Seasonal variation in nuclear DNA integrity of frozen-thawed spermatozoa from Thai AI swamp buffaloes (Bubalus bubalis)

• In this study, we investigated the susceptibility of frozen-thawed swamp buffalo sperm nuclear DNA to undergo controlled acid-induced denaturation in situ, as analysed by flow cytometry, and aimed to correlate the results with sperm head morphology over three seasons in tropical Thailand. Artificial insemination (AI) doses (n = 218) from 18 AI buffalo sires, prepared between 1980 and 1989 and 2003 and 2005, were tested and compared among three seasons, the rainy season, July-October; winter, November-February; and summer , March-June. The overall mean of DNA fragmentation index (DFI) (+/- SD) was 1.84 +/- 1.68%, range from 0.19 to 7.92%, with 0.221 +/- 0.021 of the x-DFI ranging from 0.190 to 0.350 and 0.023 +/- 0.009 of the SD-DFI ranging from 0.010 to 0.070. The DFI was consistently low (range 1.40 +/- 0.21% to 2.16 +/- 0.21%; LSM +/- SEM), with x-DFI ranging from 0.216 +/- 0.003 to 0.225 +/- 0.003 and SD-DFI ranging from 0.022 +/- 0.001 to 0.024 +/- 0.001 across the seasons. The DFI was low enough to be related to high fertility potential. However, DFI values varied statistically among seasons, being lower in the rainy season (1.40 +/- 0.21%, P less than 0.05) than in winter (2.16 +/- 0.21%) or summer (2.00 +/- 0.20%), and were also affected by the year of semen collection and processing (P less than 0.001). The proportion of morphologically abnormal sperm head shapes was low, with no significant differences between seasons. However, DFI was significantly related to the proportion of loose abnormal sperm heads (r = 0.27, P less than 0.01). In conclusion, frozen-thawed swamp buffalo sperm chromatin integrity is not seriously damaged by cryo-preservation or affected by the seasonal variations in temperature and humidity seen in tropical Thailand.

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TECHNOLOGY

TEKNIKVETENSKAP

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