Horse Vaccines: Core and Risk-Based Shots, and a California Schedule

Vaccination is one of the few parts of horse care where the evidence is simple. The diseases involved kill or cripple horses, treatment is limited, and a vaccine given on schedule prevents most cases. What owners find less simple is deciding which vaccines a given horse needs, because the list depends on where it lives, where it travels and who it meets. This page sets out the standard approach in plain terms. The actual schedule belongs to the vet who examines the horse.

The four core horse vaccines

The American Association of Equine Practitioners publishes guidelines that most vets follow, and they divide vaccines into core and risk-based. Core vaccines are recommended for all horses because the diseases are widespread, serious or a danger to people. There are four.

Tetanus comes from bacteria in soil and manure that enter through wounds, including the small punctures that nobody notices. Horses are unusually sensitive to the toxin, and the disease is nearly always fatal once signs appear, with stiff muscles, a raised third eyelid and a locked jaw. The vaccine is inexpensive and reliable.

Eastern and western equine encephalomyelitis, usually written EEE and WEE, are viral brain infections spread by mosquitoes from birds. Western equine encephalomyelitis has a long history in California, and both diseases cause fever, depression, trouble standing and often death. They are given in a single combined injection, often with tetanus.

West Nile virus is also carried by mosquitoes. Reported cases in California horses occur most years, usually between mid-summer and fall. Many infected horses show no signs, and the ones that do can have weakness, tremors and a stumbling gait. A fraction recover only partly.

Rabies is rare in horses but fatal, and the same infection is a danger to the people handling them. California has rabies in wildlife, skunks and bats among them, so the vaccine is sensible even for horses that never leave the property.

Risk-based vaccines: who needs what

Beyond those four, the list depends on the horse’s life. The vet weighs how often the horse travels, whether it mixes with horses from other barns, its age and whether any outbreak is in the area.

Equine influenza and equine herpesvirus, usually called rhinopneumonitis, spread through the air and on shared equipment. They matter for horses that go to shows, trail events, clinics or boarding barns with a lot of traffic. Protection from the vaccines is partial, which is why a vet may give them every six months to a horse that travels frequently.

Strangles is a bacterial infection of the lymph nodes of the head, spread by nasal discharge and shared water, and it can sweep through a barn. The vaccine reduces severity more than it prevents infection, and some vets reserve it for horses in barns with a history of the disease.

Potomac horse fever is more common in other regions, though cases are reported in California. Others, such as botulism or anthrax, depend on regional risk, and the vet will say if any applies. A horse that lives alone on private land and never travels has a shorter list than a horse that spends every weekend in a trailer.

A yearly schedule that fits California

Schedules differ from vet to vet, and the one that follows is a common pattern, not a prescription. Spring is the main vaccine month. The core set goes in a few weeks before the mosquitoes get going, usually March or April, which fits with the spring farrier visit and a check of weight and teeth. If the horse travels, influenza and herpesvirus vaccines are given then too, with a second dose in fall.

Mosquito season runs longer in much of the state than the calendar suggests, with West Nile cases reported into November. Some vets give a second West Nile dose in late summer in areas with heavy cases or for horses past age fifteen. The mild coast and the Central Valley have different patterns, which is why a local vet is the right source.

Rabies and tetanus follow the same annual cycle, and some vets time them with the fall check along with the dental exam. A written schedule on the barn wall or a phone reminder removes the usual cause of a lapse, which is simply forgetting.

Foals, new horses and horses with gaps

Foals from vaccinated mares usually begin their series at around four to six months, since the antibodies in the mare’s colostrum can blunt an earlier shot. They get a primary dose, a booster three to four weeks later and another around a year of age, with the schedule set by the vet.

A horse arriving with no vaccine records is treated as unvaccinated. That means a primary series, a booster a few weeks later and a yearly cycle after that. Buying a horse with a vaccination record in hand saves time and money, and it is worth asking the seller for the vet’s name.

A wound is a special case for tetanus. A horse with a deep wound or puncture and no recent tetanus shot usually gets a booster, and the vet decides how long is too long. That is one more reason to keep the dates written down. The first aid kit page lists what to keep on hand when a wound happens before the vet arrives.

Side effects and when to call the vet

Most horses take vaccines without trouble. A sore neck at the injection site, a lump the size of a walnut and a quiet day are all normal and settle in a day or two. Walking the horse lightly and giving a little gentle movement helps the neck loosen. Owners who ride the next morning usually notice a stiff neck and a reluctant horse.

Larger problems are uncommon and obvious. A swelling that grows, feels hot or oozes, a fever that continues, hives, trouble breathing, staggering, or a horse that will not eat all justify a call. Severe allergic reactions are rare, and an owner who has seen a horse react once should tell the vet before the next dose.

Records, travel and the vet

Keep a folder for each horse with the vaccine dates, product names and lot numbers if the vet records them, plus the coggins test results used at events and for crossing state lines. Boarding barns, shows and many trail events ask for proof, and some require a health certificate from a vet for travel between states. A phone photo of the page does the same job as the paper copy.

A vaccine program is not a replacement for good barn habits. Clean water buckets, isolation for new arrivals, no shared halters or brushes between unfamiliar horses, and a thermometer on hand to catch fevers early all matter alongside it. The guide to horse care puts these inside the regular daily routine, and the page on hoof care covers the foot checks that go with the spring visit.