As fall begins to creep into the high country, ranchers will soon begin collecting their cattle for the winter. Inevitably, some animals will not make the return trip, having succumbed to predators, diseases or other accidents. And for others, the culprit is altitude.

Just as headaches and nausea can plague lowland dwellers who venture into higher elevations, cattle, too, can suffer when they are taken to higher ground during the summer grazing seasons. In the worst cases, the effects are deadly.

Concern about the bovine altitude sickness, also called brisket disease, is especially acute among Rocky Mountain ranchers who rely on lush mountain grasses to feed their cattle during the summer.

Losses can range from 30 to 40 percent in cattle that are imported from lower elevations and from 0.5 to 5 percent among those raised at higher elevations.

Local ranchers are familiar with the disease, having seen their cattle die from it. Because it is strongly hereditary, the only way to prevent the disease is to identify cattle predisposed to it before they spread those genes to offspring.

Such an identification test was developed in the 1970s and has slowly gained traction since then. Ranchers said the simple test, which measures blood pressure of cattle living at high altitudes, has changed the market for cattle in areas like the Rockies.

Local research

Brisket disease generally affects cattle at elevations above 5,000 feet. The decrease in oxygen causes the heart to pump harder, building pressure.

Eventually, the heart wears out and stops beating.

A blood-pressure test, called a pulmonary-arterial pressure test, can determine if cattle are susceptible to the disease by gauging how well the cattle adjust to thin mountain air.

The test, done on first-year cattle, measures pressure on the right side of an animal’s heart. It can be taken only after cattle have acclimated to the altitude, which takes at least two months.

Low test values show the cow is unlikely to suffer from the disease.

The test can represent a powerful tool for ranchers, said Steve LeValley, an assistant professor of animal sciences at Colorado State University who did his master’s work on brisket disease at the bull-testing facilities at the Old Fort Lewis campus near Hesperus.

“Once you incorporate that (genetic resistance) into your herd, vulnerability to the disease goes down dramatically,” LeValley said.

But the disease will never disappear because animals raised at lower elevations aren’t tested before they are bought in other states and shipped here, said Beth LaShell, an agriculture professor with Fort Lewis College. The responsibility falls on high-country ranchers to get their new cattle tested.

Tim Holt, an assistant professor and veterinarian from CSU, comes to the area each spring to administer the blood-pressure tests, which cost about $30 each.

Ranchers live by the test

Davin Montoya is one of Holt’s loyal customers. Before the test, about 1 percent of his cattle died of brisket disease.

Every spring, Holt comes to his ranch, where about five other ranchers also bring their cattle to get tested. Montoya breeds cattle and said that now, the greatest demand is for animals with low blood pressure.

He won’t use a bull for breeding that hasn’t been tested, Montoya said.

Other ranchers also said the test is now part of their business.

Barbara Jefferies said her husband started paying attention to bulls’ blood pressure numbers after one or two of their cattle died of brisket disease.

Now, “if there is a male animal that has those genes, you just don’t buy him,” Jefferies said.

The quest for ideal high-altitude cattle supported Colorado State University’s test site at the San Juan Basin Research Center for decades. Before closing in 2006, the facility on the Old Fort Lewis campus operated more than 50 years testing bulls against each other on factors such as weight gain, fat ratios and pen feed efficiency.

The key, though, was the site’s high elevation, which allowed it to perform the pulmonary-arterial pressure test, said LaShell, who is also the educational coordinator at the Old Fort site.

“That’s the reason why we would have a bull test here, in the snow, where it is so remote, and we had to truck in all the food,” she said.

The entire process is an aspect of ranching that is unique to raising cattle at high elevations, Montoya said. He brought up a couple of new bulls from Texas this spring and tested their blood pressures before he decided which ones to keep.

Both, he found out, had test values way too high for the above-treeline elevations where his cattle graze.

“We couldn’t get ’em back to Texas quick enough,” he said.

ecowan@durangoherald.com