|Duff, Glenn - NEW MEXICO STATE UNIV.,NM|
|Loan, Raymond - TX A&M U., COLL. STATION|
Submitted to: American Journal of Veterinary Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 5, 2001
Publication Date: February 1, 2002
Interpretive Summary: Acute pneumonia usually occurs in transported calves within the 1st week of arrival at the feedyard. Management practices to reduce its incidence include vaccination and prophylactic medication. The opportunity to vaccinate is often limited to the assembly point immediately before transit or on arrival at the feedyard, which does not allow time for currently available vaccines to take effect before the disease occurs. Prophylactic medication on arrival has reduced the incidence of the disease and has inhibited colonization by a bacterial pathogen that is the major cause of pneumonia. Florfenicol is another antibiotic commonly used to treat pneumonia in cattle. Medication with florfenicol on arrival reduced the incidence of pneumonia and delayed the time before it occurred. It also inhibited colonization by the bacterial pathogen for several days. Since colonization by the bacterial pathogen is a prerequisite for the develop- ment of pneumonia, inhibition of colonization is a desirable goal to seek in order to prevent pneumonia. The delay of early pneumonia afforded by the antibiotic may allow time for vaccination to take effect.
Technical Abstract: This experiment was to determine the effect of florfenicol metaphylaxis and pretransit vaccination on colonization of the nasopharynx of transported steers by Mannheimia haemolytica (MH). Steers from Tennessee (n = 121), and from New Mexico (n = 84) were used. One half of the steers in each group were vaccinated before transport to a feedyard in New Mexico. Tennessee steers were vaccinated with a MH bacterin-toxoid, and New Mexico steers were vaccinated intranasally with a live leukotoxin-deficient MH. One half of the vaccinates and non-vaccinates were medicated with flor- fenicol upon arrival. Steers were observed daily for respiratory tract disease. Medication on arrival reduced the incidence of respiratory tract disease and delayed the time before respiratory tract disease did occur, but vaccination had no effect. Medication on arrival reduced the incidence of MH colonization of the nasopharynx for at least 4 days. Intranasal vaccination with live MH had no effect on colonization by wild-type MH. Vaccination elicited an increase in serum antibody titer in both medicated and non-medicated steers. Medication reduced the development of serum titers in modified-live vaccinated and in both groups of non-vaccinated steers. Prophylactic use of suitable antibiotics before transport or at the time of arrival at a feedlot is likely to reduce the incidence of acute respiratory tract disease in calves for the initial several days after arrival, which is the period when they are most susceptible to infectious organisms.