Summary. Radioactive microspheres (15 μm diameter) were used to measure capillary blood flow rates in the ovaries and ovarian follicles (Qf) in high fecund Romanov and low fecund Préalpes-du-Sud ewes at the preovulatory stage of the oestrous cycle. Additionally, assessments of the percentage of arterial blood passing through ovarian arterio-venous anastomoses were obtained.
The mean ± s.e.m. Qf per unit volume of theca ((ml/min) × 104/mm3) for non-atretic follicles in Romanov ewes was significantly greater (P < 0·05) than that in Préalpes ewes (365·8 ± 42·4, n = 19, compared with 241·3 ± 30·1, n = 14). For each breed, the mean Qf value for non-atretic follicles was 8–10 times greater than that for atretic follicles.
In Romanov ewes, total Qf ((ml/min) × 104) and Qf per unit volume of theca was greatest in small-sized follicles (3· 1–5·0 mm) while in Préalpes ewes, maximum flow was attained in larger-sized follicles (5·1–7·0 mm). The elevated Qf in small-sized follicles in Romanov ewes may be conducive to more follicles achieving maturation at a smaller diameter in this breed than occurs in the Préalpes ewes.
The absence of flow through ovarian arterio-venous anastomoses in the Romanov, but not in the Préalpes, ewes suggests different mechanisms for controlling the distribution of the total ovarian blood supply in the 2 breeds.
Keywords: follicles; blood flow; sheep; prolificacy