A pilot study on anogenital distance in non-pregnant and pregnant Merino ewes and ewe hoggets measured by calipers and image analysis

Reproductive traits are fundamental phenotypic traits selected to achieve optimal production efficiency. The aim of this study was to evaluate the use of four measurements of anogenital distances (AGD; in mm) and compare them with ewe pregnancy status, measured via pregnancy scanning, using data collected from 80 Merino ewes and 80 ewe hoggets. Digital calipers were used to measure AGDs (AC - anus to clitoris, AVV - anus to ventral vulva commissure, AF - anus to fourchette and VV - vulva length) in each sheep twice by three assessors. High-resolution images were taken for each sheep to conduct further measurements of AGD using an image analysis software. The measurements conducted with the image analysis were correlated with the pregnancy status of ewe hoggets for AF (P < 0.002), VV (P < 0.001) and AVV (P < 0.002), but no association was found for AC (P > 0.05). The measurements performed with calipers by three assessors were more variable compared to image analysis, resulting in lower correlations between the first and second measurements taken on the same animal. The relationship found between three AGD measurements (AF, AVV and VV), and pregnancy status in the ewe hoggets, demonstrates the potential to use this trait as an inexpensive method to estimate pregnancy status. The association with pregnancy status, especially in ewe hoggets, could be easily adopted by producers.