A comparison of dissected follicle numbers and follicle counts on the ovarian surface for the evaluation of ovarian follicular populations in Bos indicus cows

Ovaries (n = 140) from 70 mixed-age multiparous, lactating Brahman cross (3/4–7/8 Bos indicus) cows were used to examine the hypothesis that counts of follicles visible on the surface of the ovaries of Bos indicus cows and their classification into diameter size classes, are closely correlated with numbers of follicles in those size classes found by complete dissection of the ovary. Immediately after ovariectomy, mean diameters (long and short axes averaged) of all follicles ≥ 2 mm visible on the surface of each ovary were measured. All follicles ≥ 2 mm were dissected from the ovaries, excess stroma removed and follicle diameters measured under a stereomicroscope using an ocular graticule. For each ovary, follicles were classified in either small (< 4 mm), medium (4–8 mm) or large (> 8 mm) categories based on either diameters of surface or dissected follicles. Data for numbers of surface and dissected follicles (mean ± SE) in small, medium, large categories and total follicle numbers, respectively, were 24.4 ± 1.6 vs. 28.0 ± 1.9, 1.6 ± + 0.2 vs. 11.6 ± 1.0, 0.5 ± 0.1 vs. 0.7 ± 0.1 and 26.4 ± 1.6 vs. 40.4 ± 2.5. Correlation coefficients (r) for counts of surface and dissected follicles in small, medium, large and total follicle numbers were 0.76, 0.40, 0.69 and 0.79, respectively. Medium size follicles presented only a small translucent area on the surface of the ovary, leading to an underestimate of numbers when categorised by surface evaluation. Counts of follicles visible on the surface of the ovaries of Bos indicus cows and their classification into size classes based on estimated diameter, are closely correlated with numbers of follicles in those size classes found at dissection of the ovary for small (< 4 mm), large (> 8 mm) and total follicles but not for medium sized (4–8 mm) follicles.