Response of aged horses to vaccination
Response of aged horses to vaccination What effect does age have on the horse's ability to respond to vaccination? As with other body systems, the immune system undergoes age-related changes. (known as "immunosenescence"). This may make the animal more prone to infections and autoimmune and neoplastic diseases. A research team from the Atlantic Veterinary College, Prince Edward Island, Canada conducted a study to investigate the specific systemic antibody response in horses by looking at how they responded to vaccination. They compared the response of young adult horses (aged 4 - 12 years) with aged horses (20 years or older). A full report of the work has been published in the Journal of Comparative Pathology ( It was initially published in the Journal of Veterinary Internal Medicine in June 2008)To investigate the primary immune response, to an antigen that the horses would not have experienced before, they used rabies vaccine. |  |
Prince Edward Island is rabies-free and none of the horses had been vaccinated previously for the disease.
Influenza vaccination was used to assess the secondary ("anamnestic") response. All horses had antibodies to influenza at the start of the study - indicating that they had been exposed to the virus (or had been vaccinated) previously.
All horses were vaccinated with inactivated rabies and influenza virus vaccines. Four weeks later, half of the horses in each age group received a second influenza vaccine; the rest received a second rabies vaccination.
The researchers monitored the antibody response by collecting blood samples before the first vaccination and one-, two- and six-months later.
They found that healthy aged horses vaccinated against rabies showed a primary immune response similar to that of younger adults. However, by 6 months after vaccination the rabies antibody titres fell significantly in both age groups.
The anamnestic response was significantly reduced in the aged horses. Younger horses showed a significantly greater increase in two classes of anti-influenza antibody (IgGa and IgGb) after vaccination, compared with aged horses. This was despite the older horses having higher antibody levels at the start of the study which they maintained throughout the study.
Single radial hemolysis (SRH) gives a good indication of the level of protection against equine influenza. Using this test, the researchers found that 82% of all horses in the study had protective levels of antibodies six months after vaccination. So the age differences noted in antibody production may not be clinically significant.
The researchers also checked the serum concentrations of selenium and vitamin E, as deficiencies may adversely affect the immune system. A significant number of horses had serum selenium concentrations below ideal levels. However, the researchers could find no significant relationship between selenium status and the immune response in either the young or aged horses. With significant numbers of horses in each group with inadequate Se levels this may have reduced the ability to detect the effect of Se deficiency on the immune response.
They suggest that further research is warranted to determine the clinical significance of these findings.
For more details see:
The effect of age on the immune response of horses to vaccination.
TL Muirhead, JT McClure, JJ Wichtel, H Stryhn, RJ Markham, D McFarlane, DP Lunn.
J Comp Pathol (2010) 142, Suppl 1; S85-90.
Reproduced with kind permission of Mark Andrews BVM&S CertEP MRCVS
© Copyright Equine Science Update 2010
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Added on: 05/10/10.
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