The importance of using UK bull proofs when making breeding decisions for Jersey cows

Published 7 August 17

The first UK genomic evaluations for the Jersey breed were released in April 2017, meaning that young bulls will have a more meaningful genetic index earlier in their life.  AHDB Dairy’s animal genetics manager, Fern Pearston, explains genomics and why is it important to use UK proofs when making breeding decisions in the Q & A below:

What changed with the introduction of UK genomics?

"Previously, the only UK index a young Jersey sire had was calculated from the performance of his parents, resulting in full siblings receiving exactly the same genetic index.  In reality, breeders know that the performance of full siblings can be widely variable.

Genomics has been available for the Jersey breed for a number of years in countries such as North America and Scandinavia, and some UK breeders even sent DNA samples to these countries to be evaluated. 

The trouble was that they were not being evaluated against a UK population, and they then had to be converted back into ‘UK equivalent’ figures.

“This meant that whilst they may have been marginally more useful than the traditional parent-average indexes, they were not particularly reliable”, she said.

The difference today comes from the fact that the genomic indexes will be calculated in the UK, following a collaboration agreement between North America and AHDB in the UK. This agreement gives AHDB access to all Jersey bulls genotyped in the US and Canada, and now allows us to perform bespoke UK genomic evaluations.

The genomic codes for these sires, which are studied along each strand of DNA have been compared very closely with actual animal performance on a UK base – ranging from milk production to cell counts or from fertility to type – and it is from the relationships between the two that the genomic evaluations are being derived.

This cross-checking between the DNA and the actual performance has been undertaken for all sires used in the UK and North America over many years and it will continue to be ongoing, so ensuring the genomic predictions are as accurate and reliable as possible.

Why it is important to use UK figures?

Genetics don’t perform in exactly the same way in different countries.  In order to find bulls that are suitable for the UK systems and conditions, UK genetic and genomic evaluations need to be used.

She continued, “In addition to this, the UK has different breeding objectives to other countries.  Therefore, using the UK breeding indexes, the Profitable Lifetime Index (£PLI) or Spring Calving Index (£SCI) depending upon your system, as initial filters over other country indexes is important as the UK indexes weight traits by their economic impact on your herd milking in the UK.

Breeding for disease resistance is another reason to look at UK figures.  The TB Advantage was first released by AHDB Dairy for Holsteins in January 2016 and since April 2017 also for the Jersey breed. The TB Advantage is the first, and only, index of its kind in the world.  This index allows farmers to select bulls whose daughters are less likely to be affected by bTB and can be used alongside management procedures already in place on farm.

Furthermore, in the UK, AHDB Dairy is responsible for the genetic and genomic evaluations, giving a completely independent and unbiased estimation of how every bull will perform in UK conditions.

How to use genomics                                                          

Genomic indexes are calculated using information obtained from the animal’s genetic material (DNA).  This raises the reliability of the index from around 35% to around 50-60%, indicated in Figure 1.  Young bulls can therefore be used with greater confidence that his daughters will perform closer to expectations than a bull whose index is based just on parent-average information.  If carefully selected, young bulls with genomic indexes offer the opportunity for dairy herds to make more genetic progress.

Figure 1

Figure 1.  Reliabilities over time for traditional and genomic evaluations for bulls.

 

However, the reliability of a genomic index is still less than that of a typical proven bull based on milking daughter performance.  This means genomic indexes are more likely to change over time, and the magnitude of that change is potentially greater.                                                               

Individual young bulls with genomic indexes should therefore be used sparingly (up to a maximum of 12% of the herd per bull) and as part of a mix with daughter-proven bulls.  Proportions of maximum recommended semen usage per bull in your herd, by reliability is shown in Figure 2.

It is tempting to over-value genomically evaluated bulls, but an animal marketed as a ‘genomic young sire’ may be no better or worse than any other bull.

Figure 2

Figure 2.  Guide to proportion of semen usage for a single bull at different levels of reliability.

Breeders should ensure that they are selected the correct bull for their herd and system.  If fully milking recording, breeders can use the Herd Genetic Report available from AHDB Dairy to identify the areas of strength in their herd and also traits which they may look to improve over the next few generations and identify the bulls which meet these needs.

What is new and up and coming from AHDB Dairy which Jersey Breeders will benefit from? 

Mastitis and TB Advantage were released for Jersey bulls in April 2017.  The Mastitis index allows breeders to select bulls whose daughters have an improved resistance to mastitis.  This index helps to identify bulls with good SCC Predicted Transmitting Abilities (PTAs), where negative vales are favourable, which will also reduce the number of mastitis cases on average in their daughters. 

In addition to genomics for bulls, UK genomic evaluations have recently been released for Jersey females.  Previously, female genomic evaluations were available from other countries, however these were expressed on the country’s own base and breeding index.  In order to make these relevant to milking in the UK, breeders had to convert the foreign proofs onto the UK base. Conversions are available from AHDB Dairy, however not all traits had an equivalent trait in other countries; for example the US Jersey Udder Index does not convert to the UK Udder composite.  Not only do these conversions have a lower reliability than official proofs, they may only be able to provide part of the picture when considering the animals you want to breed from.  This is why AHDB Dairy are now providing UK genomic evaluations for Jersey females.  Genomics for females can be used to further intensify your selection pressure by identifying those superior heifers to breed your heifer replacements from. 

Finally lameness PTAs for bulls are estimated to be release in 2018.  These will help to identify those bulls whose daughters are less likely to be affected by lameness during their lifetime, tackling another big issue on farm.  Further information about the Lameness index will be available on the run up to its release.