Q. I’ve read about the PZP vaccine (porcine zona pellucida, used for fertility control in some animals), and I was wondering where I would be able to order it. I live in northern Oklahoma, and I have adopted three rescue horses. Two of these are mares, and it is in our contract that they cannot be impregnated. We have a stud that is currently separated, but we would prefer he be with the rest of our herd, rather than two pastures away. Any information would be very helpful! –Jessika Kelly, via e-mail

A. I sympathize with your question. Of course, we’d all like to see horses kept in as natural groups as possible. Unfortunately, due to a wrinkle in the federal regulations, the PZP vaccine has only been approved for use in wild horses and burros, either on the range or in sanctuaries. So it is not generally available to horse owners. Approval for such wider use would require jumping higher and much more expensive regulatory hurdles.

In the meantime, the best place to find current information on PZP is on the website of the Science and Conservation Center (SCC), in Billings, Montana (sccpzp.org). The SCC makes and distributes the vaccine and conducts required training sessions for potential users.