The repeatability of seminal characteristics of stallions.

The study examines the repeatability of seminal characteristics in stallions across several breeding seasons, to understand variations and decide upon the fertility norms.

Objectives of the Study

• The main objective of this research was to measure and analyze the repeatability or intra-class correlations of seminal characteristics in the ejaculates of laboratory and commercial stud stallions across multiple breeding seasons.
• The study aimed to facilitate better understanding of the significant variations between stallions and their seminal characteristics, thereby providing data that could help evaluate horse fertility more accurately.

Methodology

• The seminal characteristics of four laboratory stallions and 164 commercial stud stallions were examined over repeating cycles.
• Data was collected from a total of 536 and 531 ejaculates, respectively.
• The data was derived over the course of four breeding seasons from 1974/75 to 1977/78, while including stallions of nine different breeds.

Findings

• Between-stallion variation was significant for all characteristics except for the pH levels in gel-free semen.
• The repeatability of various seminal characteristics was categorized into low (less than 0.3) and moderate (0.3 to 0.6).
• Low repeatabilities were recorded for parameters like gel-free volume, pH of gel-free semen and the percentage of abnormal mid-pieces.
• Moderate repeatabilities were found for total volume, gel volume, motility, percentage of dead spermatozoa, sperm concentration, total sperm number, and percentages of head abnormalities, tail abnormalities, loose heads and cytoplasmic droplets.

Suggested Recommendations

• The researchers suggested that if a seminal examination displays characteristics below or near the recommended minimum levels, additional samples (1 or 2) should be tested before classifying a stallion as having doubtful fertility.