Table 1.
Treatmenta | Media used for selectionb | Sampling dayc | Total | ||||
---|---|---|---|---|---|---|---|
0 | 14 | 84 | 113 | 225 | |||
CON | BEA | 24 | 20 | 25 | 25 | 23 | 119 |
BEAE | 6 | 8 | 17 | 16 | 9 | 58 | |
BEAT | 9 | 9 | 19 | 22 | 19 | 79 | |
T11 | BEA | 24 | 20 | 25 | 25 | 25 | 122 |
BEAE | 6 | 8 | 15 | 20 | 14 | 65 | |
BEAT | 8 | 7 | 24 | 25 | 22 | 86 | |
Total | 77 | 72 | 125 | 133 | 112 | 519 |
Steers fed no antibiotics (control, CON) or tylosin phosphate (11 ppm; T11); administered continuously and withdrawn on day 197.
Isolates were streaked onto bile esculin azide agar (BEA) containing no antibiotics, or amended with erythromycin (8 μg/mL; BEAE) or with tylosin (32 μg/mL; BEAT).
Sampling days began at day 0 (arrival at feedlot) prior to antibiotic administration and continued until the end of the feeding trial; sample day 0 and 14 were during the silage-based diet, day 84 during the transition diet and day 113 and 225 during the grain-based diet.