Relationship between conventional semen characteristics, sperm motility patterns and fertility of Andalusian donkeys (Equus asinus)

Sperm quality has an important role in determining fertility. The aims of this study were to compare the conventional sperm parameters, plus the characteristics of the motility patterns of the different sperm subpopulations, of donkey donors with different fertility level, and to determine their relationships to fertility. Thirty ejaculates from 6 Andalusian donkeys were assessed for gel-free volume, pH, sperm concentration, motility and morphology. The fertility of donkeys was classified on the basis of pregnancy rates per cycle, where donkeys with a per cycle pregnancy rate ≥60% were considered to be “fertile” (n = 3) and those with a per cycle pregnancy rate <40% were categorized to be “sub-fertile” (n = 3). Significant differences (P < 0.001) between the “fertile” and the “sub-fertile” group were found for total and progressive motility, and for straight line velocity. Sperm variables associated (P < 0.05) with an increase in percent pregnant per cycle included total motility (r = 0.37), progressive motility (r = 0.53), curvilinear velocity (r = 0.44), straightness (r = 0.39), beat cross frequency (r = 0.44), and gel-free volume (r = 0.53). Four sperm subpopulations (sP) were identified in fresh semen: sP1 (slow and non-progressive spermatozoa, 20%), sP2 (moderately slow but progressive spermatozoa, 71.2%), sP3 (highly active but non-progressive spermatozoa, 2.9%), and sP4 (highly active and progressive spermatozoa, 5.9%). The lowest percentage (3.1%; P < 0.001) of sP4 spermatozoa was observed in the “sub-fertile” group. Three of the sperm subpopulations were related (P < 0.05) to fertility (sP2, r = 0.54; sP3, r = 0.45; sP4, r = 0.56). In conclusion, we were able to relate the fertility of donkeys with in vitro measures of sperm motility using computer-assisted sperm analysis techniques.