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Genomics improves reliability of fertility ABV

The genetic merit for fertility in the Australian dairy herd is set for further gains with genomics shown to improve the reliability of the Australian Breeding Value (ABV) for fertility which was introduced in 2003.
Australian Dairy Herd Improvement Scheme’s (ADHIS) geneticist, Dr Gert Nieuwhof, said that the main benefit of genomics is that it allows ABV(g)s – Australian Breeding Value based on genomic data – to be calculated for young bulls who have no daughters recorded.

Genomics is the use of DNA data – or gene markers – to help in the calculation of breeding values. Genomic testing can be done when an animal is any age, so breeding values can be estimated for young cows and bulls, long before performance data is available (or daughter performance data in the case of bulls).

With the traditional bull proving system, it takes many years before enough data is available from a new bull’s daughters to calculate an ABV for fertility (and many other traits) with acceptable reliability.
“Genomics changes all that – enabling an ABV(g) to be available many years earlier,” Dr Nieuwhof said.
In an analysis of fertility, the reliability of a young bull’s breeding value for fertility will, on average, increase from about 11% (based on parent average) to about 34% with the inclusion of genomics (see table).
Traditionally a bull needs about 20 daughters with a second calving before a fertility ABV with the same level of reliability can be calculated. By then, the bull would be at least five years old.

“So instead of waiting five years, genomics allows a fertility ABV with similar reliability to be available for a calf,” he said. “Genomics will allow dairy farmers to purchase semen from better bulls (including those with better fertility) several years earlier. Using these younger bulls will speed up the rate of genetic gain.

Genomics and proven bulls

Genomic data can also be incorporated into the ABV for proven bulls. The addition of genomic information changes the reliability very little for production traits. But it does improve the reliability for some other traits of interest such as fertility and survival.

Adding in genomics data improved the average reliability of proven bulls’ fertility ABV from 59% to 63% (see table).

“This increase in reliability is not as spectacular for proven bulls as it is for young bulls. But even a small increase in reliability gives farmers added confidence in the breeding value,” he said.
Dr Nieuwhof’s analysis used data from the April 2011 Holstein analysis. It is based on the average of 454 young bulls (production reliability less than 63%) and 2256 proven bulls with high reliability (production reliability greater than 63%).
“Our genomic markers are identified from a strong reference population of animals whose performance is well known in Australia. This means we can be confident ABV(g)s are the best estimate of a young bull’s performance under Australian conditions,” Dr Nieuwhof said.

Table Effect of addition of genomics on average breeding value and reliability for fertility in 454 young bulls (production reliability < 63%) and 2256 proven with high reliability (production reliability >= 63%)
Bulls
Unproven
Proven

about 5 years old

Without genomics
ABV fertility
100*
100
reliability
11%*
59%
With genomics
ABV(g) fertility
99
101
reliability(g)
34%
63%
* based on pedigree

July 2011