Gross and microscopic anatomy of the reproductive organs of the female Philippine native chicken (Gallus gallus domesticus)

The gross, histological and histochemical characteristics of the ovary and oviduct of the laying Philippine native hen are described and discussed. The native hen has one functional ovary, the left one, which resembles a bunch of grapes and contains large, medium and small round yellow follicles. The length and width of the native hen's ovary are difficult to measure because of the irregular shape of the organ. On the other hand the weight and volume are relatively low, with the weight being less than 10% of that in foreign breeds. Only the left oviduct becomes functional. It is shorter than in foreign breeds and consists of five segments: infundibulum, magnum, isthmus, uterus and vagina, in contrast to the three (fallopian tube, uterus and vagina) in mammals. The magnum is the longest and the isthmus is the shortest segment. Total length of oviduct and individual lengths of the five segments, except the isthmus are affected by the reproductive status of the bird. Histologically, the native hen's ovary is similar to that in other domestic fowls except for the apparent lack of a tunica albuginea and theca externa, the lowest number of primary and growing follicles, and the absence of mature and discharged follicles. The avian growing follicle unlike its mammalian counterpart does not posses a cumulus oophorus and a thick stratified membrana granulosa and has no antrum but a large primary oocyte with a yolk-filled cytoplasm fills the follicular sac. The native hen's oviduct is generally similar in histology to its counterparts in foreign breeds. One difference from the mammalian oviduct is the presence of special glands in the infundibulum, magnum, isthmus and uterus that secretes the Chalaza, egg albumen, shell membranes and egg shell, respectively and the sperm host glands at the utero-vaginal junction that store and keep the sperms viable. Counterpart segment in mammals are non-glandular except for the uterus that contains uterine glands to nourish the embryo before the formation of placenta. Another difference is the less extensive folds and the more open lumen of infundibulum in native hen and other avian species in contrast to its tortuous folds and labyrinthine lumen in mammals. Histochemically, collagen fibers are absent from the native hen's ovary confirming absence of tunica albuginea; elastic fibers in the perivitelline membrane and basal lamina of growing follicles perhaps allow oocyte and follicle to expand without being ruptured. Glycoprotein in basal lamina and theca interna of growing follicles has antigenic property and may help protect the growing follicle from pathogens. In oviduct of native hen elastic fibers are absent; collagen fibers are present and more abundant in infundibulum and uterus. Nucin in the magnus, isthmus and vagina lubricates and protects the oviduct from exogenous pathogens. The ovary of the Philippine native hen presents four distinct anatomical features that are quite different from its counterpart in foreign breeds and may contribute to the low production performance of native breed. These include the low weight and low volume of the ovary, the low number of primary and growing follicles and the absence of the white follicles that have the potential to develop and mature into functional yellow follicles. On the other hand, the anatomy of the oviduct does not seem to influence the production performance, particularly the quality of the egg produced by the native hen. In conclusion, the ovary and oviduct of the laying Philippines native hen are basically similar in gross and microscopic structure to their counterparts in foreign breed and mammals except for differences described above.