The Irish Cattle Breeding Federation (ICBF) has said that selecting a large team of bulls, and using them equally on cows in the herd, is a “critical element” to help manage risk in a breeding programme.
According to the ICBF, analysis of artificial insemination (AI) sires shows that there is an “over reliance” on certain sires.
If a bull falls on the Economic Breeding Index (EBI), then its progeny could also be affected. Therefore, the ICBF said, using a team of bulls equally on cows and heifers “is vital” when breeding dairy replacements to maximise the rate of genetic gain.
With a larger team of bulls and equal usage of them, the risk of some bulls going up and some bulls going down evens out, and should provide a higher reliability for the overall bull team.
The ICBF recently carried out analysis on AI bulls, based on herds that had greater than 10 AI bred dairy calves born between January and June (inclusive) 2023.
8,596 herds were involved in this analysis. The average number of bulls used in these herds was 9.6, which is above the minimum number of bulls to use as recommended by the ICBF and Teagasc (the recommended figure varies by herd size, but ranges from 7 for herds with less than 100 cows and heifers, to 14 for herds with between 350 and 400 cows and heifers).
While that figure is encouraging, the ICBF analysis also noted that the most heavily used sires accounted for 29% of calves born, “significantly above” the recommended usage of 15% of AI bred calves coming from any one sire.
Meanwhile, the three most heavily used bulls sired 63% of calves born.
“These metrics need to be improved going forward to maximise the benefits of genomic technology and to deliver maximum EBI gain for Irish farmers,” the ICBF said.
The organisation says that the best breeding policy for farmers is to use a team of bulls equally across the herd. Variability is also a key factor to increasing genetic gain.
The benefit of using a team of bulls is that the reliability of the average genetic merit of the team is “considerably greater” than the reliability of each individual bull.
The recommended number of bulls to use by herd size is set out as follows:
Herd size (incl. heifers) Minimum no. of bulls 0-100 7 100-150 8 150-200 10 200-250 11 250-300 12 300-350 13 350-400 14