Sheep: Fight footrot by using hoof scoring not gene markers
IT IS possible to reduce footrot in sheep flocks by selective breeding - and the best tool for this is ewe hoof scoring. Liz Genever, Eblex sheep scientist, says a New Zealand-developed gene marker proved ‘generally ineffective’ for pinpointing footrot resistance in a four-year Defra project led by SAC, with support from Eblex.
The research involved more than 55,000 individual hoof scores from nearly 14,000 Texel, Scottish Blackface and Mule sheep in 27 mainly commercial flocks with pedigree details from 2005 to 2007, coupled with blood sampling for molecular genetic analysis.
The extensive scoring showed the average prevalence of footrot and its precursor conditions varied widely between breeds (17-57 per cent) and farms (less than 1 per cent to nearly 60 per cent). At the same time, older ewes, ewes rearing twins and male lambs were seen as being at particular risk.
Speaking on the work, Dr Genever says: “Footrot has a low to moderate heritability in adults, confirming conventional breeding approaches can be used to improve resistance and assist in its control.
Same time of year
“It also underlines breeding for resistance will give greater and more rapid results in flocks with high levels of footrot, and that ewes should be scored more than once, ideally at the same time each year, for accurate EBV development.
“Further genetic analyses show footrot resistance is usually either favourably correlated with other traits or uncorrelated with them. This means breeding for footrot resistance will not compromise progress in other important performance traits.
“Indeed, the genetic correlations suggest selection for footrot resistance is likely to improve longevity, number of lambs reared, and lamb survival in Blackface ewes, while having no effect on the rate of growth, or muscle depth, and favourably influencing fat depth in Texel lambs.”
Dr Genever says the reason the New Zealand marker did not work well was there are ‘very different variants’ of the gene known to be involved with immunity in New Zealand sheep present in the UK Texel and Blackface breeds.
“These variants are such that no consistent correlations could be identified between footrot resistance and the genetic marker test developed at Lincoln University in New Zealand,” she says.
“Under these circumstances, the widespread use of this particular test is not recommended for these breeds. Instead, until emerging genetic technologies can be effectively harnessed for the UK, a conventional EBV approach based on routine ewe hoof scoring is considered likely to yield the best results.
“Together with the benefits of cleaner pasture, selecting for footrot resistance in this way is calculated to reduce the prevalence of the disease by between 0.5 and 1 percentage point per year, making it a valuable and particularly sustainable complement to current control strategies and well worth widespread adoption.”
KEY RESEARCH FINDINGS
- Some farms have a footrot prevalence of less than 1 per cent while others have over 60 per cent.
- Older ewes, ewes rearing twins and male lambs are at higher risk of footrot.
- Regular hoof scoring, preferably repeated at the same time of year, will help develop accurate footrot resistance EBVs.
- Selection for sheep showing resistance will not compromise progress in other important performance traits.
- There are not enough genetic similarities between NZ and UK breeds for the NZ gene marker to work in this country.