Posted on Wednesday, February 19, 2003 - 06:55 pm:
I have acquired more than 30 straws of frozen semen on a stallion that has a 25 to 30% post thaw motility. No mares were ever bred with his frozen semen, so no first cycle pregnancy data is available. My arrangement requires no up front costs for me, but a registration fee paid to the stallion owner when and if I am able to get foals. I am working with a national frozen semen firm and practitioner who has lots of experience with frozen semen, but am I wasting my time on this semen at 25 to 30 % post thaw motility?
Posted on Friday, March 14, 2003 - 12:12 am:
I have been told that when using frozen semen you only end up with about 30%. This has me a bit botherd especialy after reading your post. We have our stud at a semen center right now to see if he will freeze. The first try at thawing did not work. They colected him again and will try thawing tomorrow. It would sure be nice to hear from Jos on this subject or anyone else that has knowledge. I would also like to know if I am wasting my time by trying more times. I understand that different extenders can be used and that may help but is it really wise to do this after it did not work the first time.
Posted on Friday, March 14, 2003 - 12:33 am:
30% progressive motility post-thaw is generally considered to be the lowest level aceptable for public release of frozen semen. This may sound low, but there are several factors that must be considered:
First: The important figure is the number of sperm inseminated that are capable of fertilization. The lowest desirable number is generally considered to be 100 million, and generally close to 200 million are used by us if possible. As the 5-ml straws are commonly packed with 600 million sperm, this means that 30% = 180 million motile, which is acceptable. The 0.5-ml straws are commonly packed with 200 million sperm, with the intention that more than one straw be used for an insemination dose. Hence with that size straw, at 30%, 3 straws would give you the same number of motile sperm.
Next: There is not a reliable correlation between motility and fertility with thawed frozen semen! One can have highly motile sperm that will not get anything pregnant, and conversely, poor motility that will give acceptable pregnancy percentages.
Finally: There is tremendous stallion variability, as well as technician ability (at both the freezing and thawing ends of things), and both those factors need to be considered. 30% for one stallion may yield excellent pregnancy rates, while 60% for another yields low or zero pregnancy rates.
You need to ask questions, and the questions to ask are: "What is the first-cycle pregnancy rate for this stallion's semen"? and "How many mares were used to make up this statistical analysis". The desirable rates should ideally be in excess of 50% for frozen semen, and there should be sufficient mares to make the statistic realistic. If this rate seems low, remember that it will also include mares that were not suitable, shipments that were mishandled etc.
So - the thing you both need to do, is: Try the semen! That will tell you the most!
Posted on Friday, March 14, 2003 - 01:06 am:
Thanks for your reply Jos I just read your article on freezing semen and it was very helpful. I would like to know if trying the freezing again and again with our stallion is the way that it is normaly done. The thawing did not work the first time so we have no semen to try on a mare. How many different attemps are normaly done before a stallion is considerd no good for freezing? And what would they do diferent that could give us better results? Our stud has a good breeding record on live cover but has never been collected before.
Posted on Thursday, March 20, 2003 - 10:55 am:
There are generally a couple of ways used to try to determine semen freezing ability with a stallion. One is to use a variety of extenders the first time and see which is the best, the other is to keep freezing until one finds success. How many times? Well, I guess that depends upon how much money you want to sink into it!
Different things to try include different extenders; different freeze rates (freezing curves); pre-cooling or not; different straw sizes; different packing concentrations; etc. As you can see there are many variables to try.
It is important to be aware that there is no correlation between a stallion who has good fertility rates with live cover or cooled semen and the ability to freeze well, so that is not a measure that can be used.
Posted on Tuesday, March 25, 2003 - 08:16 am:
Update We were able to get semen froze on our stud. The people said that it is common that it does not freeze/thaw well the first time or two if they have not been "used" for some time. That was something that I did not know but I guess that it makes sense.
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