Udder health in dairy cattle infected with Neospora caninum

Blood samples were collected from 3449 cows on 57 representative Ontario dairy herds during the summer of 1998 and analysed for antibody to Neospora caninum using an ELISA. Forty-eight herds (2742 cattle) contained at least one N. caninum-seropositive animal. Two composite milk samples were collected from all cattle: the first on the day of blood collection and the second 68 to 365 days later. All milk samples were submitted for bacteriological culture. Ontario Dairy Herd Improvement Corporation (DHI) data were available for 3162 cattle in the 57 herds at the time of bleeding. Furthermore, complete DHI data were available for 1658 cattle that were culled between 12 and 24 months following blood collection. Using a standardised ELISA sample-to-positive (S/P) cut-off of ≥0.45, the corrected seroprevalence was 8.2% overall and 10.1% within seropositive herds. At blood collection the odds of N. caninum-seropositive cows having a high linear score (≥4.0; equivalent to a somatic cell count ≥200,000 cells/ml) was 27% less than for seronegative animals. Similarly, at the time of culling, the odds of having a high linear score was 22% less in N. caninum-seropositive cattle. Overall, linear score was lower in N. caninum-seropositive cattle at culling. After controlling for herd, parity, days in milk, and the interval between collection of milk samples, the odds of N. caninum-seropositive cattle testing positive for an environmental pathogen (i.e. environmental Streptococcus species and coliforms) on the second milk sample was 56% less than for seronegative animals. The odds were 83% less at a higher ELISA S/P cut-off of ≥0.70. Finally, the odds of N. caninum-seropositive cattle developing a new infection with a major pathogen (environmental or contagious) were 60% less than seronegative cows using the higher ELISA S/P cut-off.     

Associations between Campylobacter fetus, Haemophilus somnus, Leptospira hardjo and bovine viral diarrhea virus antibody titers in dairy cattle from a California herd

In a cross-sectional study, the associations of age, serological status against Campylobacter fetus (CF), Haemophilus somnus (HS) and Leptospira hardjo (LH) with the seroprevalence of bovine viral diarrhea virus (BVDV) in dairy cattle were evaluated. Six hundred and thirty cattle from a herd in Tulare county of California were included in the study. Blood samples from the cattle were collected in December 1986. Enzyme-linked immunosorbant assay (ELISA) was used to determine the positive or negative status of cows against CF, HS, LH and BVDV antigens. Loglinear analysis was used to describe the relationships of four categorical variables with the seroprevalence of BVDV. The final loglinear model was interpreted as a logit model and obtained by conditioning on explanatory variables in the model found to relate significantly with BVDV seropositivity. The hierarchical logit model included two two-way interactions (BVDV × HS and BVDV × LH) and a three-way interaction (BVDV × CF × age). HS-seronegative cattle had 4.7 times greater odds of being BVDV-seropositive compared with HS-seropositive cattle. In contrast, LH-seropositive cattle had 2.7 times increased odds of BVDV seropositivity compared with LH-seronegative cattle. The presence of the three-way interaction term in the model involving age, CF and BVDV seroprevalence implies that among heifers, CF-seronegative and CF-seropositive animals had about the same odds of BVDV seropositivity (e.g. adjusted odds ratios = 20.5 vs. 24.5), whereas, among cows, CF-seronegative animals had at least twice the odds of being BVDV-seropositive than those of CF-seropositive animals (e.g. adjusted odds ratios = 23.0 vs. 11.0).     

Neospora-associated abortion episode over a 1-year period in a dairy herd in north-east Spain

This report describes a retrospective study based on serological screening, performed on a Neospora-associated abortion episode over a 12-month period in a dairy herd in north-east Spain. During the 1-year study period, the overall abortion rate for the herd was 23.2% (38 abortions of 164 diagnosed pregnancies). The data analysed were those derived from blood samples collected from the whole herd (n = 237) and from diagnosed pregnancies. Antibodies to Neospora caninum were found in 35.4% of the cattle with 44% of seropositive pregnant animals aborting over 1-year period. Based on the odds ratio, the risk of abortion was 12.2 times higher (P < 0.0001) in the Neospora-seropositive animals than in seronegative animals and significantly higher during the second term of gestation (P < 0.01) than during the first and third terms. Abortions were not found to be associated with parity status or season of pregnancy, and the common risk factors associated with pregnancy loss in the geographical area of the study. Age-related differences in N. caninum seroprevalence were not statistically significant, indicating vertical transmission as the main route of infection. Indeed, a high percentage of congenitally infected offspring was observed (90.6%) and the farm had been free of dogs for the last 7 years. Our results suggest that, when a dairy herd shows an increased incidence of abortions due to Neosporosis, maternal serology can be a good indicator of the abortion risk in individual cows, and that the effects of factors normally related to abortion, such as parity and pregnancy season, may be masked.     

Serological status and abortion rate in progeny obtained by natural service or embryo transfer from Neospora caninum-seropositive cows

Bovine neosporosis is an important disease in dairy herds in Argentina. Embryo transfer (ET) technology offers the opportunity to minimize vertical transmission of neosporosis. The objective of this work was to compare the serological status and the incidence of abortion between heifers obtained via natural service and heifers obtained by ET from Neospora-infected cows. Progeny from eight Neospora-infected cows belonging to a commercial dairy farm where ET was routinely performed were studied. Between 1996 and 2001, 16 and 15 heifers were obtained by natural service and ET, respectively. Serostatus and reproductive performance were recorded in both progeny. Serostatus was determined by indirect fluorescent antibody test (IFAT). All heifers obtained by natural service were seropositive and six of 16 pregnancies ended in abortion. All heifers obtained by ET were seronegative and only two abortions of 15 pregnancies were recorded.     

Neospora caninum antibodies in commercial fetal bovine serum

The protozoan parasite Neospora caninum is a major cause of abortion in cattle throughout the world. In the process of propagating Neospora in vitro and producing specific antibodies for development of diagnostic assays in the food supply, our laboratory identified the presence of bovine antibodies to N. caninum in fetal bovine sera. The sera were produced commercially and preferentially recommended for tissue culture use and monoclonal antibody production. Seventeen different fetal bovine serum samples of different grades and from four different companies were examined for the presence of total IgG, IgG₁, IgG₂, and IgM specific for N. caninum. All of the tested serum samples recognized N. caninum specific bands on Western blot. Low IgG serum also recognized these antigens but with lower intensity. Antibody response was also evaluated using a commercially available ELISA kit for N. caninum.     

Serological Status and Abortion Rate in Progeny Obtained by Natural Service or Embryo Transfer from Neospora caninum‐Seropositive Cows

Bovine neosporosis is an important disease in dairy herds in Argentina. Embryo transfer (ET) technology offers the opportunity to minimize vertical transmission of neosporosis. The objective of this work was to compare the serological status and the incidence of abortion between heifers obtained via natural service and heifers obtained by ET from Neospora‐infected cows. Progeny from eight Neospora‐infected cows belonging to a commercial dairy farm where ET was routinely performed were studied. Between 1996 and 2001, 16 and 15 heifers were obtained by natural service and ET, respectively. Serostatus and reproductive performance were recorded in both progeny. Serostatus was determined by indirect fluorescent antibody test (IFAT). All heifers obtained by natural service were seropositive and six of 16 pregnancies ended in abortion. All heifers obtained by ET were seronegative and only two abortions of 15 pregnancies were recorded.     

Associations of Neospora caninum seropositivity with gestation number and pregnancy outcome in Danish dairy herds.

The prevalence and distribution of seropositivity towards the protozoan parasite Neospora caninum were studied in single blood samples from 1561 cows from 31 Danish dairy herds. Blood samples were analysed by an indirect enzyme-linked immunoassay and an indirect fluorescent-antibody test. Seroprevalence in 15 herds with previous abortions assigned to neosporosis ranged from 1% to 58%, with a mean frequency of 22%. In eight out of 16 herds without a history of N. caninum related abortions, no seroreactors were found. In the remaining eight herds, the seroprevalence ranged from 6% to 59%. The prevalence and distribution of seropositivity, gestation number prior to sampling, and breed were related to abortions and perinatal deaths using a random-effects logistic-regression model. Abortion risk was significantly increased in seropositive animals (OR=3) and in 2nd-gestation cows (OR=3). Perinatal death was significantly influenced by gestation number and breed, but not by serostatus. Reproductive performance and culling risk of cows were not affected by serostatus. Seropositivity increased with “age” (i.e. gestation number) (P=0.02). In open cows, seropositivity tended to decrease with distance from calving (P=0.05). The proportion of seropositive pregnant cows increased with trimester (P=0.02).     

Neospora‐associated Abortion Episode over a 1‐Year Period in a Dairy Herd in North‐east Spain

This report describes a retrospective study based on serological screening, performed on a Neospora‐associated abortion episode over a 12‐month period in a dairy herd in north‐east Spain. During the 1‐year study period, the overall abortion rate for the herd was 23.2% (38 abortions of 164 diagnosed pregnancies). The data analysed were those derived from blood samples collected from the whole herd (n = 237) and from diagnosed pregnancies. Antibodies to Neospora caninum were found in 35.4% of the cattle with 44% of seropositive pregnant animals aborting over 1‐year period. Based on the odds ratio, the risk of abortion was 12.2 times higher (P < 0.0001) in the Neospora‐seropositive animals than in seronegative animals and significantly higher during the second term of gestation (P < 0.01) than during the first and third terms. Abortions were not found to be associated with parity status or season of pregnancy, and the common risk factors associated with pregnancy loss in the geographical area of the study. Age‐related differences in N. caninum seroprevalence were not statistically significant, indicating vertical transmission as the main route of infection. Indeed, a high percentage of congenitally infected offspring was observed (90.6%) and the farm had been free of dogs for the last 7 years. Our results suggest that, when a dairy herd shows an increased incidence of abortions due to Neosporosis, maternal serology can be a good indicator of the abortion risk in individual cows, and that the effects of factors normally related to abortion, such as parity and pregnancy season, may be masked.     

Clinical signs and diagnosis of a severe primary infection with BVDV subtype 1b in a dairy herd

As a result of a BVDV infection in a herd consisting of 95 adult cattle 17 cows aborted their calves within a period of 3.5 months, one third got severe diarrhoea, 3 cows died and an increased percentage of the cattle got lochiometra after calving or abortion. The disease was diagnosed by paired serological testing of cattle with diarrhoea or abortion and post mortem examination of several aborted calves. From one foetus BVDV virus was isolated and subsequently subtyped by sequencing. Of aborting cattle, the testing results were influenced by the interval between infection and abortion. These results indicate that a primary infection with BVDV subtype 1b can cause severe clinical symptoms in a dairy herd.     

弓形虫和新孢子虫交叉反应抗原MIC7A对小鼠的免疫保护效力分析

弓形虫和新孢子虫是两种亲缘关系接近的顶复亚门原虫，二者之间存在一定程度的交叉免疫保护作用，这种作用可能是基于交叉反应抗原产生的。本研究旨在表达并鉴定弓形虫和新孢子虫的交叉反应抗原TgMIC17A，通过将其应用于小鼠的免疫保护试验，评估该抗原对弓形虫和新孢子虫感染产生的交叉免疫保护作用。对TgMIC17A进行基因克隆和原核表达，通过免疫印迹试验鉴定其反应原性和交叉反应性。重组蛋白免疫小鼠后测定血清特异性IgG抗体水平，评价其免疫原性。二免后，分别用1×10³个弓形虫Pru速殖子、1.5×10⁷个新孢子虫Nc1速殖子攻虫，对小鼠的体重变化、存活率进行监测，并在攻虫30 d后检测各组存活小鼠的脑荷虫量，评价TgMIC17A重组蛋白免疫小鼠后对弓形虫和新孢子虫的交叉免疫保护效果。结果显示，rTgMIC17A可以被弓形虫和新孢子虫的阳性血清识别，相较于未免疫组小鼠，免疫组小鼠体内可产生高水平特异性IgG抗体(P＜0.01)，且感染弓形虫或新孢子虫的脑荷虫量均显著降低(P＜0.01)。本研究克隆并表达了TgMIC17A，鉴定其为新孢子虫和弓形虫的交叉反应抗原。该抗原可以刺激小鼠产生较好的体液免疫反应，并对弓形虫和新孢子虫的感染产生一定的交叉免疫保护作用，可以为弓形虫和新孢子虫共感染的防治，以及筛选具有交叉免疫保护力的重组疫苗提供可借鉴的研究资料。     

A stochastic model for simulation of the economic consequences of bovine virus diarrhoea virus infection in a dairy herd

A dynamic, stochastic model simulating the technical and economic consequences of bovine virus diarrhoea virus (BVDV) infections for a dairy cattle herd for use on a personal computer was developed. The production and state changes of the herd were simulated by state changes of the individual cows and heifers. All discrete events at the cow level were triggered stochastically. Each cow and heifer was characterized by state variables such as stage of lactation, parity, oestrous status, decision for culling, milk production potential, and immune status for BVDV. The model was controlled by 170 decision variables describing biologic and management variables including 21 decision variables describing the effect of BVDV infection on the production of the individual animal. Two markedly different scenarios were simulated to demonstrate the behaviour of the developed model and the potentials of the applied modelling principle. The validation problem in relation to the model was discussed. A comparison between real and simulated data using data from a published case report was shown to illustrate how user acceptance can be obtained.     

Predicting the probability of abortion in dairy cows: a hierarchical Bayesian logistic-survival model using sequential pregnancy data

Although abortion contributes substantially to poor reproductive health of dairy herds, little is known about the predictability of abortion based on age, previous abortion or gravidity (number of previous pregnancies). A poor understanding of effects of maternal factors on abortion risk exists, in part, because of methodological difficulties related to non-independence of multiple pregnancies of the same cow in analysis of fetal survival data. We prospectively examined sequential pregnancies to investigate relationships between fetal survival and putative dam risk factors for 2991 abortions from 24,706 pregnancies of 13,145 cows in nine California dairy herds. Relative risks and predicted probabilities of abortion (PPA) were estimated using a previously described hierarchical Bayesian logistic-survival model generalized to incorporate longitudinal data of multiple pregnancies from a single cow. The PPA increased with increasing dam age at conception, with increasing number of previous abortions, and if the previous pregnancy was aborted >60 days in gestation. The PPA decreased with increasing gravidity and with increasing number of days open. For cows that aborted, the median time to fetal death decreased slightly as gravidity increased. The study considers several methodological issues faced in epidemiologic investigations of fetal health, including multi-modal hazard functions, extensive censoring and non-independence of multiple pregnancies. The model improves our ability to predict bovine abortion and to characterize fetal survival, which have important applications to herd health management.     

Preliminary observations on the effect of parity on first day ultrasonic detection of embryo and its organs in bovine

The aim of this study was to determine the effect of parity on the first day of ultrasonic detection of embryo and its organs using 8 MHz frequency. For this purpose, six nulliparous heifers, five primiparous cows and six multiparous cows of the Holstein breed were selected and mated by a single bull from the herd. From day 16 after mating, cows and heifers were examined by ultrasonography thrice weekly for the day of first detection of the embryo and its organs. The mean of first-day detection in heifers, primiparous and multiparous cows was as follows, respectively: allantois on days 22.3, 23 and 25.8; embryo proper on days 21.8, 23 and 27; heartbeat of embryo on days 26.1, 26.6 and 31.1; amnion on days 31, 31 and 30.8; limb buds on days 29.5, 28.8 and 30.6; stomach (abomasum) on days 32.2, 38.6 and 36.8; spinal column on days 32.6, 33.4 and 37.3; placentomes on days 33.3, 37 and 35.3; eyes on days 35.1, 35.4 and 38.6 and lens on days 40, 41.4 and 44. Although the mean of first day observation of all structures in heifers tends to be earlier than in the other groups, statistically, allantois, the embryo proper and its heartbeat in heifers and primipara were visualized significantly earlier than in multiparous cows. However, there were no differences between heifers and primiparous cows.     

Neospora caninum serostatus and milk production of Holstein cattle

OBJECTIVE: To determine whether Neospora caninum serostatus was associated with milk production among Holstein cattle in Ontario. DESIGN: Case-control study and cross-sectional observational study. ANIMALS: 3,702 Holstein cows in 83 herds (case-control study) and 3,162 Holstein cows in 57 herds. PROCEDURE: Herds in the case-control study were grouped on the basis of N. caninum abortion status. Herds in the observational study were considered representative of Ontario dairy herds. The N. caninum serostatus of individual cows was determined with a kinetic ELISA. Milk production was modeled to compare seropositive with seronegative animals while controlling for parity, days since parturition, and herd clustering. RESULTS: In the case-control study, 305-day milk production of seropositive cows was significantly less than milk production of seronegative cows in herds with abortions attributable to N. caninum infection and in herds with abortions attributable to pathogens other than N. caninum, but not in herds without abortion problems. In the observational study, 305-day milk production for seropositive cows was not significantly different from milk production of seronegative cows. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that the association between N. caninum serostatus and milk production in Ontario Holstein dairy cattle may depend on abortion status of the herd. In herds with abortion problems, regardless of cause, N. caninum-seropositive cattle produced less milk, whereas in herds without abortion problems, N. caninum-seropositive cattle produced the same amount of milk as seronegative cattle.     

The significance of leptospiral titres associated with bovine abortion

To investigate relationships between serological titres to 2 serovars, pomona (L. pomona) and hardjo (L. hardjo), of Leptospira interrogans and abortions, log linear and logit models were fitted to herd and individual cow data from cattle serologically negative for brucellosis. Serological titres to both serovars were significantly related to abortions in individual cows, with L. pomona having a stronger relationship than L. hardjo. L. hardjo was not significant when herd data were analysed. Differences between dairy and beef cattle in the serological titres found to both L. pomona and L. hardjo were detected when data sets of all cattle or cattle with no history of abortion were analysed. The beef/dairy differences may be due to different management practices and/or to different geographical distributions of both serovars and populations of beef and dairy cattle. If there are no cattle in a herd with a reciprocal titre of 3000 or greater for L. pomona, it is unlikely that L. pomona is associated with the abortion problem. There was no specific L. hardjo titre which separated high and low probabilities that the serum came from a cow or herd with an abortion history.     

Time to first calving and calving interval in bovine virus diarrhoea virus (BVDV) sero-converted dairy herds in Norway

Dairy herds in M?re and Romsdal County, Norway (regarded as initially free from the bovine virus diarrhoea virus (BVDV) infection) were studied retrospectively from 1992 to 1996. The herd reproductive performance (time to first calving, calving interval, and number of breeding services) was investigated for a potential effect of BVDV sero-conversion. The herd culling pattern--possibly affecting the above measurements--was included for investigation. Two different statistical models were used: the generalised estimating equation (GEE) method and multilevel modelling using Gibbs sampling. Though slightly different estimates resulted, both models agreed on an effect of BVDV in the second year after sero-conversion on the herd average time to first calving by--on an average-- 14-16 days. In subsets of case herds testing positive for BVDV antibodies among young stock, the impact on time to first calving tended to be more pronounced by an additional increase of 18 days. No effect on the number of breeding services for heifers or cows was observed (indicating a need to search for other determinants than reduced conception risk). There appeared to be no effect of BVDV on the herd average calving interval. There was a tendency for a higher risk for reporting animals lost/died in sero-converted herds, which we believe might be related to the occurrence of mucosal disease.     

Association of herd BHV-1 seroprevalence with respiratory disease in youngstock in Estonian dairy cattle

The associations between herd bovine herpesvirus 1 (BHV-1) seroprevalence, along with other infectious and farm management factors with bovine respiratory disease (BRD) in dairy calves and heifers, were investigated. Serum samples from 103 dairy cattle herds were analyzed for antibodies against BHV-1, bovine respiratory syncytial virus (BRSV), bovine viral diarrhea virus (BVDV), and Mycoplasma bovis (M. bovis). A questionnaire was used to record herd management practices. A high occurrence of respiratory disease in unweaned calves was associated with low to moderate and high prevalence of BHV-1 among cows (OR=14.8, p=0.005 and OR=19.2, p=0.002, respectively) and positive BVDV status of a herd (OR=5.1, p=0.02). The presence of BVDV in a herd was related to a high incidence of respiratory disease in heifers 3-16 months old (OR=4.3, p=0.027). Based on the results of multiple correspondence analysis, holding youngstock separately from cows until pregnancy, introducing new animals and the activities of on-farm employees may contribute to a higher incidence of BRD.     

Serology of a Neospora abortion outbreak on a dairy farm in New Zealand: a case study

AIM: To describe the kinetics of serological titres after an abortion outbreak in April-May 1995 due to Neospora caninum affected 17 dairy cows in a herd of 320. METHODS: Thirty-five cows, that had either aborted, carried mummified calves, were not pregnant or calved normally were: bled several times at regular intervals and the sera tested for Neospora antibodies in the indirect fluorescence antibody test (IFAT). RESULTS: Maximal IFAT titres of up to 1:4000 occurred within 6 weeks of the abortion outbreak, decreased over the next 2 months to < or = 1:200 and remained at this level until the next scheduled bleed a further 2 months later. A rise in titres was subsequently observed in the cows that had aborted or were not pregnant (at the time of the abortions) or had carried mummified foetuses. Seroconversion was also observed in some of the control cows, which had, up until then, remained seronegative. A dog and cat in contact with the cows in the herd investigated were, however, negative in the IFAT. CONCLUSIONS: Maximal serological titres in Neospora abortions are observed within weeks of the abortion event and then quickly return to very low levels. Subsequently, a recrudescence of titres can be observed in infected cows during the next pregnancy, without it being associated with repeat abortions.