Fertility of stallions with abnormalities of the sperm acrosome.

This research study is about the detection of sperm abnormalities in seven stallions and the impact of these abnormalities on their fertility. Despite the observed anomalies, ranging from 27-74%, the stallions managed to sire foals with pregnancy rates between 12.5 to 100% per oestrous cycle.

Research Study Details

• The research was conducted over two years and focused primarily on seven stallions which were found to have a high incidence (27-74%) of acrosomal abnormalities in their ejaculated spermatozoa.
• The most common abnormality in these stallions was the presence of a ‘knobbed sperm’ defect. This was observed through various microscopic techniques including nigrosin-eosin, Giemsa, and haematoxylin and eosin stained semen smears under light microscopy, as well as buffered formal-saline and in glutaraldehyde-fixed wet mounts under phase contrast and differential interference microscopy.

Sperm Abnormalities

• The ‘knobbed sperm’ defect was visible as a flattened apical ridge, a tongue-like flap on the acrosome’s top surface, or a bead-like protrusion coming out from the apical ridge.
• Other than the ‘knobbed sperm’ abnormality, a cystic swelling was also seen on the surface of the acrosomal part of the ‘knobbed sperm’ as per the electron micrographs in the study.
• The spermatozoa of three out of the four stallions examined also showed ‘crater defects’ in the sperm nucleus. These ‘crater defects’ were observed through phase contrast, differential interference, and electron microscopy.

Fertility of the Stallions

• In spite of these observed sperm abnormalities, all the analyzed stallions successfully sired foals.
• The fertility, quantified by a successful pregnancy rate per oestrous cycle among the mares served by these stallions ranged widely from 12.5% to 100%. This demonstrates that despite the acrosomal abnormalities and sperm defects, the stallions were still capable of impregnating mares.
• The results indicate that ‘knobbed sperm’ defect and other observed sperm abnormalities do not necessarily lead to infertility in stallions, although the range in success rate suggests that it may impact the efficiency of fertilization.