Relationship of pulmonary arterial pressure and terrain use of Angus cows grazing high-altitude foothill rangelands

• Cattle use of rugged rangeland was not related to pulmonary arterial pressure.•Pulmonary arterial pressure was not useful for predicting terrain use of cows.•Pulmonary arterial pressure of cows at 1 and 5+ years of age were not correlated.

Pulmonary arterial pressure (PAP) score is used as an indicator trait for risk of hypoxia-induced pulmonary hypertension, which is commonly termed high altitude disease and observed in cattle grazing at altitude ≥1500 m. We hypothesized that cows with higher PAP score would avoid using high elevations, steep slopes and areas far from water while grazing foothill rangeland. During 2013 and 2014, forty-one mature Angus cows from a breeding population of cattle selected for tolerance to high altitude were tracked with global positioning system (GPS) collars for 27 and 17 days, respectively. These cows grazed a 1210 ha foothill rangeland pasture with a vertical relief of 2150–2411 m. Pulmonary arterial pressure was measured for each animal at 1 year of age (yearling PAP; 38.2 mm Hg±5.1 SD mm Hg) and before tracking (mature PAP; 42.6 mm Hg±3.7 SD). Yearling PAP score was not correlated with the mature PAP score (r=0.23, P=0.15). Terrain use varied among individual tracked cows, and the range among cows within the same pasture was 59 m (2204 m±15 SD) for average elevation use, 4.7% points (8.9%±0.2 SD) for average slope use and 247 m (446 m±77 SD) for average distance from water. No correlation was detected between mature PAP scores and terrain use metrics (mean elevation, slope and distance from water of tracked locations; r=−0.16, 0.24, 0.25; P>0.10). Similarly, no correlation was detected (P>0.10) between yearling PAP score and terrain use metrics. Yearling and mature PAP scores were not correlated (P>0.50) to indices of terrain use that combined elevation and slope use (rough index) and elevation, slope and distance from water (rolling index). Yearling PAP and mature PAP were not useful predictors (P>0.10) of terrain use in multiple regression analyses. Angus cows in this study were apparently adapted to high elevations and PAP score had little, if any, relationship with their metrics of grazing distribution of foothill rangeland. In situations where elevation was higher, terrain was more rugged or cattle were not adapted, results may differ from those observed in this study.