Gonadosomatic and Histomorphological Bases of Sterility in Intergeneric Hybrid Male Mule and Hinny Ducks

Reproductive failure due to hybrid sterility is common among vertebrates, including birds. This study ex-amined the causes of sterility in intergeneric hybrid male Mule and Hinny ducks by comparing their gona-dosomatic index (GSI) and testicular histo-architecture with those of their parental species: Muscovy (Cairina moschata) and Mallard (Anas platyrhynchos) ducks. Testes from ten males of each genotype were collected, weighed, and processed histologically using Hematoxylin and Eosin staining. Analysis of vari-ance showed that genotype significantly (P<0.05) influenced testis size (TS) and GSI. Mallard ducks had the highest TS (24.30 g) and GSI (1.74%), followed by Mule (TS: 9.73 g; GSI: 0.30%) and Hinny ducks (TS: 8.06 g; GSI: 0.27%), while Muscovy ducks recorded the lowest (TS: 2.49 g; GSI: 0.09%). Left testes were generally larger than right ones across all genotypes, though not significantly (P>0.05). Histological analysis revealed normal testicular organization in Muscovy and Mallard ducks, with all spermatogenic stages (spermatogonia, spermatocytes, spermatids, and spermatozoa) present, as well as mature sperm cells in the seminiferous tubules and epididymides. Conversely, Mule and Hinny males exhibited impaired sper-matogenesis characterized by production of only primary spermatocytes and epididymal vacuoles devoid of mature sperm cells. It is concluded that the sterility of Mule and Hinny hybrid males is not related to testis size or GSI but results from their inability to complete spermatogenesis and produce mature sperm cells capable of fertilization of ova.