Jozef Laureyns

Calf-Level Factors Associated with Bovine Neonatal Pancytopenia – A Multi-Country Case-Control Study

Bovine neonatal pancytopenia (BNP), a high fatality condition causing haemorrhages in calves aged less than 4 weeks, was first reported in 2007 in Germany and subsequently observed at low incidence in other European countries and New Zealand. A multi-country matched case-control study was conducted in 2011 to identify calf-level risk factors for BNP. 405 BNP cases were recruited from 330 farms in Belgium, France, Germany and the Netherlands by laboratory confirmation of farmer-reported cases. Up to four calves of similar age from the same farm were selected as controls (1154 calves). Risk factor data were collected by questionnaire. Multivariable modelling using conditional logistic regression indicated that PregSure®BVD (PregSure, Pfizer Animal Health) vaccination of the dam was strongly associated with BNP cases (adjusted matched Odds Ratio - amOR 17.8 first lactation dams; 95% confidence interval – ci 2.4, 134.4; p = 0.005), and second or more lactation PregSure-vaccinated dams were more likely to have a case than first lactation vaccinated dams (amOR 2.2 second lactation; ci 1.1, 4.3; p = 0.024; amOR 5.3 third or more lactation; ci 2.9, 9.8; p = <0.001). Feeding colostrum from other cows was strongly associated with BNP if the dam was not PregSure-vaccinated (amOR 30.5; ci 2.1, 440.5; p = 0.012), but the effect was less if the dam was PregSure-vaccinated (amOR 2.1; ci 1.1, 4.0; p = 0.024). Feeding exclusively dam’s milk was a higher risk than other types of milk (amOR 3.4; ci 1.6, 7.5; p = 0.002). The population attributable fractions were 0.84 (ci 0.68, 0.92) for PregSure vaccination, 0.13 (ci 0.06, 0.19) for feeding other cows’ colostrum, and 0.15 (ci 0.08, 0.22) for feeding dam’s milk. No other calf-level factors were identified, suggesting that there are other important factors that are outside the scope of this study, such as genetics, which explain why BNP develops in some PregSure-colostrum-exposed calves but not in others.

A survey on biosecurity and management practices in selected Belgian cattle farms.

The shift from cure towards prevention in veterinary medicine involves the implementation of biosecurity, which includes all measures preventing pathogens from entering a herd and reducing the spread of pathogens within a herd. In Belgium no studies have considered the implementation of biosecurity measures in the daily management of cattle farms. Therefore the aim of the study was to map the current application of biosecurity measures in Belgian cattle farms in the prevention of disease transmission within and between farms. Between March 2011 and April 2013 the data were collected as part of a larger cross-sectional study, conducted to identify risk factors for reinfection with BVDV in cattle herds assumed free from BVDV. Questionnaire data from 33 dairy farms, 16 beef farms and 25 mixed (dairy and beef cattle) farms were analyzed using a combination of a linear scoring system, a categorical principal component analysis and a two-step cluster analysis to differentiate these farms based on their biosecurity levels and visit frequencies. Further enhancement of preventive measures considering external and internal biosecurity was still possible for each farm, as none of the farms obtained an overall high biosecurity level. Three groups of cattle farms were differentiated with a biosecurity level varying from low to high-medium, of which the group with the lowest biosecurity level mainly consisted of mixed farms. Animal-to-animal contacts with cattle from other herds were frequently possible as only 12% of the farmers purchasing cattle quarantined purchased animals at least three weeks and contacts over fences on pasture were possible in 70% of the herds. Basic biosecurity measures such as farm-specific protective clothing and boots were present in the majority of the farms, but they were insufficiently or incorrectly used. Cattle farms were very often visited by professional visitors of which the herd veterinarian, the AI technician and the cattle salesman most frequently entered the farm. It can be concluded that few biosecurity measures were undertaken by Belgian cattle farmers, thereby exposing themselves to the risk of disease transmission within and between farms. Especially in regions with a high cattle density, small distances to neighbouring farms and high frequencies of professional visits, a farm-specific preventive strategy should be developed, thereby using the facilities often already present on the farm.

Virulence comparison and quantification of horizontal bovine viral diarrhoea virus transmission following experimental infection in calves

Bovine viral diarrhoea virus (BVDV) causes persistent infections by infecting the fetus of susceptible animals during gestation. These persistently infected (PI) animals are important sources of infection. On the contrary, transiently infected (TI) animals are believed to be less important, but transient infections with a severe BVDV-2 strain can spread explosively. To assess the importance of TI cattle in the epidemiology of BVDV, two experimental infections were performed to determine basic reproduction ratios (R0). In each experiment three calves were infected via intranasal inoculation and housed together with seven susceptible animals. Two strains isolated in Belgium were used, a virulent BVDV-1b and a virulent BVDV-2a field isolate, resulting in an R0 of 0.25 (95% CI 0.01; 1.95) and 0.24 (95% CI 0.01; 2.11), respectively. A PI animal was then introduced to the remaining uninfected animals and produced an R of +∞ (95% CI 1.88; +∞). These results support the suggestion that TI animals, compared to PI animals, contribute only a limited amount to BVDV spread. Additionally, the severe clinical symptoms observed in the field with these isolates could not be reproduced during these experiments, suggesting that other factors besides strain virulence influence the clinical manifestations evoked by BVDV.

Association between herd exposure to BVDV-infection and bulk milk somatic cell count of Flemish dairy farms

The purpose of this study was to investigate the statistical association between herd bovine viral diarrhoea (BVD) status based on bulk milk antibody detection and monthly bulk milk somatic cell count (BMSCC) as a reflection of the udder health. A distinction was made between vaccinating and non-vaccinating herds via a questionnaire concerning BVD-vaccination. No significant difference in BMSCC was found between vaccinating (228,300 cells/ml; SD 180,019) and non-vaccinating (237,070 cells/ml; SD 77,900) herds. Non-vaccinating herds (n=243) were selected, and the relationship between a single BVDV-antibody titre and the BMSCC of each herd over a 12-month observation period evaluated. For this purpose, the non-vaccinating herds were divided into five groups depending on bulk milk BVDV-antibody titres. Overall, no significant relationship between the antibody titre and the BMSCC was found. Still, when comparing the category with the lowest S/P ratio (essentially BVDV-naïve herds; BMSCC=211,390 cells/ml) with the combined four other categories (BMSCC=242,790 cells/ml), a significant difference in BMSSC was observed (P=0.01).

Herd-level animal management factors associated with the occurrence of bovine neonatal pancytopenia in calves in a multi-country study

Since 2007, mortality associated with a previously unreported haemorrhagic disease has been observed in young calves in several European countries. The syndrome, which has been named ‘bovine neonatal pancytopenia’ (BNP), is characterised by thrombocytopenia, leukocytopenia and a panmyelophthisis. A herd-level case-control study was conducted in four BNP affected countries (Belgium, France, Germany and the Netherlands) to identify herd management risk factors for BNP occurrence. Data were collected using structured face-to-face and telephone interviews of farm managers and their local veterinarians. In total, 363 case farms and 887 control farms were included in a matched multivariable conditional logistic regression analysis. Case-control status was strongly associated with the odds of herd level use of the vaccine PregSure® BVD (PregSure, Pfizer Animal Health) (matched adjusted odds ratio (OR) 107.2; 95% CI: 41.0–280.1). This was also the case for the practices of feeding calves colostrum from the calf’s own dam (OR 2.0; 95% CI: 1.1–3.4) or feeding pooled colostrum (OR 4.1; 95% CI: 1.9–8.8). Given that the study had relatively high statistical power and represented a variety of cattle production and husbandry systems, it can be concluded with some confidence that no other herd level management factors are competent causes for a sufficient cause of BNP occurrence on herd level. It is suggested that genetic characteristics of the dams and BNP calves should be the focus of further investigations aimed at identifying the currently missing component causes that together with PregSure vaccination and colostrum feeding represent a sufficient cause for occurrence of BNP in calves.