Heifer-Sexed Semen in AI
In recent years, heifer-sexed semen has become more available. Is this too good to be true? Well, it’s real, but there are some things to consider:
1) The current pregnancy rate with sexed semen is slightly lower (around 50-55%, compared with 60-65% for conventional semen)
2) Sexed semen is more expensive to produce & therefore purchase (up to 3 times the cost)
3) The guarantee of a heifer calf is 90-98% (an occasional calf will be the other sex)
To know more about AI, see the AI article on our website
How to make sexed semen work for you:
* Only use cows with proven fertility (not the female who you have had trouble getting in calf in the past), or heifers
* Make sure lactating cows are at least 50 days post calving, and indeed have started cycling again
* Watch their body condition – not too skinny & certainly not too fat
* Only AI those females that have had an observable standing heat &/or their heat detector has obviously indicated standing heat (whether you use natural cycles or a syncronisation program). Good monitoring for standing heat & heat detectors are essential.
* AI 18-24 hours after first sign of standing heat (not 12 hours as with conventional semen). This is more significant in cows, compared with heifers.
* If using fixed-time AI programs, only inseminate those who have shown signs of standing heat (seen standing &/or heat detectors have gone off).
What is the science behind heifer-sexed semen?
It is basically conventional semen that has been “sorted” into sperm with an X-chromosome only. This is done with various methods, and this technology has hanged over the last 30 years to a point now where some companies are now giving a 96-97% guarantee of heifers. Considering we started at 70% 30 years ago, this is significant. Most companies only quote 90% heifer calves however.
This process of “sorting” the sperm does have a very slight affect on their quality, and hence the slightly reduced conception rate. The optimal number of sperm in a sexed straw is 2-4 million (compared with 15-20 million in conventional semen), but interestingly, research has failed to show any significant improvement in conception by increasing the number of sperm per straw. On some farms, where they have been using heifer-sexed straws for a while, and take into account the above mentioned precautions, pregnancy rates approaching the conventional semen pregnancy rates are achieved (60-65%).
When sexed semen is used in an embryo transfer program, similar results are found, but the same precautions prevail. You get the same heifer guarantee, and a slightly reduced number of usable embryos. See the ET article on our website
Because of the significant cost of the set-up for the machinery that produces sexed semen, only some collection centres can produce this product. Sadly, in Australia, the only facility that can do this will not take horned bulls, so currently, the only sexed Highland semen is coming in from Scotland & the USA.
