Current Progressive Dairy digital edition
Advertisement

0808 PD: How to use sexed semen in dairy cattle breeding

David Wilson Published on 19 May 2008

Sexed semen, also called Gender Enhanced Semen (GES) has been commercially available in the U.S. dairy industry for approximately one year.

This technology is being used on a limited basis, and there seems to be considerable interest in this new tool on dairy farms. Information regarding some of the questions, and as much as they are currently available, the answers regarding this emerging technology, is presented below.

advertisement

advertisement

How well does sexed semen sorting work?
After decades of research and application, flow cytometry used to sort sperm cells in single file has emerged as the dominant technology. Because X chromosome-bearing sperm have approximately 3.9 percent more DNA than Y-bearing sperm, a fluorescent dye that binds to DNA is used to measure sperm cells’ DNA content. When individual sperm cells are exposed to laser light, those with higher fluorescence are identified as those that will produce females. The sperm are passed in a specific alignment through a flow cytometer machine at 3,000 to 5,000 sperm per second, making this a time- consuming and expensive process.

Several early published reports stated that sperm are separated with 85 to 90 percent accuracy. However, at least one commercial supplier of GES guarantees that at least 90 percent female calves will be born. As data is becoming available, it appears to be accepted that 90 percent accuracy in sexing semen is being achieved.

What is the effect of sexed semen on fertility?
There is some potential for confusion regarding this question. Many publications state that fertility with GES is reduced by approximately 30 percent, but others say approximately 10 to 20 percent. Nevertheless, they usually mean the same thing; it depends on whether one describes the percentage of “normal” fertility with unsexed semen or the percentage of all breedings. Talking with Roy Wilson, the Technology Development Manager of Genex, Inc., he stated some typical examples of this.

If conception rate at first breeding of virgin heifers in a given herd is normally 70 percent, the expected conception rate with GES is 50 to 55 percent; if normal conception rate is 60 percent, one would expect 40 to 45 percent with sexed semen. Thus, the difference between these rates is 15 to 20 percent, but if one considers it a percentage from either 70 or 60 percent, respectively, it becomes more like 30 percent. So the difference in conception percentage across all breedings is typically a 15 to 20 percent decrease with GES.

Roy also mentioned that although GES breeding is not currently recommended for older cows that have had at least one calf (this will be addressed later), research by he and others suggest that this drop in conception percentage is similar in older cows as well as heifers.

advertisement

Understandably, the fact that approximately two million sperm are contained in sexed semen straws versus 15 to 20 million sperm in conventional straws is often reported to be a major cause of infertility. I asked Roy about this. He said that commercial costs and semen availability dictate the reduced sperm per straw under current conditions. However, research has shown that if 20 million sex-sorted sperm are loaded per straw, approximately half of the decreased fertility is still present.

For reasons not understood, sperm from sex-sorted semen conceive similar to other sperm, but more embryos die within the first seven days following conception. He also said that from his research experience he does not think this is from physical damage from the sorting; something else such as possibly the DNA-binding dye is damaging some sperm cells.

What is the cost difference for GES?
Of course the answer varies with commercial suppliers and particular bulls. Roy said that typically sexed semen costs $32 to $50 per unit, while conventional semen costs $9 per unit. He usually thinks of it as $20 to $25 more per unit, costing two to four times as much as conventional semen. Judging by some publications over the last year, it appears that the cost difference may be narrowing, as often happens when new technology is adapted commercially.

Is sexed semen use recommended only for first breeding of virgin heifers?
This does appear to be the standard recommendation. Roy said that from his experience, all farms will see decreased conception with use of sexed semen, and it is similar in older cows to heifers, again a 15 to 20 percent difference in conception rates as described above. He mentioned that four major stud bulls have this exact recommendations on GES use:

“First service of virgin heifers observed in standing heat.”

Many farms nevertheless use GES on the second service of virgin heifers observed in standing heat.

advertisement

For any synchronized, timed breedings, the use of GES is not recommended. If producers want to use it this way, Roy tells them they must observe standing heat, but this method is still not recommended.

What about the use of sexed semen on highly valued cows to get more heifer calves to sell?
Of course, this is a complicated financial decision based on demand for calves from individual cows. Roy has consulted with some herds using GES to breed cows that are superovulated and flushed to harvest high-priced embryos, hoping to get more female calves. He said that this has been “hit or miss,” not overly successful.

I could find no refereed published information on whether superovulated embryos conceived using sex-sorted sperm are more prone to embryonic loss. The use of sexed semen on genetically valued animals where more calves of one sex or the other are wanted seems like a logical practice in the future.

Does GES affect dystocia or stillbirth rate?
It has been speculated that this technology resulting in 90 percent heifer calves born will reduce dystocia because female calves are smaller. I think Roy is correct; as time passes and we get more data, this picture should become clearer.There is no refereed publication on this subject.

It has been speculated that there may be more stillbirths resulting from sexed semen. Roy said that he has followed the studies on this subject, and there is no demonstrated increase in stillbirths. Again, I found no refereed publications addressing this.

Right now there is no definitive answer to the above two questions, but so far there is no evidence for concern.

What percentage of breedings in the dairy industry now use sexed semen?
Roy’s data suggests that 5 percent of all U.S. dairy heifer A.I. breedings now use sexed semen.

Is use of GES profitable?
Because of the high cost and reduced fertility of GES, this is a pertinent question. An article in The Bovine Practitioner 41:2, Summer 2007, “Sexed Semen: Economics of a New Technology” by Dr’s. John Fetrow, Mike Overton and Steve Eicker, examines this complicated question. I like one model in this paper that shows breeding with sexed semen only at the first observed standing heat in virgin heifers, their conception rates being 60 percent with conventional versus 45 percent with sexed semen, a $30 per unit price increase for GES and springing heifers worth $1,800. There is a loss of $9 per heifer with GES. However, as the authors point out, if the differential in semen price and the decrease in conception rates can be improved, this could become a profitable technology.

The authors also touch on, but do not put into their models, another important point that others have also mentioned about sexed semen. If a dairy farm is in expansion mode, and has the facilities to handle the increased cow numbers, sexed semen resulting in more heifer calves being born could allow herd growth with more options for culling older cows and reduce or avoid the need to purchase replacements from outside the herd.

From my experience, the benefits of more culling options together with avoiding the biosecurity danger of purchasing outside animals, even springing heifers, could be tremendous. Increased control of financially devastating diseases is more likely with the above benefits.

The future
It seems quite clear that the biotechnology of selecting semen likely to produce offspring of one sex or the other works. Just as well with the adoption of so many other technologies and practices, the increased cost and infertility associated with this resource may be reduced in the future.

As long as our industry does not really need approximately 50 percent bulls, and has comparatively more demand for cows, the application of this emerging technology is likely to have a place in the dairy industry. It appears that it already does for herds wishing to expand or to have more options for culling older cows. PD

—Excerpts from Utah State University Dairy Newsletter, Vol. 30, No. 7

David Wilson
Extension Veterinarian
Utah State University

LATEST BLOG

LATEST NEWS