Page 74 - August 2016

“Also, a lot of the earlier vaccines for animals are produced with older technol- ogy. Zoetis used the most current methods to include micro-filtration in building this vac- cine, which helps remove extraneous proteins that can cause reactions. We will be watching our data very closely as we go through this reproductive season,” he says.
Most of the questions asked during inter- views at the launching of this new product involved how to use this vaccine. “Zoetis recommends vaccinat-
ing healthy horses (six months or older) prior to exposure, giving
an initial dose, then
a second dose three or four weeks later. With most vaccines, if you are vaccinating a pregnant mare, it
is generally recom- mended that she should get a booster during the third tri- mester of pregnancy,” says Carter.
Zoetis has not yet
conducted a study
on duration of immunity. “This will be an ongoing experiment in the field for the next few years. This is one of the things we’ll be looking at. Currently, annual vaccination is recommended. If it works in horses like it does in other species, an annual booster should be adequate,” Carter says. At this point, it appears that the product is packaged only in individual one-milliliter doses. Eventually, it may become available in multi-dose bottles.
Dr. Stuart Brown, Hagyard Equine Medical Institute, Lexington, Kentucky, says it took some time to convince drug companies there was a need for an equine vaccine. “For most of the other domestic species, there are very good, effective vaccines available. The abortion issue in horses has been debated for a long time. Some people thought it was just a regional problem in central Kentucky, but veterinar- ians in other regions—especially in Arkansas, Mississippi, Texas, Oklahoma, Florida, and the Carolinas—have reported abortions related to exposure to the leptospire organism,” he says.
It took a while to get momentum going toward a vaccine, and Zoetis brought it to the marketplace. “Even though it is not labeled for abortion, it looks like it would be protective, and prevent the shedding of leptospires into the environment and prevent the potential symp- toms of the other syndromes,” Brown says.
There were some risks in using the cattle vaccine, which was the only option for horse owners for many years. Some horses experi- enced local injection site reactions and some
suffered systemic illness and depression fol- lowing vaccination. “One of the risks when using cattle vaccine in horses is the fact that cattle are much more resistant to the effects of endotoxin. Horses don’t tolerate the cattle vaccine very well, so you don’t want to use it on a mare that might founder when exposed to endotoxin,” says Brown.
“The equine vaccine is designed specifi- cally for horses, and the safety studies went well. They reported only one reaction out of about 2,000 horses, and it was a mild reac- tion,” he says.
He and Dr. Carter collaborated earlier on studies to help show the need for an equine vaccine. “We had a couple of years in which the horse industry here suffered significant losses due to lepto infections and abortions,” says Brown. “There was also a high prevalence of renal disease in young horses (weanlings/ short yearlings) during the winter months, especially in 2006.”
“Here in Kentucky, we see abortion problems from December through February. During the last week in February, the number of cases generally drops off. We think this has
a lot to do with the wildlife population; this
is where we are getting the greatest exposure and risk. Our problems in horses coincide with breeding season for skunks and raccoons in this region, when these animals are moving around more. As I travel the countryside during those winter months in our five-county central
Kentucky region, I see a huge increase in dead skunks and raccoons on the road. During their wandering, they probably present a greater exposure risk for the horses in this area, with contaminated urine close to where those horses feed or water,” he explains. Cases of leptospiro- sis in horses escalate during this time.
“The group at the University of Kentucky did a great job in looking at this. We had a situ- ation about that time at a large Thoroughbred farm where a number of compromised foals were born with lepto infections and renal disease. That farm lost newborn foals and diagnostics found a high prevalence of the lepto serovar grippotyphosa in those mares. They tied this to raccoons and recovered the organ- ism from some fence-line feeders the mares were using at those barns where they had a high number of cases. They captured some of the raccoons along the creek, and those raccoons were all infected.” Brown says. Raccoons eat the horse feed and were probably urinating where the horses were eating.
“We began to look at this further, wonder- ing what the national prevalence might be for exposure in horses. Every time we talked to
a drug company about producing an equine vaccine, they didn’t think there was enough opportunity to recover investment costs because they thought lepto only occurred in a few locations,” says Brown.
“Craig Carter felt strongly that we knew about it here because we were looking for it,
Dr. Stuart Brown, Veterinarian at Hagyard Equine Medical Institute, Lexington, Kentucky
72 SPEEDHORSE, August 2016
Trying to keep a horse that is suffering from uveitis from going blind can be a challenging and expensive process, and much damage may already be done by the time the problem is even recognized.
equine health