The distribution of small preantral follicles within the ovaries of prepubertal African elephants ( Loxodonta africana)

Abstract

Background Data on the distribution of primordial (single layer of squamous granulosa cells), early primary (some granulosa cells cuboidal) and primary (all granulosa cells cuboidal) follicles, grouped together as small follicles (SF) within the ovary of the elephant is lacking, yet such information is necessary to be able to estimate accurately the total numbers of small follicles in the ovaries of elephant throughout their lifespan. Aim To determine if the density of SF differs between ovaries, between the surfaces of an ovary, or between the interpolar and intermarginal zones of an ovary. Materials/methods Stereological techniques were employed on 25 μm thick histological sections of the ovaries recovered from 12 prepubertal elephant calves aged 2 months to 4.5 years. Cell densities were calculated using the optical brick method and Cavalieri's principle for volume calculation. Results The density of SF (numbers of SF per unbiased counting frame [UCF]) did not differ between the left (1.11 ± 0.39 (mean ± sd)) and right (1.10 ± 0.39) ovaries ( P = 0.82, n = 12), or between the lateral (median 1.24; interquartile range 0.85–1.39) and medial (1.03; 0.76–1.36) surfaces of the ovary ( P = 0.22, n = 24) or among the 5 segments of the ovary between the two poles ( P = 0.20, n = 24). The third of the cortex nearest to the mesovarial margin of the ovary had fewer small follicles per UCF (0.85; 0.51–1.28) than the middle third (1.01; 0.78–1.42; P = 0.034), and the third adjacent to the free margin (1.27; 0.79–1.51; P = 0.0024), n = 24 per group. Conclusion Providing a random sample is taken from the full interpolar and intermarginal dimensions of ovary of a non-pregnant elephant, the density of small follicles throughout the cortex may be accurately measured using stereological techniques applied to one of its surfaces.