Monday, July 26, 2010

Response of aged horses to vaccination

How does age affect 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 (20years or older).

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.

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.

To test the anamnestic response (the rapid production of specific antibodies on renewed exposure to the antigen) they monitored the response to influenza vaccination. 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.

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