14 Effect of Pulmonary Arterial Pressure and Precipitation Interaction on Reproductive Performance in Angus Heifers in South Central Wyoming

Abstract Variable precipitation in the western United States impacts forage availability, potentially influencing fertility. Furthermore, producers located above 1,500 meters contend with high altitude disease (HAD) due to reduced atmospheric oxygen, potentially resulting in right sided heart failure. Pulmonary arterial pressure (PAP) score is an indicator trait of HAD. The physiological stress of elevated PAP score could compound environmental stress, such as variable precipitation. Thus, the objective of this study was to investigate the interaction of precipitation and PAP score on beef heifer fertility. Data for this study were sourced from the Colorado State University Beef Improvement Center (CSU-BIC; 1993-2019; n = 3,834; 2,150 to 2,411 m elevation) near Saratoga, Wyoming. Records included identification, birth year, yearling year, yearling weight (YW), PAP, first service conception (FSC), overall heifer pregnancy (HPG) and sire. Precipitation data were sourced from the National Oceanic and Atmospheric Administration. Three classifications were created: cumulative precipitation from birth to breeding, precipitation from heifer birth to weaning, and precipitation from heifer weaning to breeding. Initial models contained sources of variation of precipitation classification, PAP, YW and a PAP by precipitation classification interaction for the response of HPG and FSC. Logistical regression was executed followed by analysis of variance. Yearling weight was a predictor of FSC (P < 0.01) while weaning to breeding precipitation was a predictor for HPG (P < 0.05). In general, the PAP by precipitation interaction was not detected; however, PAP by weaning to breeding precipitation tended to predict HPG (P < 0.10). A favorable, positive relationship was detected between YW and FSC (bi=0.00120 to 00120 to 0.00124; P < 0.01). A favorable, positive relationship also existed between weaning to breeding precipitation and HPG (bi=0.2528, P < 0.05). Those results suggested that increased precipitation during the development period from weaning to breeding was advantageous to HPG. The results also provided evidence to suggest that precipitation and PAP may interact to influence breeding success. Thus, we conclude that increased precipitation during the weaning to breeding period appears advantageous to overall breeding success of Angus heifers in a high-altitude production system.