Possibility of ‘improving the accuracy of genomic evaluations’
New research – completed by the Irish Cattle Breeding Federation (ICBF) – revealed that the accuracy of genomic evaluations could be further improved “if genotyped cows were also included in the reference population”.
The reference population is needed for genomic selection. It is a large genotyped population of animals with accurate performance information – such as milk yield or fertility.
The associations between the DNA and performance measures are then derived from this population.
Presently, there are “over 8,000 informative animals within the Irish Holstein-Friesian reference population”.
Currently, according to the ICBF, the “average reliability of genomic proofs of young animals is 63%”.
A recent validation exercise, completed by the ICBF, revealed the accuracy of genomic evaluations is 16-35% more accurate than evaluations based solely on parental average.
However, it says, including “genotyped cows” in the population will “improve the accuracy by a further 5% to 10% over just using information on sires”.
Value of genotyping females in the herd
The current cost of genotyping all female calves in a herd is “€22/head (incl. VAT)”.
Although, according to the ICBF, the cost of genotyping female dairy calves can be “recouped through better selection of herd replacements”.
Using an example to explain this, it stated: “A herd that keeps 80% of heifer calves as replacements and has a replacement rate of 21% has an expected net benefit of genotyping of €33 per heifer retained.”
Other benefits, as stated by the ICBF, include: confirming parentage; identifying lethal/major genes; estimating inbreeding; and predicting the breed composition of an animal.
The ICBF also expressed the importance of “selecting a team of bulls when using genomic sires to minimise the risks associated”; these being a change in the EBI of an individual animal as more information accumulates.
Advising farmers, it said: “A bull team should be used with the minimum team size being dependent on the herd size; this achieves a bull team reliability of 95%.”
The table above shows the recommend number of bulls for each herd size.
To conclude, the ICBF stated: “Genomic selection is accelerating the rate of genetic gain in EBI through the more accurate identification of genetically elite males and females.
“It is, however, important to minimise risk associated with genomic selection by using large bull teams.”