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Firewall tactics from PRRS vaccination strategy

by 5m Editor
8 September 2007, at 12:00am

By John Richardson, Pig Business Manager at Intervet. Pig mortality clearly has a financial penalty - typically adding 50 pence to the cost of producing each pig sold for every one per cent increase in mortality. However, the angst that these escalating or persistently high mortality rates can cause owners and stock people is also very considerable.

This was the situation for William Childerhouse on his 1200-place pig-finishing unit in East Anglia.

William's business contract finishes pigs for production and processing company Bowes of Norfolk. His straw-based, scrape-through system - typical of many farms in the area - houses between 20 and 40 pigs a pen. The unit follows all-in; all-out principles and is depopulated after each batch of pigs. Buildings are thoroughly cleaned and disinfected, to a very high standard, allowed to dry, and rested before re-stocking.

The Childerhouse unit is a typical East Anglian straw-based pig finishing system.

Pigs enter the unit at around 35kg and are usually supplied from two outdoor breeding units. Both are routinely tested for PRRS and are shown to be negative. The growers perform well, in terms of growth rate, and mortality for around six weeks. However, at between four and six weeks post entry, they begin to cough, succumb to respiratory infections, which is soon followed by a late onset PMWS. PDNS is also evident and thought to be a result of underlying PCV2.

Herd vet Ian Dennis MRCVS, of the Oakwood Veterinary Group, initially prescribed in-feed antibiotics to tackle the respiratory disease complex. Several of the latest high-potency injectable antibiotics were also used, but results proved inconsistent and had little impact on overall pig performance.

With mortality touching 14 per cent, losses amounting to up to 175 pigs a batch and an FCR of 3.68 per pig (on dead-weight calculations). The disease complex needed addressing and something radical had to be done, said William.

Further investigation

The buildings are old, but in good order, and thoroughly cleaned and disinfected between batches of pigs.

Ian suggested further investigations and so pigs were blood tested on entry to the unit. The same pigs were then sampled again six to eight weeks later. Apart from the usual serology, the samples were also run through Intervet's PRRS VetCheck service at Sci-Tech Laboratories.

This free diagnostic service provides results within 24 hours - which is just what you want when you are trying to identify the cause of a problem on farm, says Ian Dennis. "The results proved to be very informative. All pigs sampled were found to be PRRS negative on entry, but at around six weeks later a high percentage of them were PRRS positive," he explains.

Further investigations, on a number of pigs sent to the VLA at Bury St Edmunds, confirmed the prevalence of both PRRS virus and PCV2. A result that puzzled both Jim Burling, Bowes pig production manager and Ian Dennis. How could pigs supplied from two confirmed PRRS negative sources and then housed in a fully sanitized, isolated unit contract PRRS virus within eight weeks post arrival?

Both Ian and Jim considered the likely sources of risk to be from pigs, people, feed lorries and residual PRRS virus contaminating the buildings. They ranked the factors in order of transmission potential and drew conclusions. Due to the repeated pattern in which the respiratory breakdowns occurred, they both agreed that residual PRRS contamination of the buildings was the 'most likely' cause of disease.

It was decides to start a vaccination policy with the next batch of pigs using Porcilis PRRS vaccine The pigs were vaccinated on entry to the unit using Intervet's patented intra-dermal vaccination gun (IDAL). The vaccine is 'blown' at extremely high-velocity through the skin without actually having a needle puncture the dermal layers as with a traditional intramuscular injection. The process is swift and hygienic - there is no risk of transmitting infective material from pig to pig. And, as the IDAL gun does not use needles there is no need to stop and change them, so enables rapid vaccination with minimal stress. It took staff at the Childerhouse unit less than four hours to vaccinate approximately 1200 pigs weighing 35kg by using the IDAL gun.

Improvements
The performance of the first two vaccinated batches of pigs through the system was monitored closely. Both showed good performance and were very consistent. For the first batch FCR to 73kg dead weight was 3.24 and mortality was a commendable 3.8 per cent, which was a substantial improvement compared with the previous unvaccinated batches. The benefit, excluding improved growth rate, was calculated to be worth £7.88 a pig - proving the vaccination policy was economically worthwhile.

In this case, vaccinating PRRS negative pigs was aimed at protecting all of the stock against infection - because on this unit it was felt that some of the pigs were managing to contract the virus from the environment. The vaccination policy, when supported by thorough cleaning and hygiene protocols, produces an effective 'fire-break' and so prevents PRRS from infecting the stock and existing as residual infection.

Results from the above batch and those of the subsequent two unvaccinated groups of pigs are shown in the table.

Table 1: Performance in relation to PRRS vaccination status
Batch number Source Farms PRRS Vaccinated Dead wt FCE Mortality % 1 Outdoor A & B No 3.68 14.1 2 Outdoor A & B Yes 3.24 3.88 3 Outdoor A & B Yes 3.24 3.89


Blood sampling showed that these batches remained serologically negative for PRRS virus. The subsequent batches of pigs brought into the unit were not vaccinated and the health status and performance has been sustained.

Combined approach

The results from William Childerhouse's unit demonstrate that PRRS virus can be effectively removed from the disease complex by using a combination of thorough clean-down procedures and by vaccinating with Porcilis PRRS for at least two consecutive batches of pigs finished through the farm.

But PRRS vaccination of growing pigs need not be a permanent policy. The vaccine can be used as a tool to break the disease cycle.

Ceasing vaccination certainly can be considered, as long as routine monitoring of both PRRS status and the performance of successive batches is carried out. It can then be re-introduced in subsequent batches if records indicate a dip in performance. However, it is vitally important for producers to seek veterinary advice before changing any vaccination policy.


Further Reading

- Find out more information on PRRS by clicking here.


September 2007