From the results of her trial, Professor Dewey concluded that a two-dose vaccination against PCV2 resulted in improved performance in the finishing phase. Compared to a single-dose vaccination programme, the two-dose protocol resulted in higher average daily gain, more pigs marketed in the ideal weight range, more kilos of pork sold, fewer pigs sent to the secondary slaughterhouse and most importantly, more money to the producer, she said.

Professor Dewey is Chair of the Department of Population Medicine at Ontario Veterinary College, University of Guelph, Canada. She was speaking at a seminar organised by Intervet Schering-Plough Animal Health at the VIV Asia show in Bangkok, Thailand in March 2011.

The study was started, explained Professor Dewey, because local pig producers in Ontario were concerned about the returns from different PCV2 vaccination protocols. They had observed that a two-dose programme seemed to give better growth rates than a single-dose product.

The Guelph trial was carried out on a commercial farm with a history of problems with PCV-associated disease (PCVAD) in the form of wasting in growing and finishing phases.

Within litters, piglets were allocated to one of three groups: a single-dose PCV2 vaccination; a two-dose vaccination (Circumvent; ISPAH); or an unvaccinated control group. There were more than 1,000 pigs in each treatment group and 100 controls. All pigs were vaccinated at three weeks of age – the controls with saline – and the two-dose group also at six weeks of age.

All three groups were penned separately after weaning. At 11 weeks, the pigs were moved off-site for growing/finishing. They were sold over a six-week period when they weighed 107kg+, and the barn was emptied after 98 days of production.

Three slaughterhouses were used for the trial. The aim was to send as many pigs as possible to the plant that paid a bonus of C$10 to 15 for pigs that met the weight criteria – 'high return' abattoir. A 'medium return' abattoir was the next alternative: it accepted lighter pigs and paid producers based on weight but without a bonus. The third option, the 'low-return' abattoir, was the last choice for pigs with serious problems; producers lost money on pigs sent to this slaughterhouse.

During rearing, the pigs were weighed (at three, 11, 19 and 23-27 weeks of age), mortalities and the slaughterhouses to which pigs were sent were noted, and the pigs were checked for viraemia by testing blood, nasal and saliva.

At three weeks of age, there were no differences between the groups in terms of bodyweight or gender mix.

Average Daily Grain (ADG) in Nursery

During the nursery phase, the two-dose pigs had a higher ADG that the other two groups.

At 11 weeks, the two-dose group still had a higher ADG than the single-dose group, while the controls were intermediate. There was no significant difference between the groups in the number of pigs off-sort.

Viraemia Status

Professor Dewey said the results showed the control pigs were more likely to be viraemic at each testing stage, and that the single-dose pigs were more likely to be viraemic at 15 and 19 weeks of age that the two-dose group. The single-dose groups became more viraemic over time.

Fewer two-dose pigs were viraemic than single-dose or the controls overall the proportions of non-viraemic pigs were 54, 92 and 15 per cent, respectively, for the single-dose, two-dose and control groups.

Turning to individual animals, fewer two-dose pigs were viraemic only once, which indicates that they were viraemic for a shorter period, and they carried a lower viral load in the blood than the other two groups.

In terms of the overall PCV load in the barn, Professor Dewey said that the two-dose treatment reduced virus spreading compared to the controls, which the single-dose treatment intermediate.

The single-dose treatment did not prevent virus shedding, she added.

ADG in Growing/Finishing

Viraemia in the single-dose group was associated with a reduction in ADG in weeks 11 to 19 and up to 19 weeks of age.

From 11 weeks of age to market and during the grower phase, both groups of vaccinated pigs grew significantly faster than the controls.

In the finisher phase, however, the two-dose group grew significantly faster than either of the other groups.

The single-dose pigs grew more slowly in the finishing phase that during the growing phase. This showed the adverse impact of viraemia on ADG, said Professor Dewey.

Number and Weight of Pigs Marketed

Of the pigs that were marketed, more than 99 per cent of the two-dose group went to the 'high return' abattoir, compared to 80 per cent of the single-dose group, with the controls intermediate. However, only control pigs had to be sent to the 'low return' abattoir because they were underweight.

The proportion of pigs sent to the 'high return' abattoir were 95, 76 and 87 per cent for the two-dose, single-dose and control treatments, respectively.

Conclusions

Professor Dewey, identified a number of important implications from her trial. The two=dose PCV2 vaccination treatment protected pigs to the end of the finishing period. The single-dose treatment did not protect the pigs against viraemia, which affected ADG, as shown by the slower rate of gain from 19 weeks to market than between 11 and 19 weeks of age.

From her results, Professor Dewey said that the two-dose protocol is recommended because of the higher average daily gains, more pigs marketed within the ideal weight range, more pork sold, fewer pigs sent to the secondary abattoir and more money to the producer.

Further Reading

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Find out more information on Post-Weaning Multisystemic Wasting Syndrome (PMWS) by clicking here.

March 2011