Age-Related Changes in the Anatomy and Histology of Reproductive Organs, and Steroid Hormone Profiles in Male and Female Guinea Fowls (Numida Meleagris)

Abstract

Despite the potentials and contributions of guinea fowls to economic and social life in Ghana, research efforts directed at these birds, particularly, in the area of reproductive biology has been very limited. A study involving a total of 359 local guinea fowls (192 males and 162 females) was conducted, and documented the developmental changes in the external anatomy, gross anatomy and histology of the reproductive organs, and changes in steroid hormone (testosterone in males, and 17 -oestradiol and progesterone in females) synthesis in male and female guinea fowls from hatching until adulthood. These parameters were also compared between breeding and non-breeding birds. The study also determined the stages of spermatogenesis and seminiferous epithelial cycle, biometric, vent and molecular sexing in guinea fowls. Testicular asymmetry and compensatory growth in the testes of guinea fowls were also assessed. Age-related changes were analysed using univariate analysis for completely randomised design and means separated using Tukey's test/ Kruskal-Wallis test and medians separated by Mann-Whitney U-test. Seasonal differences in variables measured and differences between left and right testicular variables were determined using two-tailed t-test/Mann-Whitney U-test. Biometric and vent sexing were accomplished using discriminant function analysis. All comparisons were made at 5% level of significance. External biometric traits and phalli dimensions distinguished between male and female birds at 94% and 98.3% levels of accuracy, respectively. During molecular sexing, females produced 2 bands of 396 bp and 344 bp, while males produced only the larger band. Testicular anatomical biometric traits increased significantly (p<0.0001) from 8 weeks of age, and stabilised between 16 and 20 weeks of age. Total germ cell population per testis and testicular histological morphometric parameters increased significantly (p<0.0001) from 12 weeks of age and stabilised between 20 and 24 weeks of age. All ducts within the epididymal region increased (p<0.0001) in luminal diameters and stabilised from 20 weeks of age. In the female guinea fowl, the ovary and oviduct were discernible and measurable at hatching. Highly significant (p<0.0001) increases were seen in ovarian and relative ovarian weights, and oviducal weights and lengths between 24 and 28 weeks of age. Even though increases in oocyte and follicular diameters were significant (p<0.05) from hatching until 16 weeks of age, the increases were minimal relative to those seen thereafter. On the basis of oocyte diameter, the first phase of yolk deposition occurred between hatching and 20 weeks of age when oocyte diameters ranged between > 0.06 mm to 3.1 mm, the second phase between 20 and 26 weeks of age when the diameter ranged between over 3.1 mm to 6 mm, and the third and final phase between 27 and 28 weeks of age when oocyte diameters grew beyond 6 mm, until a maximum of 22.9 mm was attained, these were yellow follicles. All ovarian follicular morphometric traits showed inconsistent increases until 16 weeks of age. Mucosal folds in all sections of the oviduct increased significantly (p<0.0001), from 4 until 28 weeks of age. Peripheral testosterone concentrations increased gradually from 4 weeks of age, and peaked at 20 weeks of age. In females, plasma 17 -oestradiol decreased gradually to a minimum at 16 weeks of age, and then began to increase gradually until 28 weeks of age when it plateaued. Peripheral progesterone concentrations, on the other hand, fluctuated considerably during sexual development. Eleven steps of spermiogenesis and 9 stages of seminiferous epithelial development were recognised in the guinea fowl testis. Breeding males had significantly (p<0.05) higher anatomical biometric parameters than their non-breeding counterparts. Both qualitative and quantitative histological changes were observed in regressing testis and epididymis. Peripheral testosterone concentrations were also higher (p<0.05) in breeding than non-breeding males. In non-breeding females, all ovarian and oviducal gross anatomical features had significantly (p<0.05) regressed. Marked qualitative histological changes were also noticed. Mucosal folds in all regions of the oviduct except the infundibular lip were higher (p<0.05) in breeding females. Breeding females had higher (p<0.05) peripheral oestradiol levels than non-breeding females. Guinea fowls could be sexed more accurately with molecular than biometric and vent sexing. Testicular anatomical biometric and histological morphometric traits began to stabilise at sexual maturity and 4 weeks following sexual maturity, respectively. Testosterone seems to play a role in the development and stabilisation of these testicular histological variables. Three phases of yolk depositions were found in the guinea fowl. The results of the present study suggest oestradiol might play a role in oviducal growth and yolk deposition. The classification of seminiferous epithelial cycle in the guinea fowl is similar to those in other birds and mammals. The reproductive organs of both male and female birds had regressed in non-breeding birds. Oestradiol and testosterone concentrations in male and female birds, respectively, might play a role in non-breeding of guinea fowls during certain times of the year. Compensatory growth occurred in both the testes.