|
Treatmenta
|
Medium used for selectionb
|
Number of animals
|
Sampling dayc
|
Total
|
|---|
| | | |
B
|
C
|
D
|
E
| |
|---|
|
CON
|
MC
|
5
|
5
|
5
|
5
|
5
|
20
|
| |
MT
|
50
|
15
|
19
|
47
|
30
|
111
|
| |
MA
|
50
|
0
|
8
|
1
|
17
|
26
|
|
T
|
MC
|
3
|
3
|
3
|
2
|
3
|
11
|
| |
MT
|
30
|
12
|
10
|
27
|
25
|
74
|
| |
MA
|
30
|
2
|
0
|
1
|
10
|
13
|
|
TS
|
MC
|
3
|
3
|
3
|
3
|
3
|
12
|
| |
MT
|
30
|
23
|
26
|
29
|
29
|
107
|
| |
MA
|
30
|
15
|
14
|
7
|
15
|
51
|
|
V
|
MC
|
3
|
3
|
3
|
3
|
3
|
12
|
| |
MT
|
30
|
11
|
6
|
25
|
27
|
69
|
| |
MA
|
30
|
2
|
2
|
5
|
16
|
25
|
|
Total
| | |
94
|
99
|
155
|
183
|
531
|
- a Steers were fed no antibiotics (control, CON), or chlortetracycline and sulfamethazine (44 ppm; TS); chlortetracycline (11 ppm; T) or virginiamycin (31 ppm; V) administered in two discrete periods (see Figure 1).
- b Isolates were collected by plating fecal slurries onto (i) MacConkey agar (MAC) containing no antibiotics (control, MC), or amended with tetracycline hydrochloride (4 μg/mL; MT) or with ampicillin (50 μg/mL; MA).
- c Sampling days occurred during each of the four phases of the feeding trial (see Figure 1).
