By Jessica Domel
Multimedia Reporter

To protect Texas’ native bighorn sheep population, the Texas Parks and Wildlife Department (TPWD) and the Borderlands Research Institute (BRI) at Sul Ross State University are studying methods to control the growing aoudad (barbary sheep) population in Far West Texas.

Aoudad are not native to Texas. They were imported from the arid mountain ranges of Northern Africa in the 1950s to provide additional hunting opportunities.

Since then, they’ve thrived in the desert landscape of West Texas.

Over the past several years, TPWD has studied the species and their impact on native wildlife.

In 2018, researchers learned aoudad can carry mycoplasma ovipneumonia (MOV) and spread it to desert bighorn sheep, often leading to the death of the sheep.

“Of all the [aoudad] that we saw that tested positive for that bacteria, none of them showed signs of being sick,” Froylan Hernandez, TPWD desert bighorn sheep program leader, said. “There was no nasal discharge. There was no coughing. The animals appeared in good health.”

After that finding, TPWD partnered with the Texas A&M School of Veterinary Medicine to study MOV in aoudad.

“We artificially inoculated some wild, or free-ranging, aoudad that we captured in Hudspeth County and took them down to a holding facility at the A&M vet lab,” Hernandez said in an interview with the Texas Farm Bureau Radio Network. “They went through a series of tests there, and yes, most of the aoudad showed signs of carrying the bacteria.”

During that research, the aoudad did have nasal discharge that can be associated with MOV, but Hernandez said they were also stressed.

“It is a drastic change of habitat from West Texas to College Station, plus the confined area they were in was next to the airport. There were a lot of stressors involved that probably influenced the aoudad getting sick,” Hernandez said.

In the second phase of research, the department captured some free-ranging bighorn sheep on Elephant Mountain and took them to a holding facility at Mason Wildlife Management area.

After a 20-30 day acclimation period, some aoudad were brought in.

“Again, those aoudad were artificially infected with MOV from domestic sheep. Most domestic sheep carry that bacteria,” Hernandez said. “Then, we tested to see if the bacteria could be transmitted through an indirect source—shared water sources.”

Part of the study also included co-mingling of the aoudad and bighorn sheep to see if aoudad could transmit MOV through direct contact.

“In both cases, it appears that yes, aoudad can transmit that bacteria and infect bighorns through a shared water source without direct contact,” Hernandez said.

The study also revealed aoudad in the same pen or area with bighorn sheep can transmit MOV to the sheep directly.

“There are several disclaimers with that. It was a controlled setting. It was forced contact. How often do aoudad actually come into direct contact with bighorns?” Hernandez said. “So, there are things that still need to be looked at, but that prompted us to take it a step further and to look into a wild setting.”

Current research aligns with another study underway on aoudad competing with native mule deer for food and habitat.

TPWD and BRI placed satellite GPS tracking collars on mule deer and aoudad in the Quitman and Chinati Mountains and are monitoring their interactions.

As for bighorn sheep and the impact aoudad have on them, TPWD, BRI and other partners are now studying ways to manage the spread of the disease by managing the aoudad population.

One potential control method is aerial gunning.

“If you have a hundred aoudad on the landscape and all hundred are infected with the bacteria, then through aerial gunning, you reduce the number of infected aoudad on the landscape until you essentially lower the prevalence of the bacteria out there,” Hernandez said.

TPWD has already sampled the aoudad in the Chinati and Quitman Mountains and have a baseline for MOV infection rates in those areas.

After the aerial gunning is conducted, staff will test the animals for MOV.

“We should be able to compare the prevalence of infections on the landscape,” Herandez said.

That will give the department a good idea as to whether or not aerial gunning is an effective MOV and aoudad management tool and can help save Texas’ desert bighorn sheep population.

Ninety percent of desert bighorn sheep that are infected with MOV eventually die.

“Nasal discharge and coughing are probably two of the bigger signs that alert observers that they (bighorn sheep) might be infected,” Hernandez said. “Once they get infected, they rarely clear it or it’s very difficult for the animals to clear it, and they succumb to the disease or to the pneumonia.”

Some animals clear MOV infections fine, but may still carry the bacteria and shed it on the landscape.

Ewes infected with the bacteria but survive it are likely to infect their offspring, and often, the lamb won’t make it six months.

“That’s very evident in populations that have gone through pneumonia events because you see a reduction in lamb recruitment. It’s very, very low,” Hernandez said.

MOV is a problem in western states where domestic livestock, primarily sheep and some goats, interact with wild sheep like desert bighorns and aoudad and can infect them.

“Luckily, we don’t have domestic sheep anywhere close to our native bighorn ranges, but because aoudad are able to carry the disease, that is concerning to us,” Hernandez said. “That prompts us to look into the aoudad aspect of it. It’s concerning to us because if aoudad are able to transmit the disease on a free-ranging landscape, we might be in the same situation all these western states face.”

Currently, there is no vaccine for MOV, but research is underway.

The problem is, once a vaccine is developed, it may require multiple doses.

“To have the [free-ranging] animals on hand to give them the proper dosage at the appropriate time is very, very challenging,” Hernandez said.

Domestic sheep, which may be handled more often than free-ranging sheep, may be easier to vaccinate against MOV once a vaccine is available.

In the meantime, TPWD is also exploring other ways to protect desert bighorn sheep from MOV like testing water sources that may be shared by aoudad and desert bighorn sheep.

“We’ve already done some water testing in several mountain ranges, and it does seem to carry some pathogens,” Hernandez said. “On one occasion, we detected a minute level of bacteria in one of those water sources but because it was a minute level, almost just a trace, is it really going to cause anything in the sheep? We think not.”

The good news is the MOV bacteria is not very strong and degrades quickly in water.

“In the event that an aoudad came and drank, and maybe five minutes later, a bighorn comes and drinks, is there potential for transmission?” Hernandez said. “Those are some of the things we’re looking at next.”

TPWD is also using the data gathered from the GPS collar studies to identify potential hotspots were aoudad are congregating that may increase MOV transmission.

The multi-year research project is also a multi-partner project. TPWD, the BRI, Texas Tech University, the Texas Bighorn Society, Wild Sheep Foundation, Mule Deer Foundation, private landowners and others are all involved.