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Where to next for genetic indexes?

A new clutch of genetic indexes is expected to be launched in 2017. What traits will they improve, who will collect data and who determines the genetic direction? Ann Hardy reports.

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A mastitis index for all dairy breeds is likely to be launched next year.
A mastitis index for all dairy breeds is likely to be launched next year.

Genetic improvement is moving at a faster pace in the Holstein population than ever in the breed’s history, thanks to better recording of data, the ability to share the data across a variety of platforms, and the growth in our understanding and use of genomics.

 

As a result we have seen worthwhile genetic progress in traits such as somatic cell count, female fertility and lifespan, alongside continued improvement in the more traditional traits of milk, fat and protein.

 

Today, virtually anything which can be measured and recorded can be improved through breeding, as long as it is proven to be a trait with a genetic background. So, what will be the next genetic indexes to be brought into use for the UK Holstein, who will collect the data and what will drive this forward?

 

Marco Winters, head of animal genetics for AHDB Dairy, says we can expect three new indexes in 2017 and more are in the pipeline not far behind.

Mastitis

“Mastitis is something we looked at in 2010, as part of the Expanding Indices Project, a Defra and industry consortium led by the then Scottish Agricultural College,” says Mr Winters.

 

“Since that time farmers, through their milk recording organisations, have more than doubled the amount of data collected and we have been working towards an index for all dairy breeds for launch next year.

 

“Ongoing work has established that the heritability of mastitis – or the amount of variation that can be explained by genetics – is about 7%, which indicates that some improvement will definitely be possible by breeding for this trait.”

 

However, he points out we have already made some improvement in mastitis by breeding for lower cell counts.

 

“Somatic cell count and mastitis are closely related and there’s a correlation of about 0.7 between the two traits,” says Mr Winters.

 

“This means by breeding for lower cell counts, we have improved the genetics of mastitis too, but because the relationship between the two is not perfect – which would be shown by a correlation of 1.0 – we can achieve better results by breeding for mastitis itself.”

 

This is a principle Mr Winters is keen to stress, as breeding for the trait you want to improve is always more effective than breeding for a proxy or related trait.

 

“The milk recording organisations (MROs) now have well over one million records of mastitis cases, which means we have a lot of information regarding which bloodlines have the best mastitis resistance,” he says.

 

“We will use this information in the calculation of a mastitis resistance index which we hope will help every herd breed healthier cows, and we see this trait as a high priority as we strive as an industry to improve animal welfare and cut antibiotic use.”

Lameness

Dr y matter intake indexes are slowly being launched around the world.

Lameness is another health and welfare issue which is increasingly unacceptable and, as with all health issues, it should be addressed through better management in the first instance.

 

“But again we are confident that breeding can play a role and we know the heritability of lameness in the UK is about 8%,” he adds.

 

As with mastitis, he says it is another trait which has improved through selection in favour of related traits, with selection for both locomotion and foot and leg conformation playing a positive role.

 

“But we have not made as much progress as we had hoped,” says Mr Winters, “and this may be because the correlation between lameness and these other traits is not particularly high.”

 

The answer he says is to work with actual records of lameness itself, and, as with mastitis, these records are now collected more consistently and in greater volume than ever before.

 

“Our two data sources at this stage are again the MROs, who now keep records of lameness events, but we are adding to this with data which is collected by Holstein UK,” he says.

 

“The breed society has been collecting information about digital dermatitis for many years, so we will use this trait together with some others in the calculation of the index,” he says.

 

“And although we are using some proxy traits – such as foot angle, locomotion, angularity and body condition score, all of which have been shown to have an influence on lameness – we will make far more progress by using the records for lameness itself.”

 

As with mastitis resistance the plan is to launch a lameness index in 2017, but this, in particular, will be a work in progress as more information is introduced, and initially the index will only be calculated for the Holstein breed.

 

“There will be a ‘version two’ of the lameness index which will include foot trimmers’, vets’ and other data as the more actual lameness information we can include in the index the more reliable it will be,” he says.

 

Dry matter intake (DMI) indexes are now considered to be the Holy Grail of genetic indexes and are slowly being launched around the world.

 

“Feed accounts for the majority of a farm’s variable costs, so the potential savings to be made from selection of animals which eat a little less and convert their feed into milk more efficiently is huge,” says Mr Winters.

Complex trait

Marco Winters

However, he says feed efficiency itself would be such a complex trait to develop as an index that DMI as a stand-alone index is a more straightforward approach at this stage.

 

“We are using two sources of data to develop a DMI index – the first is actual dry matter intake collected through a collaborative international project involving nine countries and 10 data sets,” he says. “The UK has played a central role in this project as much of the feed intake data has come from the Langhill herd in Scotland, managed by Scotland’s rural college SRUC.”

 

The second source of data comes from the mid-infrared (MIR) analysis of milk, which – through work undertaken by NMR and SRUC – is revealing particular signatures which are proving to be reliable indicators of cows in negative energy balance.

 

“We may soon have this information available for hundreds of thousands of UK-housed cows, and – with the additional availability of genomic information – it won’t be long before we have a Predicted Transmitting Ability for DMI,” says Mr Winters.

 

“Even though this is not 100% accurate it will be by far the best predictor of DMI we have ever had and we are now working together with NMR and our partners EGENES at SRUC on embedding this information into the routine AHDB genetic evaluation service in 2017,” he says.

Longer term

Other developments are likely to be a little further ahead, with genetic indexes for carcass traits for dairy sires probably the next in line and maybe methane emissions even further down the road.

 

“Genetic indexes are constantly under review and any changes are based on the direction the industry has already taken, the progress it has made and predictions of future needs based on domestic and world market information,” says Mr Winters.

 

“At AHDB Dairy, this role is undertaken by the Genetics Advisory Forum, which comprises, and is advised by, stakeholders such as farmers, scientists, breed societies, milk recording organisations, and the AI and milk processing industries.

 

“This forum takes its responsibility for genetic improvement for the dairy breeds very seriously indeed, and knows that with the tools now available to AI companies and dairy breeders it is possible to make rapid genetic progress in whatever the chosen direction,” he says.

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