Lag effect of microclimatic conditions on DNA integrity of frozen-thawed bovine sperm

The objective of this study was to investigate the effect of microclimatic conditions on DNA integrity of bovine sperm. DNA fragmentation of frozen-thawed sperm was analyzed in monthly semen samples of nine AI bulls ejaculating in weekly routine for one year. The extent of DNA fragmentation was determined using the Sperm Chromatin Structure Assay (SCSA™) and quantified by the DNA fragmentation index (DFI) and the percentage of sperm showing high DFI values (%DFI) immediately (0 h) and 3 h (3 h) after thawing. Microclimatic factors (ambient air temperature, relative humidity, dew point) were recorded in hourly intervals throughout the year. Their mean values were calculated for seven different time periods (up to day 56) preceding ejaculation (day 0). DFI (P < 0.01) and its relative change between 0 h and 3 h (P < 0.05) were related to the set of microclimatic parameters recorded the last 11 days and from day 49 to 43 prior to ejaculation, respectively. A significant relationship was detected between %DFI and microclimatic parameters of days 35-29 preceding ejaculation (P < 0.05), while the degree of change of %DFI from 0 h to 3 h was related to microclimatic parameters recorded from day 28 to 22 before ejaculation (P < 0.05). Dew point and relative humidity appeared to be the strongest and weakest predictors of DNA integrity, respectively. In conclusion, the results of the present study showed a lag effect of microclimate on DNA integrity of frozen-thawed bovine sperm. However, microclimatic parameters of a single time period before ejaculation could not be identified as the source of variation of different SCSA parameters.