Choice of staining technique affects the morphological assessment of epididymal feline sperm

Morphological examination of spermatozoa remains a valuable tool for determining the quality of feline sperm for cryopreservation and/or for use in artificial insemination. Numerous staining techniques have been employed for feline sperm assessment, and several variations have also been reported. Forty-eight domestic cats were castrated and epididymal sperm samples were obtained. Sperm morphology was assessed using two staining methods, an air-dried stain (Giemsa-Wright) and a wet stain (eosin-nigrosin), to determine their relative abilities for estimation of the proportion of normal and abnormal spermatozoa. The effects of centrifugation and the cooling process on sperm morphology were also analysed. The mean percentage of morphologically normal spermatozoa was significantly lower in eosin-nigrosin-stained samples than in Giemsa-Wright-stained preparations (46.5% vs 53.4%; P < 0.01), both examined by conventional light microscopy. Results concerning head, midpiece and tail sperm abnormalities suggest that these methods differ in their capacity to identify sperm anomalies in cat. Although no significant differences were observed for secondary abnormalities, cytoplasmic droplets were significantly lower in Giemsa-Wright-stained samples (P < 0.01). Centrifugation or refrigeration of sperm samples did not affect the epididymal sperm morphology in evaluated samples. This study highlights the necessity of minimising morphological assessment variations in order to eliminate subsequent errors and to improve the reproducibility of sperm morphology assessment in different laboratories.