Effects of timing of chlortetracycline in combination with decoquinate on growth performance, health, and carcass characteristics of feeder steers

Abstract

Steer calves (n=1690) were used in a 220-day study to evaluate the effects of chlortetracycline (CTC) plus decoquinate (DEQ) on health and performance of feedlot cattle. Treatments were (1) control (CON); (2) CTC+decoquinate early (CTC+DEQ Early), and (3) CTC+decoquinate delayed (CTC+DEQ Delayed). Ten mg of CTC/lb (22 mg/kg) body weight (BW) was fed daily for 5 consecutive days beginning either on day 0 (Early) or day 6 (Delayed); decoquinate was fed at 22.7 mg/100 lb (45.4 kg) BW for 28 days. There were 6 pens per treatment, and 85 to 105 steers per pen. Steers in the CTC+DEQ groups had higher (P<0.01 to 0.05) dry matter intake and average daily gain than CON steers, but feed efficiency did not differ among treatments. Respiratory morbidity and re-treatment rates were lower (17 vs 23%, and 11 vs 22%, respectively, P<0.01) for steers in the CTC+DEQ groups than for those in the CON group. Timing of the initial CTC treatment had minimal effect on health and performance; however, feeding CTC for at least 10 days during the receiving period reduced morbidity and improved overall performance.