Abstract
Pulmonary hypertension (PH) can cause heart failure in cattle and is measured with pulmonary arterial pressure (PAP). Although historically associated with high elevation (> 1,500 m), PH and heart failure are increasing in moderate altitude feedlots. High elevation production systems wean and stocker calves before placing them in feedlot finishing systems of moderate elevations on the Great Plains of North America. The objective was to evaluate PAP and growth of steers finished at moderate or high elevation with varied lengths of post-weaning grazing. Forty steers from Colorado’s Beef Improvement Center (2,150 m) with PAP averaging 41.5 ± 0.5 mmHg were randomly assigned to one of four management groups: 1) traditional stocker and finishing system (i.e., grown and finished at 1,420 m beginning at 10 months of age), 2) extended stocker grazing at high elevation (2,150 m), but finishing at 1,420 m at 18 months of age, 3) stocker and finishing at high elevation (2,150 m) at 24 months of age, or 4) grass finishing (2,150 m) > 24 months of age. Weight and PAP data were analyzed with a repeated measures model. Effects of group, PAP-date, and their interaction (P < 0.01) were observed. Pre-harvest, steers in the stocker-finishing group at high elevation had higher PAP than the moderate elevation finishing groups (52.9 > 46.5 ± 1.7 mmHg), but PAP (41.1 ± 1.6) was unchanged across dates in the grass finishing group and lower than the grain-fed groups. Pre-harvest live weight averaged 621.6 ± 11.8 kg in all three grain finishing groups, whereas grass finishing steers weighed 436.6 ± 11.5 kg on these dates. In summary, grain-fattening appeared to cause PH independent of elevation. Steers grazing in a high elevation grass finishing system did not experience increased PAP, but required several more months of grazing to reach harvest criteria.
Keywords: finishing, production system, pulmonary arterial pressure