Influence of season on testicular morphometry and semen characteristics in Martina Franca jackasses

As other European donkey breeds, Martina Franca could be considered an endangered breed because of the population number (48 jackasses and 515 jennies in 2011). To increase donkey population and breed biodiversity preservation, several research projects on donkey reproduction have been performed; however reproductive seasonality has been only partially investigated in jackasses. For this reason the aim of this study was to investigate the effect of seasons and of long (spring to summer; SS) and short (autumn to winter; AW) day length periods, on reproductive physiology of Martina Franca jackasses, in particular on: (1) testicular morphometric characteristics, (2) behavior, through the evaluation of the reaction time, and finally, (3) semen characteristics. Seven adult and reproductively mature Martina Franca jackasses were enrolled. For each jackass, a morphometric evaluation of both testes was performed once for every season, before the first seasonal collection. Semen was collected, by artificial vagina, weekly for a whole year (52 collections per donkey); at each collection the reaction time was recorded and a complete semen evaluation was performed immediately after collection. No differences in testicular measures were observed neither between left and right testis nor during the four seasons. A lower reaction time was observed in spring and summer compared with autumn and winter and during the period SS compared with AW. Total volume was significantly higher in winter compared with all the other seasons; gel-free volume was higher in winter compared with summer and autumn. Mean sperm concentration was significantly lower in winter compared with spring and summer and in AW compared with SS. Total and progressive motility and membrane integrity did not show any significant difference between season and between SS and AW. A lower average path velocity was observed in autumn compared with spring and summer, and in summer a higher straight line velocity compared with spring and autumn, and a lower curvilinear velocity compared with winter were found. No differences in amplitude of lateral head displacement, beat cross frequency, straightness and linearity were observed neither between seasons nor in SS versus AW. Seminal pH did not show any seasonal difference; also sperm morphology did not show any significant difference during the whole year. This study demonstrated that under our climatic and management conditions Martina Franca donkey stallions do not show significant differences in testicular morphometric characteristics during the year, even if a certain seasonal influence exists on reaction time and some seminal parameters. Considering the variable temperature and photoperiod during the four seasons where the study was performed, this lack of substantial differences could be related to a characteristic of the Martina Franca breed.