Effects of tilmicosin phosphate, administered prior to transport or at time of arrival, and feeding of chlortetracycline, after arrival in a feedlot, on Mannheimia haemolytica in nasal secretions of transported steers.
OBJECTIVE
To determine effects of time of administration of tilmicosin and feeding of chlortetracycline on colonization of the nasopharynx of transported cattle by Mannheimia haemolytica (MH).


METHODS
454 steers (body weight, 200 kg).


METHODS
3 studies included 4 truckloads of steers assembled and processed in the southeastern United States. For each truckload of steers, a third received tilmicosin before transportation (PRIOR), then all were transported to a feedlot in New Mexico (23 hours). At arrival (day 0), another third received tilmicosin (ARR). The remaining third did not receive tilmicosin (control steers [CTR]). Steers in studies 1 and 2 were housed in a feedlot, and steers in study 3 were housed on wheat pasture. One half of the steers from each group in studies 2 and 3 were fed chlortetracycline on days 5 to 9. Steer with signs of respiratory tract disease were treated. Nasal swab specimens were examined for MH to determine colonization.


RESULTS
PRIOR and ARR steers had a lower incidence of respiratory tract disease and MH colonization than CTR steers, but PRIOR and ARR steers did not differ. Feeding chlortetracycline did not have an effect.


CONCLUSIONS
Tilmicosin can inhibit MH from colonizing the nasopharynx of cattle. Because tilmicosin inhibits the growth of MH in the respiratory tract, medication with tilmicosin prior to transport should reduce the incidence of acute respiratory tract disease during the first week at the feedlot when calves are most susceptible to infectious organisms.
Frank
G H
GH
Respiratory Diseases of Livestock Research Unit, USDA, Agricultural Research Service, National Animal Disease Center, Ames, IA 50010, USA.
Duff
G C
GC
D000284:Administration, Oral; D000821:Animal Feed; D000818:Animals; D000900:Anti-Bacterial Agents / Q000008:administration & dosage / Q000627:therapeutic use*; D019072:Antibiotic Prophylaxis / Q000662:veterinary*; D002417:Cattle; D002418:Cattle Diseases / Q000382:microbiology / Q000517:prevention & control*; D002751:Chlortetracycline / Q000008:administration & dosage / Q000627:therapeutic use*; D004334:Drug Administration Schedule; D018942:Macrolides; D008297:Male; D009297:Nasal Mucosa / Q000378:metabolism* / Q000382:microbiology*; D009516:New Mexico; D009919:Orchiectomy; D015661:Pasteurellaceae / Q000187:drug effects* / Q000254:growth & development / Q000302:isolation & purification; D016871:Pasteurellaceae Infections / Q000188:drug therapy / Q000517:prevention & control / Q000662:veterinary*; D012140:Respiratory Tract Diseases / Q000188:drug therapy / Q000662:veterinary*; D015144:Southeastern United States; D014186:Transportation; D015645:Tylosin / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000627:therapeutic use*
D000900:Anti-Bacterial Agents; D018942:Macrolides; D002751:Chlortetracycline; C052319:tilmicosin; D015645:Tylosin