Jerseys and genomics

Published 8 January 10

Genomically selected bulls of Holstein, Jersey and other dairy breeds are now being marketed from countries as diverse as North America, Scandinavia and New Zealand, leaving the British breeder with a potentially confusing array of figures with which to tussle when making breeding choices.

Geneticist, Marco Winters, director of DairyCo breeding+ has lent his support to the technology, describing it as 'a significant advance which could speed the rate of genetic gain, help focus attention on bulls with the most important commercial traits and ultimately herald a revolution in animal breeding'.

But he is equally keen to issue a warning. "These are still early days," he says. "Dairy bulls are being marketed in this country which in some cases are little more than young bulls with a bit of extra information based on genomics.

"Quite legitimately, they are being given genetic indexes, but it is essential that UK farmers are aware that these indexes are derived from the animal's DNA and not from a conventional progeny test proof.

"These are more reliable than Pedigree Indexes derived from parent PTAs (Predicted Transmitting Abilities), but they are not as reliable as indexes based on progeny performance."

Since their introduction, both DairyCo and Interbull (the body responsible for international genetic evaluations) have been working with AI companies, breed societies and academic institutions to establish the most transparent and accurate means of converting these indexes to a UK reference scale, and in the short term, this can be done using a conversion formula available from DairyCo breeding+.

"But we hope that Interbull will be in a position to publish full international figures by early 2011, although until that time, we will assist breeders with comparisons wherever we can," says Mr Winters.

Warning breeders to be aware that some breeding companies publish genomic evaluations without making any attempt to convert to a UK-equivalent at all, he says: "This is extremely confusing and virtually meaningless to UK breeders and I'd advise them to ask the companies concerned to provide the information on a UK-equivalent scale."

One difficulty which relates specifically to the Jersey breed concerns the small number of bulls being progeny tested.

"Around 2,000 bulls are needed to create a reliable reference population [see box], so smaller populations, such as that of the Jersey breed in the UK, will either have to rely on the large countries to provide genomically evaluated bulls, or they will have to collaborate with these countries so that we can produce genomically enhanced evaluations for British bulls too," he says.

Asked whether this is a disadvantage to the UK's Jersey breeding industry, Mr Winters says: "At this stage it is, but the technology is moving forward fast and may help create meaningful data for UK bulls. We currently use around 54,000 'snips' [see box] to measure genetic variance between animals but before very long, we will see over 500,000 snips being routinely measured.

"When we get to this point, we may be able to understand the effects of the genes on genetic variation far better than we do today, so it's possible we may be able to translate Holstein derived information to create a reference population for Jerseys within the UK and move on to genomic evaluations for young UK Jersey animals.

"But it's important that we don't lose sight of the fact that progeny testing is still the gold standard for evaluating a bull's genetic merit," says Mr Winters.

"I'd recommend Jersey breeders remain focused on using reliable progeny tested bulls with good PLI [Profitable Lifetime Index] figures in their breeding programmes, and I would advise them to carefully consider the amount of usage of genomically evaluated young bulls guided by their reliability - and always use them as a team rather than focus on individuals.

"The team is more likely than the individual to perform close to expectations and there will therefore be less scope for disappointment.

"In other words, as with any semen purchase, you need to balance the quality of genetics on offer against the reliability of the product - or the risk against the reward," he concludes.

Genomic technology

  • Genomic selection is based on the measurement of an animal's DNA which can be taken from almost any cell of its body.
  • The measurement reveals a pattern of DNA sequences or SNPs (pronounced 'snips').
  • By comparing SNPs with animal performance for thousands of animals (a reference population), links between genomics and actual performance have emerged.
  • These associations lead to the production of genomically enhanced Predicted Transmitting Abilities, which are sometimes referred to as gPTAs.
  • Genomically enhanced PTAs are now being published for Jersey bulls in North America, Scandinavia and New Zealand, where significant numbers of proven Jersey bulls are available, which are needed for the generation of reliable figures.
  • Genomic PTAs can be produced for animals of any age but they tend to be published for young bulls which are too young to have PTAs based on their progeny's performance.
  • Genomic PTAs are likely to have reliabilities of around 50-60 per cent on the UK scale, which is higher than a Pedigree Index based on parent average but lower than a widespread progeny proof.
  • A progeny proof remains the gold standard for the assessment of an animal's genetic merit.
  • Breeding companies will currently continue to progeny test bulls by conventional means, but they will be able to select the bulls they test more accurately by using genomics.
  • DairyCo breeding+ will closely monitor the success of the technology and issue advice based on an evolving knowledge.
  • Always check that the source of figures is DairyCo breeding+, which will give you assurance of an independent quality assessment of bulls.

Article produced for Jersey Journal, January 2010