Case Study: Factors influencing pulmonary arterial pressure in cattle of the San Juan Basin Research Center 4-Corners Bull Test data

High altitude disease (HAD) in cattle is historically a consequence of hypoxia-induced pulmonary hypertension at elevations ≥1,500 m. Mean pulmonary arterial pressure (mPAP) is an indicator of an animal's risk of HAD and is moderately heritable (h2 = 0.26 to 0.34). The objective of this study was to evaluate genetic (i.e., breed) and environmental factors influencing yearling mPAP in growing beef bulls. Data consisting of pen, birth year (BY), breed, end test age, bull test weights, ADG, and mPAP (45.1 ± 12.3 mmHg) measures were obtained from the San Juan Basin Research Center, 4-Corners Bull Test Station (elevation 2,255 m). Records were from 1989 to 2005 (n = 2,426). Bulls of 10 pure and various breed crosses represented 73 different owners. A model of mPAP = Pen_BY + Breed + error was fitted. In an ANOVA for model building, Pen_BY (concatenated fixed effect proxy for contemporary group) and breed were significant (P < 0.05); however, end test age, bull test weights, and ADG did not account for significant variation in mPAP (P > 0.05). Results also suggested that breed (P < 0.001) was an important factor influencing mPAP. Using a least squares means separation approach, we found an estimated 17.4-mmHg range in mPAP between breeds, where Composite bulls had the lowest adjusted mPAP and Simmental bulls had the highest. Knowledge of genetic (i.e., breed) and environmental factors influencing mPAP could be helpful in reducing the incidence of HAD in beef cattle.