The use of beef bull semen reduced the risk of abortion in Neospora-seropositive dairy cows

There is an evidence that the epidemiology of neosporosis differs in dairy and beef cattle, such that beef cattle carry a lower risk of abortion. The aim of the present study was to establish whether artificial insemination using semen from beef bulls could reduce the risk of abortion in dairy cows seropositive for the Neospora caninum parasite. Our study was based on yearly serological screening for neosporosis and on the confirmation of Neospora infection in aborted fetuses in two high-producing dairy herds with a mean 28% seroprevalence of N. caninum antibodies. The study population comprised of 273 pregnancies in seropositive animals: 156 pregnancies monitored after insemination using Holstein-Friesian semen and 117 after insemination using beef bull semen. Abortion rates for these animals were 28.2% (77 of 273), 34.6% (54 of 156) and 19.7% (23 of 117). Logistic regression analysis indicated no significant effects of lactation number and previous abortion on the abortion rate. Based on the odds ratio, a 1-unit increase in the Neospora antibody titre yielded a 1.01-fold increase in the abortion rate. The likelihood of abortion was two times higher for cows in one of the two herds and 2.8 times lower (one of 0.36) for pregnant cows inseminated with beef bull semen rather than Holstein-Friesian semen. Our results indicate that the use of beef bull semen can reduce the risk of abortion in dairy cows, and suggest that annual screening for neosporosis, specifically the antibody titre to the protozoan, could be an useful predictor of abortion risk in reproductive health programmes.     

Prevalence of Neospora caninum antibodies in cattle from Santarém, Pará, Brazil

Prevalence of anti-Neospora caninum antibodies was measured in serum samples randomly collected from dairy (40 cows from four farms) and beef cattle (120 animals from 12 farms) from the municipality of Santarém, Pará State, Brazil, calculated by using the Win Episcope 2.0 statistical program. The presence of anti-N. caninum antibodies was determined by indirect immunofluorescence-antibody test with a cut-off value of 1:100. We found that 13 farms (81.25%) showed infection rates above 10%, which indicates widespread distribution of N. caninum in the region. The frequency per animal was 19%. No difference was observed between the prevalence values in dairy and beef animals or between farms, which was probably due to the small number of dairy farms examined. The results confirm, for the first time, the presence of anti-N. caninum antibodies in cattle from Pará State and the necessity to further investigate the epidemiology of N. caninum in the Amazon region.     

Neospora caninum seroprevalence in dairy and beef cattle from the northwest region of Spain, Galicia

Herd and individual animal seroprevalence for Neospora caninum (N. caninum) in dairy, beef and mixed cattle were obtained in all populations within the Galician Farmer Sanitary Defence Associations (ADSG) in 2004. All animals ≥1 year of age were examined serologically by indirect ELISA. 1147 dairy herds (37,090 animals), 1464 beef herds (20,206 animals) and 141 mixed herds (2292 animals) were surveyed. True herd seroprevalence was estimated to be 80.6% (87.7% dairy, 76.7% beef and 78.4% mixed herds), true animal seroprevalence was estimated to be 23.2% (21.9% dairy, 25.1% beef and 24.9% animal to mixed herds), and within-herd seroprevalence was estimated to be 25.4% (23.6% dairy, 28.3% beef and 28.6% to mixed herds). Seropositivity was significantly associated with herd type (higher in dairies), herd size (increased when herd size increases), animal type (higher in beef) and age (lineal increase with the age). Results obtained in this study will be used for the development of a N. caninum control programme in the ADSG in Galicia.     

Outbreak of abortion associated with Neospora caninum infection in a beef herd

Abortion outbreaks caused by infection with Neospora caninum in beef cattle have not been well documented. Neospora caninum infection was confirmed in 4 fetuses that were aborted by cattle in a 350-head beef herd; an additional 58 cattle aborted during the next 2.5 months. Overall, 44.4% (157/354) of the cattle in the herd did not become pregnant or experienced fetal loss during this period. Initially, 81.3% (282/347) of the herd was seropositive for antibodies to N caninum, and seropositive cows were 6.2 times as likely to not be pregnant as were seronegative cows. Other potential causes of abortion were not identified in this herd. Following the outbreak, few cattle in the herd or in a second exposed herd seroconverted, but high antibody titers persisted in most seropositive cattle through the end of the calving season. Evidence of cow-to-fetus transmission of the organism was detected in > 82% of seropositive cows.     

Prevalence of anti-Neospora caninum antibodies in cattle and dogs from Western Amazon, Brazil, in association with some possible risk factors

For evaluation of the prevalence of anti-Neospora caninum antibodies and its associated risk factors, serum samples from 2109 cattle (11 beef, 50 dairy and 25 mixed farms) and 174 dogs were examined in the State of Rond?nia, Western Amazon, Brazil. An inquiry was applied in each farm. Sera were examined by the Indirect Fluorescence Antibody Test (IFAT) using cut off dilution of 1:25 for cattle and 1:50 for dogs. Statistical association between the serologic status and several variables were analyzed by linear and logistic regression. The overall herd prevalence of anti-N. caninum antibodies for 86 farms was 72% (61.3-81.2%). Prevalence values were 100, 70 and 64% in beef, dairy and mixed herds, respectively. Herd prevalence in beef herds was significantly different (P<0.05) from dairy and mixed herds. The overall animal prevalence of N. caninum in cattle was 8.8%. Prevalence values by animal were similar in different production types (P>0.05), with values of 9.5, 11.2 and 9.7% for beef, dairy or mixed cattle, respectively. Antibodies were found in 12.6% of the 174 examined dogs. Sixteen (22.8%) out of 70 farms with dogs had at least one dog with anti-N. caninum antibodies. The occurrence of antibodies in cattle was statistically associated with farms having more than 25 cows (OR 9.7, 95% IC 2.9-32.2; P=0.0002). There was no significant association between the presence of the dogs, jungle contact or reproductive variables with the occurrence of antibodies in cattle.     

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.     

Seroprevalence of Neospora caninum infection following an abortion outbreak in a dairy cattle herd

OBJECTIVE: To investigate the seroprevalence of Neospora caninum infection in a commercial dairy cattle herd, 15 months after detection of an abortion outbreak. PROCEDURE: Sera from the whole herd (n = 266) were examined for N caninum antibodies by indirect fluorescent antibody test (IFAT) and immunoblot analysis. Herd records were reviewed to collate serological results with abortion history, proximity to calving, and pedigree data. RESULTS: The seroprevalence of N caninum infection was 24% (63/266) for IFAT titre > or = 160, 29% (78/266) for immunoblot positive (+ve), and 31% (82/266) for IFAT > or = 160 and/or immunoblot +ve; 94% (59/63) of animals with IFAT > or = 160 were immunoblot +ve. The association between seropositivity (IFAT > or = 160 and/or immunoblot +ve) and history of abortion was highly significant (P < 0.001); the seroprevalence was 86% (18/21) in aborting cows, compared with 30% (50/164) in non-aborting animals. The abortion rate for seropositive cows was 26% (18/68) compared with 3% (3/117) for seronegative animals. IFAT titres of infected cows were higher within 2 months of calving than at other times (P < 0.001). The association between seropositivity in dams and daughters was highly significant (P = 0.009). CONCLUSIONS: The abortions were associated with N caninum infection and there was evidence of reactivation of latent infection close to calving and congenital transmission of infection. Immunodominant antigens identified by immunoblots may prove useful for improved diagnostic tests.     

Neospora caninum infection does not affect the fertility of dairy cows in herds with high incidence of Neospora-associated abortions

This present study, was designed to establish whether Neospora caninum infection affects the fertility of high-producing dairy cows, and was based on yearly serological screening for neosporosis and on the confirmation of N. caninum infection in aborted foetuses. Assessment was made of 7518 artificial inseminations (AI) (applied to parous cows) performed in three herds. Of these inseminations, 2540 (33.8%) resulted in pregnancy; 34% of which corresponded to seronegative cows (2226 of 6556 AI performed in seronegative cows) and 32.6% to seropositive animals (314 of 962). Abortion occurred in 97 (30.1%) of the 314 pregnancies recorded in dams seropositive for N. caninum, while only 93 (4.2%) of the 2226 pregnancies in seronegative animals ended in abortion. Logistic regression analysis indicated no significant effects of N. caninum antibody titre, days in milk and milk production at insemination on fertility. Factors found to affect fertility were herd, season of insemination, lactation and insemination number, semen-providing bull and AI technician. Our results indicate that N. caninum infection does not affect the fertility of high-producing dairy cows.     

An abortion storm in cattle associated with neosporosis in Taiwan

An abortion storm associated with acute neosporosis involving 18 cattle was observed in a dairy farm in Taiwan. Aborted fetus age ranged from 3 to 8 months. Of the 38 cattle in that farm examined during the abortion storm, 52.6% (20/38), 13.2% (5/38) and 10.5% (4/38) contained both IgG and IgM, only IgG and only IgM antibodies to Neospora caninum, respectively. No antibody to N. caninum was detected prior to the abortion storm. Follow-up study conducted a year later showed that 23 out of 28 cattle had sero-converted. Since some cattle were positive to either only IgG or IgM, we suggest that both IgG and IgM should be tested for diagnosing neosporosis. Neosporosis surveillance of naive cattle herd is recommended.     

A longitudinal study of Neospora caninum infection on three dairy farms in Brazil

Neospora caninum is an apicomplexan protozoan parasite that is one of the most important infectious causes of abortion in both dairy and beef cattle in many countries. The objectives of this longitudinal study were to determine the prevalence, rates of vertical and horizontal transmission of N. caninum and hazard for culling of N. caninum-seropositive animals in three Brazilian dairy herds. Blood samples from all animals were collected nine times at each of the three farms over a two-year period. Serum was tested for antibodies against N. caninum using the indirect fluorescent antibody test with a cutoff value of 1:100. The percentage of N. caninum-positive samples at each sampling time ranged at Farm I from 3.32% to 11.71%, at Farm II from 3.90% to 22.06% and at Farm III from 3.90% to 22.06%. The number of positive serological reactions varied in relation to the number of repeated samples taken from individual animals at each farm. In all herds, there was a high degree (P<0.05) of association between the N. caninum serological status of dams and daughters. The seropositive conversion rate was estimated as 0.37%, 3.00% and 6.94% per 100 cow-years at Farms I, II and III, respectively. The seronegative conversion rate was estimated as 31.58% and 11.11% per 100 cow-years at Farms I and III, respectively. In all herds, there was no difference (P>0.05) in the culling rate between the cattle that were seropositive cattle and seronegative for N. caninum infection. The results from this study confirm the importance of vertical transmission in the epidemiology of N. caninum. Although a few positive seroconversions indicated horizontal transmission, it does not appear to be the major route of infection for N. caninum.     

Seroprevalence of neosporosis in beef and dairy cattle breeds in Northeast Hungary

In order to assess the seroprevalence of bovine neosporosis with indirect fluorescent antibody test (IFAT), blood samples were collected randomly from 1063 beef and dairy cattle belonging to 12 different breeds in Northeast Hungary. Antibodies to Neospora caninum were detected in 27 (2.5%) of the animals, kept on 19 of the 42 settlements included in this survey. Since samples were collected on 50 farms, herd prevalence amounted to 38%. The percentage of cattle with seroconversion increased with age, suggesting a postnatal source of infection. The highest rate of positivity was detected in Aberdeen Angus (3.3%) and Holstein-Friesian cows (3.2%), and the lowest in Limousine (0.9%), but no breed predisposition was statistically substantiated. Neosporosis was more prevalent in dairy (3.4%) than in beef (1.9%) cattle, although the difference was not significant. Only three out of the seropositive cows, all of them Holstein-Friesians, had a history of abortion.     

Diagnostic significance of Neospora caninum DNA detected by PCR in cattle serum

A nested PCR that successfully detected Neospora caninum DNA in serum of cattle was used for investigation of selected abortion cases and in a study of healthy pregnant cows at an abattoir. N. caninum DNA was not detected in serum from antibody positive dams that aborted due to N. caninum, but was present in serum of some antibody negative dams that aborted due to other causes. N. caninum DNA was also found in the serum of about half of the animals that aborted of undetermined cause, but was not detected in cow sera from two beef cattle herds in Western Australia with no recent history of abortion. In the abattoir study of 79 dams and their foetuses N. caninum DNA was found in serum of 3 dams and in material from 11 foetuses. The majority of the cows and all foetuses were antibody negative. Our findings suggest that there is no obvious relationship between the presence or absence of N. caninum DNA in serum and the presence of antibodies to N. caninum in dams, the presence of N. caninum DNA in foetuses or abortion due to N. caninum. This is the first report of the detection of N. caninum DNA in serum of cattle rather than the white blood cell fraction. It indicates the presence of free tachyzoites and/or parasite DNA in circulation. The results suggest that persistent infection in the absence of antibodies is a possible outcome of N. caninum infection. Infection of foetuses in the absence of antibodies supports the possibility of persistent infection due to immunotolerance to an early in utero infection. It is therefore important to test for N. caninum DNA as well as antibodies for the detection of exposed and/or infected animals. However, the presence or absence of N. caninum antibodies or DNA did not support nor exclude N. caninum as the cause of abortion. Additional criteria are required for a positive diagnosis of abortion caused by N. caninum.     

Seroprevalence of Neospora caninum in dairy and beef cattle with reproductive disorders in Japan

Serum samples from 145 dairy and 65 beef cattle with reproductive disorders and 54 normally calving dairy cattle (controls) in Japan were tested for presence of Neospora caninum antibodies by use of an indirect fluorescent antibody test (IFAT, titer 1:200). Overall, seroprevalence of N. caninum was significantly higher (P < 0.001) in dairy cattle (20.0%, 29/145) than in beef cattle (1.5%, 1/65). In cattle which aborted, seroprevalence of N. caninum was significantly higher (P = 0.041) in dairy cattle (26.1%, 23/88, compared with controls (3.7%, 2/54)) than in beef cattle (5.0%, 1/20), indicating that neosporosis might be a more common problem in dairy cattle than in beef cattle in Japan. Seropositive cattle were 9.2 times more likely to abort compared to seronegative cows. Abortions associated with N. caninum seropositivity in this study were most frequently observed in the second trimester, and the mean gestational age of the fetuses aborted from seropositive dams was 5.7 months. In conclusions, N. caninum seems to be causing serious economic losses in the dairy industry in Japan. This is the first report on an objective comparison of seroprevalence of dairy and beef cattle with reproductive disorders in Asia.     

Relationship between rainfall and Neospora caninum-associated abortion in two dairy herds in a dry environment

The possible direct relationship between climate variations and abortion in Neospora caninum-infected cows has not been studied. The objective of this study was to determine whether climate changes could be a risk factor for abortion in N. caninum-infected cows, and was based on yearly serological screening for neosporosis and on the confirmation of N. caninum infection on aborted fetuses in two high-producing dairy herds with a mean 27% seroprevalence of N. caninum antibodies. The final population study was comprised of 357 pregnancies in seropositive animals. Logistic regression analysis indicated no significant effects of herd, N. caninum antibody titre, climate variables during the first and third trimesters of gestation, mean and maximum temperature-humidity index values during the second trimester of gestation, and previous abortion on the abortion rate. Based on the odds ratio, a 1-unit increase in lactation number yielded a 0.85-fold decrease in the abortion rate. The likelihood of abortion was 1.9 times (1/0.54) lower for pregnant cows inseminated with beef bull semen compared with Holstein-Friesian bull semen. The likelihood of abortion decreased significant and progressively by factors of 0.5, 0.41 and 0.3 for the respective classes 40-49, 30-39 and <30 rainfall mm during the second trimester of gestation (using the class >or=60 rainfall mm as reference). As a general conclusion, it seems that increased rainfall in a dry environment can compromise the success of gestation in N. caninum-infected cows. Attempts should therefore be made to reduce environment effects during the second trimester of gestation, a period in which the immune response of cows is diminished.     

Seroprevalence of Neospora caninum in aborting dairy cattle in the Czech Republic

A serological survey for antibodies against Neospora caninum in aborting cattle was carried out in the Czech Republic. Serum samples from 463 aborting dairy cows originated from 137 farms from different parts of the Czech Republic were tested for presence of N. caninum antibodies by use of an enzyme-linked immunosorbent assay (ELISA) and an indirect fluorescent antibody test (IFAT). Antibodies (> or = 1:640) to N. caninum were found in 18 (3.9%) of 463 aborting cows. Farm prevalence in aborting cows was 12.4% (17/137). The antibody titres of cows were 1:200 (9 cows), 1:640 (7 cows), 1:1280 (3 cows), 1:2560 (3 cows), 1:5120 (3 cows), 1:10,240 (2 cows) and 1:20,480 (0 cow). A case-control study was conducted to estimate the association of N. caninum infection and abortion. For this 407 serum samples were collected from cows on five dairy farms with repeated occurrence of endemic and sporadic abortion of unidentified etiology. These samples were obtained from aborting cattle (n=44) and normally calving cattle (control group; n=363) and tested for N. caninum antibodies by an immunofluorescent antibody test (IFAT). Overall, 3.19% (13/407) of cows sampled had positive N. caninum fluorescence with a cut-off titre of 1:200. The prevalence of N. caninum was significantly higher (P<0.05) in the aborting group (13.64%; 95% confidence interval (CI): 5.2, 27.4) than in the control group (1.93%; 95% CI: 0.8, 3.9). A strong association between seropositivity and abortion was found, with seropositive cows being eight times more likely to abort than seronegative cows (odds ratio=8; 95% CI: 2.6, 25.1). This first report on the serological prevalence of N. caninum in cows in the Czech Republic verified a strong association between N. caninum infection and abortions in five dairy farms. Thus, the neosporosis should be considered in differential diagnosis of bovine abortion.     

The Use of Beef Bull Semen Reduced the Risk of Abortion in Neospora‐seropositive Dairy Cows

There is an evidence that the epidemiology of neosporosis differs in dairy and beef cattle, such that beef cattle carry a lower risk of abortion. The aim of the present study was to establish whether artificial insemination using semen from beef bulls could reduce the risk of abortion in dairy cows seropositive for the Neospora caninum parasite. Our study was based on yearly serological screening for neosporosis and on the confirmation of Neospora infection in aborted fetuses in two high‐producing dairy herds with a mean 28% seroprevalence of N. caninum antibodies. The study population comprised of 273 pregnancies in seropositive animals: 156 pregnancies monitored after insemination using Holstein–Friesian semen and 117 after insemination using beef bull semen. Abortion rates for these animals were 28.2% (77 of 273), 34.6% (54 of 156) and 19.7% (23 of 117). Logistic regression analysis indicated no significant effects of lactation number and previous abortion on the abortion rate. Based on the odds ratio, a 1‐unit increase in the Neospora antibody titre yielded a 1.01‐fold increase in the abortion rate. The likelihood of abortion was two times higher for cows in one of the two herds and 2.8 times lower (one of 0.36) for pregnant cows inseminated with beef bull semen rather than Holstein–Friesian semen. Our results indicate that the use of beef bull semen can reduce the risk of abortion in dairy cows, and suggest that annual screening for neosporosis, specifically the antibody titre to the protozoan, could be an useful predictor of abortion risk in reproductive health programmes.     

Seroepidemiology of beef and dairy herds and fetal study of Neospora caninum in Argentina

The purpose of the present work was to study the epidemiology of Neospora caninum in beef and dairy herds in the Humid Pampas of Argentina. The seroprevalence of N. caninum was evaluated in 2414 serum samples of cows from beef and dairy farms. An indirect fluorescent antibody test (IFAT) was used to determine specific antibodies. The sera was screened at a dilution >or=1:200 and >or=1:600 in cows with reproductive disease antecedents and without them, respectively. Cows without history of reproductive diseases from nine beef and fifteen dairy farms were grouped according to the percentage (> or or 相似文献   

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.     

A nationwide survey on seroprevalence of Neospora caninum infection in beef cattle in Uruguay

Bovine abortions due to Neospora caninum infection have been reported worldwide and its economic impact on the beef industry has been acknowledged as a problem. Uruguay has the largest export value of beef per acre in South America. However, no data on the prevalence of N. caninum infection have been available in this country. The objective of this study was to estimate the prevalence and distribution of N. caninum infection in beef cattle in Uruguay through a nationwide survey. A two stage sampling design was used with farms being selected in stage one and animals being selected in stage two. A brief questionnaire was administered on each farm. Seroprevalence of N. caninum in 4444 beef cattle from 229 farms in all the counties, except Montevideo, of Uruguay was determined by an ELISA. The data were then analyzed to identify associations between infection and variables such as type of animal (cow or heifer), herd size, use of veterinary advice, productivity of the soil in relation to the national average, use of improved grass, use of mineral salts, use of supplemental feed, and presence of a dog(s) on the farm. The estimated proportion of positive farms for all the beef cattle operations was 69.2% (95% confidence interval [CI], 53.7-84.7). The overall cattle seroprevalence was estimated as 13.9% (95% CI, 11.6-16.3). The prevalence estimation by animal category was 14.3% (95% CI, 11.4-17.2) for beef cows and 12.9% (95% CI, 10.0-15.8) for beef heifers. There was no significant difference in the estimated prevalence between the two animal types. There was no significant difference in the animal level prevalence of N. caninum infection among different herd sizes. None of the herd demographic or management variables was significantly associated with the seropositivity to N. caninum infection. In conclusion, these results show that N. caninum infection is common among beef herds across Uruguay. Since the beef industry is one of the key industries in Uruguay, the economic effect and risk factors of N. caninum infection among beef cattle in this country should be further evaluated in the near future.     

Neospora abortions in dairy cattle: diagnosis, mode of transmission and control

AIM: To determine the contribution of Neospora caninum to abortions on a dairy farm in NSW (Australia), determine the mode of transmission and develop and trial a control option for infection. METHODS: Two whole herd bleeds were conducted 12 months apart and the association between serological status and abortion events were calculated for a number of bovine abortifacients. Family trees were constructed for N. caninum seropositive cattle in the herd. Some N. caninum seropositive cows were culled from the herd and no female offspring was retained from seropositive cows. RESULTS: At the first whole-herd bleed in December 2002 a seroprevalence of 10.2% for N. caninum infection was detected. Cows with N. caninum infection were 13 times more likely to abort than uninfected ones. Seventy-five percent of seropositive animals in the herd were related, suggesting a high degree of congenital infection/transmission. Only 15% of infections were likely to be postnatally acquired. Selective culling of seropositive cows and not breeding from them reduced the number of seropositive animals. Only one newly sero-converted cow was detected at the second whole-herd bleed 12 months later. CONCLUSIONS: Seroepidemiological approaches were able to establish a high degree of association between N. caninum infection and low-level abortion in the dairy herd. Vertical transmission of infection was the predominant mode of infection and hence control efforts aimed at selectively culling seropositive animals from the herd were highly successful in reducing the level of infection.