Gestation Length Index

A dairy genetic index, which provides a prediction of gestation length for a bull’s calves and can be used as a management tool when shorter gestations will help to bring calvings from later inseminations back on track.

Gestation Length Predicted Transmitting Abilities (PTAs) are based on over 7.5 million calving records. The data show that sex of the calf and lactation number affect gestation length so these factors have been considered in the model used to calculate Gestation Length PTAs.  Due to the sex of the calf being accounted for, use of sexed semen does not affect the prediction ability of this model.

Research by our partners at EGENES-SRUC found the heritability of gestation length to be 43% indicating that genetics plays a large role in reducing gestation length.

How to use Gestation Length PTAs

Gestation Length is expressed in days and range from +7days (longer) to -7days (shorter). For every one point change in a bull’s Gestation Length PTA, a change of one day of gestation length for the bull’s calf is predicted. For example, a bull with a -5 Gestation Length is expected to have his calves born 5 days earlier compared to a 0 PTA bull.

Gestation Length is published as a stand-alone trait. Dairy bulls with UK information and young genomic bulls have had Gestation Length PTAs on the AHDB website since April 2021 with the expectation that the PTA will extend to beef bulls in the future.