Repeatability of anogenital distance in Holstein cattle and its association with embryo yield and quality

• Author / Creator

  Rajesh, Iswarya

• Reproductive phenotypes that are easy to measure, have high genetic variation and heritability along with good repeatability are being explored for genetic selection of cows for improved fertility. In this regard, anogenital distance (AGD; the distance from the center of the anus to the base of the clitoris) is a promising new reproductive phenotype. In Holstein cows, AGD was inversely associated with the measures of fertility, had high genetic variation and moderate heritability. The repeatability of AGD and the mechanism underlying its association with greater fertility in short-AGD cattle are not unknown. Therefore, we explored this novel reproductive phenotype for its repeatability through different physiological phases. Furthermore, to understand the mechanism behind the inverse association between AGD and fertility we hypothesized that embryo yield and quality will be greater in cattle with short AGD than in those with long AGD.
  The first study was designed to test the repeatability of AGD at different ages (from 0 to 15 mo) and different physiological states (phases of the estrous cycle, gestation and lactation). We hypothesized that AGD at birth can be used to predict adult AGD and that AGD measurements will be highly correlated at different ages and physiological states. Contrary to our expectation, AGD at birth was not correlated with the adult AGD, but AGD measured at 6 mo of age was correlated with adult AGD. The AGD measurements at the different phases of the estrous cycle, gestation (except at 270 d of gestation), and lactation were highly repeatable within an individual.
  The second study determined the differences in yield and quality of embryos in cows and heifers with short and long AGD using the superovulated model. We also posited that antral follicular count, anti-Müllerian hormone, and superovulation response will be positively associated. Although the mean number of preovulatory follicles and corpora lutea (indicators of superovulation response) or embryo yield did not differ, the proportion of preovulatory follicles was greater, and transferable quality embryos tended to be greater in cows with short AGD than in cows with long AGD. Similarly, the proportions of fertilized eggs out of total structures recovered, and transferable quality embryos out of total structures recovered were greater in short-AGD cows than in long-AGD cows. In heifers, the proportions of total structures recovered (embryos/ova), fertilized eggs, transferable and Grade-1 (best quality) embryos were greater in cows with short AGD than in cows with long AGD. However, AGD was not associated with antral follicular count and anti-Müllerian hormone.
  
  In conclusion, AGD measured before 6 mo of age did not reflect adult AGD, although AGD was highly repeatable at most physiological phases measured during adult life except during late gestation (270 d). No AGD-related differences in embryo yield and quality were found in heifers but the proportions of fertilized eggs and transferable embryos out of total recovered were greater in short-AGD cows than in long-AGD cows. Findings from Chapter 3 imply that AGD is measurable with high reliability at any physiological state. Findings from Chapter 4 imply that the improved fertility in short-AGD cows reported by others may be due to proportionately greater fertilization rate and embryo viability in short-AGD cows than in long-AGD cows. The latter findings must be validated in a larger population.

• Subjects / Keywords

  • Fertility
  • genetic selection
  • Dairy cows

• Graduation date

  Spring 2021

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-r12v-gk88

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.