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Abstract

Objective—To estimate when foot-and-mouth disease virus (FMDV) would first be detected in bulk tank milk of dairies after exposure to FMDV.

Sample Population—Hypothetical dairy herds milking 100, 500, or 1,000 cows.

Procedures—For each day after herd exposure to FMDV, infection, milk yield, and virolactia were simulated for individual cows with low and high rates of intraherd transmission to estimate when a PCR assay would detect virus in bulk tank milk. Detection limits were based on assumptions for the number of virus genomes per milliliter of milk and for analytical sensitivity of a PCR assay.

Results—A mean of 10% of the cows was predicted to have FMD lesions from 7 to 8 days and from 13.5 to 15 days after herd exposure for herds with high and low intraherd transmission rates, respectively. Herd bulk milk volume decreased by 10% by 8.5 to 9.5 days and by 15 to 16.5 days after herd exposure for herds with high and low transmission rates, respectively. Mean times by which FMDV would be first detected in bulk milk were 2.5 days and 6.5 to 8 days after herd exposure, which were extended for 10 to 11 days and 17 to 18 days for herds with high and low transmission rates, respectively.

Conclusions and Clinical Relevance—PCR screening of bulk milk for FMDV would likely detect FMDV in dairy herds several days sooner than might be expected for owner reporting of clinical signs and thus should be worthy of consideration for regional, national, or global FMD surveillance.

Full access
in American Journal of Veterinary Research

Abstract

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)

Full access
in Journal of the American Veterinary Medical Association

SUMMARY

Objectives

To estimate the extent to which abortion risk in dairy cattle during subsequent pregnancies was associated with congenitally-acquired Neospora caninum infection and previous abortions.

Animals

468 Holstein cattle.

Procedure

Newborn heifer calves were tested for evidence of congenital infection attributable to N caninum and examined repeatedly until the completion of their second lactation for serologic status and evidence of abortion.

Results

Compared with noninfected cows, congenitally infected cows had a 7.4-fold higher risk of abortion during their initial pregnancy and a 1.7-fold higher risk of aborting the first pregnancy during their first lactation. During the first pregnancy of their second lactation, congenitally infected cows that had aborted previously had a 5.6-fold higher risk of abortion, compared with cows that had not previously aborted and that were seronegative. The fetal risk period for N caninum-associated death began sooner and extended later during the initial pregnancy, compared with subsequent pregnancies.

Conclusion

Congenitally acquired N caninum infection can cause a substantial number of abortions during the initial pregnancy of heifers, with abortion risk attributable to N caninum decreasing in subsequent pregnancies, possibly because of selective culling. Subsequent abortions can be expected in congenitally infected cows that have aborted previously. (Am J Vet Res 1997;58:1381–1385)

Free access
in American Journal of Veterinary Research

Objective

To determine whether cows seropositive to Neospora caninum produced less milk during their first lactation than seronegative cows.

Design

Repeated-measures, prospective study.

Animals

372 Holstein cows in their first lactation.

Procedure

Cows were tested repeatedly before and during their first lactation for antibodies to N caninum. One-way and repeated-measures ANOVA were used to determine whether mean daily milk weights and milk weights from Dairy Herd Improvement Association testing were less for seropositive cows than for seronegative cows.

Results

Weekly mean daily milk weights for the 118 seropositive cows were significantly less than those for the 254 seronegative cows, and milk production for seropositive cows (mean, 55.2 Ib/cow/d) was 2.5Ib/cow/d less than that for seronegative cows (mean, 57.7 Ib/cow/d). Analysis of results from Dairy Herd Improvement Association testing revealed that production of seropositive cows was less for milk (3.1 Ib/cow/d), fat-corrected milk (3.6 Ib/cow/d), and fat (0.14 Ib/cow/d) than production of seronegative cows.

Clinical Implications

The economic impact of N caninum infection in dairy cows can include reduced revenues from decreased milk production, which may warrant culling of young, seropositive replacement stock. (J Am Vet Med Assoc 1997;210:672–674

Free access
in Journal of the American Veterinary Medical Association

Abstract

Objectives

To estimate the extent to which cows infected with Neospora caninum were culled, compared with noninfected cows, and to identify differences in reasons for culling between infected and noninfected cows.

Animals

442 Holstein cows on a commercial dairy with 36% seroprevalence for N caninum.

Procedure

Culling of cows was done after first calving without knowledge of N caninum serologic status.

Results

Risk of a seropositive cow dying was not different from that of a seronegative cow (P = 0.50). Seropositive cows were culled 6.3 months earlier than seronegative cows, and had a 1.6 times greater risk of being culled, compared with seronegative cows (P = 0.004), after adjusting for culling risk associated with abortion. For cows culled for low milk production, culling risk for a seropositive cow was twice that for a seronegative cow (P = 0.007).

Conclusions

The economic impact of N caninum infection in dairy cattle can be expected to extend beyond that for abortion alone. Costs of the disease also may include premature culling and diminished milk production.

Clinical Relevance

Plans to control N caninum infection on dairies should include consideration that benefits may include reduction in premature culling and increase in milk production. (Am J Vet Res 1996;57:1559–1562)

Free access
in American Journal of Veterinary Research

Summary

A prospective observational study was performed to determine whether palpation per rectum of cows in the first 6 weeks of gestation to diagnose pregnancy contributed to fetal attrition. Pregnancy diagnoses were made by private practitioners as part of their routine herd-health service on 9 dairies in the San Joaquin Valley of California. To determine whether there was an association between abortion and fetal age at time of palpation, the probability of abortion was tested as a function of fetal age at palpation, controlling for possible modifying and confounding effects of herd, age at conception, gravidity, parity, and number of days-in-lactation at conception. Results of logistic regression analyses for 19,411 pregnancies followed for up to 90 days after palpation indicated that, during the 28- to 42-day period, palpation of fetuses earlier in the period was associated with a significantly (P < 0.0001) low probability of abortion, compared with that for palpation later in the period. An association between abortion and palpation of fetuses > 42 days of age was not found. Results were suggestive that, given conditions and techniques typical of private practice, fetal death may not be a usual manifestation of early palpation of cows to diagnose pregnancy, rather, that there may be a slight increase in risk of fetal death as the fetal age at palpation increases from 28 to 42 days.

Free access
in Journal of the American Veterinary Medical Association

Abstract

Objective—To estimate direct and indirect contact rates on livestock facilities and distance traveled between herd contacts.

Sample Population—320 beef, dairy, goat, sheep, and swine herds, 7 artificial insemination technicians, 6 hoof trimmers, 15 veterinarians, 4 sales yard owners, and 7 managers of livestock-related companies within a 3-county region of California.

Procedure—A questionnaire was mailed to livestock producers, and personal and telephone interviews were conducted with individuals.

Results—Mean monthly direct contact rates were 2.6, 1.6, and 2.0 for dairies with < 1,000, 1,000 to 1,999, and ≥ 2,000 cattle, respectively. Mean indirect contact rates on dairies ranged from 234 to 743 contacts/ mo and increased by 1 contact/mo as herd size increased by 4.3. Mean direct monthly contact rate for beef herds was 0.4. Distance traveled by personnel and vehicles during a 3-day period ranged from 58.4 to 210.4 km. Of livestock arriving at sales yards, 7% (500/7,072) came from ≥ 60 km away, and of those sold, 32% (1,180/3,721) were destined for a location ≥ 60 km away. Fifty-five percent (16/29) of owners of large beef herds observed deer or elk within 150 m of livestock at least once per month.

Conclusions and Clinical Relevance—Direct and indirect contacts occur on livestock facilities located over a wide geographic area and at a higher frequency on larger facilities. Knowledge of contact rates may be useful for planning biosecurity programs at the herd, state, and national levels and for modeling transmission potential for foot-and-mouth disease virus. (Am J Vet Res 2001;62:1121–1129)

Full access
in American Journal of Veterinary Research

Abstract

Objective—To develop a spatial epidemic model to simulate intraherd and interherd transmission of footand- mouth disease (FMD) virus.

Sample Population—2,238 herds, representing beef, dairy, swine, goats, and sheep, and 5 sale yards located in Fresno, Kings, and Tulare counties of California.

Procedure—Using Monte-Carlo simulations, a spatial stochastic epidemic simulation model was developed to identify new herds that would acquire FMD following random selection of an index herd and to assess progression of an epidemic after implementation of mandatory control strategies.

Results—The model included species-specific transition periods for FMD infection, locations of herds, rates of direct and indirect contacts among herds, and probability distributions derived from expert opinions on probabilities of transmission by direct and indirect contact, as well as reduction in contact following implementation of restrictions on movements in designated infected areas and surveillance zones. Models of supplemental control programs included slaughter of all animals within a specified distance of infected herds, slaughter of only high-risk animals identified by use of a model simulation, and vaccination of all animals within a 5- to 50-km radius of infected herds.

Conclusions and Clinical Relevance—The FMD model represents a tool for use in planning biosecurity and emergency-response programs and in comparing potential benefits of various strategies for control and eradication of FMD appropriate for specific populations. (Am J Vet Res 2003;64:195–204)

Full access
in American Journal of Veterinary Research

Abstract

Objective—To assess estimated effectiveness of control and eradication procedures for foot-andmouth disease (FMD) in a region of California.

Sample Population—2,238 herds and 5 sale yards in Fresno, Kings, and Tulare counties of California.

Procedure—A spatial stochastic model was used to simulate hypothetical epidemics of FMD for specified control scenarios that included a baseline eradication strategy mandated by USDA and supplemental control strategies of slaughter or vaccination of all animals within a specified distance of infected herds, slaughter of only high-risk animals identified by use of a model simulation, and expansion of infected and surveillance zones.

Results—Median number of herds affected varied from 1 to 385 (17% of all herds), depending on type of index herd and delay in diagnosis of FMD. Percentage of herds infected decreased from that of the baseline eradication strategy by expanding the designated infected area from 10 to 20 km (48%), vaccinating within a 50-km radius of an infected herd (41%), slaughtering the 10 highest-risk herds for each infected herd (39%), and slaughtering all animals within 5 km of an infected herd (24%).

Conclusions and Clinical Relevance—Results for the model provided a means of assessing the relative merits of potential strategies for control and eradication of FMD should it enter the US livestock population. For the study region, preemptive slaughter of highest-risk herds and vaccination of all animals within a specified distance of an infected herd consistently decreased size and duration of an epidemic, compared with the baseline eradication strategy. (Am J Vet Res 2003;64:205–210)

Full access
in American Journal of Veterinary Research

Abstract

Objective—To assess relative costs and benefits of vaccination and preemptive herd slaughter to control transmission of foot-and-mouth disease (FMD) virus (FMDV).

Sample Population—2,238 herds and 5 sale yards located in Fresno, Kings, and Tulare counties of California.

Procedure—Direct costs associated with indemnity, slaughter, cleaning and disinfecting livestock premises, and vaccination were compared for various eradication strategies. Additional cost, total program cost, net benefit, and benefit-cost value (B/C) for each supplemental strategy were estimated, based in part on results of published model simulations for FMD. Sensitivity analyses were conducted.

Results—Mean herd indemnity payments were estimated to be $2.6 million and $110,359 for dairy and nondairy herds, respectively. Cost to clean and disinfect livestock premises ranged from $18,062 to $60,205. Mean vaccination cost was $2,960/herd. Total eradication cost ranged from $61 million to $551 million. All supplemental strategies involving use of vaccination were economically efficient (B/C range, 5.0 to 10.1) and feasible, whereas supplemental strategies involving use of slaughter programs were not economically efficient (B-C, 0.05 to 0.8) or feasible.

Conclusions and Clinical Relevance—Vaccination with a highly efficacious vaccine may be a cost-effective strategy for control of FMD if vaccinated animals are not subsequently slaughtered and there is no future adverse economic impact, such as trade restrictions. Although less preferable than the baseline eradication program, selective slaughter of highest-risk herds was preferable to other preemptive slaughter strategies. However, indirect costs can be expected to contribute substantially more than direct costs to the total cost of eradication programs. (Am J Vet Res 2003;64:805–812)

Full access
in American Journal of Veterinary Research