Interaction of donor age, parity and repeated recovery of cumulus–oocyte complexes by ovum pick-up on in vitro embryo production and viability after transfer

• In vitro embryo production declined over a fourth month of repeated OPU.
• The negative response of Korean beef cattle to repeated OPU highlighting breed/genetic effect.
• The repeated OPU reduced pregnancy and calving rates of produced embryos.
• Parity number, donor age as well as individual variation influence OPU performance.

The objective of this study was to investigate the effect of age and number of parities on the potential of the Korean native cow (Hanwoo breed) as oocyte donor in ovum pick-up and subsequent in vitro embryo production. All animals were divided into two different groups based on age (3–6 and 7–9 years) and parity (2–3 and 4–7). Ovum pick-up (OPU) was performed to ten Korean native cows over a 4-months period at intervals of 3–4 d (twice weekly). The population of follicles (≥3 mm diameter) present in both ovaries and the grades of all cumulus-oocyte complexes (COCs) retrieved were recorded. All COCs were matured, fertilized and allowed to develop in vitro and the morphological quality of embryos was evaluated before transfer to recipients. There were 18.4±5.7 (mean ± SEM) follicles available for aspiration throughout the experiments; the population of follicles decreased from 19.1±6.3 in the first month to 16.9±4.2 in the last month (p≤0.05). However, with advancement in age and parity of animals, there was an increase in number of ovarian follicles. Furthermore, the average number of COCs retrieved was 12.5±5.6 in the first month and this number was reduced in the fourth month (10.4±5.4). The total number of recovered COCs was increased in old cows with increased number of parities. Consequently, embryo production decreased from 4.8±3.1 to 4.2±2.8 on the first and last months, while, it was increased in old cows than young ones (p≤0.05). Furthermore, animals with high number of antral follicular count produced more COCs and embryos. Therefore, we concluded that repeated OPU of Korean native cows resulted in significant decrease in the in vitro production of embryos in young compared with old cows; this has negatively impacted embryo survival after transfer.