The altitude at which a calf is born and raised influences the rate at which mean pulmonary arterial pressure increases with age

Abstract

Right heart failure secondary to pulmonary hypertension is a leading cause of mortality among suckling beef calves in the Rocky Mountain region. The objective of this study was to track changes in pulmonary arterial pressures (PAP) in healthy calves born and raised at altitudes ranging from 1,470 to 2,730 m. It was hypothesized that calves located at higher altitudes would show a greater increase in mean PAP (mPAP) with age than would be experienced by calves located at lower altitudes. The rationale is that high altitude hypobaric hypoxia causes a greater rate of vascular remodeling and, consequently, greater resistance to blood flow than calves located at lower altitudes. A prospective study was conducted on 5 cohorts of suckling calves from 4 herds located at altitudes of 1,470, 2,010, 2,170, and 2,730 m. In total, 470 PAP measurements were obtained from 258 calves. As hypothesized, calves located at altitudes ≥2,170 m showed a significant increase in mPAP with age (P ≤ 0.002) whereas calves at 1,470 m did not (P = 0.16). Except for calves at 2,170 m (P < 0.001), systolic PAP did not increase with age (P ≥ 0.16). Diastolic PAP increased with age at altitudes ≥ 2,170 m (P ≤ 0.09) but did not change in calves at 1,470 m (P = 0.20). In summary, mPAP and the rate at which mPAP increases with age are positively associated with the altitude at which calves are born and raised.