Reference | Berge_2006_AppandEnvMic (10249)

A clinical trial was conducted in California on a commercial calf ranch located in the southern San Joaquin Valley. A total of 120, day-old, random source dairy bull calves were purchased from a commercial calf supplier. These calves were enrolled over a 2-day period, followed through 28 days of age, and then sold. Calves originated from several dairy farms, were comingled on the transportation truck, and were representative of dairy bull calves destined for beef. No information on dairy source was provided with the calves, though no more than three calves could have come from a single farm. The calves were randomly off-loaded from the trailer by the calf dealer. No further randomization was attempted, and calves were assigned to treatment groups in the order they were removed from the calf trailer. Calves were placed in newly constructed wooden hutch units. The feeding strategy and vaccination program were identical to those of the ranch’s commercially raised calves for beef or heifer replacement On the day of arrival, all calves received 1.86 liters of a plasma-derived colostrum supplement (Lifeline; APC, Ames, Iowa) and were vaccinated as previously described (7). The trial was designed with four study groups consisting of 30 calves each. In group 1, calves were housed separately from the other experimental groups in an area that had not previously housed calves. Hutches were elevated 30 cm above a concrete floor that had been scraped clean and disinfected with a 0.52% sodium hypochlorite solution prior to the trial. Environmental samples taken from the concrete area prior to the start of the trial were culture negative for E. coli and Salmonella. The area was enclosed by a steel and plastic mesh fence. A biosafety area was provided for caretakers and consisted of a plastic tarp where protective clothes, boots, and gloves were used. Prior to entry into the calf area, boots were disinfected with 0.52% hypochlorite solution and 0.15% iodine solution baths. Separate, new feeding equipment was used for this group. Milk bottles and grain were transported to the calves without coming into contact with any other calf ranch equipment or soil. Calves in this group were managed without using antimicrobials in the milk replacer. Therapeutic treatments consisted only of nonantimicrobial alternatives (Table 1). Calves in group 2 received no antimicrobials in the milk replacer and only nonantimicrobial treatments, as described for group 1. These calves were housed in a row separate from the rest of the calf ranch facility. No specific measures were taken to isolate these calves from the calf ranch environment. In group 3, calves were housed adjacent to and within 1 meter of group 2. Group 3 calves received no antimicrobials in the milk replacer but received individual antimicrobial therapy for clinical disease (Table 1). The antimicrobials used to treat disease were primarily ceftiofur hydrochloride and occasionally penicillin G procaine and tilmicosin. Nonantimicrobial alternatives as described above were used concurrently with antimicrobial treatments. In group 4, calves were housed adjacent to and within 1 meter of group 3. At each feeding, they received a medicated milk replacer containing tetracycline hydrochloride (22 mg/kg of body weight/day; TET-324) and neomycin sulfate (22 mg/kg/day). The antimicrobials were diluted in water and added directly to each bottle before the milk replacer was added in the milk-mixing stage. Therapeutic treatment options were the same as for group 3.

Using two sterile cotton-tipped swabs, rectal fecal samples were taken from all calves on days 1, 14, and 28.

AST Method: Disk Diffusion

Reference explicitly reports AST breakpoints: True

Reference reports using a MIC table: Uncertain