The extra hour of daylight in the evening with the springing forward of clocks surely confirms that spring is finally arriving here in central Illinois. Horse owners will, no doubt, welcome the opportunity to spend more time riding and, at the same time, think of scheduling spring vaccinations. The purpose of this article, then, is simply to provide some insights into appropriate vaccination of your horse as the cold months give way to warmer months ahead.
At the outset, a review of the principles behind a vaccination program might prove helpful. In other words, what criteria should be used to decide what vaccines to give a horse?
Deciding Whether to Give a Vaccine to a Horse
First of all, we consider the risk of a particular disease occurring. This risk is based on the horse’s anticipated exposure to the causative agent, the horse’s environment, geographic region, age, breed, use, and gender. For example, a horse that lives on its own and does not comingle with other horses is unlikely to be at a significant risk of exposure to infectious respiratory disease viruses. In contrast, a horse that travels to shows where it does comingle with other horses is likely to be at significant risk of exposure to respiratory disease.
Secondly, we consider the consequences to a horse if it contracts a particular disease regardless of whether the risk of exposure is very remote. The consequences to human health of contracting a particular disease from an infected horse are also an important consideration. Rabies is a prime example of a disease with very remote risk of exposure but where the consequences of contracting the disease are devastating. Tetanus is another example of a disease with low risk but devastating consequences.
Thirdly, we consider the likely effectiveness of a vaccine against the disease. If a vaccine has not been proved effective, it is difficult to argue a case for giving it.
Fourthly, we consider the potential for adverse reactions to a vaccine. Some horses have profound adverse reactions to vaccines where the risk of giving a vaccine probably outweighs any benefit.
Lastly, we consider the cost of the vaccine compared to the potential cost of the horse contracting the associated disease. The cost of vaccinating may include time and labor as well as the vaccine itself while the potential cost of the disease in terms of medical treatment, etc., may be significantly less.
It should also be remembered that vaccination is not a substitute for poor management practices. Likewise, while vaccines generally minimize the risk of disease, they cannot prevent disease in all circumstances. Vaccines as well as boosters, where applicable, should be administered appropriately prior to likely exposure to the disease.
Core and Risk-Based Vaccines
Having provided some background on the principles of vaccination in general, we now move on to the vaccines themselves. First of all, vaccines can be categorized as either core or risk-based. Core vaccines are considered those which protect from diseases endemic to a region (i.e., known to exist in the region), diseases with public health significance, diseases considered to be highly infectious, and diseases that pose a risk of severe disease or even death.
The vaccines considered core include Eastern Encephalomyelitis, Western Encephalomyelitis, West Nile, Rabies, and Tetanus. Rabies and tetanus are given once a year, and the time of year is generally not important. However, Eastern Encephalomyelitis, Western Encephalomyelitis, and West Nile are diseases that are transmitted by insects. These insects are generally only encountered in late spring through early fall in this region. Another important factor is that the vaccines for these three diseases are only considered effective for six to eight months. As a result, if they are given too early in the year, they may no longer offer sufficient protection in the early to mid fall when the insects may still be active. We, therefore, recommend vaccinating for these diseases no earlier than the end of March or early April. If, however, you take your horse to warmer climates in the fall, winter, or spring, it is likely advisable to vaccinate for these three diseases twice a year.
The need for risk-based vaccines typically varies depending on region, population within a region, and individuals within a particular population. The list is lengthy and includes anthrax, botulism, equine herpesvirus, equine influenza, equine viral arteritis, leptospirosis, Potomac Horse Fever, rotavirus, snake bites, and strangles. It is beyond the scope of this article to discuss the risks posed by these particular diseases. Such a discussion should be embarked upon with your local veterinarian who is best placed to assess the risks involved for your horse and the appropriate use of available vaccines.
This article does not serve to replace an appropriate conversation with your veterinarian. Such consultation is part and parcel of an effective vaccination program, especially with regard to risk-based vaccines as mentioned. This point cannot be stressed enough. Your local veterinarian is best placed to assess the particular risks to which your horse is exposed. Thanks for reading and we wish you and your horse the best of health in the warmer months to come.
—Dr. Hugh Duddy, equine intern