Area veterinarians assert there is no proof behind claims that the West Nile virus vaccination has any detrimental effect on pregnant horses, but rancher Lynn Bowers, who has lost six colts this year, says he thinks differently.
Bowers, a Moffat County resident who is a fifth-generation quarter horse breeder, has seven mares, six of which were vaccinated against West Nile virus. The colts of all six died -- three through miscarriage, two shortly after birth and one was stillborn.
"It's been quite a hit on the whole colt-raising industry," Bower said. "Some people are raising hell."
He blames the deaths on a lack of information available about the vaccine when it was first issued.
"Veterinarians publicized the information they received," Bower said. "They just didn't know."
The vaccine was released in 2002 as a quick response to the fast-spreading West Nile virus, which can be fatal to horses.
The vaccine has been issued conditionally, meaning it hasn't been fully tested. It had undergone vigorous testing but hasn't yet been tested on animals in clinical conditions.
Despite that, veterinarian Wayne Davis said most people believed it works. He said in 2.5 million doses, five horses contracted West Nile virus, but three of them had not received the booster vaccination.
The horses had not been exposed to the virus.
When the vaccine was released, veterinarians recommended that all horses, including pregnant mares, be vaccinated.
That position has changed after horse breeders reported several colt deaths to mares that have been vaccinated. Now the state veterinarian is recommending that pregnant mares not be vaccinated but Davis said the decision is based on public perception, not sound science.
"So far, from what I've read and from what I've seen from the state veterinarian, it looks like the concerns are bogus," he said. "There's absolutely no proof there is a problem but because of that perception that there is a problem, the state veterinarian has recommended that people don't vaccinate pregnant mares."
Davis said he believes the media has exacerbated the problem.
"There's absolutely no evidence that the vaccination caused miscarriages or birth abnormalities. That just happens sometimes," Davis said.
He says statistics show the chances of the vaccine causing problems are slim.
But losing six colts from six horses that were vaccinated paints a different picture for Bower.
"It doesn't matter how many I did or didn't lose, it could happen to anyone," he said.
He doesn't sell the horses, so he said he did not take an economic hit and he doesn't blame veterinarians.
"Some veterinarians told (horse owners) to vaccinate and they did it," Bowers said. "But the vets didn't know. It wasn't their fault."
Davis said he did not recommend the vaccine for pregnant mares because it was a new product without a proven track record. He still does not recommend it on the advice of the state veterinarian but hasn't seen a connection between the vaccination and deaths of colts.
"I haven't had very many people tell me they lost colts," he said. "It doesn't look like there's been an increase in miscarriages outside of expected parameters."
He does admit that over time there is a chance a connection between the vaccination and colt deaths may be established.
Veterinarian and horse owner Lane Kihlstrom has lost five colts this year but he said none of their mothers were vaccinated against West Nile virus. He's investigated their deaths. One death was caused by a birth defect. The other four were from four different diseases -- none of which were West Nile virus.
"It's just bad luck," he said. "We've not seen any greater number of defects than normal."
Kihlstrom vaccinated all of his studs and his non-breeding mares and still recommends that all horses, including mares, be vaccinated.
"I think it would be malpractice if I didn't until there's some conclusive evidence," he said. "All my clients' horses are doing good. I've vaccinated more mares than not."
Bower's ray of sunshine is that the one mare that was not vaccinated gave birth to a healthy colt named Flame.
"I was so tickled we did have one colt and everyone has had such tough luck, but there is a ray of sunshine," he said.
Symptoms of West Nile virus are neurological. Signs include coordination difficulties, lethargy and head pressing. They are similar to those of sleep sickness and wobblier syndrome, Davis said.
Clinical signs in horses with West Nile virus infection vary. Some horses may show few or no signs of illness. The most common signs include an unsteady gait, depression or apprehension, hind-limb weakness, difficulty in rising, and muscle tremors. A small number of horses may develop muscle weakness that progresses to paralysis of all four limbs, inability to rise and death within two to nine days.
About one in four of the horses showing signs of illness developed fever.
Horses affected by West Nile virus do not need to be euthanized. Many horses display mild clinical signs and can recover from the disease with supportive care. Horses are humanely euthanized only when they are suffering from illness from which they will not be able to recover. Horses with WNV do not need to be quarantined since infected horses cannot transmit the disease to other horses or humans.
Other than symptomatic and supportive veterinary care, there are no specific treatments for horses with West Nile virus.