Bayesian latent class analysis of the characteristics of diagnostic tests to assess the passive immunity transfer status in neonatal Belgian Blue beef calves.

The aim of the current study was to assess the diagnostic characteristics of radial immunodiffusion (RID), capillary electrophoresis (CE) and digital brix refractometry (Bx) for the diagnosis of failure of passive transfer (FPT) of immunity in neonatal Belgian Blue beef calves in the absence of a gold standard using a Bayesian latent class model. Belgian blue beef calves (n = 202) from a large farm in the south of Belgium were blood-sampled at 48-72 h of age and tested for FPT. The true prevalence of FPT in this population of calves was 34.5 % (95 % BCI: 26.1-44.3) using a FPT cut-off point of 10 g IgG/L. This true prevalence increased to 66.3 (95 % BCI: 56.9-74.8) and 88.9 % (95 % BCI: 83.1-93.2) at FPT cut-off points of respectively 18 and 25 g IgG/L serum. The Bland-Altman plot comparing the RID and CE methods, revealed that the serum IgG concentrations obtained by RID were on average 2.25 (95 % CI 1.62-2.88) g/L higher than those measured by CE. Optimal cut-off values for CE, corresponding to the FPT values as measured by RID of 10, 18, and 25 g IgG/L serum, were respectively 10, 15, and 20 g IgG/L. The overall diagnostic accuracy of the three diagnostic tests was comparable at the FPT cut-off point of 10 g IgG/L serum (i.e. 85 %). At higher cut-off points for FPT, the RID and CE assays presumably performed better that the Bx method. In conclusion, we demonstrated that: (1) the CE method is a good alternative for the RID assay, the latter having important constraints when considering its practicality, and (2) the Bx method is a cheap and user-friendly indirect method to evaluate the FPT in new-born Belgian Blue beef calves.

Evaluation of a protocol to reduce the incidence of neonatal calf diarrhoea on dairy herds.

Calf diarrhoea causes substantial economic losses in cattle herds worldwide. Neonatal calves are particularly sensitive to infections with enteropathogens. The present study focused on prevention against the main infectious causes of neonatal calf diarrhoea i.e. Escherichia coli, rota- and coronavirus, and Cryptosporidium parvum. Dairy herds (n=24) with a high percentage of neonatal calves scouring (>10%) were included and calves were sampled for the presence of these four enteropathogens. To decrease diarrhoea problems among neonatal calves, a standard protocol was tested on 13 herds (treatment group) where both C. parvum and either E. coli or rota- or coronavirus were identified as being involved, the other 11 herds served as control group. The protocol consisted of 2 points of action: preventive vaccination of dams against E. coli, rota- and coronavirus, and preventive administration of halofuginone lactate to newborn calves. The average percentage of calves suffering from neonatal diarrhoea (39.7% versus 14.3%, P<0.01) and the average percentage of faecal samples positive for C. parvum (34% versus 11%, P<0.05) differed significantly between control herds and treatment herds after implementation of the protocol. No significant differences between control and treatment group were observed in the percentage of calves excreting E. coli, rotavirus and coronavirus, both before and at the end of the trial. Furthermore, risk factors potentially associated with the development of neonatal calf scours were determined. Non-significant results were obtained for the effect of the protocol on duration of diarrhoea and the effect of the colostral IgG quantity on the risk of diarrhoea. Passive immunity transfer status of the calves, measured both before the onset and at the end of the study, were non-significant between groups.