Graduate Thesis Or Dissertation
 

Chemical analysis of three forage plants collected from pastures suspected of inciting acute bovine pulmonary emphysema

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  • A two-year study was made of pastures suspected of inciting acute bovine pulmonary emphysema (ABPE) in east-central Oregon. Objectives of this study were (1) to determine the vegetation composition of these pastures, (2) to determine seasonal trends of tryptophan, crude protein, and nitrogen/sulfur ratios in selected pasture plants, (3) to determine daily utilization immediately after cattle were introduced to these pastures, (4) to relate cattle foraging habits to development of symptoms of ABPE, and (5) to determine common herd characteristics and management practices on ranches frequently affected by ABPE. Frequency data collected from plant communities on inciting pastures on the Lemcke and Palmer ranches showed a large number of species on these meadows. Kentucky bluegrass, Nebraska sedge, and common rush were common to me sic portions of all pastures studied. These three species were collected over the 1973 growing season and analyzed for tryptophan, crude protein and the nitrogen/sulfur ratio. Tryptophan content decreased from May 24 to September 4, with the largest change occurring over the first half of the season. It was determined that a 1000 lb cow eating the forage with the highest tryptophan level would have to ingest 43.8 kg (dry weight) of material to assimilate an equivalent amount of a single dose of tryptophan administered in laboratory induction of ABPE. This amount of forage could only be ingested over a period of several days. Crude protein content of Nebraska sedge, common rush, and Kentucky bluegrass declined from the first sampling to the last and decreased most rapidly early in the season. Crude protein of all plants was adequate for lactating range cattle through the soft dough stages of plants sampled. Crude protein content of Kentucky bluegrass in latter stages of seed development were not adequate to maintain lactating range cows. Nitrogen/sulfur ratios of Nebraska sedge, common rush, and Kentucky bluegrass varied more than tryptophan or crude protein within sampling periods. A decrease in nitrogen/sulfur ratios was noted over the season, the most rapid decline occurring during the last part. Sulfur content of all samples was adequate to maintain lactating range cows. No conclusions were drawn concerning the involvement of the nitrogen/ sulfur ratio in ABPE. Utilization measurements taken on me sic portions of the Lemcke and Palmer pastures showed Kentucky bluegrass, common rush, and Nebraska sedge utilized on the Lemcke ranch and birdsfoot trefoil, Kentucky bluegrass, bluebunch wheatgrass, smooth brome, and Nebraska sedge selected by cattle on the Palmer ranch. Observations of grazing habits of cattle on the Lemcke and Palmer pastures in 1972 and 1973 failed to correlate grazing patterns with development of symptoms of ABPE. Questionnaires were completed for six ranch operations that had recent histories of ABPE. Factors common to all six areas were (1) occurrence of the disease between early July and mid-October, (2) appearance of symptoms after a change from relatively dry, sparse to relatively succulent, abundant forage, (3) a natural water source, (4) apparent high susceptibility of mature, lactating Herefords, (5) unpredictable morbidity, and (6) high probability of recurrence of symptoms after ABPE had been diagnosed in a herd. Determination of cattle diets on ABPE-inciting pastures and chemical analysis of additional plant species is suggested for future work. Investigation of summer forage on frequently victimized ranches and continued compilation of case history information is also needed.
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Déclaration de droits
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