Sperm motility patterns in Andalusian donkey (Equus asinus) semen: effects of body weight, age, and semen quality

Abstract

The aims of this study were to (1) identify sperm subpopulations with specific motion characteristics in fresh Andalusian donkey ejaculates; (2) evaluate the effects of individual donkey and ejaculates within the same donkey on the distribution of the subpopulations found; and (3) explore the relationship between the age and the body weight of donkey donors, the sperm quality parameters, and the sperm subpopulations structure. Sixty ejaculates from 12 Andalusian donkeys (five ejaculates per donkey), ranging in age from 4 to 15 years, were collected. Immediately after collection, sperm characteristics (volume, sperm concentration, objective sperm motility, and sperm morphology) were assessed. Donkeys were evaluated for body weight. Significant (P < 0.05) correlations were established between the body weight of the donkeys and the pH (r = -0.52), sperm motility (percentage of motile spermatozoa: r = -0.31; percentage of progressive motile spermatozoa: r = -0.34), and total sperm abnormalities (r = 0.38). The correlations of the age with the measures of semen quality were low and not significant (P > 0.05). A multivariate clustering procedure separated 65,342 motile spermatozoa into four subpopulations: subpopulation 1, consisting of slow and nonprogressive spermatozoa (15.4%), subpopulation 2, consisting of moderately slow but progressive spermatozoa (35.9%), subpopulation 3, consisting of highly active but nonprogressive spermatozoa (18.5%), and subpopulation 4, consisting of highly active and progressive spermatozoa (30.2%). The distribution of these subpopulations varied significantly (P < 0.05) according to several parameters such as the individual donkey, the ejaculate of the same donkey, the total motility, and the overall sperm concentration. Our results show the existence of four well-defined motile sperm subpopulations in Andalusian donkey ejaculates, and suggest a high heterogeneity in the ejaculate structure in donkey. The relationship between the distribution of the sperm subpopulations and individual donkey, total motility, and sperm concentration shows that the spermatozoa of each have different motility patterns. However, the proportions of sperm subpopulations in the ejaculates did not vary with age and body weight. Finally, the study of discrete subpopulations of motile spermatozoa could lead to a substantial increase in information acquired during donkey semen analysis.