By Merial Animal Health* - Since it first appeared in the UK during the early 1990s, PRRS (comonly know as Blue Ear in the UK) has continued to have a negative influence on the health status and reproductive performance of UK pig herds. The effects of PMWS have compounded the problem in recent years.

Delegates to the 4th International Symposium on Emerging and Re-emerging Pig Diseases in Rome confirmed that the diseases, which both cause significant falls in numbers of pigs reared per sow per year, are undermining herd performance in many parts of the world. The UK is no exception.

One bright spot on the horizon is the growing body of evidence from the field and published data that demonstrate the efficacy of Merial's killed PRRS vaccine PROGRESSIS® in restoring productivity to PRRS-affected herds. As such, it represents an important tool in helping UK producers improve the health status of their herds and the industry's competitiveness.

Speaking at the conference, Dr Eileen Thacker of the College of Veterinary Medicine at Iowa State University, explained that vaccines exist which can decrease the impact of PRRSV on the breeding herd. As a result of her work with both killed and live PRRS vaccines, Dr. Thacker raised some important points relating to PRRS control using these vaccines. It was found that killed vaccines induced a significant cell-mediated immune response thought to be important in controlling PRRS virus infection. In addition, it was shown that following challenge by PRRS virus, important sero-neutralising antibodies were consistently boosted by the use of a killed vaccine. Repeated vaccination with a killed vaccine did not impair this immune response, as was observed following the repeated use of a live vaccine.

The reason, Dr Thacker speculated, is that the immune response induced by a killed vaccine such as PROGRESSIS differs from the live virus (or live vaccine) infection, avoiding the detrimental effects of Blue Ear virus on the immune systems. Another key advantage of using a killed PRRS virus vaccine is that there is no risk of shedding vaccine virus into the population.

"Blue Ear remains a huge problem for the pig industry," comments Brian Rice, Merial's Swine Business Head for the UK & Nordic region. He added: "It is generally accepted that much needs to be done to improve herd performance. In addition to the seemingly endless onslaught from PMWS, controlling diseases such as Blue Ear in the breeding herd must have a major role to play in restoring productivity. Only killed PRRS vaccines have been permitted for use in breeding animals in the UK and field experience with PROGRESSIS reinforces the view that controlling underlying Blue Ear problems within a herd will improve overall performance."

Trials prove positive

A number of recent field studies in Spain, Czech Republic and Denmark have clearly demonstrated the benefit of adopting the PROGRESSIS killed vaccine in herds afflicted with Blue Ear .

In Spain, vaccinating PRRSV-negative gilts with PROGRESSIS during the quarantine stage before introducing them to a positive herd minimised acclimatisation problems caused by exposure to Blue Ear. Two similar farms in the Toledo region were compared, although neither Farm A with 325 sows nor Farm B with 250 sows showed any overt clinical sign of PRRSV or had fertility problems with sows or gilts. Gilts arriving in quarantine on Farm B were vaccinated with PROGRESSIS, while gilts on Farm A were quarantined but left unvaccinated. These had a significantly higher rate of infertility compared with the vaccinated animals on Farm B.

In the Czech Republic, trials were conducted on a 300-sow farrow-to-post-weaning (up to 10w-old) unit that had suffered an outbreak of PRRSV annually since January 2000. Each outbreak caused reproductive disorders, an increase in the number of non-productive days, low numbers of piglets per sow per year, difficulties in acclimatising gilts, metritis and diarrhoea in newborns. In the autumn of 2002, the unit implemented a programme of vaccination, with two initial injections of PROGRESSIS given three weeks apart.

This resulted in a 22% increase in live births per sow per year, a 45% decrease in stillborns, a 28% increase in piglets weaned per litter and a 33% increase in pigs weaned per sow per year. The programme also resulted in a 32% reduction in non-productive days, a reduction from 22.57% to 6.08% in the numbers of gilts returning to oestrus and a fall from 24.99% to 12.87% in the number of sows returning to oestrus. Researchers also noted a yield improvement of more than five piglets per sow per year.

In Denmark, a 450-sow unit was depopulated, sanitised and SPF high-herd-health status gilts introduced. Despite careful application of biosecurity rules, the herd became reinfected with PRRSV European strain, Mycoplasma and APP serotype 6. Thereafter it suffered from abortions, a high prevalence of returns to heat, weak piglets and low farrowing rate. A programme of vaccination with PROGRESSIS introduced in October 2002 resulted in three additional weaned piglets per sow per year and a reduction of almost 50% in the numbers of stillborn piglets per sow per year. The work also demonstrated an increase in the number of weaned pigs per litter, a reduction in non-productive days per litter, a lower number of sows returning to heat, plus an improved farrowing rate.

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