Q. I have questions about a vaccine for snakebites: My own veterinarian has not mentioned this but my neighbor’s vet recommended that they vaccinate their horses against rattlesnake venom. Last summer six horses in two-mile radius of our farm sustained snakebites, and I am trying to anticipate the upcoming season. I was told by my neighbors the vaccine is a series of three injections, and often horses develop a temporary swelling or irritation at the injection site. Can you tell me more about this vaccine? Is it effective against all rattlesnake species in the United States? Is a horse that previously has been bitten by a rattlesnake more or less likely to have a severe reaction if bitten again?

Betty Fey, via e-mail

A. There is, indeed, a rattlesnake vaccine labeled for horses. And I must disclose that I have done collaborative research work with the company that produces the vaccine, Red Rock Biologics. The rattlesnake vaccine is made with venom from the Western Diamondback Rattlesnake, and in vitro studies showed it to be effective in neutralizing this snake’s venom. We know that rattlesnake venoms, while different in many ways, are also similar in many ways and contain many similar toxins. This knowledge would lead one to believe that antibodies made against one rattlesnake venom may be at least partially effective at neutralizing other rattlesnake venoms. Scientific studies have shown that some rattlesnake venoms are more similar than others; however, a vaccine against any one venom would not likely provide protection against all rattlesnake venoms in the United States or elsewhere. So, the answer to your second question is that it is unlikely that antibodies produced from vaccination with the (Western Diamondback) rattlesnake vaccine would be fully protective against every species of rattlesnake in the United States. To my kno