Objectives—To determine whether vaccination with
a killed vaccine prevents fecal shedding of Mycobacterium
avium subsp paratuberculosis, to compare
effectiveness of a culture and cull program in vaccinated
and nonvaccinated herds, and to compare
paratuberculosis-related preventive management in
vaccinated and nonvaccinated herds.
Design—Cross-sectional study (study A) in vaccinated
(n = 25) and nonvaccinated (29) herds of dairy
cows. Longitudinal study (study B) in vaccinated
(n = 2) and nonvaccinated (2) herds of dairy cows.
Procedure—In study A, fecal samples were obtained
from adult cows in herds with and without a history
of vaccination with a killed vaccine. Management
measures were evaluated. In study B, fecal samples
were obtained 4 times at 6-month intervals from
cows older than 6 months. Cows that had positive
test results were removed from the herd directly after
the outcome of the culture.
Results—In study A, differences were not detected
among the 25 herds that were vaccinated; culture
results were positive for M avium subsp paratuberculosis
in 4.4% of herds. In 29 herds that had not been
vaccinated, culture results were positive in 6.7%. In
study B, the percentage of positive results on culture
decreased from 10.9% and 5.7% to 3.5% and 0%,
respectively in the 2 vaccinated herds. In the 2 nonvaccinated
herds, percentages decreased from 6.1%
and 16.5% to 0% and 2.3%, respectively.
Management practices were different between herds
that were vaccinated and herds that were not; owners
of herds that were not vaccinated followed more
preventive management procedures and practiced
less feeding of raw milk to calves.
Conclusions and Clinical Relevance—Vaccination
of calves with a killed vaccine does not prevent transmission
of M avium subsp paratuberculosis; therefore,
hygienic practices remain essential in herd management.
(Am J Vet Res 2001;62:270–274)
Case Description—The owner of a herd of 74 Holstein-Friesian cattle reported decreased milk production, weight loss, and coughing among lactating cows. Owner-initiated antimicrobial treatment was unsuccessful; 1 lactating cow died, and 50% of the lactating cows had clinical signs of respiratory distress, such as tachypnea and coughing.
Clinical Findings—On the basis of history, physical examination findings, and fecal examination results, affected animals were determined to have Dictyocaulus viviparus (lungworm) infestation. The disease history suggested that the herd contained cows with subclinical patent lungworm infestations; after introduction of susceptible heifers, the pastures had become heavily infested with D viviparus and clinical problems subsequently developed in both newly introduced and resident cows.
Treatment and Outcome—Affected and unaffected heifers and adult cows were treated with a pour-on formulation of eprinomectin (0.5 mg/kg [0.23 mg/lb]). One animal died, but 2 weeks after treatment, clinical signs among affected cattle were markedly improved. Ten weeks after treatment, milk production improved from 23 kg/cow/d (51 lb/cow/d) to 28 kg/cow/d (62 lb/cow/d).
Clinical Relevance—The outbreak provides additional evidence that dictyocaulosis is becoming more common among adult dairy cattle, rather than almost exclusively affecting young stock. This may be attributable to anthelmintic use and management practices on dairy farms. Combined with anecdotal reports of an increase in the incidence of dictyocaulosis among adult cattle in North America, D viviparus infestation should be included as a differential diagnosis for decreased milk production, weight loss, and coughing among adult dairy cattle.
Objective—To determine whether insertion of an internal teat sealer (ITS) at the end of lactation would prevent development of new intramammary infections (IMIs) during the nonlactating period.
Design—Controlled clinical trial.
Animals—939 Holstein-Friesian dairy cows from 16 herds.
Procedures—Results of bacteriologic culture of milk samples collected 14 days prior to the end of lactation were used to assign cows to groups (group 1 = negative results for all quarters; group 2 = positive results for ≥ 1 quarter). Quarters of cows in group 1 were treated with an ITS or a single intramammary dose of cloxacillin; quarters of cows in group 2 were treated with cloxacillin in conjunction with an ITS or with cloxacillin alone. Milk samples were collected at the end of lactation and within 8 days after calving.
Results—Regardless of whether the outcome of interest was new IMIs caused by any pathogens, major pathogens, environmental pathogens, or streptococci other than Streptococcus agalactiae, quarters in group 2 treated with both cloxacillin and an ITS were less likely to develop a new IMI than were quarters treated with cloxacillin alone. For cows in group 1, no significant difference in risk of new IMIs was found between treatments.
Conclusions and Clinical Relevance—Results suggest that for dairy cattle with an IMI late in the lactation period, intramammary administration of cloxacillin at the end of lactation followed by insertion of an ITS enhanced protection against development of new IMIs, compared with use of cloxacillin alone.