Luteal function induced by transvaginal ultrasonic-guided follicular aspiration in mares.

This study investigated if follicular aspirations (removal of fluid) from horse ovaries using ultrasound guidance could lead to the production of important hormones, namely progesterone, in similar concentrations as in natural ovulation. The research concluded that functional tissue (Corpus luteum) capable of producing progesterone can indeed be induced through follicular aspiration, provided that the follicle size is at least 35 mm.

Research Methodology

• The study included 58 mares (female horses) specifically crossbreeds. They were subjected to transvaginal follicle aspiration which is a less invasive method to extract ovarian follicles from the ovaries, guided by the assistance of ultrasound.
• The horses were arbitrarily placed into one of three categories, based on the diameter of their dominant follicle: 25-29mm, 30-35mm, or greater than 35mm. A control group consisted of mares who had naturally occurring ovulations, to provide a benchmark for comparison.
• Serum concentrations of progesterone, a key hormone produced by the luteal tissue following ovulation, were monitored in all the mares.

Research Findings

• Progesterone levels were higher in mares with natural ovulation compared to those undergoing follicular aspiration across all size categories. This emphasizes the role of natural ovulation in optimum progesterone production.
• In the group with follicular diameter of 25-29mm, the serum progesterone concentration declined by 0.365 ng/ml/day from the day of the aspiration until the 8th day.
• Conversely, in the mares which had follicle diameters of 30-35mm and greater than 35mm, the serum progesterone concentration increased on a daily basis. The rate of increase was more in mares with natural ovulation, highlighting their superior ability to produce progesterone.
• Among 25 mares that formed Corpora Hemorragica (a form of Corpus luteum indicating ovulation) after follicular aspiration, 92% had higher progesterone levels on the 8th day after aspiration, with majority of these mares having follicles larger than 25-29mm in diameter.

Research Implications

• Results from this study indicate that manipulating ovarian function through follicular aspiration can induce a functional Corpus luteum, which actively produces progesterone in mares.
• Moreover, it was found that a minimum follicular diameter of 35mm is necessary to achieve progesterone concentrations comparable to those achieved through natural ovulation.
• This finding may have significant implications concerning equine reproductive management and its related procedures like in vitro fertilization (IVF) or embryo transfer where artificial methods are required to stimulate oocyte (egg) production.