CHARACTERISTICS OF THE OVARIAN-FUNCTION I N NONPREGNANT BREEDING MARES AT THE BEGINNING OF THE OFFICIAL BREEDING-SEASON

Functional state of ovaria was investigated in 6 stud farms in 102 mar es at the beginning of official breeding season (in February). Blood s amples were collected three times with intervals of 5-8 days and the l evel of Plasma progesterone (P4) was determined. Simultaneously, the f ollicular activity was judged by rectal palpation, as well as by means of transrectal ultrasonic echography. Of the 88 appreciable mares, th e ovarian function of 33 (38%) proved to be cyclic. Corpus luteum pers istens (CLP) was diagnosed altogether in 2 cases (2%). Of the acyclic animals (n = 53 = 60%) 12 (14%) were qualified to be in the so-called deep stage of acyclia due to the total lack of follicular activity. On ly follicle with a smaller (<3 cm) diameter could be found in 32 mares (36%, early stage of transition-season period. Another 9 animals (10% ) were qualified to be in the late stage of transition period accordin g to the follicular diameter of larger than 3 cm. Functional state of ovaria of earlier not served, newly installed mares younger than 5 yea rs old (Table 1) and in mares earlier pregnant at least once and foale d/aborted within 3 months showed the less favorable characteristics (T able 2). systematic, hard work also delayed the first ovulation, indic ating the start of breeding season (Table 3). Many unnecessary service was done in mares being in the transition-season period and showing m ore or less regular heat in January and February (Table 4). Mares with cyclic ovarian function even in February of being in the progressed s tage of transition-season period, became pregnant at an earlier period of the year (Table 5). Based on the results obtained, it has been poi nted out that the start of official and biological breeding seasons di d not coincide in all cases even in the Hungarian studs. Thus, it is e xpected that the rate of fertilized mare can be increased by methods c apable of influencing the growth ot' follicle, as well as the first ov ulation (light completion, gestagenic period-treatment) and by the app lication of up-to-date infertility diagnostic methods.