Crawford, Natalie Faye, authorEnns, R. Mark, advisorThomas, Milton, advisorHolt, Timothy, committee member2016-01-112016-01-112015http://hdl.handle.net/10217/170406High altitude disease (HAD), commonly known as brisket disease, is a natural occurring phenomenon in cattle. This disease occurs most often in high altitude (> 1,500 m) environments, where adaptability to the hypoxic conditions may be insufficient. Pulmonary arterial pressure (PAP) scores are the most useful tool available to cattle producers in predicting an animal’s susceptibility to HAD. The all-encompassing objectives for this thesis were to delineate the important factors influencing PAP scores and understand the relationships between PAP scores and other performance traits, where selection for more favorable PAP may have adverse effects on those performance traits. Two sources of data were used for this thesis: Historical records from the San Juan Basin Research Center, 4-Corners Bull Test (1983 to 2005; n = 2,041) and from the Colorado State University Beef Improvement Center (1993 to 2014; CSU-BIC; n = 8,718). For the 4-Corners study, data of yearling age and breed of cattle were used to determine how PAP varies with regards to both of these effects. The model of birth year, pen, breed, and yearling age effects on yearling PAP revealed these terms were all significant predictors of PAP (P < 0.01). With every one-day increase in yearling age, PAP increased by 0.03 (± 0.01) mm Hg (P < 0.01) with a mean PAP of 45.2 ± 12.8 mm Hg. Breed was found to be a highly significant factor (P < 0.001) in the model influencing PAP scores for bulls developed at high altitude. There was a 13.8-mm Hg range between breeds with the lowest adjusted PAP estimate to those with the highest adjusted PAP. The results suggested that appropriate breed selection based on reduced PAP scores could be advantageous in reducing the susceptibility of cattle to HAD and subsequent death due to pulmonary hypertension and right heart failure. The CSU-BIC data contained production weight traits of birth (36.2 ± 5.1), weaning (213.5 ± 31.8), yearling (345.6 ± 83.9), and post-weaning gain (121.9 ± 63.7) and PAP (42.4 ± 9.9) scores and these data were used to estimate heritabilities and relationships amongst them (mean ± SD; kg). Single-trait, two-trait, and multi-trait models revealed genetic correlations between PAP and the weight traits ranging from -0.11 ± 0.10 to 0.23 ± 0.08. An advantage to using a multi-trait model over a two-trait model is the increase in heritability due to the increase of information from more traits evaluated. Results of this study suggested that selection for lower PAP should not have adverse effects on the growth performance traits evaluated.born digitalmasters thesesengCopyright and other restrictions may apply. User is responsible for compliance with all applicable laws. For information about copyright law, please see https://libguides.colostate.edu/copyright.beef cattlebreedgrowthhigh altitude diseasepulmonary arterial pressureText