Objective—To estimate the extent to which infection
with Mycobacterium avium subsp paratuberculosis
(MAP) of cows in a large dairy was attributable to the
infection status of their dams.
Design—Retrospective longitudinal study.
Animals—625 dam-daughter pairs of Holstein cows.
Procedure—Serologic test results were compared
between cows and their dams. Logistic regression
was used to assess whether a cow's serologic status
was associated with its dam's serologic status.
Infection with MAP attributable to being born to a
seropositive dam was estimated for individual cows
and for the herd.
Results—Cows with seropositive dams were 6.6
times as likely to be seropositive, compared with
cows of seronegative dams. For seropositive cows
born to seropositive dams, 84.6% of seropositivity
was attributable to being born to a seropositive dam
and 15.4% to other exposures, including exposure as
calves to flush water that contained feces of adult cattle.
For the herd as a whole, the seropositive status in
34% of seropositive cows was attributable to being
born to a seropositive dam.
Conclusions and Clinical Relevance—For dairy
herds that breed seropositive cows, subsequent
transmission of MAP to their daughters, either congenitally
or via exposure to feces and colostrum of
the dam shortly after birth, can contribute substantially
to maintaining prevalence of MAP in a herd.
Removal of seropositive, clinically unaffected cows
and their daughters would be necessary to reduce
infection with MAP attributable to congenital or periparturient
transmission from dam to daughter. (J Am
Vet Med Assoc 2005;227:450–454)
Objective—To compare the efficacy of a lacteal-derived colostrum replacer (LDCR) for the prevention of failure of passive transfer of immunity (FPT) in calves with that of pooled maternal colostrum (MC).
Design—Randomized field trial.
Animals—568 heifer calves from 1 California dairy.
Procedures—Calves were randomly allocated to 1 of 2 treatment groups and fed 2 doses (200 g of IgG) of an LDCR or 3.8 L of pooled MC. From each calf, blood samples were collected before and approximately 24 hours after treatment. Serum IgG and total protein (TP) concentrations were quantified with standard methods, and the apparent efficiency of IgG absorption was calculated.
Results—At 24 hours after treatment, mean serum TP and IgG concentrations were significantly lower for calves fed pooled MC (TP, 4.77 g/dL; IgG, 7.50 g/L), compared with those for calves fed the LDCR (TP, 5.50 g/dL; IgG, 15.15 g/L). Calves fed the LDCR were 95% less likely to develop FPT (OR, 0.05; 95% confidence interval, 0.03 to 0.08) than were calves fed pooled MC. However, the mean IgG concentration in the pooled MC fed during the study (21.1 g/L) was substantially lower than that (64.3 g/L) determined for representative samples of pooled MC from other southwestern US dairies during a national survey.
Conclusions and Clinical Relevance—Results indicated that, on this particular dairy, calves fed an LDCR were at less risk of developing FPT than were calves fed pooled MC. The LDCR evaluated was a viable alternative for the prevention of FPT in calves.
Objective—To evaluate associations between Mycobacterium avium subsp paratuberculosis (MAP) and caudal fold tuberculin (CFT) test results in cattle.
Design—Longitudinal and cross-sectional evaluations.
Animals—1 California (approx 3,600 cows) and 3 Colorado (approx 640, 1,190, and 1,480 cows) dairy herds considered free of Mycobacterium bovis infection.
Procedures—In the California herd, the association between CFT response and MAP status was determined with ELISA and mycobacterial culture of feces within 1 year before and after CFT testing. The association between CFT and MAP status in all herds was modeled with mixed-effects logistic regression.
Results—In the California herd, significantly higher odds of being classified as suspect by CFT were found for cows with results of MAP ELISA negative before and positive after CFT testing (OR, 5.6) and cows positive before and after CFT testing (OR, 8.1). Higher odds were found for cows positive for mycobacterial culture of feces before and negative for culture after CFT testing (OR, 4.6) and cows negative for mycobacterial culture of feces before and positive for culture after CFT testing (OR, 13.2). All herds had higher odds of being classified as suspect by CFT testing for cows with positive results for ELISA (OR, 2.9) or mycobacterial culture of feces (OR, 5.0), compared with cows with negative results of the same tests.
Conclusions and Clinical Relevance—A strong association was found between positive MAP test results and being classified as a suspect by CFT testing. Within-herd MAP prevalence may affect specificity of CFT testing for tuberculosis in cattle.
Objective—To use mathematical modeling to assess the effectiveness of control strategies for porcine reproductive and respiratory syndrome (PRRS) virus on a swine farm.
Sample—A hypothetical small, medium, or large farrow-to-weaning swine farm in the Midwestern United States.
Procedures—Stochastic models were formulated to simulate an outbreak of PRRS on a farm. Control strategies assessed in those models included none (baseline) and various combinations of mass immunization, herd closure, and gilt acclimatization. Nine different models resulting from the combination of low, moderate, or high PRRS virus virulence and small, medium, or large herd size were simulated. A stabilized status, the outcome of interest, was defined as the absence of positive PCR assay results for PRRS virus in 3-week-old piglets. For each scenario, the percentage of simulations with a stabilized status was used as a proxy for the probability of disease control.
Results—Increasing PRRS virus virulence and herd size were negatively associated with the probability of achieving a stabilized status. Repeated mass immunization with herd closure or gilt acclimitization was a better alternative than was single mass immunization for disease control within a farm.
Conclusions and Clinical Relevance—Repeated mass immunization with a PRRS modified-live virus vaccine with herd closure or gilt acclimitization was the scenario most likely to achieve a stabilized status. Estimation of the cost of various PRRS control strategies is necessary.