Advice on genomic bull teams changes

The advice offered to farmers when it comes to selecting genomic bulls to breed the next generation of replacements is set to change.

Previously, farmers who used genomic bulls were advised to use a team of at least five bulls. However, this recommendation has changed to eight genomic bulls per 100 cows and it varies depending on herd size.

This move comes on the back of the recent drop in EBI for some high-profile AI bulls, which resulted in many farmers questioning whether a team of five was sufficient to manage risk within their breeding programme.

Furthermore, another reason the advice has changed is due to the relatedness of some of the genomic bulls currently being used in AI.

Initial calculations carried out by Teagasc and the ICBF, which resulted in the five bull team recommendation, were based on the use of five unrelated sires.

However, since the introduction of genomics, this has not been the case and very often farmers find themselves using half brothers within their bull teams.

Given this, Teagasc and the ICBF have recently reviewed the underlying research regarding bull teams to include a number of additional factors.

These include: relatedness between sires in a bull team; an increase in the EBI reliability of the bull team from 90% to 95%; and the impact of increasing herd size when considering the minimum bull team number.

Guidelines for bull team usage:

Did farmers follow the previous recommendations?

As mentioned earlier, the previous recommendation advised farmers to use a team of at least five genomic bulls.

During the review of the recommendation, the ICBF also reviewed the current adherence to the principle of bull team usage.

It looked firstly at data from calves born in the year to date, which indicated that 5,973 dairy herds had more than 10 AI-bred calves born in 2017.

The average number of bulls used in these herds was 7.5, which is significantly above the minimum of five advocated by Teagasc and ICBF.

Whilst this is positive, the ICBF found that the most heavily used bulls sired 69% of the calves born and only 18% of herds adhered to the principles of even usage of bulls.

These trends are a major concern in the context of managing risk in breeding programmes and highlight a very significant challenge that must be addressed to maximise the benefits of new technologies such as genomics.

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