Quantification of the DNA difference, and separation of X- and Y-bearing sperm in alpacas (Vicugna pacos)

Sperm sexing is an emerging reproductive technology which has been successfully used to produce offspring of a pre-determined sex in domestic and wildlife species but has yet to be applied to New World camelids. The aims of the present study were to (i) optimize the Hoescht 33342 (H33342) staining concentration for the flow cytometric separation of X and Y chromosome-bearing alpaca (Vicugna pacos) sperm nuclei, (ii) separate alpaca sperm nuclei into high purity (>90%) populations bearing the X- and Y-chromosome and (iii) determine the DNA difference between X- and Y-bearing sperm in alpacas. Semen was collected from alpacas and sperm nuclei stained with H33342, incubated and analysed using a high-speed cell sorter (SX-MoFlo). H33342 staining concentrations of 36, 54, 72 or 90 microm did not affect the proportion of correctly oriented sperm nuclei (43.3 +/- 3.9, 46.4 +/- 3.7, 44.5 +/- 4.0 and 51.1 +/- 2.5% respectively) nor the speed of sorting (1381 +/- 160, 1386 +/- 123, 1371 +/- 133 and 1379 +/- 127 sperm nuclei/s). Sort reanalysis determined high levels of purity for X- and Y-enriched populations (96.6 +/- 0.7% and 96.1 +/- 1.1% respectively). The DNA difference, based on fluorescence intensity (determined by the SX-MoFlo), was 3.8 +/- 0.06%. These data demonstrate for the first time that alpaca sperm nuclei can be separated into high purity populations and the potential for applying sperm sexing technology to New World camelids.