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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

Objective

To estimate the extent to which exposure to Leptospira hardjo before or at the time of first parturition was associated with infertility and abortion during the first lactation among dairy cows that had not been vaccinated for ≥ 12 months.

Animals

207 first-lactation cows from a herd of 2,000 lactating cows.

Procedure

Cows were tested for antibodies to L hardjo within 40 days after calving. Time from calving to first breeding, time from calving to conception, number of breedings per conception, and risk of abortion were compared between cows seropositive for L hardjo and cows that were seronegative.

Results

For the 9 (4.3%) cows that were seropositive for L hardjo, median time from calving to conception (132.6 days) was significantly longer than time for seronegative cows (95.4 days). Cows that were seropositive were twice as likely (relative risk, 2.07) to fail to conceive as seronegative cows. Mean number of breedings required per conception for seropositive cows (3.4) was significantly higher than that for seronegative cows (2.1). The proportion of seropositive cows that aborted was not significantly different from the proportion of seronegative cows that aborted.

Conclusions and Clinical Relevance

Exposure of nonvaccinated dairy cows to L hardjo can be associated with a subsequent reduction in fertility, as indicated by a greater time from calving to conception and higher number of breedings required per conception. The efficacy of leptospiral vaccines should be assessed to determine whether vaccination will minimize herd infertility associated with L hardjo infection. (J Am Vet Med Assoc 1999;215:515–518)

Free access
in Journal of the American Veterinary Medical Association

Abstract

Objective—To estimate risk and identify risk factors for congenital infection with bovine viral diarrhea virus (BVDV) not resulting in persistent infection and examine effect of congenital infection on health of dairy calves.

Animals—466 calves.

Procedures—Calves from 2 intensively managed drylot dairies with different vaccination programs and endemic BVDV infection were sampled before ingesting colostrum and tested with their dams for BVDV and BVDV serum-neutralizing antibodies. Records of treatments and death up to 10 months of age were obtained from calf ranch or dairy personnel. Risk factors for congenital infection, including dam parity and BVDV titer, were examined by use of logistic regression analysis. Effect of congenital infection on morbidity and mortality rates was examined by use of survival analysis methods.

Results—Fetal infection was identified in 10.1% of calves, of which 0.5% had persistent infection and 9.6% had congenital infection. Although dependent on herd, congenital infection was associated with high BVDV type 2 titers in dams at calving and with multiparous dams. Calves with congenital infection had 2-fold higher risk of a severe illness, compared with calves without congenital infection.

Conclusions and Clinical Relevance—The unexpectedly high proportion of apparently healthy calves found to be congenitally infected provided an estimate of the amount of fetal infection via exposure of dams and thus virus transmission in the herds. Findings indicate that congenital infection with BVDV may have a negative impact on calf health, with subsequent impact on herd health. (Am J Vet Res 2003;64:358–365)

Full access
in American Journal of Veterinary Research

Abstract

Objective—To develop models that could be used to predict, for dairy calves, the age at which colostrumderived bovine viral diarrhea virus (BVDV) antibodies would no longer offer protection against infection or interfere with vaccination.

Design—Prospective observational field study.

Animals—466 calves in 2 California dairy herds.

Procedure—Serum BVDV neutralizing antibody titers were measured from birth through 300 days of age. The age by which colostrum-derived BVDV antibodies had decayed sufficiently that calves were considered susceptible to BVDV infection (ie, titer ≤ 1:16) or calves became seronegative was modeled with survival analysis methods. Mixed-effects regression analysis was used to model colostrum-derived BVDV antibody titer for any given age.

Results—Half the calves in both herds became seronegative for BVDV type I by 141 days of age and for BVDV type II by 114 days of age. Rate of antibody decay was significantly associated with antibody titer at 1 to 3 days of age and with whether calves were congenitally infected with BVDV. Three-month-old calves were predicted to have a mean BVDV type-I antibody titer of 1:32 and a mean BVDV type-II antibody titer of 1:16.

Conclusions and Clinical Relevance—Results provide an improved understanding of the decay of BVDV-specific colostrum-derived antibodies in dairy calves raised under typical field conditions. Knowledge of the age when the calf herd becomes susceptible can be useful when designing vaccination programs aimed at minimizing negative effects of colostrum-derived antibodies on vaccine efficacy while maximizing overall calf herd immunity. (J Am Vet Med Assoc 2002;221:678–685)

Full access
in Journal of the American Veterinary Medical Association

Abstract

Objective—To determine the prevalence and effect of Neospora caninum infection and persistent infection (PI) with bovine viral diarrhea virus (BVDV) on weight gain, morbidity, and mortality rate in dairy-breed steer calves located on a feedlot in California.

Design—Prospective cohort observational study.

Animals—900 dairy-breed steer calves in 2 pens.

Procedures—The 3- to 4-month-old calves were evaluated for serum antibodies against N caninum and infection with BVDV at entry to the feedlot. Five months later, sera were again analyzed for anti–N caninum antibodies; calves that were determined to have BVDV infection initially were retested to evaluate PI status. Average daily gain, morbidity, and deaths were recorded for all calves.

Results—Among 900 calves, prevalence of N caninum infection was 16.7% (95% confidence interval, 14.3% to 19.3%); prevalence of BVDV-associated PI was 0.2% (95% confidence interval, 0.03% to 0.9%). Morbidity rate and time to first illness were not significantly different between calves that were seropositive or seronegative for N caninum.Atthe second sample collection, weight and average daily gain of calves that were seropositive for N caninum was less than that of seronegative steers in 1 pen, whereas these measures did not differ between groups in the other pen. Statistical power was insufficient to evaluate the effect of BVDV PI on any outcome measurement.

Conclusions and Clinical Relevance—Although N caninum serostatus had no significant effect on morbidity rate, some seropositive calves had reduced growth, compared with seronegative calves, 5 months after entry to the feedlot.

Full access
in Journal of the American Veterinary Medical Association

Abstract

Objective—To estimate transmission of bovine viral diarrhea virus (BVDV) and crude morbidity and mortality ratios in BVDV-vaccinated and unvaccinated dairy heifer calves managed under typical dairy drylot conditions.

Design—Randomized clinical trial.

Animals—106 female Holstein calves.

Procedure—Seroconversion rates for BVDV types I and II and proportional morbidity and mortality ratios were compared between calves given a killed BVDV type-I vaccine at 15 days of age and a modified-live BVDV type-I vaccine at 40 to 45 days of age (n = 53) and calves given no BVDV vaccines (53). Sera were collected at 45-day intervals as calves moved from individual hutches to corrals holding increasingly larger numbers of calves. Seroconversion was used as evidence of exposure to BVDV.

Results—Crude proportional morbidity (0.16) and mortality (0.17) ratios for control calves did not differ significantly from those of vaccinated calves (0.28 and 0.12, respectively). The proportion of control calves that seroconverted to BVDV type I through 9 months of age (0.629) was significantly higher than that of vaccinated calves that seroconverted, unrelated to vaccination, during the same period (0.536). Estimated overall protective effect of vaccination against BVDV type I through 4 to 9 months of age was 48%. The proportion of control calves that seroconverted to BVDV type II (0.356) was not different from that of vaccinated calves (0.470).

Conclusions and Clinical Relevance—Findings suggest that calfhood vaccination may be an appropriate strategy to help reduce short-term transmission of some but not necessarily all strains of BVDV. (J Am Vet Med Assoc 2001;219:968–975)

Full access
in Journal of the American Veterinary Medical Association

Abstract

Objective—To develop a method of probability diagnostic assignment (PDA) that uses continuous serologic measures and infection prevalence to estimate the probability of an animal being infected, using Neospora caninum as an example.

Animals—196 N caninum-infected beef and dairy cattle and 553 cattle not infected with N caninum; 50 dairy cows that aborted and 50 herdmates that did not abort.

Procedure—Probability density functions corresponding to distributions of N caninum kinetic ELISA results from infected and uninfected cattle were estimated by maximum likelihood methods. Maximum likelihood methods also were used to estimate N caninum infection prevalence in a herd that had an excessive number of abortions. Density functions and the prevalence estimate were incorporated into Bayes formula to calculate the conditional probability that a cow with a particular ELISA value was infected with N caninum.

Results—Probability functions identified for infected and uninfected cattle were Weibull and inverse gamma functions, respectively. Herd prevalence was estimated, and probabilities of N caninum infection were determined for cows with various ELISA values.

Conclusions and Clinical Relevance—Use of PDA offers an advantage to clinicians and diagnosticians over traditional seronegative or seropositive classifications used as a proxy for infection status by providing an assessment of the actual probability of infection. The PDA permits use of all diagnostic information inherent in an assay, thereby eliminating a need for estimates of sensitivity and specificity. The PDA also would have general utility in interpreting results of any diagnostic assay measured on a continuous or discrete scale. Am J Vet Res (2002; 63:318–325)

Full access
in American Journal of Veterinary Research

Abstract

Objective—To evaluate risk of bovine viral diarrhea virus (BVDV) infection between birth and 9 months of age for dairy replacement heifers raised under typical dry-lot management conditions.

Design—Longitudinal observational study.

Animals—446 calves.

Procedure—Calves were randomly selected from 2 dairies that used killed and modified-live BVDV vaccines. Repeated serologic and BVDV polymerase chain reaction assays were used to estimate risk of BVDV infection in calves of various ages (1 to 60 days; 61 to 100 days; 101 days to 9 months) and to estimate overall infection rate by 9 months of age.

Results—Risk of BVDV infection increased with age (maximum risk, 150 to 260 days). Proportion of calves infected with BVDV by 9 months of age was higher for dairy A (0.665), compared with dairy B (0.357). Percentage infected with BVDV type I did not differ between dairy A (18.2%) and dairy B (15.2%), whereas percentage infected with BVDV type II for dairy A (50%) was twice that for dairy B (21%). Between 210 and 220 days of age, infection with BVDV regardless of type was > 1.3%/d on dairy A and 0.5%/d on dairy B.

Conclusions and Clinical Relevance—Under drylot conditions, a considerable amount of BVDV infection may occur before 9 months of age. Risk of infection increases with age. Although dairies may appear to have similar management practices, there can be considerably different risks of BVDV infection among dairies. (J Am Vet Med Assoc 2001;219:1426–1431)

Full access
in Journal of the American Veterinary Medical Association