RELATIONSHIPS AMONG TREATMENT FOR RESPIRATORY-TRACT DISEASE, PULMONARY-LESIONS EVIDENT AT SLAUGHTER, AND RATE OF WEIGHT-GAIN IN FEEDLOT CATTLE

Objective-To quantify the effects of treatment for clinical respirator y tract disease and pulmonary lesions identified at slaughter on rate of weight gain in feedlot cattle. Design-Prospective longitudinal stud y. Animals-469 feedlot steers. Procedure-Clinical respiratory tract di sease was monitored between birth and slaughter. Steers were weaned at approximately 6 months old and entered into the feedlot for a mean of 273 days. Mean daily weight gain (MDG) was monitored during the feedi ng period. Lungs were collected at slaughter and evaluated for gross l esions indicative of active or resolved pneumonia. Results-Mean daily weight gain during the feeding period was 1.30 kg, and ranged from 1.1 6 to 1.46 kg within individual pens. Thirty-five percent of steers rec eived treatment for respiratory tract disease between birth and slaugh ter, whereas 72% had pulmonary lesions evident at slaughter. Among ste ers treated for clinical respiratory tract disease, 78% had pulmonary lesions, whereas 68% of untreated steers had pulmonary lesions. Pulmon ary lesions at slaughter were associated (P <0.01) with a 0.076-kg red uction in MDG during the feeding period. Treatment for clinical diseas e was not associated with MDG after adjustment for the effect of pulmo nary lesions. Clinical Implications-Treatment of clinically affected f eedlot cattle may be inadequate to prevent significant production loss es attributable to respiratory tract disease.