The influence of somatotropin and oocyte aspiration on transvaginal ultrasound-guided oocyte recovery and ovarian health in cattle

The emerging fields of transgenics, cloning, in vitro fertilization, and breed improvement rely on the availability of oocytes of known origin. Somatotropin has been reported to increase ovarian follicular populations in several species. It is less clear whether the number of oocytes which can be aspirated from those follicles is increased correspondingly. The hypothesis that exogenous ST alters the intrafollicular environment in a way which diminishes the ability to non-surgically recover oocytes from yearling beef cattle will be tested. My secondary objective was to assess any potential negative consequences of the oocyte aspiration procedure on the ovarian health or subsequent reproductive efficiency of donor animals, resulting from the impact of repeated ovarian puncture. ^ Several experiments were conducted using transvaginal ultrasound-guided aspiration technology. Heifers were aspirated from four times each to 19 times each, depending on experiment, using daily or sustained-release ST, along with a decreased nutritional plane, for treatment. ^ Nutritional plane did not impact follicle number or size distribution, or oocyte number, quality or growth. Likewise, treatment with sustained-release ST (one 500 mg injection every 2 wk) did not alter follicle number or size distribution, or oocyte number or quality. Daily ST injection (33 μg/kg body weight/day) resulted in increased follicle populations without a corresponding increase in oocyte numbers, indicating a suppressive effect of ST on oocyte aspiration. Moreover, the increased follicular populations were observed after one week of ST treatment. Further, follicle sizes and oocyte quality and growth were unchanged by daily ST injection, as was stage of oocyte maturation. In addition, daily ST treatment increased follicular thecal cell layer diameter, while leaving other follicular components unaltered. Aspiration increased short-term ovarian bleeding and scarring at sites of puncture, and delayed the ability of the donor animals to subsequently breed. This research further defines the relationship between folliculogenesis and oocyte maturation, specifically the role that ST may play in the interaction of these two events. Findings may result in adjustment of treatment protocols under consideration in both human and bovine IVF and transgenesis programs.