By Andrew sandeen
According to the American Embryo Transfer Association, 448,826 bovine embryos were transferred into recipients in 2019, 68% of which had been produced by in vitro fertilization (IVF) methods. In the same year, 122,431 ovum pick up (OPU) sessions were completed, recovering more than 2 million oocytes for the purpose of IVF (Demetrio et al., 2020).
Ovum pick up is a well-established process for collecting oocytes which entails puncturing follicles on the ovaries of a donor heifer or cow and collecting the fluid and oocytes inside. In a laboratory, high quality oocytes can be taken through a process for fertilization and early maturation before being transferred into recipient cattle. The OPU process is commonly repeated every two weeks for a single donor.
There are a variety of questions that come up regarding the benefits and drawbacks of performing OPU and IVF, which often lead to conversations about genetic progress, costs, and animal handling. One question that has been asked is about the potential negative impacts of repeated OPU procedures on the fertility of donor animals.
When IVF donors are undergoing OPU sessions, there are certainly some potential impacts on the interplay of hormones and various physical characteristics of the ovaries, including hemorrhage, infiltration with immune cells, and fibrosis (Viana et al., 2003). When follicles are aspirated, some of the follicular cells may luteinize and produce progesterone (Viana et al., 2003). There can be a thickening of connective tissue and hardening around the ovaries (Petyim et al., 2001). The process may even cause adhesions (Viana et al., 2003). These impacts do not necessarily interfere with the ability of the ovaries to resume normal functionality, but the extent of the damage does seem to be proportionally related to the extent of follicle aspiration activity over weeks and months.
In beef calves, after follicle aspiration procedures had been performed a total of 7 times between 3 and 14 months of age, and there was no significant change in follicular wave activity or conception rate after first insemination (Brown et al., 1996).
Different results were found in a study where reproductive performance and culling data were examined from a Florida dairy herd with extensive embryo transfer and IVF activity (Figueiredo et al., 2020). After varying numbers of OPU sessions, beginning as early as 10.6 months of age, the fertility of virgin heifer donors was negatively impacted by OPU. The rate of pregnancy to first insemination was approximately 15% lower when compared to either non-donors or heifers which had been flushed for embryo transfer. However, no significant difference was observed in conception rates among older donors in the lactating herd.
In postpartum beef cows, after a series of four OPU sessions, fertility to fixed time AI was not significantly affected (Aller et al., 2010). However, it should be noted that there were only ten cows per treatment group for the study and numerical differences suggested a potential negative effect.
More research is needed to make any strong claims regarding the effects of repeated OPU procedures on fertility of heifers or cows. However, it is probably safe to say that, after looking at ovarian morphology and reproductive performance following follicle aspiration procedures in the few studies that have been done, there is at least some physical impact on the ovaries that could potentially affect later fertility. In a commercial setting, hopefully the benefits of OPU-IVF will outweigh whatever those risks may be.
Source : psu.edu