Relationships between age, parity, endometrial fibrosis, early pregnancy rate and uterine blood flow in mares

Aim of this study was the examination of relationships between age, parity, incidence of endometrial fibrosis, early pregnancy rate and uterine blood flow in mares. Material and methods: Twenty-two mares were examined between days -2 and 12 (0 = ovulation). Animals were divided into two groups according to age and parity. Mares with an age ranging from 3 to 9 years were characterized as "young" (n = 11) and animals with an age of 10 to 19 years as "old". Ten of the mares were nulliparous and 12 uni- or pluriparous. Endometrial fibrosis was determined according to criteria by Kenney and Doig (1986). Results: Out of the 22 mares, 13 showed an endometrial fibrosis (category Ila, Ilb and III, respectively). After insemination with extended semen 8 of the mares became pregnant. The investigations were performed with a colour Doppler sonograph equipped with a 7.0 MHz microconvex-probe. Blood flow was visualized in both uterine arteries. Time-averaged maximum blood flow velocity (TAMV), and vascular-diameter (D) were determined and blood flow volume (VOL) was calculated. VOL values showed similar cyclic changes in all mares (p < 0.05). Cyclic changes in VOL were caused by variations in TAMV; D did not change during the examination period (p > 0.05). VOL was higher (p < 0.05) in aged, uni- or pluriparous and mares with endometrial fibrosis than in "young", nulliparous and mares without endometrial fibrosis. In contrast to pregnant animals uterine VOL values increased (p < 0.05) in barren mares within 12 hours after insemination. Conclusion and clinical relevance: The results show that the investigation of uterine blood flow by transrectal colour Doppler sonography provides important information concerning the fertility of mares.