4M™: Gender Purity you can Trust!

In a recent study, STgenetics® proved their commitment to gender purity in their sex-sorted product (Evans et al., 2019). After analyzing 9,447 calvings between 2016 and 2018, STgenetics concluded that their sex-sorted semen with a reported female purity of 91% in the lab resulted in a female calf crop of 90.3% in the field. STgenetics understands the substantial value of calving a heifer out of a quality sex-sorted product which is why they continue to design and implement new techniques and technologies in their labs to maintain a consistent gender purity in their SexedULTRA4MTM product.   

How are sperm sorted?

To briefly review the biology of sperm production, sperm cells are created by the process of meiosis in which a cell containing all the chromosomes of an animal gets divided into 4 cells that each contain half of the chromosomes of the original cell. These cells are called gametes, eggs in females and sperm in males. In bovine, each cell normally contains 30 pairs of chromosomes for a total of 60 chromosomes with a breakdown of 29 autosomes and one pair of sex chromosomes. Females have two copies of the X chromosome, while males have one X and one Y chromosome. The graphic below shows the process of meiosis to produce sperm cells.

STgenetics has substantially advanced the science of sperm sorting in the past 5 years to improve efficiency, productivity, fertility, and gender purity. To understand these improvements, we first need to review how sperm are sorted. When a bull is collected, his semen is evaluated based on several quality control parameters. Next, a stain is introduced to the ejaculate which binds to the DNA content in each cell. When comparing all chromosomes, X chromosomes have the most DNA content while Y chromosomes have the least DNA content. The sorting technology is based on the typical content difference between X- and Y- chromosome-bearing sperm which in cattle is about 4%. Genesis™ Digital sperm sorting systems orient sperm in a single file and measure the fluorescence of each of the sperm cells to determine their DNA content when excited by a laser. A charge is then applied to each droplet that contains viable sperm based on their DNA content. These droplets are then deflected into tubes collecting X-bearing sperm, Y-bearing sperm, and undetermined, dead, or no sperm. Before this sorting process begins, each bull’s semen goes through a process of purity analysis.

How is gender purity analyzed?

         The Geneisis™ Digital sperm sorting systems are verified to confirm that the setup is accurate for the desired sex ratio in the lab by utilizing a Genesis I Analyzer™ (Figure 1) to evaluate gender purity before each ejaculate is sorted.

The Genesis I Analyzers™ are calibrated using certified nuclei as a standard to confirm the instrument is aligned and validated prior to purity analysis (Figure 2). Once calibrated, a sample of 3,000 to 5,000 cells is analyzed for gender purity. This calibration process is a standard procedure in all STgenetics labs to validate that the sperm sorters are operating properly, and that the final product meets our strict guidelines.

Several technological developments have contributed to increased accuracy in gender purity analysis. STgenetics has developed a proprietary method for the specific purpose of purity analysis which provides for better orientation of the sperm, so they can be identified properly as X or Y bearing sperm. This technology has helped to increase sorting accuracy across all breeds as each breed varies in the difference in DNA content of the X and Y chromosome. STgenetics has also designed an application specific software for sperm purity analysis, which allows for the clear visualization of sperm sub-populations as shown in Figure 3a, 3b, and 3c.

How does STgenetics verify that their product has the desired gender purity in the field?

STgenetics diligence in testing their product has proven a reliable formula for producing the desired heifer crop in the field. In order to verify gender purities in the field, the sex ratios of over 9,000 calvings from 7 STgenetics bulls were estimated. The semen originated from 400 individual freezes, for which lab purities were averaged by bull and compared to the female calf ratio in the field, as depicted in Figure 4. As the results indicate, the purity analysis in the lab, which averaged 91.1%, yielded on average a 90.3% heifer calf ratio in the field. The Institut de L'Elevage Idele, an organization appointed by the French ministry of agriculture as technical center for agriculture, reported similar findings using sex-sorted semen with a 91% female calf ratio in the field from 1,063,500 calvings between 2015 and 2019. These results demonstrate the accuracy of STgenetics’ procedures, which ensure a quality heifer crop from their SexedULTRA4M™ products.

Evans KM, Heuer C, González-Marín C, Vishwanath R. High resolution purity analysis of sex sorted sperm and the correlation to field results. J Dairy Sci 2019;102:29.