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Characterization of ano-genital distance and its relationship to fertility in Holstein heifers.

J. E. Carrelli



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Characterization of ano-genital distance and its relationship to fertility in Holstein heifers.
J. E. Carrelli*1, M. Gobikrushanth1, M. G. Colazo2, D. J. Ambrose2,1. 1Department of Agricultural, Food, and Nutritional Science, University of Alberta Edmonton, AB, Canada, 2Livestock Systems Section, Alberta Agriculture and Forestry Edmonton, AB, Canada.

Improving female fertility has become a key breeding goal in the dairy industry, where various measures of reproductive fitness have been incorporated in merit indices worldwide however; due to low heritability, the genetic progress for reproductive traits has been slow. With recent industry advancements, additional traits with the potential to complement current traits are beginning to be reviewed and implemented into selection programs. Ano-genital distance (AGD, the distance from the center of the anus to the base of the clitoris) is a sexually dimorphic trait believed to reflect prenatal androgenization during a heifer's reproductive programming window. In a preliminary report, AGD in primiparous and multiparous cows was inversely related to fertility and exhibited moderate heritability. Thus, AGD may be a useful reproductive phenotype for the future of genetic selection. The objective of this study was to (1) characterize AGD and (2) determine if the same inverse relationship exists between AGD and fertility in nulliparous heifers. AGD was measured in 671 Holstein heifers across western Canada and data was analyzed using UNIVARIATE, MIXED, GLIMMIX and LIFETEST procedures of SAS. Mean age at AGD measurement was 485 � 78 d, AGD was normally distributed with a mean (�SD) of 114 � 11.5 mm, ranging from 81 to 148 mm. Mean AGD was used to categorize heifers into short (<114 mm) and long (≥114 mm) AGD groups, and associations with fertility were determined. Heifers with short-AGD achieved pregnancy earlier (444 � 8.5 vs. 457 � 8.4 d; P < 0.01) and more efficiently (1.6 � 0.13 vs. 1.8 � 0.13 times bred; P = 0.02) than those with long-AGD. In addition, heifers with short-AGD had greater pregnancy to first artificial insemination than heifers with long-AGD (62.2 � 5.7 vs. 52.5 � 5.8%; P = 0.01) however; the rate of pregnancy up to 540 d of age did not differ between short- and long-AGD groups (95 vs. 95%; P = 0.80). In summary, an inverse relationship between AGD and fertility measures in nulliparous heifers is apparent, strengthening the potential for AGD to be used as a fertility trait in future selection programs. Studies using a larger population are needed to corroborate these findings.

Keywords: heifer fertility, reproductive phenotype, genetic improvement.