What in the World is the “Ano-genital Distance”?

Holstein heifers ( Maureen Hanson )

Dairy researchers may have unearthed yet another factor that affects productivity and profitability.

It’s called the “ano-genital distance,” and it may be predictive of fertility in both heifers and cows. 

The ano-genital distance (AGD) is defined as the distance from the anus to the clitoris in cattle. It is measured similarly in other species as well. AGD is a physical characteristic that researchers believe is influenced by androgen (testosterone) exposure during a critical period of a heifer’s fetal development. 

Because previous research has tied differences in the AGD with several reproductive outcomes in humans and laboratory animals, dairy researchers have launched preliminary explorations into whether or not it is a significant factor in dairy reproduction. The initial studies and their findings include:

  1. University of Saskatchewan cow study – In a 2016 study published in the Journal of Animal Science, 93 lactating cows (35 first-lactation; 58 second-or-higher lactation) cows were measured using a digital caliper. Three measurements were taken, and the average was used to classify each animal, showing a range in AGD from 95.7 to 149.0 mm. Cows with AGDs of approximately 112 mm and under were classified as “SHORT,” and 130 mm and over as “LONG.” All cows received timed AI at approximately 75 days postpartum following a Presynch/Ovsynch protocol. Compared to cows in the LONG ADG group, cows in the SHORT group had: 
  • 2.4 times higher odds of becoming pregnant at first insemination.
  • Approximately 28 fewer days open than the LONG group.
  • An average of 0.5 fewer inseminations to achieve conception.

 There was not significant difference between the first-lactation and higher-lactation status of cows in this study.

  1. University of Alberta heifer study – Researchers at the University of Alberta investigated whether a similar relationship could be found in virgin heifers. Their study, published in the 2020 Proceedings of the Western Canadian Dairy Seminar, compared reproductive outcomes of heifers based on their AGD. Heifers from 11 Alberta and British Columbia dairies were enrolled, for a total of 671 animals. ADG was evaluated in all of the heifers by a single individual. The ADG range for animals in the study was 81 to 148 mm. An ADG of 114 mm was used as a cutpoint between “SHORT” and “LONG” classification. Cows in the SHORT group:
  • Were an average of 13 days younger at conception.
  • Required and average of 0.2 fewer inseminations to achieve pregnancy.
  • Achieved about 10% more pregnancies to first AI service.

Both research teams concluded that the AGD could have application as a new fertility trait for evaluation of breeding stock, but also noted the findings were preliminary, and that more research on the subject is needed.