69 AN EASY-TO-PERFORM METHOD TO ASSESS VIABILITY OF FELINE FREEZE-DRIED SPERM

Abstract

Freeze-drying sperm seems to be the ultimate alternative to preserve sperm cells from endangered species because of its easiness in transportation and storage of samples. This technique has already been used for equine, bovine, murine, rabbit, canine, and feline sperm cells. However, it is still important to verify the DNA integrity of such samples to produce viable offspring. The objective of this study was to verify the reliability of acridine orange (AO) staining to assess DNA damage of feline freeze-dried sperm samples. Three normospermic cats were used as sperm donors, and sperm samples were collected with the use of an artificial vagina without the presence of an oestrous queen. The control group (G1) used only fresh semen. To increase the range of sperm variability before freeze-drying, the sperm samples were supplemented with 2 extenders, namely SOF (G2) and human tubal fluid (G3). These extenders were selected because of their lack of cryoprotectant agents with a view to producing membrane damage and thus putting DNA integrity at risk. Samples were taken to a freeze-dryer (Edwards do Brasil, Brazil) to produce stable free-dried sperm. Over 50 samples were assessed for DNA damage by using AO and alkaline comet assay (CA). Acridine orange taints red/orange the sperm cells that present sperm damage, and CA shows long comet tails for cells with DNA damage. The CA was selected to countercheck the AO results owing to its higher accuracy. Nevertheless, both AO and CA count 100 cells per analysis, and a total of 3 repetitions per sample were sufficient. For the statistical analysis, SAS PROC GLM was used, and the significance level was set at 0.05. The AO staining showed that the G1 samples had a greater DNA damage (27.1%) if compared with G2 (15.2%) and G3 (23.1%; P < 0.0001). Nevertheless, G2 and G3 displayed sufficient DNA integrity throughout the whole lyophilization process. The CA, which is a more precise evaluation technique, proved that the groups had distinguished results but still were ordered in the same way: G1 was the one with more DNA damage (17.7%), G3 was second (14.4%), and G2 was third (3.2%) in DNA alterations. Just like AO, the CA showed difference among treatments (P < 0.0001). Since AO is a technique that requires very little sophistication and presented about the same results as the very elaborate CA method, it might be used on a daily basis to assess feline sperm DNA that underwent the freeze-drying process.