South Dakota's state veterinarian says further testing of cattle herds could reveal some more instances of a reproductive disease that causes cows to abort their young, but he doesn't expect an outbreak like one that hit western South Dakota in 2005.
The state saw no cases of bovine trichomoniasis — or trich — last year and just one the previous year, but veterinarians recently diagnosed trich in two Oglala Lakota county cattle herds and one herd operating in Corson and Ziebach counties. The disease poses no risk for humans, as it affects only a cow's reproductive system, but its occurrence can quickly cut into a rancher's bottom line, said State Veterinarian Dustin Oedekoven.
"This is certainly one of those diseases that can be economically devastating," Oedekoven said.
The disease is caused by a protozoal organism that lives indefinitely in the sheath of an infected bull. Once a bull transmits the disease to a female through breeding, it causes an inflammation in the reproductive tract that results in the loss of the pregnancy, according to the South Dakota State University Extension Service. Infected cows can clear themselves of the infection, but bulls remain positive for life.
South Dakota's 2005 outbreak — in which vets confirmed 45 cases of the disease, all west of the Missouri River — prompted the Animal Industry Board to issue several rules to prevent its spread:
- Any non-virgin bull must be tested negative for trichomoniasis prior to being sold, loaned or leased in South Dakota for breeding purposes
- Any non-virgin bull entering South Dakota must be tested negative for trichomoniasis
- No non-virgin and non-pregnant female cattle may be imported, loaned, leased nor acquired for breeding purposes in South Dakota
Oedekoven said the rules have greatly reduced the occurrence of the disease, but trich can occur in remote areas of the Badlands because the separation of bulls doesn't always happen. He said the state's low numbers in recent years might have also nudged many in the industry toward complacency with vaccinations.
"If we don't have a case for a while, everyone kind of forgets to vaccinate and pretty soon we've got a problem," he said.
Beth Carlson, North Dakota's deputy state veterinarian, said that state hasn't seen any cases of the disease for several years, "and I believe that was an imported animal in a cooperative grazing situation."
Carlson said North Dakota doesn't have in-state testing requirements, but it has interstate movement regulations similar to South Dakota and it the movement of open cows, which are females yet to be bred.
Ranchers are often unaware of the problem until the disease is well established in the herd. Some signs that the disease may be present in a herd include a high number of open cows, cows showing signs of heat when they should be pregnant and the presence of many late-calving cows, according to the Animal Industry Board.
The board offers several steps that ranchers can take to help prevent their herds from infection:
- Only purchase and use virgin bulls for breeding
- If purchasing non-virgin bulls, they should be tested negative prior to breeding
- Perform timely pregnancy testing of females and promptly remove open cows to be sold for feeding and slaughter
- Maintain good border fencing to help keep livestock in their respective pastures
"The neighboring herds are at risk," Oedekoven said. "Bulls sometimes hop the fence."