A comparative study of two methods to determine acrosome integrity of frozen-thawed boar sperm: FITC-PNA/EthD-1 versus Coomassie blue staining

Abstract

Coomassie blue staining has been reported as an effective and inexpensive method for evaluating the acrosome integrity of spermatozoa, though to date its use to evaluate cryopreserved boar sperm has not been reported. Moreover, there is no information concerning the agreement between Coomassie blue staining and fluorescein isothiocyanate conjugated peanut agglutinin and ethidium homodimer (FITC-PNA/EthD-1) methods for assessing sperm acrosome integrity for any species. The current study was performed to determine the efficacy and agreement between Coomassie blue and FITC-PNA/EthD-1 staining methods for evaluating the acrosome integrity of frozen-thawed boar sperm. A total of 25 semen samples were cryopreserved using lactose-egg yolk-based extender and loaded into 0.5 PVC-French straws. Sperm motility and motion characteristics were determined using a computer-assisted sperm analysis system. Sperm viability and plasma membrane integrity were evaluated using the SYBR-14/EthD-1 and hypo-osmotic swelling test, respectively. Acrosome integrity of frozen-thawed boar sperm was evaluated using both FITC-PNA/EthD-1 and Coomassie blue staining to assess the association between sperm acrosome integrity and agreement between these two methods. The average percent acrosome integrity of frozen-thawed boar sperm as determined by FITC-PNA/ EthD-1 and Coomassie blue staining was 48.8 ± 12.6% and 52.6 ± 13.6%, respectively (P>0.05). Interestingly, Coomassie blue staining found a correlation between sperm viability and acrosome integrity (r=0.609, P=0.002), while FITC-PNA/EthD-1 staining did not (P>0.05). However, the acrosome integrity of frozen-thawed boar sperm evaluated by FITC-PNA/ EthD-1 and Coomassie blue staining was significantly correlated (r=0.448, P=0.025, n=25). The Bland-Altman plot determined that this agreement was acceptable. In conclusion, the acrosome integrity of the frozen-thawed boar sperm assessed via Coomassie blue staining was significantly correlated with that obtained via the FITC-PNA/EthD-1 staining method, and the two methods showed good agreement. Moreover, the significant association between the acrosome integrity of frozen-thawed boar sperm determined by Coomassie blue staining with other sperm quality parameters indicates that this is an effective method for assessing the acrosome integrity of frozen-thawed sperm in pigs.