Seminal parameters and field fertility of cryopreserved donkey jack semen after insemination of horse mares

Abstract

Reasons for performing study: As mule production is often concentrated in remote areas of the world, a simplified semen cryopreservation protocol is required.

Aim: To compare the seminal parameters of cryopreserved donkey semen in lactose-EDTA and lactose-yolk extenders and the fertility rates on horse mares.

Methods: TRIAL 1: Sperm total and progressive motility, vigour (scale 0-5), morphology (major and minor defects) and plasma membrane integrity (HOST) were evaluated in 25 ejaculates from 5 donkey jacks immediately after collection (raw), after chilling to 5°C (chilled) and after freezing/thawing. The semen was mixed with skimmed-milk extender, centrifuged, and then re-suspended in lactose-EDTA or lactose-yolk extender. Semen was loaded into 0.5 ml straws and chilled to 5°C for 1 h, after which samples were either evaluated (chilled semen) or placed above liquid nitrogen for 20 min prior to immersion. Seminal parameters were evaluated by ANOVA and Tukey's test. TRIAL 2: Cryopreserved semen from 3 males was used to inseminate 53 mares at 60 oestrous cycles randomly assigned to lactose-yolk (n = 30 cycles) or lactose-EDTA (n = 30 cycles) extenders. Pregnancy diagnosis was performed 15 and 25 days post ovulation. The pregnancy rates were compared using Chi-squared tests.

Results: TRIAL 1: No significant differences were evident in any seminal parameters between extenders after either chilling or cryopreservation. Total and progressive motility were significantly (P<0.05) lower in cryopreserved semen than raw and chilled semen for both extenders. TRIAL 2: Pregnancy rates did not significantly differ between extenders (lactose-EDTA extender 53.33 and 43.33%; lactose-yolk 50.0 and 46.66% for Days 15 and 25 post ovulation, respectively).

Conclusions: Cryopreservation of donkey semen using the simplified lactose-yolk extender resulted in similar seminal parameters and fertility rates when compared to lactose-EDTA extender.

Potential relevance: Lactose-yolk extender may be advocated as a simple, easy to prepare extender, for use in geographically isolated enterprises producing mules throughout the world.