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

The first ‘Gestation Length’ 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.

2. 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 ‘Gestation Length’ from his very first evaluation compared to the one after the genotype has been included.

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

4. Irish Data
The gestation length of his own calves born here on Irish farms is the final piece of the jigsaw in terms of his ‘Gestation Length’ index.

Reliability %
The number of herds that his progeny are born in together with the number of herdmates that were born around the same time will determine by how much his reliability figure increases.

Bull example:

‘KYA’ (Cornamuckla Lord Harry K222) is the most heavily used Angus AI Sire in recent years. To-date he has over 60,000 calves registered to him in the ICBF database. In terms of steps 1-3 above: His backpedigree is in the ICBF database, as is his genotype. His sire ‘CTE’ has a short ‘gestation length’ index. ‘KYA’ has no foreign data contributing to his gestation length index here.

In terms of his ‘Irish Data, the ‘Gestation Length’ data of his progeny can be seen in the ICBF ‘Animal Search’ facility:
1. Go to
2. Go to the Animal Search facility down the right hand side of the website and enter in ‘Cornamuckla Lord Harry K222’ (or his AI Code ‘KYA’).
3. Click on the blue button that says ‘Replacement Graphics’.
4. Click on ‘Gestation’.
5. Scroll down to the table that says ‘Sire Progeny and Progeny Herdmate Information’.

As can be seen from the above data: The 46737 calves sired by ‘KYA’ that had inseminations recorded on their dams were born on average 3 days earlier than their herdmates.

Putting all of these pieces of information together results in ‘KYA’ being rated as a bull with a very short gestation length. He is 5 stars for ‘Gestation Length’ both within and across breed.