Use of antibiotics and roxarsone in broiler chickens in the USA: analysis for the years 1995 to 2000.

In 1995, an antibiotic (ANT) was used in starter, grower, and withdrawal (WD) feeds by 94.3, 98.2, and 75.1% of broiler production units, but by 2000, ANT use had declined to 64.8, 66.9, and 48.1% respectively. Roxarsone (ROX) was used in the starter and grower feeds by 69.8 and 73.9% of production units. Bacitracin (BAC) was used more frequently than other antibiotics in the starter and grower feed. Virginiamycin (VIR) was used most frequently in the WD feed. Most units (69.4%) reported use of two different antibiotics. The use of programs comprising two ANT decreased, whereas programs with a single ANT increased during the period of study. A combination of ionophore (ION) + ROX + ANT was employed most frequently in the starter and grower feeds, whereas an ANT alone was used most frequently in the WD ration. The use of ION + ROX + ANT declined from 1995 to 2000, but use of ION + ROX increased. There were no significant differences in calorie conversion whether plants used ION + ROX + ANT, ION + ROX, or ION + ANT. The number of days to rear birds to 2.27 kg was significantly greater for production units using ION + ROX. Mortality was lower for units that used ION + ROX + ANT and ION + ROX than for those that used ION + ANT. Production units that used ION + ANT were more likely to rear birds to a weight greater than 2.5 kg than to 2.0 to 2.5 kg. Units in the South and Central states were more likely to use an ION + ROX than those in the Northeast and Atlantic states, whereas for ION + ROX + ANT the reverse was the case. The cost of medicating with ION + ROX + ANT decreased from 1995 to 1998.