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Association of oocyte and early embryo morphology with age and the establishment and maintenance of pregnancy after ICSI in mares




Frank-Guest, Bethany Linda, author
Carnevale, Elaine, advisor
Seidel, George, Jr., committee member
Hendrickson, Dean, committee member

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Increasing maternal age in humans, horses and lab animals has been associated with a decrease in fertility. Oocyte quality and morphology have been implicated as primary causes of reduced fertility in older mares. Selected oocyte morphological parameters have been correlated with pregnancy development in humans and horses. Objective measurements of morphology to assess oocyte quality would provide a critical evaluation and help identify zygotes with the highest developmental potential for transfer, to optimize recipient utilization and pregnancy rates. The hypotheses of the research were that oocyte and early embryo morphology differ with donor mare age and correspond with developmental potential. Objectives for the first study were to compare: 1) oocyte donor age with oocyte morphology and developmental competency after ICSI, and 2) oocyte morphology with developmental competency (cleavage, early pregnancy, late pregnancy and pregnancy loss) after ICSI. Objectives for the second study were to compare developmental potential of ICSI produced embryos with: 1) oocyte donor age, and 2) cleavage characteristics, and 3) rate of embryonic development. Oocytes were collected from donor mares in a clinical ICSI programs. The mares were divided into the following age groups and fertility categories: 1) 3-13 yr with Known fertility, 2) 2-13 yr with Unknown fertility, 14-19 yr, 20-23 yr and 24-27 yr. Approximately 24 h after induction of follicle maturation, and oocytes were collected and cultured approximately 18 h before being stripped of cumulus cells. Photographic images (200x) were captured before oocytes were injected with sperm. Images of oocytes were measured using digital calipers within a computer software program. Ooplasm volume was larger (p<0.05) for oocytes from mares 14-19 yr and 20-23 yr than mares 3-13 yr Known than for mares 24-27 yr. Perivitelline space volume was similar between mares 3-13 yr Unknown and mares 20-23 yr, but was smaller (p<0.05) between mares 3-13 Unknown and the other age groups. Oocyte diameter (OD) was smaller (p=0.05) between oocytes from donors 3-13 yr Known and donors 14 -19 yr, but similar among all other groups. Inner zona pellucida diameter (IZPD) differed (p=0.03) only between mares 14-19 yr and mares 3-13 yr Unknown, with oocytes from mares 14- 19 yr having the largest numerical IZPD and mares 3-13 yr Unknown having the smallest IZPD. Ooplasm diameter (OpD) was smaller (p≤0.02) for oocytes from mares 3-13 yr Known than from mares 14-19 or 20-23 yr. The diameter of the zona pellucida with the surrounding matrix (ZPTM) was greater (p<0.05) for mares 3-13 yr Unknown than for all other groups. The rate of embryo development (hours per cell) prior to oviductal embryo transfers was faster (P<0.05) for embryos that did versus did not produce an early pregnancy and tended (P≤0. l) to be faster for embryos that did versus did not produce a late pregnancy. Embryonic vesicles that had a more rapid increase in diameter were more often (p<0.05) maintained to the late pregnancy stage. Donor mare age exerted a large effect on the development and outcome of pregnancies. Oocyte morphology was not a reliable indicator of oocyte developmental potential, although speed of early embryonic development was associated with embryonic competency.


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Mares -- Reproduction


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