Morphology of spermatozoa in semen from stallions of normal fertility.

This research examined the structure of sperm cells in fertile stallions, noting several unique characteristics including an asymmetric head, a tail placed alongside instead of behind, a small acrosome, and the presence of microtubules in the neck.

Semen Collection and Examination

• To study the unique morphology of stallion spermatozoa, semen samples were collected from three fertile stallions. The process involved the use of an ‘open’ artificial vagina.
• The researchers then closely examined these samples under scanning and transmission electron microscopy. These powerful microscopic techniques provided a detailed look at the spermatozoa at the cellular level, enabling the identification of unique and common traits.

Morphology of Stallion Spermatozoa

• The research identified several specific morphological features of stallion spermatozoa that differentiate them from spermatozoa in other mammals. These include an asymmetric head, an abaxial (or off-center) position of the tail, and a relatively small acrosome.
• The asymmetric head of the stallion’s spermatozoon is a significant deviation from normal sperm cell structure, which typically features a symmetric head.
• The abaxial position of the tail is another distinct trait where the tail is not situated directly behind the head (as is common in other mammals) but is instead located alongside the head.
• Another identifying trait of the stallion spermatozoa is the size of the acrosome, which happens to be smaller in volume compared to other mammals. The acrosome is a cap-like structure over the anterior part of a sperm cell’s head that contains enzymes. During fertilization, these enzymes help the sperm cell penetrate the egg.
• Finally, the presence of microtubules in the neck of the stallion’s spermatozoa was noted as a unique feature. Microtubules are microscopic cylindrical structures that are involved in maintaining cell shape and structure, transport within cells, and cell division.