Effect of pulmonary arterial pressure and precipitation on reproductive performance in Angus heifers in south central Wyoming
Reproductive success is important for profitability of the commercial beef operation. However, fertility is affected by many physiological and environmental factors. Age and weight directly influence puberty in cattle, which is also influenced by nutrition. Many areas in the western United States where beef cattle are produced are arid rangelands that rely on natural precipitation. In addition, irrigation systems are often contingent on snowmelt. This variable water availability effects forage production and nutrient availability for developing heifers relying on forage resources. Due to this, precipitation amount is of concern to beef producers. Furthermore, in areas of the mountain west above 1,500 meters, producers have to contend with high altitude disease (HAD) as a result of reduced atmospheric oxygen. This can be a fatal disease in cattle that is a consequence of right sided heart failure. Pulmonary arterial pressure (PAP) scores are indicator traits of HAD, and can be used to diagnose cattle at risk for the disease, or animals in the early stages of pulmonary hypertension and (or) heart failure. There is concern that the physiological stress of elevated PAP score could compound environmental stressors, such as variable precipitation. Thus, the objective of this study was to investigate the effects of precipitation and PAP score on beef heifer fertility. Data used 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 where an Angus cow herd of 420 mother cows are managed for research purposes. 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 (https://www.ncdc.noaa.gov/cag/county/time-series, March 3, 2021). From these data, three classifications were created: cumulative precipitation from birth to breeding, precipitation from heifer birth to weaning, and precipitation from heifer weaning to breeding. Mean FSC was 47% (± 10%) while average HPG was 85% (± 8%). Average PAP score was 41.09 mmHg (± 7.52 mmHg) and average YW was 308.52 kg (± 47.85 kg). Cumulative precipitation averaged 56.01 cm (± 8.74 cm), birth to weaning precipitation averaged 26.97 cm (± 5.94 cm) and weaning to breeding precipitation averaged 29.06 cm (± 5.89 cm). Initial models contained sources of variation of precipitation classification, PAP, and YW for the response of HPG and FSC. Logistical regression was executed and analysis of variance (ANOVA) revealed that regardless of classification, precipitation was a significant source of variation for HPG (P<0.01). Yearling weight was an important predictor for FSC (P<0.01) and PAP was an important indicator of both HPG and FSC (P<0.05). A favorable, positive relationship was detected between precipitation and HPG (βi= 0.06 to 0.07; P<0.01). A favorable, positive relationship also existed between YW and FSC (βi= 0.00120 to 0.00124; P<0.01). The favorable, negative relationship between PAP and reproductive success suggested that lower PAP scores were advantageous for heifer reproductive success (βi=-0.0091 to -0.0168; P<0.01). Following the execution of the initial models, the heifer's sire was included in the models as a random effect to assess potential genetic effects in the analyses of FSC and HPG. Precipitation was still an important source of variation for HPG (P<0.01) and similar results were found with YW (P<0.01) in these models. However, PAP was an important source of variation for HPG (P<0.01), and a tendency was observed for FSC (P<0.10). These results suggested a moderate to strong genetic effect exist in prediction of heifer fertility traits. Relationships between precipitation and HPG were favorable and positive (βi= 0.05 to 0.07; P<0.01) and YW relationships were also favorable and positive for FSC (βi= 0.00128 to 0.00134; P<0.01). Pulmonary arterial pressure was a favorable, negative relationship with HPG (βi= -0.0180 to -0.0185; P<0.05). The results suggested that sire, PAP score and precipitation directly affect heifer fertility. Thus, we conclude that low PAP scores and higher precipitation are advantageous for breeding success of purebred Angus heifers.
genetics, pulmonary hypertension, beef heifers, reproduction, precipitation
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