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Genomics value for pedigree breeders

Genomics is expected to fast-track genetic gain in the Australian dairy industry, with predictions that its use for sire selection could double the rate of genetic gain in herds. There are also benefits from genotyping females, although the value is likely to be realised initially by pedigree breeders followed by the commercial farm level.

In this article we report on a presentation by Dr Jennie Pryce to the Applied Genomics for Livestock Breeding Conference, held in May in Melbourne.

Dr Pryce, a Senior Research Scientist with the Victorian Department of Primary Industries, is a key member of the Dairy Futures CRC research team. Part of their work is to support the Australian Dairy Herd Improvement Scheme (ADHIS).
Dr Pryce analysed the potential applications for genomics technologies for Australian dairy herds and pedigree breeders. The initial uses of genomic technology will be seen at the bull level with pre-screening of young sires and marketing of genomically tested bulls rapidly becoming the norm. However the next application of the technology – the testing of cows – will be at the farm level.

Dr Pryce concluded that at the moment the mass genotyping of cows did not seem a strong proposition for selecting replacement females at the commercial farm level. “However the situation is completely different for pedigree breeders who may realise increased genetic merit of cow families, and future bull dams and/or better sale prices from genotyped heifers of high genetic merit.” For pedigree breeders, genotyping females could be a useful tool for heifer sales, selecting the best replacements, mating plans to control inbreeding, and confirming parentage. In time its application as a breeding tool for commercial heifers and cows will increase as both the reliability of the test and increases and costs come down.

ABV(g)s
Genomic testing allows a heifer’s breeding value to be calculated from birth. The reliability of this ABV(g) can be as high as 60%. “That’s equivalent to a cow with many lactation records and is a much higher reliability than an ABV based on a heifer’s pedigree alone, which is about 30%” she said.

Dr Pryce said that as genotyping young heifers provides not only provides greater reliability it also provides greater confidence to farmers when making breeding and culling decisions. This technology also enables breeders to evaluate the merit of full siblings which to date would only be based off parent average and therefore the ‘best’ animal could not be readily determined. It will also allow for greater analysis of cow families in breeders herds. As a result pedigree breeders may also use ABV(g)s in their mating plans to select females for flushing (see case study on the five ET sisters) and to work out the best combination of bull-cow matings.

Dr Pryce said that genotyping young heifers would also alleviate concerns over potential preferential treatment as the genomic part of the breeding value would be unbiased. “This could result in higher rates of genetic gain in breeders herds and potentially greater sale prices for genotyped heifers or embryos. Or over time, it may become the norm for sale heifers or embryos to be marketed with an ABV(g).”

“The idea is to maximise a specific breeding objective – such as APR – while constraining inbreeding.” Inbreeding erodes profit through reduced fertility, yield and health.

Dr Pryce expects genomic testing of sires will see farmers using larger numbers of bulls for shorter periods of time. Generations will turnover more rapidly potentially making it harder to keep track of pedigrees. “Genotyping gives us a much more precise estimate of inbreeding than can be achieved with pedigree. So genotyping females may become a useful tool when using mating plans to manage inbreeding.

Parentage testing
Genomic testing can confirm parentage with 100% certainty if the parents have also been genotyped.

Using genotyping to work out parentage may be particularly useful for herds where large numbers of calves are born over a brief period, making it logistically difficult to work out the sire and dam of every calf and to control inbreeding.
ADHIS and Holstein Australia are investigating the delivery of such a service with more information regarding parentage discovery to be detailed in the coming months.

July 2011