Updated Gestation Length figures

Gestation length refers to the number of days that the fetus is developing between insemination and calving. ICBF have recently updated the gestation length figures based on insemination and calving data recorded over the past number of years. These updated figures will result in more accurate expected calving dates for animals going forward. The new figures are now reflected in the dairy and beef expected calving profiles. Go to ‘View Profiles’ and ‘Expected Calving’ to view the expected calving dates for animals in your herd. (Gestation length figures will be reviewed on an annual basis).

Currently, the average gestation length in cattle is 283 days however, there is considerable variation between the different breeds. The tables below detail these updated changes for each of the major dairy and beef breeds.

Table 1. Current gestation length in days for the major dairy breeds.

Table 1 shows the average gestation length for each of the major dairy breeds. The Holstein Friesians have the shortest gestation length at 279 days. Previously, the gestation length for Holstein Friesians was 281 days.

Table 2. Current gestation length in days for the major beef breeds.

Table 2 shows the average gestation length for each of the major beef breeds. The Aberdeen Angus on average have the shortest gestation at 283 days while Blonde d’Aquitaine on average have the longest at 294 days. (Within each of these breeds you will also have animals with shorter and longer gestations).

How is a bull’s ‘Gestation Length’ figure calculated?

There are 4 factors that will both contribute to what ‘Gestation Length’ index figure a bull starts out with and also how it changes over time.

  1. Ancestry information- When a bull is born, they receive a ‘Parent Average’. As the name suggests, it is an average figure that is derived from the index figures of his sire and dam at the time of his birth. If the index figure for a close relative of the bull changes significantly then this will also affect the bull himself also.
  2. Genomics- When a DNA sample has been taken for a bull and genotype result comes back, this genomic information is then included in his evaluation. The additional information that comes from the genotype results in an increase in the bull’s reliability figure and can also cause a change in the bull’s gestation length.
  3. Foreign Data- If a bull has an index for ‘Gestation Length’ in another country and this data is sent to ICBF, it can feed into the gestation length figure in Ireland. ICBF routinely gets files from countries such as France and the UK.
  4. Irish Data- The gestation length of the bull’s own calves born on Irish farms is the final piece of the jigsaw in terms of his ‘Gestation Length’ index.

To view the gestation length information on a bull, use the ICBF ‘Animal Search’.

  1. Enter the bull details into the animal search e.g. FR4513 Ballygowan Albert
  2. Click on the ‘Calving’ tab

3. Click on the ‘Gestation’ tab

If we take the example of FR4513 Ballygown Albert, we can see he has 11,446 calves included in his gestation length figure in the November 2020 evaluation which is 278 days compared to 279 days for his herd mates.

Correct and consistent data recording is key to ensuring the accuracy of gestation lengths. Recording insemination data is essential for calculating a bull’s gestation length more accurately over time as well as providing an expected calving date for the cow.  Insemination records are loaded straight to the ICBF database from the AI handhelds or alternatively, farmers can record the data themselves via their HerdPlus log-in (desktop or app) or via their farm software package.