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New genetic index launched to help breed against bovine tuberculosis

Later this month a new genetic index will be introduced to help dairy farmers breed cows which have improved resistance to bTB. Farmers Guardian talks to Marco Winters, head of genetics for AHDB Dairy, about TB Advantage, the first index of its kind in the world.

 

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Q: How is the TB Advantage index calculated?

TB Advantage is calculated using data from animals which react to the official bTB skin test and are sent to slaughter, as recorded by the Animal and Plant Health Agency.


Because there are close to 650,000 animal records used in the analysis, breeding patterns can be established and more resistant bloodlines identified. All this information is used in the calculation of the TB Advantage index.

Q: How is the new index expressed?
like all genetic

Like all genetic indexes used by UK dairy farmers, TB Advantage is based on predicted transmitting ability.


It indicates the degree of resistance to bTB a bull is predicted to pass on to its offspring and is expressed on a scale which typically runs from -3 to +3. A positive rating is desirable and the average score for all bulls is zero.

Q: When and where is this index published?

The index will be published by AHDB Dairy as part of the routine dairy cattle genetic evaluations service in April, August and December.


It be available from January 19, on the AHDB Dairy website at www.dairy.ahdb.org.uk

Q Which cattle breeds can benefit from the index?

In the first instance, TB Advantage will only be available for the Holstein breed but work is currently underway to establish whether the index can be extended to other dairy and beef breeds.

Q: Is TB Advantage available for males and females?

The index will be calculated for bulls and any females which have been genotyped.

Q: Is the index available for daughter-proven and young genomic sires?

The index is available for all Holstein sires which either have daughters milking in the UK (daughter-proven bulls) or have had their genotype (DNA) measured (genomic bulls).


In effect, this means there will be virtually no commercially available Holstein bulls which do not have a TB Advantage score.

Q: How do we know the index will work?

Whenever there is a genetic component to any trait, it is possible to select in favour of this trait as part of a breeding strategy. This will inevitably lead to genetic improvement.


We can see there are differences in susceptibility to bTB between different sires and we have measured the heritability of the trait.


The heritability of bTB resistance is about 9 per cent. This means of all of the variation we can detect in bTB resistance, about 9 per cent is due to genetics. This figure is on a par with some other traits cattle breeders have been improving over a number of years.


Somatic cell count (SCC), for instance, is almost exactly comparable in heritability and has become an important part of most milk producers’ breeding strategies. As a result, average genetic indexes for SCC in the national dairy herd has significantly improved. All of this gives us confidence TB Advantage will work.

Q: How do we know we are identifying animals which genuinely have bTB by basing this index on the skin test?

All confirmed reactors to the skin test are included as we know the test rarely identifies animals which do not have bTB. Extensive veterinary research has clearly shown, of all the animals tested, less than one in 1,000 show up as false positives.


If we only included animals with lesions – showing advanced stages of bTB – we would miss valuable data from the analysis, including many animals at the early stage of disease.

Q: Is better resistance to bTB linked to any other traits?

Analysis has found animals with a positive TB Advantage score are, on average, more likely to have a better SCC, daughter fertility index and a higher overall profitable lifetime index (£PLI).


This is unsurprising as the daughters of a bull which is said to transmit better resistance to infectious diseases, such as bTB, would be expected to have generally better health and fertility, which is reflected in the animal’s £PLI.


Furthermore, every other measured trait has been analysed alongside the new TB index and there are no negative correlations.


This means selection in favour of a positive TB Advantage score will, on average, have no detrimental effect on any other trait.


However, farmers should look at each bull on a case-by-case basis, as any individual could have weaknesses which should be avoided, irrespective of the averages.

Q: How should this index be used as part of a breeding strategy?

When breeding cattle, too much emphasis on any one area can detract from others so farmers should continue to select their service sires on the basis of all of the traits important to their business.


There are many factors which should influence whether farmers choose to add this index to their breeding criteria. These are likely to include whether their herd is in or close to a bTB affected area or whether they feel having progeny by a bull with a better TB Advantage score will give them some commercial benefit.


If all other traits are equal, it would definitely be preferable to use a bull with a positive TB Advantage rating.


Using bulls with an extremely negative score is inadvisable as it is likely to increase the susceptibility of a herd to bTB.

Q: How reliable is the TB Advantage index?

Genetic indexes are published with a reliability figure which gives an indication of how likely the index is to change as more information is added.


The reliability for TB Advantage ranges from 20-99 per cent, with an average of 65 per cent for bulls with UK daughters, and 45 per cent for those with a genomic index.


Although the reliability of genomic predictions is currently less than for some other indexes, TB Advantage can still be used a part of a herd’s breeding strategy and has shown to be valuable in predicting future performance.

Q: Will using TB Advantage affect daughters’ reaction to the mandatory tuberculin skin test?

Extensive research undertaken at the University of Edinburgh’s Roslin Institute has determined there is no expectation breeding for better resistance to bTB will have any significant effect on the usefulness of the tuberculin skin test.


However, having bTB evaluations allows the effectiveness of the skin test to be monitored over time.

Q: How will using this index affect the incidence of bTB in the national cattle herd?

If TB Advantage is used as a breeding tool, fewer animals are expected to become infected and fewer herds will be placed under movement restriction.


Infectivity will also decline, which means less disease will be passed both on to other cattle and to other reservoirs of the disease.


Precise numbers are impossible to predict because the rate of improvement is dependent on the uptake of the index by cattle breeders alongside other measures taken to combat the disease.


However, if a farmer chooses a +3 TB Advantage bull over a -3 one, his herd would be expected to experience six fewer cases of bTB per 100 cows in one generation and could accumulate these benefits over subsequent generations.

Q: How does using the index influence other measures to be taken against the spread of bTB?

All other measures should continue to be taken to protect cattle against bTB irrespective of a farmer’s choice of bull.
This includes maintaining high levels of biosecurity, protecting cattle against infected wildlife and routinely monitoring cattle for the disease.

 

Background to TB advantage

Research into the genetics of bTB was undertaken jointly by the University of Edinburgh, Roslin Institute and Scotland’s Rural College (SRUC) and supported by Defra and the Welsh Government.

Variation
Their work showed there is genetic variation between animals and it established the degree of heritability of bTB resistance. AHDB Dairy corroborated these findings with its research partners, SRUC and Roslin; funded the implementation of a genetic index; and embedded the TB Advantage into the national genetic evaluation service.

  • More information
Details on bTB control measures, the TB Advantage and other aspects of bTB can be found at The TB Hub at www.tbhub.co.uk

The main reason for travelling abroad to train was the volume of cows made available.


When in Washington in 2013, I was training on a 27,000-cow dairy unit and was on similar-sized units in Melbourne in 2012.


I was getting to put my hand in hundreds of cows each day and, as they say, practice makes perfect.

Q Did you find any differences between the way things are done in Australia and America compared to the UK?

The actual insemination of cows is similar in America and Australia, although when in the USA, I learned how to palpate ovaries to feel for corpus luteums [a temporary endocrine structure in the ovaries] allowing me to make the best breeding decisions when presented with a cow thought to be in heat. This is now a technique used in this country.


In the UK, semen is deposited in the cervix, but I was taught to horn-breed in the US, where the semen is deposited in both horns, increasing the rate of conception.

Q How was the farming different in these two countries to our own?

Q How was the farming different in these two countries to our own?

Farming in these countries is different, with larger scaled farms than in the UK. But I was impressed with the farms I visited, as they were efficient, consistent and everything was run almost like clockwork.


Breeding-wise, they seem to be one step ahead. They genomic test their whole herd, then breed the top genomic 30 per cent to sexed semen, with the rest going to beef semen which always speeds up the genomic value of the herd.

Q How would your training have been different in this country?

Working with Cogent, I had to go through a significant training programme covering all aspects of fertility management with fully qualified trainers.


The programme featured specific training on cow signal types, all physical and technical aspects of the reproductive cycle, best practice, handling semen and a whole lot more.


The company’s specialists will emerge from training with a benchmark of ideal practices which are continually monitored throughout their career.


The most important aspect is customer service. Making sure my farmers are happy with the service I provide is important to both my company and me.


I call most of my farmers as regularly as possible, especially before their breeding season. The customer service aspect of my job can often take the most time, which may include giving my customer the best advice if he wants to try different bulls, or just taking five minutes to look at a calf which a farmer is delighted with.


It is all part of the job I love.

Q Has your training helped you in your own business?

I have learned how to put embryos in and have just passed my epidural course. With the amount of embryos we put in at home, I am hoping a big cost saving will be made for my own business.

Q How do you think technologies are going to move forward?

There can be no doubt the agricultural industry is moving forward rapidly and the importance of the right technology, genetics and services will only become greater.


Automated technologies have the potential to change the way we manage cows and, in the future, I believe we will be able to understand the whole herd’s condition in a way we previously might have only dreamed of.


Tomorrow’s dairy farm will not just amount to better returns at the farmgate, but the implementation of state-of-the-art technologies will ensure the farm is ultimately more productive, sustainable and efficient.


However, I also firmly believe UK dairy farmers will still have an important role to play. New tools to help farmers make more timely and informed decisions will lead to better productivity and improved profitability, but technology cannot always replace a person with good ‘cow sense’.


The farm of the future will certainly reap the benefits of new technology, but the importance of a team spirit, good management skills and regular visits from reproductive specialists will remain as vital as ever to bottom line success.

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