Difference in volume of X- and Y-chromosome-bearing bovine sperm heads matches difference in DNA content

BACKGROUND: To investigate the possibilities of sperm head volume as a sorting criterion for gender preselection, we determined the magnitude of the difference in volume of X- and Y-chromosome-bearing bull sperm heads. MATERIALS AND METHODS: Bovine sperm heads were sorted on the basis of their DNA content in X- and Y-chromosome-bearing fractions, using an existing flow-cytometric technique. Images of sperm heads of both populations were recorded using Differential Interference Contrast (DIC) microscopy. After reconstructing the DIC images, the area and the optical thickness of sperm heads of both populations were determined. RESULTS: We found a difference in volume of X- and Y-bearing bovine sperm heads matching the difference in DNA content (3.5-4%). CONCLUSIONS: Our findings indicate that volume can be used as a criterion to distinguish X- and Y-chromosome-bearing sperm, making development of a technique to sort X- and Y-chromosome-bearing sperm based on head volume theoretically possible. A strong advantage of such a technique over the existing technique based on DNA content would be that X- and Y-chromosome-bearing sperm cells could thus be sorted without subjecting them to any staining