Prophylactic tilmicosin medication of feedlot calves at arrival.

The parenteral administration of the antibiotic tilmicosin given on arrival at a feedlot was evaluated in a group of 304 steer calves. These calves were allotted to 24 pens so that there were 12 replicates of both the control and medicated groups. The treatment rate was reduced significantly during the first five days (p < 0.05) and during the first month (p < 0.01) of the feeding period in the medicated group. The average days from arrival until first treatment for respiratory disease was increased to 21 days in the medicated group compared to 9 days (p < 0.01) for the controls. The medicated group had improved average daily gain (p < 0.01) and feed efficiency (p < 0.01) over the trial period when compared to the nonmedicated animals.