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Theses and Dissertations

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Browsing Theses and Dissertations by Subject "altitude"

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    Pre-weaned beef calf mortality on high altitude ranches in Colorado
    (Colorado State University. Libraries, 2013) Neary, Joseph Michael, author; Garry, Franklyn, advisor; Gould, Daniel, committee member; Knight, Anthony, committee member; Dargatz, David, committee member
    Nationwide Colorado has the 14th largest beef cow population. The sale of cattle and calves is Colorado's highest grossing agricultural product generating over $3 billion annually. Many of the 11,600 cow-calf operations are located at high elevations in the Rocky Mountains. Producer reports suggest that a large number of these ranches experience high pre-weaned calf death loss, as high as 20% of the calf crop, between branding in the spring and weaning in the autumn. During this time many cow-calf operations graze their animals on high altitude mountainous pastures. Due to the extensive, inaccessible nature of the mountainous terrain there have been limited prior investigations of the death loss problem. For the present study physiological, pathological and epidemiological investigations were performed to characterize the problem. A survey of Colorado's beef producers found that the odds of a producer having a greater than average calf death loss increased with increasing altitude. This greater death loss was mainly due to respiratory problems and pulmonary hypertension (also known as high altitude disease or brisket disease). Postmortem examination of calves revealed that approximately equal numbers of calves died from bronchopneumonia and pulmonary hypertension even on ranches that have selected for low pulmonary artery pressure herd sires for over 20 years. The postmortem lesions obtained from calves with pulmonary hypertension suggest that our current understanding of the disease is insufficient. Overlap of clinical signs makes appropriate treatment decisions by producers difficult. Typically, cases of bronchopneumonia occurred earlier in the summer grazing season than cases of pulmonary hypertension, which occurred in the late summer-early fall period. Blood biochemical values for healthy calves at altitude (9,000 ft. or 2,743 m) were strikingly different from literature reports of similarly aged calves sampled at lower altitudes. This reflects the extreme physiological challenges associated with life at high altitude. Arterial blood-gas analysis determined that calves at high altitude have lower oxygen tensions than expected despite hyperventilation. Hematocrit and hemoglobin levels were not significantly increased over age-matched calves at sea level despite chronic hypoxia. In summary, this project determined that high levels of pre-weaned calf death loss occur on high altitude cow-calf operations due to bronchopneumonia and pulmonary hypertension. Why these diseases are particularly problematic is discussed. Further studies are necessary if the problem is to be addressed.