Microanatomy of ovary in laying and non-laying emu birds (dromaius novaehollandiae)

The micronatomical observation was carried out on ovaries of six mature female emu birds at their non-laying stage and six female birds at their laying stage. The female reproductive system of the emu consisted of an unpaired ovary appearing as bunch of grapes and was covered externally by germinal epithelium consisting of a single layer of cuboidal cells. The ovarian follicles of different stages of development, atretic follicles and post ovulatory follicles (corpus luteum) were seen in the cortex. The medulla consisted of collagen and reticular fibres, blood vessels, nerve bundles and smooth muscle fibres. The primary follicles consisted of a single layer of flattened granulosa cells around the oocyte and were smallest among the follicles. The diameter of these follicles varied from 77.47 ± 7.55 µm in non-laying birds to 80.66 ± 5.49 µm in laying birds. The secondary follicles were larger than the primary follicles and consisted of an oocyte with granular cytoplasm surrounded by a single layer of cuboidal granulosa cells. The diameter of secondary follicle was 145.64 ± 10.98 µm in non-laying birds and 174.86 ± 6.72 µm in laying birds. The tertiary and quaternary follicles were located close to the surface of the ovary and quaternary follicles were suspended from the ovary by follicular stalks in laying emu birds. The vacuolated cells identical to the interstitial cells of the stroma formed oval to spherical thecal glands. The diameter of quaternary follicle varied from 927.24 ± 48.71 µm in non-laying birds to 1119.66 ± 61.93 µm in laying birds. These follicle measured upto 3.28 cm in diameter in laying birds as they were filled with enormous amount of yolk. Follicular atresia was observed in various stages of the development of the ovarian follicles. The granulosa and thecal layers were disrupted and degenerated and invaded into the oocytes of atretic follicles. The post-ovulatory follicle (or corpus luteum) was observed in the cortex of the ovary.