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  • Author or Editor: Kevin D. Pelzer x
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Abstract

Objective—To determine the baseline costs of bovine leukemia virus (BLV) infection, including costs of clinical disease and subclinical infection, in a dairy herd representative of the mid-Atlantic region and compare these costs with the cost of a test-and-manage BLV control program.

Design—Stochastic spreadsheet model.

Sample Population—A commercial Holstein dairy herd with 100 milking cows.

Procedures—A spreadsheet model was developed. The overall cost of infection included the cost of clinical disease (ie, lymphosarcoma [LS]) and the effects of subclinical infection on milk production and premature culling. Model input values and distributions were designed to reflect economic conditions in the mid-Atlantic region. Relative costs of infection and control were calculated for infection prevalences of 20, 50, and 80%.

Results—Estimated mean cost to the producer per case of LS was $412; for a herd with a 50% prevalence of BLV infection, annual incidence of LS was 0.66. Mean annual cost of subclinical infection at a 50% prevalence of infection was $6,406. Mean annual cost of a test-and-manage control program was $1,765. The cost of clinical disease and subclinical infection varied substantially with the prevalence of infection, whereas the cost of control varied with herd size.

Conclusions and Clinical Relevance—Results suggested that a basic BLV control program may be economically beneficial in herds in which the prevalence of BLV infection is ≥ 12.5%. Farm-specific considerations may factor prominently when weighing the costs and benefits of an individual BLV control program. (J Am Vet Med Assoc 2003;223:346–352)

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in Journal of the American Veterinary Medical Association

Abstract

Objective—To determine the association between serologic status for bovine leukemia virus (BLV) and culling rates by use of survival times in a commercial Holstein dairy herd.

Design—Longitudinal study.

Animals—593 milking cows.

Procedure—Cattle were tested for antibodies against BLV by use of agar gel immunodiffusion or ELISA 4 times each year from 1989 to 1993 and then annually through 1999. Dates of birth, first calving, and culling or death were obtained from Dairy Herd Improvement Association records. Most cows were enrolled in the study on the date of first calving. Survival times were compared among seropositive, seronegative, and seroconverted cows with the Kaplan-Meier method and a Cox regression model stratified on the basis of year of birth.

Results—Complete records were available for 593 of 685 (87%) cattle in the dairy herd during the study period. Median survival time for all cows was 31.7 months. Survival times, which correspond to cull rates, did not differ significantly between seropositive and seronegative cattle, whereas cattle that seroconverted during the study had a significantly longer survival time. Year of birth was positively and significantly associated with survival time.

Conclusions and Clinical Relevance—BLV serologic status was not associated with cull rate as measured by survival time in this dairy herd. This finding is in contrast to results of studies that used survival analysis techniques; our results may influence management decisions concerning BLV. (J Am Vet Med Assoc 2003;223:229–231)

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in Journal of the American Veterinary Medical Association

Abstract

Objective—To determine whether vaccination with a monovalent Leptospira borgpetersenii serovar Hardjo strain hardjobovis vaccine coupled with parenteral long-acting oxytetracycline treatment would improve the reproductive performance of beef cows.

Design—Randomized controlled field trial.

Animals—1,446 Angus-cross beef cows in 8 locations.

Procedures—Cows were given 2 doses, 4 weeks apart, of vaccine (treatment; n = 741) or placebo (control; 705). Cows in the treatment group were also given a single dose of a longacting oxytetracycline formulation (20 mg/kg [9.1 mg/lb], SC) at the time of booster vaccination. Estrus synchronization was performed, followed by fixed-time artificial insemination; bulls were introduced 14 days after insemination. Serum and urine samples were obtained on a random subset of cows (n = 194) for detection of serologic titers and leptospiruria, and locations were categorized as positive or negative for leptospirosis on the basis of detection of leptospiruric cows.

Results—No differences in pregnancy and calving rates between treatment and control groups were detected. Pregnancy rate following artificial insemination was lower among cows in locations positive for leptospirosis than among cows in locations negative for leptospirosis; however, overall pregnancy rate, calving rate following artificial insemination, and overall calving rate did not differ between groups when cows were grouped on the basis of location leptospirosis status.

Conclusions and Clinical Relevance—Results suggested that under the conditions of the present study, administration of a monovalent Leptospira vaccine in conjunction with systemic administration of oxytetracycline did not significantly improve reproductive performance of beef cows.

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in Journal of the American Veterinary Medical Association