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).     

Validation of a bulk tank milk antibody ELISA to detect dairy herds likely infected with bovine viral diarrhoea virus in New Zealand

AIMS: To assess the sensitivity and specificity of a bulk tank milk (BTM) antibody enzyme-linked immunosorbent assay (ELISA) to detect likely infection of a dairy herd with bovine vi- ral diarrhoea virus (BVDV). The ELISA was subsequently used to estimate the prevalence of likely infected herds in parts of the North Island of New Zealand.

METHODS: BTM samples from 724 randomly selected dairy herds in the Waikato, Bay of Plenty and Northland regions of New Zealand were tested for BVDV antibodies. From this group, 20 herds were again randomly selected from each of the quartiles of the ELISA percentage inhibition (%INH) result. From each participant herd, serum from 15 randomly selected calves aged 6–18 months and 15 cows was collected and tested using an indirect blocking ELISA for BVDV antibodies.

RESULTS: Among serum results from calves from 50 herds available for analysis, 34 (68%) herds were classified as likely non-infected (0-3 seropositive among 15 calves) and 16 (32%) as likely infected (5–15 seropositive among 15 calves). Receiver- operator characteristic (ROC) analysis identified an optimal cut-off for BTM of 80%INH associated with 81% sensitivity and 91% specificity for likely herd infection. The prevalence of BVDV antibodies in cows within herds and %INH for BVDV in bulk milk were positively correlated (p<0.01). The association between bulk milk %INH and the prevalence of BVDV antibodies in calves was stronger than the same association in cows. Based on the threshold of 80%INH, the 95% confidence interval (CI) for prevalence of likely infection in the 724 herds in the Waikato, Bay of Plenty and Northland regions of New Zealand was 12–17%. Vaccination against BVDV was not significantly associated with the likely infection status of the herd based on prevalence of BVDV antibodies among calves.

CONCLUSION: An ELISA test result for BVDV antibodies in BTM ≥80%INH can be used as a threshold to indicate the presence of likely infection with BVDV in dairy herds in New Zealand, with 81% sensitivity and 91% specificity.     

Serological evidence for exposure to bovine viral diarrhoea virus in sheep co-grazed with beef cattle in New Zealand

ABSTRACT

Aims: To determine whether sheep that co-grazed with cattle that were suspected to be positive for bovine viral diarrhoea (BVD) virus had serological evidence of exposure to the virus.

Methods: Eighteen commercial farms that routinely co-grazed cattle and sheep in the same paddocks were recruited through purposive sampling. The recruiting veterinarians identified nine farms with cattle herds that were known or highly suspected to be positive for BVD and nine farms that were considered to be free of BVD. Blood samples were taken from 15 ewes aged 1 year on each farm and samples were submitted to a commercial diagnostic laboratory to test for antibodies against pestiviruses using an ELISA. All samples that were positive were then tested using a virus neutralisation test (VNT)for antibodies against BVD virus.

Results: Of the 270 blood samples, 17 were positive for pestivirus antibodies by ELISA and these originated from two farms that were known or suspected to have BVD virus-positive cattle. None of the samples from the nine flocks co-grazed with cattle herds that were known or suspected to be BVD virus-negative were positive for pestivirus antibodies. Within the two positive farms, 2/15 samples from the first farm and 15/15 samples from the second farm were antibody-positive. When the 17 positive blood samples were submitted for VNT, all 15 samples from the second farm tested positive for BVD virus antibodies with the highest titre being 1:512.

Conclusions and clinical relevance: In this small sample of New Zealand sheep and beef farms with suspected BVD infection in cattle, there was evidence of pestivirus exposure in co-grazed sheep. Although we were unable to confirm the origin of the exposure in these sheep, these findings highlight that farmers who are trying to eradicate BVD from their cattle should be mindful that the infection may also be circulating in sheep, and both populations should be considered a possible risk to each other for generating transient and persistent infections. Further work is needed to estimate the true prevalence of New Zealand sheep flocks that are affected by BVD and the associated economic impacts.     

乳牛流产胎儿中新孢子虫的鉴定

在血清学调查的基础上，进行了流产胎牛体内新孢子虫的鉴定。取新孢子虫血清抗体阳性乳牛的流产胎牛的脑、心、肺、脾、肝等组织进行病理学检查，经HE染色观察到脑组织中存在类似于新孢子虫包囊样结构，经免疫组织化学染色排除刚地弓形虫包囊的存在，确认该包囊为新孢子虫包囊。同时提取流产胎牛脑组织DNA，应用新孢子虫特异性引物Np6／Np21进行PCR扩增，扩增出的特异性目的争带的序列与新孢子虫标准株Nc-1的gene5序列的一致性为98％。首次证实我国大陆流产胎牛脑组织中存在新孢子虫。     

Effect of Neospora caninum-serostatus on culling, reproductive performance and milk production in Dutch dairy herds with and without a history of Neospora caninum-associated abortion epidemics

We quantified the effect of Neospora caninum (NC)-serostatus on culling and (re)production in 83 herds randomly selected from the Dutch dairy herd population (random group) and in 17 herds that had experienced an abortion epidemic associated with NC infection (epidemic-abortion group). In the random group, a single whole-herd blood sampling was done during the spring of 2003, while in the epidemic-abortion group whole-herd blood sampling was done repeatedly at least once a year starting after the abortion epidemic during the period 1997–2000 until the summer of 2004. Serological test-results for NC were given as ‘negative’ (N), ‘low-positive’ (LP) and ‘high-positive’ (HP). For analysing the time to culling, calving interval and age of first calving, survival analysis was used. For categorical reproduction parameters either a logistic-regression model (abortion, non-return after 1st insemination) or a Poisson-regression model (number of inseminations per pregnancy) was used. For milk production a linear-mixed model was used. All models were controlled, if applicable, for confounding variables like parity, production, season, year and abortion and adjusted for within-herd clustering.

In random herds, HP serostatus increased the hazard for culling 1.73-fold (95% CI: 1.37–2.19) compared to N and LP serostatus. Compared to N serostatus, LP and HP serostatus in epidemic-abortion herds increased the odds for abortion 1.88-fold (95% CI: 1.41–2.52) and 1.72-fold (95% CI: 1.38–2.14), respectively. No other reproduction parameters were associated with NC-serostatus in the random or epidemic-abortion herds. We found no effect of serostatus on milk production in the random group. In contrast, milk production of LP and HP serostatus in the epidemic-abortion group was respectively, 0.72 kg milk/day (95% CI: 0.15–1.03) and 0.59 kg milk/day (95% CI: 0.13–1.30), less during the first 100 days of lactation in the first year after the abortion epidemic compared with N serostatus.     

Factors associated with colostrum quality in individual cows from dairy herds in the Waikato region of New Zealand

AIMS: To examine associations between various cow-level factors and quality of first-milking colostrum (measured as Brix), and to evaluate herd-level associations between vaccination against calf diarrhoea and colostrum quality, in cows from dairy herds in the Waikato region of New Zealand.

METHODS: A single colostrum sample was collected, by complete udder evacuation, from each of 20 cows from 29 dairy herds in the Waikato region of New Zealand during the 2016 spring calving period. Vaccination pre-partum with a calf diarrhoea vaccine was used in 15 herds. Each colostrum sample was tested using a digital Brix refractometer. The body condition score of each cow was recorded at the time of sample collection and farmers provided records of clinical mastitis and facial eczema from the previous 12 months, as well as the age and breed of cows. Associations between cow-level variables in non-vaccinated herds and Brix were examined using a multivariable linear mixed model and estimated marginal means obtained for different categories.

RESULTS: Mean Brix of 281 samples from cows in non-vaccinated herds was 18.7 (SD 0.26)%; 63/281 (22.4%) samples had Brix ≥22% and 152/281 (54.1%) had Brix ≥18%. Mean Brix of colostrum samples from cows aged ≥6 years (20.2 (95% CI=19.1–21.2)%) was higher than for samples from 2-year-old cows (18.6 (95% CI=17.3–19.9)%) (p=0.005). Colostrum that was collected at the first milking on the day of calving had higher Brix (20.0 (95% CI=19.1–20.9)%) than colostrum collected from cows that calved the previous day (17.5 (95% CI=16.5–18.4)%) (p<0.001). Mean Brix of colostrum samples from cows which produced ≥8?L (18.2 (95% CI=17.1–19.2)%) tended to be lower than from cows which produced <8?L first-milking colostrum (19.1 (95% CI=18.3–20.0)%) (p=0.08). Among vaccinating herds, 9/15 (60%) had ≥60% colostrum samples with Brix ≥18% compared with 4/14 (29%) of non-vaccinating herds (p=0.04).

CONCLUSIONS AND CLINICAL RELEVANCE: Colostrum quality, as measured by Brix, was associated with the total volume of first-milking colostrum, interval from calving to colostrum collection and cow age. Vaccination against calf diarrhoea was associated with a higher proportion of colostrum samples with adequate Brix. Careful selection of colostrum donor cows should ensure newborn calves are fed adequate quality colostrum which should be beneficial in preventing failure of passive transfer of IgG. Testing of colostrum from individual cows with a Brix refractometer is advocated for the selection of colostrum for feeding newborn calves.     

Factors associated with variation in Neospora caninum bulk-milk S/P ratios in initially bulk-milk negative testing Dutch dairy herds

We conducted a study on 81 initially bulk-milk ELISA negative dairy herds taken from a random sample of Dutch dairy herds to evaluate variation in bulk-milk S/P ratios and to study reasons for bulk-milk conversion. These herds were repeatedly (3-month intervals) tested between April 2004 and August 2005 and serostatus of all animals had previously been established as negative (N), low-positive (LP) or high-positive (HP). Of these herds, herd- and test-related factors associated with variation in sample over positive (S/P) ratios were analysed using a multivariable linear-mixed model with ‘herd’ as random effect. In addition, changes of animal serostatus in converting herds were described. S/P ratios were calculated as the optical density of the bulk-milk sample minus the optical density of the negative serum control divided by the difference in optical density between the positive and negative serum control.

Sixteen bulk-milk conversions in 12 dairy herds were seen with few indications of serological conversion in lactating cattle except for one herd in which recrudescence of infection appeared likely in nine cows. The effect of HP serostatus on bulk-milk S/P ratio was 2–3 times stronger compared with LP serostatus. In addition, bulk-milk S/P-ratio increased when the proportion of HP animals between 1 and 60 days in milk increased and decreased when the average milk-production level of the herd increased. Besides these herd-related factors, the use of different ELISA-testkits between test rounds had a significant effect on the S/P-ratio in bulk-milk samples.     

Factors associated with Neospora caninum serostatus in cattle of 20 specialised Costa Rican dairy herds

Twenty-five specialised Costa Rican dairy farms (located in the Poás area) were used to determine neosporosis seroprevalence and the association of seropositivity with environmental and management factors. The farms involved were selected intentionally and all of them use VAMPP 5.1 (Veterinary Automated Management and Production Control Programme) as management-information system. Holstein–Friesian, Jersey and crosses between them were the most-frequent breeds in these herds. The number of females per farm varied from 41 to 296. Our cross-sectional study had two phases. In the first phase, we determined the presence or absence of seropositivity at herd level. For the second phase, all females in 20 seropositive farms were bled. Serum samples were tested for antibodies to Neospora caninum using an indirect enzyme-linked immunosorbent assay (ELISA). A questionnaire with factors mentioned in the literature was administered to the farmers. Logistic regression (LR with herd as random effect) was used to assess the relationships of the serostatus at the individual level with characteristics of the cows and environmental factors. In the first phase all herds had >20% seropositive females; therefore, all herds were eligible for the second phase. In the second phase, the overall prevalence was 39.7% (1191/3002), and within-herd prevalences were between 25.0 and 70.5%. Age 3–6 years, parity ≤2 of the dam of the cow, Jersey breed and lack of purposive sampling to diagnose abortive infectious disease were associated with positive serostatus; other management and environmental factors did not show significant associations. The lack of association between management and environmental factors with serostatus might be because all farms were exposed to a considerable number of potential factors. That all herds of this study were seropositive for neosporosis and the within-herd prevalence was considerable raises questions about how far the infection is spread in other dairy areas of Costa Rica.     

Elimination of bovine viral diarrhoea virus in New Zealand: a review of research progress and future directions

The major impacts of bovine viral diarrhoea (BVD) on cattle health and production have prompted many countries to embark on national elimination programmes. These programmes typically involve identifying and removing persistently infected (PI) cattle in infected herds and implementing biosecurity measures, such as pre- or post-movement testing. In order to design a systematic national control programme to eliminate BVD in New Zealand, which achieves the greatest benefits to the industries at the lowest cost to individual farmers, an accurate understanding is necessary of the epidemiology, economics and social motivation for BVD control in New Zealand. In this article we briefly review the pathogenesis of BVD, transmission and diagnosis of BVD virus infection, and effectiveness of vaccination. We summarise the current state of knowledge of the prevalence, risk factors for transmission, and financial impacts of BVD in New Zealand. We describe control programmes in Europe and then discuss the challenges that must be addressed to design a cost-effective national control programme to eliminate BVD in New Zealand.     

Loser cows in Danish dairy herds: definition, prevalence and consequences

During the last few years, many Danish dairy farmers have expressed increasing concerns regarding a group of cows, which we have chosen to term ‘loser cows’. Until now, a loser cow has not been described scientifically. We defined a loser cow on the basis of a clinical examination of the cow. A total of 15,151 clinical examinations were made on 6,451 individual cows from 39 randomly selected, large Danish dairy herds with loose-housing systems using a clinical protocol. Scores for the clinical signs lameness, body condition, hock lesions, other cutaneous lesions, vaginal discharge, condition of hair coat and general condition were converted into a loser cow score. Cows with a loser cow score of 8 or more were classified as loser cows. The overall prevalence of loser cows was 2.15%, 4.50% and 2.98% during the first, second and third round of herd visits, respectively.

The associations between the loser cow state and milk production, mortality, morbidity, culling and workload for the farmer were evaluated using data from herd visits and from the Danish Cattle Database and a number of different statistical techniques. It was concluded that the loser cow state has significant negative consequences for both the farmer and the cow. On average, loser cows yielded 0.61 to 2.24 kg energy corrected milk less per day than non-loser cows depending on parity. Hazard ratio for death or euthanasia was 5.69 for loser cows compared to non-loser cows. Incidence rate ratio for disease treatments was 0.69 for non-loser cows compared to loser cows. Loser cows were often culled in an ‘unfavourable’ way and generally caused extra workload for the farmer.

A simplified version of the loser cow score was evaluated and is recommended for future research and use in practice.     

Incidence of leptospiral abortion in Brazilian dairy cattle

We examined dams' paired serum samples and foetal kidneys (histopathologically and attempting leptospiral cultures) from 120 Brazilian Holstein abortions from 10 herds near Sao Paulo, Brazil, in 1996. Leptospiras was isolated from 15 foetuses. The Leptospira interrogans serovar hardjo was obtained from four, pomona from three and wolffi from eight foetuses. Ten of these 15 foetuses showed a four-fold rise in titres between the day of abortion and the second samples taken 15 days later. Fifty-seven other foetuses had histologic evidence of leptospires; 27 of their dams (47%) had four-fold rises in titres. In total, 72 of 120 aborted foetuses had evidence of leptospiral infection.     

Bulk milk ELISA and the diagnosis of parasite infections in dairy herds: a review

The bulk milk enzyme-linked immune sorbent assay (ELISA) is a rapid and inexpensive method of assessing herd exposure to pathogens that is increasingly being used for the diagnosis of parasite infections in dairy herds. In this paper, with the dairy herd health veterinarian in mind, we review the principles of the assay and the recent literature on the potential role of bulk milk ELISA for the diagnosis of ostertagiosis, fasciolosis, parasitic bronchitis due to cattle lung worm and neosporosis. It is generally accepted that assay results reflect exposure to the parasite rather than the presence of active infection. Bulk milk ELISA can be a useful tool for the veterinary practitioner as a component of a herd health monitoring programme or in the context of a herd health investigation. It can also play a role in regional or national surveillance programmes. However, the results need to be interpreted within the context of the herd-specific health management, the milk production pattern and the parasite life cycle.     

Genetic parameters for total lactation yields of milk,fat, protein,and somatic cell score in New Zealand dairy goats

The aim of this study was to estimate genetic parameters for lactation yields of milk (MY), fat (FY), protein (PY), and somatic cell score (SCS) of New Zealand dairy goats. The analysis used 64,604 lactation records from 23,583 does, kidding between 2004 and 2017, distributed in 21 flocks and representing 915 bucks. Estimates of genetic and residual (co) variances, heritabilities, and repeatabilities were obtained using a multiple‐trait repeatability animal model. The model included the fixed effects of contemporary group (does kidding in the same flock and year), age of the doe (in years), and as covariates, kidding day, proportion of Alpine, Nubian, Toggenburg, and “unknown” breeds (Saanen was used as the base breed), and heterosis. Random effects included additive animal genetic and doe permanent environmental effects. Estimates of heritabilities were 0.25 for MY, 0.24 for FY, 0.24 for PY, and 0.21 for SCS. The phenotypic correlations between MY, FY, and PY ranged from 0.90 to 0.96, and the genetic correlations ranged from 0.81 to 0.93. These results indicate lactation yield traits exhibit useful heritable variation and that multiple trait selection for these traits could improve milk revenue produced from successive generations of New Zealand dairy goats.     

Calf and colostrum management practices on New Zealand dairy farms and their associations with concentrations of total protein in calf serum

AIMS: To gather information on management practices and farmer attitudes to management of cows and calves during the immediate post-partum period on dairy farms in New Zealand, and to assess these practices for associations with concentrations of total protein (TP) in serum of calves 1–8 days-old.

METHOD: Between July and September 2015 blood samples were collected from calves aged between 24 hours and 7 days, from dairy farms (n=105) in nine areas in New Zealand, on three occasions throughout the calving period. Concentrations of TP were determined in all serum samples. At each visit technicians collected 1?L of the pooled colostrum that was intended for feeding to newborn calves that day. These samples were assessed for Brix, coliform and total bacterial counts. After the last sampling visit, the calf rearer or farm manager were asked to complete a questionnaire describing calf and colostrum management practices on the farm. Potential farm-level variables associated with concentrations of TP in serum of sampled calves were identified using univariable and multivariable linear mixed models.

RESULTS: Mean concentration of TP in serum of calves across all farms was 59.8 (95% CI=59.4–60.2) g/L, and was associated with region and herd size in the final multivariable model. Concentrations of TP were lower in calves from farms in Otago (56.2 (95% CI=53.4–58.9) g/L) and Southland (56.9 (95% CI=54.1–59.7) g/L) compared to calves on farms in the Far North (62.6 (95% CI=59.8–65.3) g/L), and were lower in calves from farms with a herd size >600 (58.3 (95% CI=56.7–59.8) g/L) than ≤600 (61.3 (95% CI=60.1–62.5) g/L) cows. After accounting for fixed effects, farm accounted for only 8.4% of the unexplained variation. There was no association between any of the measures of colostrum quality and concentrations of TP in serum (p>0.2).

CONCLUSION AND CLINICAL RELEVANCE: Very few herd-level variables were associated with concentrations of TP in serum. Risk factors that have been shown to be of importance in previous studies outside New Zealand were not identified as important in the current study. It is possible that, in the situation where calves are kept at pasture with their dams for prolonged periods, variables which influence how well a cow can feed its calf in the first 12–24 hours have a larger influence on concentrations of TP in serum than the collection and management of calves once they reach the rearing shed.     

Future options for brucellosis surveillance in New Zealand beef herds

It is probable that bovine brucellosis will be eradicated from New Zealand by 1990. However, continued surveillance for the disease will have to be maintained for a number of years. This paper examines alternative methods of surveillance in beef herds with a view to ensuring that the most cost effective method is used. The three surveillance methods examined are the present automated complement fixation test, abattoir surveillance, and a system based on a delayed hypersensitivity skin test using a purified Brucella protein antigen. It is concluded that despite the relatively low sensitivity of the skin test the probability of its identifying herds as infected is likely to be greater in practice than abattoir surveil- lance. The skin test is cheaper than the present complement fixation test.     

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).