Colorado ranchers use SimAngus genetics that tolerate the high-altitude environment

The Field family has been in the cattle business since the 1880s and is making plans to allow future generations to remain in the business if they so choose.
Photo courtesy Tom Field |

The Field name has been synonymous with Colorado ranching for generations. A sign of the times, the cattle operation is now a family-owned LLC headquartered in Gunnison, Colo. Tom Field, along with his brothers, Mike and Pat, make up the ownership of this operation with the longtime, expert on-ranch management of Mike Wilmore.

Beginning in the 1880s, the ranch was a Hereford operation, like many in the Gunnison area were at their onset and remain today. When Tom Field graduated from college in the early 1980s, he purchased the first Angus genetics and began crossbreeding, making F1 black baldies.

“Then in about 1990, we began using some F1 bulls,” he said. “I’m not a real breed loyal guy. Give me cattle that will work and when I find ones that work, I’m going to stick with them.”

In studying other operations that were successfully integrating Simmental genetics, Field liked the cattle and began utilizing SimAngus genetics and a few purebred Simmental bulls. On the ground performance is king for the Fields and that performance is the basis for their well-defined selection program today.

The cow-calf operation in the state’s high country is comprised of about 350 cows. Annually, 60 to 70 replacement heifers are developed with the majority finding a job within the herd. Weaned calves and bred cows are primarily the cattle marketed by the ranch. The Fields have moved toward utilizing SimAngus genetics, in part for their ability to flourish in hard country.

That simplicity allows the Fields to grow their own replacements and takes some complication out of pasture groups. The Fields have used Simmental genetics for over a decade.

“We’ve believed for a long time that hybrid bulls provide us simplicity to manage grass and pasture,” he said.

“We believe cross breeding is one of the genetic tools available to us and we aren’t willing to risk that our management is good enough in a very dynamic and harsh climate to leave that tool on the table.”


The factors that drive decision making for the Fields are well thought out and research-based. They made the choice to utilize Simmental genetics based on their high-altitude environment and the availability of PAP tested bulls. PAP, or pulmonary arterial pressure tests, predict a bull’s likelihood to develop high-altitude disease, also known as brisket disease. Cattle living above 5,000 feet are most susceptible to the disease that results in death.

The Fields draw the proverbial line on PAP testing at 40 and then, he said, do everything they can to identify early any signs of respiratory disease in calves and treat it.

“Our perception is that an animal with some genetic propensity for brisket disease and has an early respiratory event as a calf is a prime candidate for brisket disease,” he said. “In the last five years, we have not identified a mature animal that has suffered a brisket disease event. Live cows, live calves. Live cattle overcome a lot of things.”

The operation, like many in the high country of the West, depend upon public land grazing with enough for about half of the cow herd for a short time period.

“When we do go high, we’re going to pressure them at 8,000 or 9,000 feet,” he said. “We need to be cognizant and conscious of the breed type and the right management.”

The bulls Fields sourcs are tested at an altitude high enough to provide an accurate reading and allows them to systematically select bulls that fit the program that they anticipate will be successful.

“We are a no-surprise kind of genetics customer,” he said. “We hate surprises. Our manager hates surprises more than we hate surprises and we have found with disciplined selection and having a great relationship with our seedstock producer, SimAngus bulls give us the most desirable outcomes with minimal, if any, surprises.”

Soundness also is a consideration during selection, given the harsh environment and challenging climate. It is longevity, Field said, from a crossbred cow and crossbred bull that add up for the ranch.


Studying and making decisions based upon Expected Progeny Differences have allowed the Fields to use the All Purpose Index and then cull against extremes in birth weight, milk and mature size.

“We need heifers that calve with minimal assistance, if any,” he said. “and we want cows that milk in the constraints of our particular environment which is a relatively dry environment with extremes in temperature.”

Moderation is the ideal outcome from the Field’s judicious selection. To that end, the mature cows are what Field calls a metabolic package of easy calving females with great dispositions.

“All those things add up and we think we’re passing on to feed yards cattle that will grow, cattle that will grade, and cattle that will yield,” he said. “We want our feed yard customer to be successful, our packer customer to be successful, and if they’re both successful we have a fine chance to stay in business.”

Even while maintaining the goal of future generations on the ranch, the Field brothers all work off the ranch and have enjoyed building successful careers while keeping their ranch roots. The three brothers are located in Nebraska, Durango, Colo., and Boston. Much of what the brothers have learned in their careers off the ranch about management, development and innovation have translated to managing the ranch. For Fields, the knowledge of Silicon Valley isn’t that far removed from the ranch.

“From Silicon Valley, I’ve learned that when you need to adapt and make a change, do it,” he said. “Don’t wait around, don’t spend too much time overthinking it. When you know you need to pivot, to shift, do it.”

Field’s three sons and nieces share ownership in the operation, and he expects the younger Fields children also will desire some sort of involvement in coming years.

While the next generation builds their own careers, the elder Fields are using their trademark discerning, systematic style to develop long-range, succession and transition plans.

“Any success we’ve had is because we have an excellent manager,” he said. “We’ve had good help, great neighbors, and because we made the decision to build as simple an enterprise as we could, we’ve been able to make it work. We’re proud of the fact that we still have the ranch, we’re profitable enterprise, and we find for us, a huge amount of personal satisfaction from being engaged in the business with our family, our neighbors, and our community.” ❖

— Spencer is a freelance writer from Wiggins, Colo., where she and her family raise cattle and show goats. She can be reached at or on Facebook at Rachel Spencer Media.