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Livestock Disease Update: Assistant state veterinarian discusses current animal diseases in Wyoming

by Wyoming Livestock Roundup

During the 46th Annual Fremont County Farm and Ranch Days in Riverton, held Feb. 7-8, Assistant Wyoming State Veterinarian Dr. Teckla Webb provided an update on current and emerging animal diseases in the state. 

Her presentation covered a range of diseases livestock producers and horse owners across Wyoming should be aware of, including trichomoniasis (trich), brucellosis, avian influenza and neurological horse diseases. 


Webb began by discussing trich, a reportable, venereal disease of high economic importance for cattle producers. 

Although trich went undetected in Wyoming for five years, it recently started to rear its ugly head, beginning in 2022, when a positive bull was identified in Carbon County, and in January of this year, when another case was identified in Fremont County.

“We do not provide exact locations of where these bulls are found, but we have not identified any additional positive bulls at this time,” she shared.

Webb then explained, “Trich spreads from an infected bull that breeds a negative cow, and the cow will be infected within seven to 14 days. One service from an infected bull to a negative cow causes a 95 percent infectivity rate. 

Webb deemed trich a “silent disease,” noting there are no clinical signs, which is why bulls need to be tested annually. 

“Once they are positive, they become carriers for life, so one positive test condemns a bull forever,” she stated.

She also pointed out, although there are internal issues occurring in an infected cow, cows usually won’t show signs as well. Instead, cows will undergo early embryonic loss, which is often undetected by producers because the fetus is absorbed into the reproductive tract. 

Instead, producers will see a hit on productivity, suffering a smaller calf crop, decreased weaning weights and an increase in open cows and culling numbers. 

Webb explained the key to preventing trich is to limit exposure by testing bulls in the fall when they come home from breeding or in the spring before they get turned out.

She also suggested turning over the bull battery on an operation more frequently, as older bulls generally harbor more disease than their younger counterparts.

“And, limit the consequences of exposure,” she said. “Keep your breeding season short – 60 to 90 days.” 


Webb moved on to another issue of high significance in the beef industry – brucellosis. 

“It wouldn’t be a thorough talk if I didn’t discuss brucellosis,” she stated, before sharing some good news on the topic. 

“Brucellosis was found outside of the designated surveillance area in Sweetwater County at the end of last summer, and I just wanted to confirm the case is resolved,” she shared. “Over 4,000 head were tested in the trace back from people who had bought and sold from the positive herd and almost all of the herd testing has been completed.” 

Webb went on to explain Wyoming is the only state in the U.S. with brucellosis, and because it is a disease of trade significance, it is the state’s responsibility to manage it and ensure federal requirements are met to maintain a negative status.

“Wyoming is an export state. Our calves go elsewhere – Texas, Nebraska, Kansas, etc. – to get fed. So, if we find brucellosis, we need to take care of it right away in order to maintain our export status,” she said.

In order to achieve this, Webb noted the state has certain requirements in place, including requiring bangs vaccinations and conducting slaughter plant samples.  

Avian influenza 

Next, Webb provided an update on highly pathogenic avian influenza (HPAI), as the U.S. is still in the midst of biggest outbreak in the nation’s history. 

“Looking at the entire U.S., we have 81.8 million birds infected,” Webb stated. 

She continued, “Wyoming has not been spared from HPAI, but since we aren’t a commercial poultry state, we aren’t seeing it as much as other states are. My update for Wyoming is actually the same as last year because we haven’t had an official detection since this time in 2023.” 

Up until now, Wyoming has had 11 flocks and 430 birds infected – all from backyard flocks. 

She explained, “HPAI is primarily spread through migratory waterfowl. As of Jan. 1, 2022, we’ve had 163 HPAI detections in wild birds, but in the past couple of weeks, we’ve seen some more positive birds coming into our state.” 

Webb noted producers should be extra vigilant in coming months, as migration season is around the corner.

“These birds are going to fly up from the South, straight across our state,” she said. “So, it is really important to keep your birds safe.” 

To do this, she suggested limiting contact with wild waterfowl by ensuring free-range birds don’t have access to areas that attract wild birds, putting a roof over the chicken house so wild birds can’t defecate inside, covering feed beds and implementing solid biosecurity measures when handling birds. 

Neurological horse diseases

Lastly, Webb brought up the interesting case of increased neurological horse disease instances this past year. 

“During the first week of August 2023, we had nine cases of neurologic horses in Wyoming, which is a lot in one week,” she stated. “We had six reports in Fremont County, two in Park County and one in Big Horn County.” 

“This quickly became a topic of concern at the state level because a lot of neurologic horse diseases look similar and some of them have pretty significant impacts,” she continued. “Rabies, for example, is contagious to humans, which is really concerning. We were also concerned about viral encephalitis diseases – diseases which cause brain swelling – including eastern equine encephalitis, western equine encephalitis and West Nile Virus (WNV).” 

Webb noted in 60 percent of cases, testing confirmed WNV, and although there is a vaccine, she pointed out WNV had become somewhat of a forgotten disease in the state of Wyoming. 

As a reminder, she explained WNV is only spread through mosquitos, which serve as a host, spreading the disease from infected birds to other animals. 

In mild cases, horses will experience muscle tremors, facial twitching, incoordination, stumbling and weakness, but are usually able to recover. In more severe cases, horses will go down, experience convulsions and usually end up dead. 

“WNV has a 33 percent fatality rate in unvaccinated horses, so if you see any signs, call a vet,” she urged. 

“Prevention is key for these diseases,” she continued. “Vaccinate, vaccinate, vaccinate. Administer one in the spring so horses have full immunity by the time mosquitos come out in the summer. It’s also critical to eliminate places where mosquitos congregate and breed – old tires, bird baths, buckets, a wheelbarrow, anything that can trap standing water.” 

Additionally, Webb suggested using fly spray specifically labeled for mosquitos and keeping horses in the barn during times of day when mosquitos are most active.

Hannah Bugas is the managing editor of the Wyoming Livestock Roundup. Send comments on this article to

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