What is sexed semen?
Semen having X or Y bearing sperm to produce progenies of a desired sex either female or male (with about 80-90% accuracy) is known as sexed semen. Sex sorting technology was developed by the USDA (United States Department of Agriculture) researchers in Livermore, California, and Beltsville, Maryland. The technology was patented as “Beltsville Sperm sexing technology”. The commercialization of sexed semen started in United States in 2001 with a license granted to Sexing Technologies (ST), Texas. At present, ST commercially produces sex sorted semen in many countries of Europe, USA, Canada, Mexico, Brazil, China, Japan etc.
How Sexed Semen is produced?
Sperm are sorted by identifying differences between the X- and Y- bearing sperm. The X-chromosome (female) contains about 3.8% more DNA than the Y-chromosome (male) in cattle. This difference in DNA content is used to sort the X- from the Y- bearing sperm.
Among several methods for semen sexing, flow cytometry based sorting has emerged as most efficient. The technology is refined through the decades and finally sex sorting is possible at the purity of more than 90%. The technique is well standardized, patented and commercialized in USA, Europe and other countries.
Other methods for sex sorting of sperm (Albumin Gradient/ Percoll gradient/ Gradient swim down, Free flow electrophoresis, Identification of H-Y antigen, Centrifugal counter current distribution, Genetic approaches etc.) have also emerged though these techniques needs further fine tuning for commercial viability.
Figure 1: Schematic diagram of sex sorting using flow cytometry
Photo courtesy: Sexing Technologies, USA
Is it safe?
Yes, it is safe to use sexed semen for artificial insemination. However, as sperm concentration in sexed semen straw is far less than the conventional semen straw and the sorting procedure itself damages the sexed sperm, it is reported that the conception rate is 10 to 15 % less with sexed semen as compared to conventional semen.
What are the advantages of using sexed semen?
· Producing only female calves helps the farmers to save resources that would have been shared with unwanted males.
· Production of more female calves: increase supply of replacement heifers
· Opportunity to sell surplus heifers to other farmers/farms
· Speed up genetic improvement:
o By increasing efficiency of progeny testing (PT) programme
o By increasing efficiency of embryo transfer and IVF programme
· An economic way to increase herd strength with no risk of introducing diseases by purchasing heifers from outside (improves bio-security).
· As dead, dying or damaged sperm cells are removed during the sorting process, only viable sperm are available which helps the sexed semen to be successful even at a low concentration (than conventional semen).
· By producing more female calves using sexed semen, there will be less difficult births compared to male calves (dystocia). This is particularly useful for maiden heifers.
What are the limitations of using sexed semen?
There are some limitations in terms of technology and implementation aspects of the sexed sorted semen.
Technological limitations –
· High cost of sex sorting machine
· Low sorting efficiency and speed
· Require highly skilled person to operate sex sorting machines
· Damage to the sperm due to shear force, electrostatic charge, droplet formation and sudden stop.
· Waste of approximately 50% of sperm
· Reduced freezing potential of the sorted sperm
Implementation limitations –
· High cost of the product which include the cost of the intellectual property right (Rs. 1500-4500/- dose as compared to Rs. 15-20/- dose for conventional semen)
· The conception rate with sex sorted semen is 10-15% less than the conventional semen. This factor will be more critical in Indian condition considering low artificial insemination coverage (20-25%) and low conception rate with artificial insemination (25-35%).
· There is no standard operating procedure to perform insemination with sexed semen. This is another area of concern as the sperm concentration of sexed semen ranges between 2 and 4 million/dose whereas it is 20 million/dose in conventional semen. Managing lower sperm concentration will be a challenge in the field under Indian condition.
Is it available in India?
Currently no agency is producing sexed semen in India so it has to be imported. Many states/ agencies are using imported sexed semen.
Where can I buy and what is the price?
Sexed semen is not available with all Service Providers. Approvals from Central Government (DADF) and State Governments (State AH department) would be required to obtain import permit from Director General of Foreign Trade (DGFT). Keeping complete records of its use and progeny born out of imported semen is mandatory for all users. The sexed semen is commercially available mainly from Sexing Technology, USA. However many other breeding companies in USA, Canada and Europe are producing sexed semen commercially using licence from Sexing Technology, USA.
Price of the sexed semen varies between Rs 1500-4500/- depending upon the breed and pedigree of the bull used for producing the sexed semen and the quantum of purchase.
Is it only for HF or Jersey cattle?
Yes, presently it is commercially available only for HF and Jersey breeds of cattle. Sexed semen is not available for any other Indian breed of cattle and buffaloes.
Is sexed semen used only for heifer?
Considering the high fertility rate of the heifers, it is recommended that sexed semen should be used only in heifers (especially virgin heifers) for better conception rate. However, it can also be used in cows up to third lactation with excellent reproduction record.
Prepared by Dr Siddhartha Shankar Layek, Animal Breeding Group, NDDB, Anand