Increased number of mast cells in the dominant follicle of the cow: relationships among luteal, stromal, and hilar regions.

The number of mast cells per microscopic field at 450X (0.123 mm2) was determined in the bovine ovary on Days 4, 10, and 19 of the cycle (Day 0 = estrus). Mast cells were observed in the theca externa of follicles, the external capsule of the corpus luteum, and in the stromal and hilar regions of the ovary. The stromal and hilar regions exhibited the highest number of mast cells (per field = 7.51-10.15) compared with the follicular and luteal compartments (2.65-3.70 mast cells/field). Most interestingly, on Day 19 a significant increase in the number of mast cells was observed in the theca externa of the dominant follicle (10.4 mast cells/field) compared with nondominant healthy follicles on Days 4 and 10 (2-3/field). After ovulation, the number of mast cells surrounding the corpus luteum on Day 4 was significantly lower than 19 values in the dominant follicle; this was further diminished on Day 10 of the cycle. These results indicate that the increase in mast cells associated with the dominant follicle on Day 19 may be related to its development and the decline in mast cells related to ovulation.