In mammals the only method known to reliably separate X and Y sperm for producing offspring of a specific sex is flow cytometric sorting. This method is based on the observation that X-chromosome bearing sperm of domestic animals contain 3.5-4.2% more DNA than Y-chromosome bearing sperm. Relative DNA content is determined by quantitative staining with Hoechst 33342 and DNA content measured using a modified cell sorter. The major constraint to widespread application of this technology has been the slow sorting rate. Using modified standard speed cell sorters, sample flow rates average 2,000 sperm/sec with 25-35% orientation. Recently, a high speed sorter (MoFlo®) modified for sperm sorting has been used and increases sorting rate by approximately 5-fold. Further, an orienting nozzle has been developed which increases the percentage of sperm that are orientated thus increasing the sort rate by a further 2 to 3-fold. Combined, these improvements have increased the production of sorted sperm from approximately 0.3 x 106/h with conventional sorters to at least 4 x 106/h with the high speed sorter. Preliminary testing suggests that purity of sort and sperm viability are not compromised by increased sorting rates. Pregnancies have been established in pigs and cows with sorted sperm from a modified MoFlo fitted with a novel nozzle. The improvements outlined here greatly enhance the Beltsville Sperm Sexing Technology and make it realistic to consider trials using sex sorted sperm for conventional AI as well as deep uterine AI in cattle.
Proceedings of the New Zealand Society of Animal Production, Volume 58, , 16-18, 1998
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