01 May 2024

Bull teams: Equal usage required to lessen risk

With the breeding season kicking into gear on many farms, Teagasc and ICBF recommend that teams of AI bulls are used when breeding dairy cows and heifers.

Selected on the basis of breeding replacement heifers, a balanced team of dairy AI sires should be used, as this will increase the reliability of the sire team as a whole. For a typical 100-cow dairy herd, at least eight bulls should be used, with no more than 15 straws (i.e., 15% matings) to any individual bull.

A recent data analysis completed by ICBF revealed the extent to which farmers are using bull teams and how some sires are being overused. Based on dairy herds that had >=10 AI bred dairy calves born between January 1, 2023, and June 30, 2023, the ICBF analysis found:

• Some 8,569 dairy herds had more than 10 AI bred calves born in this period;
• The average number of bulls used in these herds was 9.6;
• The most heavily used AI bulls in these herds accounting for 29% of the total calves born – higher than the Teagasc and ICBF recommendation of no more than 15% by any one sire;
• The three most heavily used bulls sired 62% of the calves born;
• 70% of the herds used greater or equal the minimum number of AI bulls recommended.

Although farmers tended to use a sufficient team of bulls, a common mistake being made is that individual bulls within the team are being overused. The uneven usage of bulls results in over usage of certain bulls. This carries a level of risk, as if the bull’s EBI was to subsequently fall then the genetic merit of their progeny is going to be impacted as a consequence.

To ensure the benefits of genomic technology and to deliver maximum EBI gain for Irish farmers are achieved going forward, using a sufficient number of bulls equally across the herd is a priority.

The size of the bull team varies by the size of the herd, with the recommendations included in table 1 below. Your Teagasc advisor can also help you to calculate this correctly.

Table 1: Recommended bull team sizes

Also read: Producing quality calves to ensure repeat custom

Also read: 10 things to consider before the breeding season starts

Also read: A refresher on sexed semen