Q:What is your opinion on giving half-doses of routine vaccinations to horses with EPM (equine protozoal myeloencephalitis)? My veterinarian says that they are more sensitive to vaccines because their immune systems are compromised. However, I've also read that a half-dose of vaccine in an adult horse is worthless. My horse has already received half-doses of everything. What, if anything, can I do at this stage to ensure that he is protected?

Jordan

A:I would not give half doses of vaccines, as that may not elicit a full and protective immune response. I would suggest spreading out the vaccinations rather than giving 5 or 6 antigens all on the same day. I would give individual vaccinations separated by at least 3 weeks.

Regarding how much protection a horse will get from half-doses, unfortunately there is no blood test to determine if your horse is fully protected after those half-doses. I would consider re-vaccinating only for those diseases that are a significant threat in your area

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