CONSULTANCY: Animal Health & Welfare
Distinguishing subtypes of E. coli O 57:H7
The bacterium Escherichia coli O157 presents a serious public health problem in Scotland: shed asymptomatically by infected cattle, it has the potential to cause serious illness, renal failure and even death in humans. Different populations of E. coli O157 present in field samples can be distinguished using Pulsed-Field Gel Electrophoresis (PFGE), a subtyping technique which uses a restriction enzyme to “chop-up” the DNA into pieces of different sizes. We have been studying a strain (EDL933) of E. coli O157: H7 whose PFGE pattern, obtained using the restriction enzyme Xba1, differs from the pattern predicted from its DNA sequence.
Having found no errors in the reported DNA sequence in the regions near the predicted restriction sites, we sought to to establish another explanation for the discrepancy. The distribution of dam methylation sites within the genome was investigated in silico and a new PFGE pattern was predicted by assuming that, whenever the restriction enzyme Xba1 was expected to cut the DNA at a dam methylation site, no such cut occurred. The new predicted pattern agrees closely with that observed in practice. This work is important in enhancing our understanding of the relationship between PFGE banding patterns and the underlying DNA sequences of pathogens.
Digitised image of a PFGE image for strain EDL933 after Xba1 digestion, showing only five clear bands between 200 and 300 kb; the arrow indicates where an additional band is sometimes present.
Summary PFGE banding patterns for strain EDL933 after Xba1 digestion. The “Observed” column shows mean band lengths that were present on each of six separate gels; the remaining columns show the predicted band lengths depending on whether methylated restriction sites for Xba1 were cut or not.
- Sole and line lesions marked on a cow's hoof.
Intervention studies to reduce the incidence of lameness in dairy cattle
Lameness in dairy cattle causes distress to the animals and reduces their productivity. Intervention studies offer an opportunity to objectively assess strategies to reduce the incidence of lameness. However, the analysis of data from such studies is complicated by two issues. Firstly, the temporal and within-animal correlations in data collected from different claws of many different animals. Secondly, the effects of variables such as time of year, time since calving and age of the animals are unavoidably confounded. As well as developing a range of analyses using both parametric and additive models, we have established a simulation approach to evaluating the statistical power and cost of different sampling strategies to improve the efficiency of future multi-factorial studies.
Study of perceived risks to sheep health
To ensure that research priorities are aligned closely with the priorities of the industry, we have designed and analysed a survey of sheep farmers who are members of the Moredun Foundation. Our analysis identified the animal health issues that were perceived as the biggest threats to the farmers own holdings, and allowed differentiation between acute and non-acute risks. By making innovative use of generalised linear models, we identified differences in perceived risk between farmers in Scotland and England for a number of diseases including sheep scab and coccidiosis. We also found that the average reported perceptions of risk to farmers own holdings sometimes differed from the average perception of risks to the industry as a whole, with some diseases such as orf being perceived much more frequently as a threat at the farm level than at the national scale.
Percentage of Scottish farms in which each issue was reported as amongst the five most serious issues on a farmer’s own holding. Blue bars represent national estimates, while other colours identify issues (mastitis and sheep scab) with statistically significant geographical differences.