The study was undertaken in order to evaluate sperm morphology features of post-thawed semen of Tunisian Arab stallions. Forty two ejaculates was collected and frozen, during years 2009 and 2010, from 9 stallions aged between 9 to 24 years. After thawing, sperm morphology was studied after eosin-nigrosin stain. The percentages of abnormal head, mid piece, flagella, sperm with droplets and the total abnormal sperm were determined. Analysis of variance was carried out using SAS software. The results showed that all sperm morphology features varied among ejaculates within stallion and among stallions (p<0.01). The percentage of abnormal flagella and total abnormal sperm varied between young and old stallions (p<0.01). We concluded that freezing and thawing processes increased abnormal sperm that is due to cell alteration for old and young stallions, and consequently, the decrease of the quality of the thawed semen of Tunisian Arab stallions.

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| The aim of the current study was to determine the influence of steps involved in the freezing-thawing protocol on semen quality of Arab stallions. A total of 48 ejaculates were collected (step 1) and undergone the first dilution in INRA96 ® at +37°C, followed by incubation at +22°C (step 2). A second dilution with INRA Freeze ® was carried out after centrifugation and supernatant removal (step 3). The diluted semen was kept at +4°C, then packaged in straws of 0.5 ml (step 4) and frozen into liquid nitrogen at -196°C. After 48 hours of storage, the semen was thawed (step 5). The percentages of motile sperm (%MS), abnormal head (%AH), mid-piece (%AM), flagella (%AF), cytoplasmic droplets (%CD) and abnormal sperm (%TAS) were studied at each step. Results showed that the %MS and %TAS were higher in steps 1, 2, 3 and 4 as compared to those of step 5 (p<0.05). The %AM was higher in step 5 as compared to that of the other steps (p<0.1). However, the %CD and %AF were higher respectively in the step 3 (p<0.01) and step 4 (p<0.05) than those of the other steps. Consequently, the semen quality of Arab stallions was affected during the freezing-thawing protocol. So, it is recommended to study the contribution of molecules in extenders such as vitamin C or glutamine to improve sperm motility and avoid increasing abnormal sperm during the freezing-thawing protocol.

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