Evaluation of shape variability of stallion sperm heads by means of image analysis and Fourier descriptors

This study quantified and evaluated the variability of sperm head shape for 10 different stallions. Sperm head shape characteristics including sperm head length to width ratio, position of the center of gravity, curvature, and degree of roundness were assessed and analysed from images using elliptic Fourier descriptors and inverse Fourier transformation. The first four principal components accounted for 88.46–92.33% of the total variance and provided a good summary of the overall data. In the case of the ejaculate with defective sperm heads the components accounted for 97.35–98.21% of variation. The study was able to quantitatively confirm that head length to width ratio, which contributed 48.63–53.48% and 71.30–73.34% to the total variance for normal and defective sperm, respectively, was the predominant determining parameter of sperm head shape. There were no statistical significant relationships between Fourier descriptors and values of sperm concentration and/or motility.