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Matthiesen, Marieke Margarete (2011): Effect of donor age on the developmental capacity of bovine cumulus oocyte complexes obtained by repeated OPU from nonstimulated and FSH-superstimulated German Simmental heifers and cows at different life cycle stages. Dissertation, LMU München: Faculty of Veterinary Medicine
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Abstract

Similarities between the bovine female and women in terms of reproduction and fertility, such as oogenesis, folliculogenesis and reduced fertility with advanced age make the bovine a valuable model for the study of ovarian function and dysfunction as well as reproductive aging in women. The aim of the present work was to investigate the influence of donor age on follicle numbers, yield and quality of COCs obtained by repeated OPU and on the developmental competence in vitro after oocyte maturation in vitro versus in vivo. Further, the ability of oocytes from different age classes to reprogram nuclei of bovine fetal fibroblasts was studied. Since the individual is a major factor influencing parameters of fertility and results of ART in both humans and cattle, the present study used in parts the same animals to rule out inter-individual effects on the response to one or the other approach. Experiment 1 investigated the effect of donor age in non-superstimulated German Simmental heifers (n = 12, 14 months at the beginning of the experiments), young cows in their first lactation (n = 8, 2-4 years) and old cows (n = 8, 10-15 years). A total of 38 OPU sessions were performed in two experimental periods on independent sets of animals from all age classes: 5/5/5 (32 sessions) and 7/3/3 (6 sessions). In spite of a marked influence of the experimental period, a number of parameters were also significantly affected by donor age. The total number of follicles increased with age (P<0.001) and similarly, the total number of cumulus-oocyte-complexes (COCs) recovered was higher in old cows than in young cows and heifers (P<0.01). Evaluation of the follicle size distribution revealed higher percentages of small and lower proportions of medium size follicles in old cows while the COC quality was not affected. Further, the least squares mean blastocyst rate obtained after IVM and IVF of COCs was significantly (P<0.05) higher in young cows (17.4%) than in heifers (5.1%). The culture of oocytes after SCNT resulted in similar cleavage and morula rates. Experiment 2 investigated the interaction of donor age and FSH-superstimulation using the set of animals from experimental period 1 (n = 5 per age class). During 9 OPU sessions performed in 5-week intervals proportions of in vivo matured oocytes between 65.0% and 75.1% on average were obtained. FSH-superstimulation significantly increased the numbers of follicles aspirated (P<0.001) and COCs recovered (P<0.001) as compared to non-superstimulated donors. Follicle size was shifted to less small and more medium and large follicles. Further, there was a marked positive effect of FSH-superstimulation on cleavage and blastocyst rates in all age classes (P<0.001). Importantly, the developmental deficit of heifer COCs after IVM was rescued by FSH-treatment and in vivo maturation.