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The impact of genomics on cattle breeding

DNA profiling has revolutionised dairy cattle breeding and the next 12 months are crucial to the direction of the industry. The first genomic AI progeny test results are coming online and will beg the question as to whether farmers will consider using more genomic young sires rather than older proven bulls. Bruce Jobson investigates.

The US first introduced DNA genomic information into sire evaluations in January 2009 and Canada followed in August of the same year. The technology has helped the AI industry better identify the genetic potential of animals for progeny testing.

Prior to the introduction of genomics, the accuracy of a young bull’s evaluation was based on his genetic parent average and the reliability was estimated at about 35% accuracy. The introduction of genomic evaluations has increased the level of accuracy to between 65 and 70%. The increase in reliability is the equivalent of having 20 milking daughters in a bull proof.

Doubling the level of accuracy has given the AI industry increasing confidence to select the next generation of young sires. Importantly, the genomic identification of a group of ET sibling bulls allows sire analysts to better identify the best individual in the group on various type and production traits.

AI companies have been able to cut costs; some having reduced the number of sires coming forward for testing programmes on the basis that better quality young bulls have now been identified.

For example, in North America, a £133 genomic DNA profile is a cheaper identification method compared to a lengthy five-year £13,276 progeny test. Selecting one young bull from three full-brothers with identical parent-averages is therefore cost- effective.

As the genetic threshold has increased over the past four years, some young bulls have not completed progeny testing owing to lower identified profiles. In the long-term, the benefits will filter through to dairy farmers with better proven bulls entering AI being the end result.

However, let’s consider several controversial options. If all goes well, and genomic sires deliver greater accuracy as proven bulls; will breeders again consider using a five year old plus proven bull as part of their breeding programme?

Caution has been urged by several parties within the cattle-breeding industry; but as the dynamics have changed, some fast-thinking farmers have realised an opportunity beckons. Marketing elite genomic animals is a new concept and pedigree breeders are keen to maximise on the inherent potential.

Using high genomic young sires will increase the opportunity to breed a young bull for AI purposes as well as, breed a potential high genetic merit bullmother. For the first time, breeders will have more control over their destiny.

By using DNA genomic profiles, UK farmers can now evaluate male and female bovine progeny on an equivalent-basis with North American bloodlines. The mating game has changed forever. Taking the use of young bulls forward, a resulting high ranked 15 month old genomic heifer should be subsequently bred to an even higher genomic young sire in order to maximise the genetics of the next generation. And so on.

A percentage of pedigree breeders will prefer to breed the exclusive show-winning, high type animal for a particular niche market. There will also be a percentage of farmers not prepared or even wishing to breed high genetic animals. Many pedigree and commercial farmers may prefer instead to breed the next generation on the basis of quantifiable daughter improvements on the basis of proven type and production, good mammary traits and quality feet and legs.

However some pedigree breeders, keeping an open eye on the future, will opt to increase the genomic values as well as increasing the potential earning power of their animals. Meantime, commercial breeders have an immense opportunity to propel their herd’s genetic potential forward perhaps without constraints. Furthermore the cost of producing genomic young bull semen is undoubtedly cheaper for the AI industry and provides a healthy return.

There is also a strong advantage to the AI industry in providing dairy farmers with genomic young sires on a sexed-semen-basis. This is not yet widespread practise but the process would undermine the AI industry’s gross profit margin, owing to the high cost of sexed-semen production or, AI companies will have to increase the purchase price.

The advantages of providing young genomic sexed semen are obvious as more heifer calves would double the number of records in a subsequent bull proof; should anyone be interested in four years hence. Likewise, farmers may be more tempted to test genomic bulls in order to increase heifer numbers as well as, increase the herd’s genetic gain.

A few years ago, all AI companies provided young bull semen; either on a relatively cheap basis, free or, as part of a progeny incentive package. Canadian Dairy Network, an industry data organisation, has observed the recent trend of genomic sires entering Canadian progeny testing programmes.

Possibly due to increased hype or expectation, use of young genomic sires increased in Canada to 31% of all artificial inseminations, more than double the traditional level. The trend has since reverted back to about 10-18% usage during the past two years, but this may be a result of numerous high quality proven Comestar Goldwyn sons recently returning to active proven service.

These trends may again fluctuate as genomic sires return to service. Farmers may be better incentivised or confident, to consider using the next genomic generation or, as in the case of recent Goldwyn sons, revert back and capitalise on the first proven genomic progeny test results.

During the mid-1980s and 90s, the MOET concept aimed to increase the rate of genetic gain by using milk production records of two-year-old sibling sisters, in order to compare and identify their performance levels against other sibling ET female groups. Bays Leap Farm, Heddon-on-the-Wall, Northumberland, was home to the world’s first MOET herd and helped drive forward UK dairy breed development programmes.

MOET sibling young bulls (including full-brothers) were progeny tested in teams and the concept involved turning over the generations faster and maximising genetic gains – by reducing the generation interval from a then five plus to approximately three years.

Having written a MOET theory critique in 1987, one of the modules examined was to further speed up generation turnover, even faster by instead mating top indexing MOET young sires and females on a 15-month basis, rather than evaluate production records of MOET female sibling teams. This had the potential to propel genetics so far forward down the road; proven bulls would become, within a couple of generations, more or less, genetically obsolete.

According to MOET theory co-author, Professor Charlie Smith, University of Guelph, Canada and formerly of ABRO, Edinburgh, the concept had not been examined as part of the MOET theory and developing Embryo Transfer technology. Almost 25 years later, genomic science has delivered greater individual young sire accuracy and the means to deliver the identified genetic advances.

The next global sire evaluation-run, published on a thrice yearly-basis, is due to be published in April, and will provide further indications as to the reliability and accuracy of genomic young sire information. The jury is currently out and a full verdict may take further time to deliver. But for those at the leading edge of genetics, once down the genomic fast-lane; as pointed out in 1987, there may not be a turning back.

Source: Nebusiness

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