Can Distance from the Anus to the Scrotum Help Predict Bull Fertility?
Project Title
Anogenital Distance as a Potential Fertility Indicator Trait in Breeding Bulls: A Proof-of-Concept Study
Researchers
John Kastelic [email protected]
| Status | Project Code |
|---|---|
| In progress. Results expected in November, 2026 | POC.07.24 |
Background
Anogenital distance (AGD) is the distance from the anus to the external genitalia in mammals. It’s influenced by exposure to androgen hormones during fetal development in utero. In female cattle, AGD was defined as the distance from the centre of the anus to the base of the clitoris and a shorter AGD has been associated with improved fertility. However, the association between AGD and fertility in bulls is unknown.
Objectives
- Characterize the distribution and variability of AGD in bulls and determine associations between AGD, age, and body weight.
- Determine if AGD is positively associated with standard fertility indicator traits such as scrotal circumference and sperm quality, as well as siring ability in bulls.
- Determine if an AGD cut-point to predict bull fertility could be established.
What they will do
They will measure AGD in bulls, plus body weight and hip height, and make associations with fertility indicators such as scrotal circumference and sperm quality. They will also strive to obtain field fertility data (calves sired per bull) from a subset of bulls to make associations with AGD.
Bull examinations and measurements will be collected at a private purebred herd and at the University of Calgary’s W.A. Ranches in December 2024 and spring 2025. Field fertility data will be analyzed once their calves have been born, sampled and parentage tested in 2026.
Implications
The current breeding soundness evaluation (BSE) is based on assessment of the overall health, well-being and structural integrity of the bull, plus assessment of the internal and external reproductive tract and evaluation of sperm motility and morphology. The BSE does not always reliably identify sub-fertile bulls. Furthermore, above the fertility threshold, a BSE does not rank bulls according to relative fertility. This study will assess whether AGD is as (or more) reliable than a BSE to identify sub-fertile bulls and perhaps rank bulls according to relative fertility.