FAQ: How is a bull’s ‘Calving Interval’ figure calculated?

There are 4 factors that will both contribute to what ‘Calving Interval’ index figure your bull starts out with and also how it changes over time.1. Backpedigree, 2. Genotype, 3. Foreign Data, 4. Irish Data

1.Backpedigree

The first ‘Calving Interval’ index that a bull will receive is called a ‘Parent Average’ index. As the name suggests it is an average figure that is calculated from the index figures that his sire & dam have at the time of his birth. If the index figure of a close relative of the bull moves up or down significantly then this will also affect the index figure of the bull himself.

  1. Genotype

When a sample of DNA (e.g. hair or a straw of semen) is sent off and the genotype comes back this will then alter the figure that the bull got in his first evaluation run which would have been through his ‘parent average’ as explained above. So, there could be a difference in a bull’s ‘Calving Interval’ from his very first evaluation compared to the one after the genotype has been included.

  1. Foreign Data

If a bull already has an index for ‘Calving Interval’ in another country and this data is sent to ICBF then this will also have an impact on shaping his ‘Calving Interval’ index in Ireland. ICBF routinely gets files of such index values from countries such as the UK and France.

  1. Irish Data

The bull’s daughters calving date data will be the final piece of the jigsaw in terms of his ‘Calving Interval’ index.

Reliability %

The number of herds that his progeny has their ‘Calving Interval’ recorded in together with the number of herdmates that they were reared alongside will determine by how much this reliability figure increases.

Bull examples:

Ballymackeogh Lucas

‘Ballymackeogh Lucas’ is a Salers AI Sire. In terms of steps 1-3 above: His backpedigree is in the ICBF database, as is his genotype. He is by ’Jovial’ who himself is a 5 star bull for ‘Calving Interval’. He has also been genotyped and that is included in his €uro-Stars here. Being an Irish bred bull, used mostly here in Ireland, he doesn’t have any foreign data feeding into his €uro-Stars here.

In terms of his ‘Irish Data, the ‘Calving Interval’ data of his progeny can be seen in the ICBF ‘Animal Search’ facility:

  1. Go to icbf.com
  2. Go to the Animal Search facility down the right-hand side of the website and enter in ‘Ballymackeogh Lucas’ (or his AI Code ‘KKB’).
  3. Click on ‘Daughter Calving Interval (days)’ which is shaded in blue.
  4. Scroll down to the table that says ‘Sire Progeny and Progeny Herdmate Information’.

As can be seen from the above data: The 120 daughters of ‘KKB’ have an average calving interval of 374 days while their 980 herdmates have and average calving interval of 378 days. So, they are showing shorter calving intervals than their herdmates who it is assumed are being managed in the exact same way.

Putting all of these pieces of information together results in ‘Ballymackeogh Lucas’ being rated as a 5 star bull for ’Calving Interval’ in Ireland, across breed, with a 64% reliability rating.