The effect of withdrawing growth promoting antibiotics from broiler chickens: A long-term commercial industry study

A comprehensive study with close to 7 million growing broilers spanning 3 yr and 158 paired-houses was conducted in two different geographic locations under industry conditions. A limited number of farms, most having tunnel-ventilated, dark-out facilities and all having similar equipment were selected to enhance repeatability over time. Equal numbers of birds from different breeder flocks were placed in the trial and control houses. The control treatment used the current field feed coccidiostat, roxarsone, and growth-promoting antibiotics (GPA) program, and the trial was identical to the control treatment with no GPA. The average age of all flocks in the entire trial was 52 d of age. Removal of GPA from the feed resulted in an average reduction in livability of 0.2% on the Delmarva Peninsula (DMV) and 0.14% in North Carolina (NC), an average decrease in body weight of 0.03 lb on DMV and 0.04 lb in NC, and an average increase in feed conversion ratio of 0.016 on DMV and 0.0.012 in NC. Skin color scores and field condemnations were not significantly negatively impacted by removing GPA. Both male and female body weights were less uniform without GPA. Placing new litter on farms resulted in only temporary improvement in field performance of birds given no GPA. The pattern of difference for feed conversion between trial and control over time was different between geographic locations. This study clearly shows that making a decision to withdraw GPA should not be made with only limited data conducted in one location or over a short time.