Relationship among seminal characteristics, fertility and suitability for semen preservation in draft stallions

Seminal characteristics, fertility and the response to semen preservation (liquid storage and cryopreservation) were evaluated in 4 Draft stallions (Percheron 2, Breton 2). Seminal characteristics (gel-free volume, sperm concentration, sperm morphology, percentage of motile spermatozoa) were assessed in 5 ejaculates from each of the 4 stallions. The fertility of the stallions was calculated retrospectively as the accumulated pregnancy rate over 3 breeding seasons. Five ejaculates from each of the stallions were subjected to liquid storage at 5 degrees C. The percentage of motile spermatozoa (PMS) was assessed at 0, 24, 48 and 72 hr. Cryopreservation was done with a glucose-EDTA-lactose egg yolk extender and a skim milk-based extender containing clarified egg yolk (4 replicates per stallion). PMS and the percentage of spermatozoa with an intact plasma membrane (IPM) were evaluated before and after freezing. Although semen characteristics and fertility were within a physiological range, significant differences among stallions were found for gel-free volume, percentage of morphologically normal spermatozoa, PMS, and fertility but there was no clear relationship between these parameters. The response to liquid storage of diluted semen samples differed among stallions and best results were obtained in a stallion with the highest initial motility. The freezability of semen from the 4 stallions was poor with both of the freezing protocols (PMS range 13.8%-26.3%; IPM range 19.5%-38.0%). Results of liquid storage and cryopreservation were not correlated in individual stallions and were not related to their fertility. Since predictability for the response to semen preservation is low, the suitability of individual stallions for semen preservation has to be examined carefully.(ABSTRACT TRUNCATED AT 250 WORDS)