A sow that is immune to Mycoplasma hyopneumoniae or has been vaccinated will pass on antibodies to her progeny in a concentrated form via her colostrum. There has been much concern expressed over vaccinating piglets at one and four weeks of age, would maternally derived antibodies (MDAs) interfere with the vaccine and thus reduce its effect and would the piglet's immune system be developed enough to respond?
The colostrum contains very high levels of antibody, IgG the main one circulating in the blood being the dominant one (see graph 1). The piglet absorbs the antibodies mainly in the first 6 hours after colostrum consumption and intestinal closure to intact antibodies occurs by 18 hours. Piglet serum levels are about the same as the sows by 24 hours of age. Graph 1. Antibodies in the sow
(After Blecha, 2001)
Once the piglet has absorbed the antibodies then the levels start to fall and the half-life for M. hyopneumoniae antibodies is approximately 15 days. So a piglet with high initial antibody levels could still have significant levels 60 days later but one with only low levels could be relatively clear by 30 days of age. Are these levels able to have an impact on vaccination response?
A recent report from Canada (Hodgins and others, 2002) looked at the effects of MDAs on vaccinal response in young piglets. Litters from 20 naturally challenged sows were used and groups of piglets were vaccinated either at 2, 3, or 4 weeks of age. Blood was taken just prior to vaccination and 3 weeks after and serum antibody levels (IgG) were assayed to see if they had gone up in response to the vaccine.
Graph 2 Effect of MDAs on IgG response to vaccination
(From Hodgins and others, 2002)
It was shown that higher pre-vaccination IgG titres gave significantly lower responses and a vaccine neutralization effect was observed at these high levels, i.e. the post-vaccination antibody levels continued to fall. Conversely piglets with low titres responded normally to vaccination and their titres went up. High initial antibody titres did have an adverse effect on the percentage vaccination response rate to the single shot vaccine, with only 36%, 48% and 64% of pigs in the 2, 3, & 4 week old groups respectively, having higher antibody levels after vaccination than before. Age at vaccination (2, 3 & 4 weeks) had no significant effect on IgG response but MDA levels did. The pig's immune system is still immature below 4 weeks of age but the cells that produce the antibodies (B lymphocytes) are mature at 4 weeks and can respond at an earlier age.
Recent work (Jayappa and others, 2001) carried out in the US with Schering-Plough's new vaccine M+PAC® in young piglets compared vaccination at 1+3, 3+5 and 6+8 weeks of age with unvaccinated controls, which had come from a herd where the sows had been vaccinated against M. hyopneumoniae prior to farrowing. Serology was carried out at the time of the first vaccination, to determine the levels of MDAs against M. hyopneumoniae and they were found to be very high with almost 100% of piglets positive. The pigs were challenged at 16 weeks of age and the lung lesions checked 5 weeks later.
Graph 3. Protective effect of a vaccine given at different ages and different MDA levels to piglets from vaccinated sows
(From Jayappa and others, 2001)
Lung lesions were reduced with vaccination even at 1+3 weeks of age in the face of high antibody levels. Vaccination at 3+5 weeks showed a small further improvement but at 6+8 weeks there was an 82% reduction in lung lesions, as MDAs fell the vaccinal response improved. High MDAs do not prevent challenge later in life i.e. in the finishing stages so really vaccination of the sow can be considered to have a negative impact on protection of the piglet throughout its productive life. Unusually, it is better that there are low antibody levels in piglets with regard to M. hyopneumoniae so that a better vaccinal response may be achieved either by a double or single shot program depending on the farm's situation.
References:
Blecha, F. (2001) Chapter 16.Immunology In Biology of the Domestic Pig, Editors Pond W. G. and Mersmann, H. J. Published by Cornell University Press, Ithaca, pp 688-711.
Hodgins, D.C., Shewen, P.E. and Dewey, C.E. (2002) Influence of age and maternal antibodies on antibody responses of neonatal piglets to Mycoplasma hyopneumoniae. Proceedings of the International Pig Veterinary Society, Ames, Iowa, USA, 1, 255.
Jayappa, H., Davis, R., Rapp-Gabrielson, V., Wasmoen, T., Thacker, E. and Thacker, B. (2001) Evaluation of the efficacy of Mycoplasma hyopneumoniae bacterin following immunization of young pigs in the presence of varying levels of maternal antibodies. American Association of Swine Veterinarians Conference, Nashville, Tennessee, USA, 237-241.