2 infection, whereupon the virus can cross the placenta and infect fetuses in utero. Clinical signs are not usually seen in the sow and diagnostic tests aimed at the sow are unrewarding, since they do not provide a definitive diagnosis. Diagnosis is best established by identification of PCV2 antigen in microscopic examination of fetal heart.

PCVAD in younger (nursery) pigs. In North America, prior to the availability of PCV2 vaccines, clinical PCVAD was seen mostly in pigs in the finishing barn. In recent years, cases of PCVAD have been appearing in younger, nursery-age pigs a few weeks after weaning, at an age too soon after vaccination for the vaccine to protect against development of PCVAD. Diagnostic investigations revealed that these pigs were infected with PCV2 at a much earlier age than previously seen, causing PCVAD to occur in the younger, nursery-age pig.

PCV2 sow vaccination. PCV2 sow vaccination is largely dependent on whether the objective is to protect against PCV2-associated reproductive failure or PCVAD in the younger nursery pig. If the goal is to prevent PCV2-associated reproductive failure, then the aim is for a post-farrowing/pre-breeding vaccination.

Here the goal is to prevent or reduce the chances of in utero infection of the fetuses throughout gestation, thus reducing the opportunities for reproductive failure. By vaccinating, pre-breeding immunity is built up in the dam and opportunities for transmission of the virus from the infected sow to her fetuses in utero are prevented or at least reduced.

If the goal is prevention of nursery pigs being infected by PCV2 and going on to develop PCVAD at an early age, then pre-farrowing vaccination of the sow is recommended. Vaccinating the pregnant sow four to six weeks pre-farrowing provides increased amounts of anti-PCV2 immunity to the suckling piglets via colostrum, thus protecting them at the younger age, after which they develop their own active immunity when they are vaccinated around weaning time.

In reality, the timing of vaccination might be important only for the first round of vaccination. Thereafter, it becomes less critical as to when vaccination occurs once a regular program is in place to maintain a high level of immunity for the entire breeding herd. In many cases, a whole-herd blitz vaccination can be implemented at the first time of vaccination to bring herd immunity up to an equal level.

Replacement gilt vaccination. PCV2 vaccination of replacement gilts before entry into the breeding herd has already become a fairly common management practice. Since nearly all replacement gilts in North America are vaccinated as a piglet around the time of weaning, this is actually a revaccination. Revaccination is then recommended two to three weeks before entry into the breeding herd or, at latest, immediately after entry.

Boar vaccination. Boars shed PCV2 into semen. The amount of virus shed in semen may vary from boar to boar and from young versus older boars. Experiments to date have shown that although virus is in the semen, it is not in sufficient quantities in diluted AI semen to infect sows.

Nevertheless, boar stud management has included PCV2 vaccination of incoming boars before they enter the stud. Because of unknowns surrounding the effect of PCV2 vaccination on semen quality, revaccination of working boars in the stud has not been commonly practised. In a study presented at IPVS 2012 in Korea, Sponheim-Ness et al. showed that vaccinating mature boars with a one-dose PCV2 vaccine had no negative effects on sperm quality, motility, morphology or sperm count.

To summarize, the timing for vaccination of the sow is determined by which of the above two situations is the more important for sow vaccination. If it's to protect against PCV2-associated reproductive failure, then PCV2 post-farrowing or pre-breeding vaccination is recommended. If it's to protect against a younger pig developing clinical PCVAD, then a pre-farrowing vaccination is employed.

In reality, a whole-herd blitz vaccination is the protocol of choice in most instances to start a breeding herd vaccination program, since it satisfies both of the above criteria. A regular breeding herd program can then follow, or periodic blitz vaccination of the breeding herd can continue. Your veterinarian can help decide which program best suits your herd.

Gilts are vaccinated two to three weeks before entry into the breeding herd or at latest, immediately after entering the breeding herd. After entry they are integrated into the herd's regular vaccination program. Similarly, boars are vaccinated before entering the stud or herd, or immediately after entry. Boars can be revaccinated semi-annually or as determined by the veterinarian. BP

S. Ernest Sanford, DVM, Dip. Path., Diplomate ACVP, is a swine specialist with Boehringer Ingelheim Vetmedica (Canada) in Burlington. Email: ernest.sanford@boehringer-ingelheim.com