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Intervet/Schering-Plough Animal Health IPVS Symposium 2010

Why PCV2 viremia matters to swine practitioners

Cate E. Dewey,1 KevinVilaca,2 Melissa. Reindl,1 A. Francisco de Grau,3 Karen Richardson,1 Zvonimir Poljak1

1 Department of Population Medicine, Ontario Veterinary College, University of Guelph, ON Canada, N1G 2W1.2 Maitland Veterinary Professional Corp., Intervet Canada Corp, 16750 route Transcanadienne Kirkland, PQ, H9H 4M7, Canada.


Introduction

Viremia results in immune system activation that leads to a redirection of nutrients that may result in a decrease in ADG and/or an increase in feed-to-gain ratio.1 Subclinical infections with PCV2 are common2,3 They are known to occur if vaccination does not prevent viral replication4. These PCV2 subclinical infections do not require co-infections. The objective of this paper is to describe the prevalence and production impact of viremia in pigs while comparing two commercial circovirus vaccines or a placebo under field conditions.

Materials and Methods

A PRRS- and M. hyopneumoniae-free system was used for the study. At weaning, pigs were randomly assigned to be vaccinated with a one dose commercial PCV2 vaccine (n=1026) (1D); a two dose commercial PCV2 vaccine (n=1020) (2D); or saline as a placebo (n=100) (control). Both PCV2 vaccines were used according to manufacturer’s label recommendations. Individual pig weights were collected when pigs were 3, 11 and 19 weeks of age and just prior to market at about 110 kg. Individual ADG was determined between each pair of weights... To determine extent of PCV2 viremia, blood was collected from a random sample of 122 pigs at 3, 9, 15, 19, and 23 weeks of age and during the final week of shipping to market. Serum was tested with a qPCR. The proportion of viremic pigs at each sampling point by treatment group was determined. Difference in proportions was determined with a chi-square test. ADG was compared by group and by viremia status using a multiple linear regression after controlling for weaning cohort and starting weight.

Results

Starting weights did not differ by group. More pigs in the 1D (47%) and control groups (85%) were viremic than in the 2D group (8%) (p<0.01). More control pigs (73%) were viremic on at least 2 samples than 2D pigs (0%) or 1D pigs (24%) (p<0.05). Pigs that were viremic more than once, tended to have a lower ADG (by 33.8 gm/d) than pigs that were never viremic (p=0.11). The proportion of viremic pigs remained at 3% to 4% for the entire grower-finisher phase for the 2D pigs. However, this proportion increased from 11% to 39% for the 1D pigs and from 53% to 63% for the control pigs from 15 to 19 weeks of age. The ADG in the 2D group was 42g / day higher than in the 1D group from 19 weeks to market age (p<0.01). The coefficient of variation of ADG in the 2D group (19%) was lower than that of the 1D group (28%) indicating that there was more variation in the growth of 1D group.

Implications and Conclusions

The proportion of viremic pigs was higher in the control group than in the vaccinated pigs. The pigs receiving the 2D vaccine maintained a low level of viremia throughout the finisher phase whereas the pigs in the 1D group exhibited a rising proportion of viremia toward the end of the finishing phase. This viremia was associated with a lower ADG and more variation in growth performance, particularly during the final phase of production. This is the least efficient time of growth, feed conversion and facility use. This variation extends the time for marketing. Hence, viremia contributes to the overall cost of production in the 1D group.

References

1. Colditz, I.G. 2002. Effects of immune system on metabolism: implications for production and disease resistance in livestock Livest Prod Sci. 75(3): 257-268.
2. Darwich, L., et al. 2008. Transient correlation between viremia levels and IL-10 expression in pigs subclinically infected with porcine circovirus type 2 (PCV2). Res Vet Sci. 84: 194-198.
3. Krakowka, S., et al., 2005. Features of porcine circovirus-2 disease: correlations between lesions, amount and distribution of virus, and clinical outcome. J Vet Diagn Invest. 17: 213-222.
4. Fort, M., et al., 2009. Development of cell-mediated immunity to porcine circovirus type 2 (PCV2) in caesarean-derived, colostrum-deprived piglets. Vet Immunol and Immunop. 129: 101-107.



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