Comparative study of the concentration of biochemical components and steroid hormones in the follicular fluid and blood of mares in the spring transition period and in the breeding season

Follicular fluid (FF) is a natural environment for oocyte maturation and can be used for these purposes in vitro. However, due to the seasonality of equine breeding, some follicles undergo luteinization or regression during the spring transition period, which can be directly related to oocyte quality in year-round use of mares in ART programs. In order to find diagnostic criteria for selecting FF for in vitro maturation and predicting the quality of mares' oocytes, a comparison was made between the biochemical and hormonal composition of FF in the spring transition period (group I, including normal (Ia) and luteinizing (Ib) follicles) and FF from large estrous follicles of cycling mares in the breeding season (group II), as well as in the blood serum (group III). Analysis of the content of biochemical components and steroid hormones in the FG showed no quantitative differences in most components in subgroups Ia and Ib, except for total protein (p=0.048) and alanine aminotransferase (ALT) (p=0.013). Significant differences in the content of serum iron (p=0.019) and phosphorus (p=0.005) were found in the FF obtained from mares in the spring transition period and in the season of sexual activity. The concentration of testosterone, dihydrotestosterone and progesterone significantly (2-4 times) increased in the FF of estrous follicles in the mating season. It was concluded that the concentrations of progesterone, testosterone and dihydrotestosterone, taking into account the content of phosphorus and serum iron, can serve as a criterion for selecting FF for oocyte maturation in vitro. The content of progesterone, dihydrotestosterone, testosterone should be at least 100 nmol/l, 1000 pg/ml, and 16 nmol/l, and phosphorus and serum iron content within 0.74-1.1 and 46.4-57.0 mmol/l, respectively. Using these parameters of follicular fluid as criteria will determine the feasibility of its use for oocyte maturation in vitro.