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).
Animals—454 steers (body weight, 200 kg).
Procedure—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
Conclusions and Clinical Relevance—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. (Am J Vet Res 2000;61:
Objective—To determine the effect of intranasal
exposure to live leukotoxin (LktA)-deficient
Mannheimia haemolytica (MH) at the time of feedyard
arrival on nasopharyngeal colonization by wildtype
MH in calves.
Procedure—Calves from Arkansas (AR calves;
n = 100; mean body weight, 205 kg) were purchased
from an order buyer barn. Calves from New Mexico
(NM calves; n = 100; mean body weight, 188 kg) were
obtained from a single ranch. Calves were transported
to a feedyard, where half of each group was
exposed intranasally with LktA-deficient MH at the
time of arrival. Calves were observed daily for respiratory
tract disease (RTD), and nasal swab specimens
were collected periodically to determine nasopharyngeal
colonization status with MH. Serum samples
were assayed for antibodies to MH.
Results—15 AR calves had nasopharyngeal colonization
by wild-type MH at the order buyer barn, whereas
none of the NM calves had nasopharyngeal colonization.
Intranasal exposure to LktA-deficient MH
elicited an increase in serum antibody titers against
MH in NM calves, but titers were less in NM calves
treated for RTD. Exposure of NM calves to LktA-deficient
MH offered protection from nasopharyngeal colonization
by wild-type MH.
Conclusions and Clinical Relevance—Exposure of
calves to LktA-deficient MH elicited an increase in
serum antibody titers against MH and decreased colonization
of the nasopharynx by wild-type MH. Earlier
exposure would likely allow an immune response to
develop before transportation and offer protection from
nasopharyngeal colonization and pneumonia caused by
wild-type MH. ( Am J Vet Res 2003;64:580–585)
Objective—To determine effects of vaccination prior
to transit and prophylactic administration of florfenicol
at time of arrival at a feedyard on health of cattle and
colonization of the nasopharynx by Mannheimia
Animals—121 steers from Tennessee and 84 steers
from New Mexico.
Procedure—Half of the steers were vaccinated
before transport to a feedyard. Steers from
Tennessee were vaccinated with MH bacterin-toxoid,
and steers from New Mexico were vaccinated
intranasally with modified-live leukotoxin-deficient
MH. Half of the vaccinates and nonvaccinates were
randomly selected to receive florfenicol on arrival at
the feedyard. Steers were observed daily for respiratory
tract disease (RTD).
Results—Administration of florfenicol at time of
arrival reduced the incidence of RTD, delayed the
interval before onset of RTD, and reduced the incidence
of MH colonization of the nasopharynx for at
least 4 days, but vaccination did not have any effect.
Vaccination elicited an increase in serum antibody
titers to MH. Administration of florfenicol at time of
arrival reduced the development of serum antibody
titers in intranasally vaccinated steers and both
groups of nonvaccinated steers, but intranasal vaccination
did not affect colonization by wild-type MH.
Conclusions and Clinical Relevance—Administration of florfenicol at time of arrival
decreased the incidence of MH organisms in the
nasopharynx and delayed the onset of RTD.
Prophylactic use of suitable antibiotics is likely to
reduce the incidence of acute RTD in calves for several
days after arrival at feedyards, which is the period
when they are most susceptible to infectious organisms.
(Am J Vet Res 2002;63:251–256)
Objective—To compare shedding patterns and serologic responses to bovine coronavirus (BCV) in feedlot calves shipped from a single ranch in New Mexico (NM calves) versus calves assembled from local sale barns in Arkansas (AR calves) and to evaluate the role of BCV on disease and performance.
Animals—103 feedlot calves from New Mexico and 100 from Arkansas.
Procedures—Calves were studied from before shipping to 35 days after arrival at the feedlot. Nasal swab specimens, fecal samples, and serum samples were obtained before shipping, at arrival, and periodically thereafter. Bovine coronavirus antigen and antibodies were detected by use of an ELISA.
Results—NM calves had a high geometric mean titer for BCV antibody at arrival (GMT, 1,928); only 2% shed BCV in nasal secretions and 1% in feces. In contrast, AR calves had low antibody titers against BCV at arrival (GMT, 102) and 64% shed BCV in nasal secretions and 65% in feces. Detection of BCV in nasal secretions preceded detection in feces before shipping AR calves, but at arrival, 73% of AR calves were shedding BCV in nasal secretions and feces. Bovine coronavirus infection was significantly associated with respiratory tract disease and decreased growth performance in AR calves.
Conclusions and Clinical Relevance—Replication and shedding of BCV may start in the upper respiratory tract and spread to the gastrointestinal tract. Vaccination of calves against BCV before shipping to feedlots may provide protection against BCV infection and its effects with other pathogens in the induction of respiratory tract disease.
Objective—To detect bovine adenovirus serotype 7
(BAV-7) infections in calves by use of viral isolation
and serologic testing.
Animals—205 postweaning calves.
Procedure—121 calves were assembled by an order
buyer through auction markets in eastern Tennessee
and transported to New Mexico where they were
commingled with 84 healthy ranch-reared calves.
Tests included viral isolation in cell culture from
peripheral blood leukocytes (PBL) and detection of
serum BAV-7 antibodies by use of microtitration viral
Results —BAV-7 was isolated from PBL of 8 calves
and seroconversion to BAV-7 was detected for 38 of
199 (19.1%) calves. Concurrent bovine viral diarrhea
virus infections were detected in most calves from
which BAV-7 was isolated.
Conclusions and Clinical Relevance —Results of our
study indicate that BAV-7 infections can be found in
postweaning commingled calves and may develop
more commonly in calves with concurrent infections
with viruses such as bovine viral diarrhea virus
(BVDV). (Am J Vet Res 2002;63:976–978).