Sperm was first discovered in 1678, although the scientist who first saw it under a microscope thought it was a parasite! It took a further 100 years of research to work out that sperm were actually the agents of fertilisation, and another 100 years to clearly understand the detailed events that are necessary for fertilisation.
In 400BC, before they even knew about sperm, it was thought that the right testicle produced male offspring and that the left produced females so by tying up the left testicle, you were guaranteed a boy! Sexed semen technologies have been around for over 30 years; it was first successfully carried out in rabbits in 1989. Flow cytometry is the technology that made sexed semen commercially available in cattle and is still in use today. Because the X chromosome (female) is bigger than the Y chromosome (male), it takes up more of the fluorescent dye. This then enables the sperm to have a different electric charge applied according to how much they show up the dye. X sperm have a positive charge and are pulled in one direction when an electric charge is applied; the male Y sperm are pulled in the opposite direction and they are sorted into separate collection tubes.
This process damages the sperm to some degree so, on average, pregnancy rates are around 25% lower than conventional semen. This is why we generally recommend using it on maiden heifers as they have better fertility than cows. This damage is not compensated for by increasing the number of sperm in the straw. SexcelTM is a new sexing technique that has been launched recently. It still uses flow cytometry but instead of applying an electric charge, the Y sperm are disabled using a laser. This technique should be less damaging to the female sperm as everything ends up in the same collection tube. Initial results from the USA look good but it will be nice to see data from the UK as that starts to come in.
Benefits Of Using Sexed Semen In The Dairy Herd
- Helps to expand the herd without the need for buying in.
- Fewer ‘low value’ bull calves produced – also reduces society’s concerns over bull calves being a ‘waste product’.
- Reduced risk of dystocia (difficult calving) which leads to reduced risk of retained placenta and uterine infection.
- Increased rate of genetic gain when used on maiden heifers (particularly if combined with genomic testing)
- Increased milk – heifers that give birth to heifers at their first calving give +445kg milk in their first lactation compared to those that have bull calves.