A few years ago my self and the veterinarian that I worked for, embarked on a small study. With the cooperation of a friend who has a compounding lab. To developed a pure progesterone implant that would give us a ~90 day duration. It was based on the Norplant idea that was used in women for a few years. Unlike the cattle implants that were used for a short time. This implant contained nothing but pure progesterone. Unfortunately the vet I worked for was not as dedicated to the project as I was, and we were unable to finish the project. However we did learn some things from it. 1: that it will work and maintain acceptable levels of >4.0 for 60 days. I felt that by increasing the concentration of the implants and still maintaining the small size so as to limit the sites needed. We could possibly achieve our goal 90 days duration at blood levels of >4.0. 2: we learned that the product released much more uniformly if implanted in the fatty tissue of the crest rather than in the muscle of the neck. In addition this resulted in fewer site reactions. Our intention was never to go into the business of manufacturing the product or marketing it per say. What we were going to do was after all our field trials, sell it and our field trial information to a manufacturer and let them work on the FDA approval and such. We never got to this point unfortunately, however I still think we were on the right track and this certainly needs more research. To see if it could be made to work reliably.
The cost we found would be about that of repository progesterone injections for the same period. The obvious gain is convenience, with the exception of the fact that progesterone blood levels could not be done as long as the implant was in place. As they can with withdrawal of repository progesterone injections or the use of Regu-Mate.
I just thought you might find this interesting and would like your thoughts on this.
Posted on Tuesday, January 09, 2001 - 05:58 am:
I am not aware of any long-term progesterone implant of the type you are describing, but Thorne BioScience have developed a time-release progesterone and estradiol combination that is in biodegradable microspheres. I believe it is still in the final USDA testing stages, pending final release under the name "Saber P+". This is aimed at giving a full course of progesterone and estradiol over a 12 to 14 day period (which will then be followed by PGF2a treatment and will result in a pinpointed estrus). I recognise that this is a far cry from your 90 days and is used for a different reason, but I thought you might still be interested.
Although the above drug (Saber P+) will have a use in horses, it's primary market is, I believe, the porcine industry - and here we come to a crux! There is really insufficent market impact (read "profit") for commercial development of a drug such as this in the equine world only - sadly.
Repositol progesterone (Depo-Provera) use has received mixed reviews concerning assisting in pregnancy maintenance, but then so has "Regumate". The eternal question being - if not supplemented, is the affected mare liable to abort because of low progesterone, or does she have low progesterone because she is aborting from some other cause? This has been the eternal problem in attempting to develop a "control group" for researching this.
Your information is very interesting though. If anyone knows more, I will be interested to hear.
Jos I could not agree more with your assessment of the roll progesterone or the lack there of, plays in abortions. I'm sure you would agree that the real reason behind it's use as a supportive or preventative therapy is for the most part because the industry doesn't have anything else to blame it on at the current level of our knowledge.
Unfortunately it always reminds me of something that an old time vet told me once after a long bout with a particularly tough neonatal case that turned out successful. I complimented him on the heroic efforts and stated that he saved this foal. His reply to me was "perhaps or perhaps not, what do you suppose would have happened if I had done nothing?" Interesting point of view I must say. And something that we all need to remind our selves of once in a while, when we start to get that God like feeling with our successes.
I have always been of the mind that at some point perhaps way down the road or perhaps sooner, that all the use of hormonal intervention and so called therapy may come back and bite us in our behind. That has already proved to be the case in several instances. All for no other purpose than to try and comply with an unrealistic breeding season window. That has been imposed on the industry by people who have no knowledge of reproduction what so ever.
Ft. Dodge currently markets two P&E implants for cattle. They are called SYNOVEX-S [200mg of progesterone and 20 mg of estradiol] and SYNOVEX-C [100mg of progesterone and 10 mg of estradiol]. Could or has either of these been used in horses?
Posted on Thursday, January 02, 2003 - 09:32 am:
Neither of the above implants have been shown to be successful for estrus control in the mare with any degree of repeatability.
Ever use CIDR-B implants in horses? Combined with an E 17-B shot, I wonder if it would work.
Jos Posted From: 220.127.116.11
Posted on Thursday, October 30, 2003 - 02:05 pm:
The usual problem with using implants of any type to induce timely estrus is that there is not a predictable end to the controlled release period, so there is not an accurate hormonal rebound effect such as is seen with the daily-dose injectable P&E. A similar problem is seen when estradiol cypionate or benzoate is used rather than estradiol 17b. There is a compounded single-treatment time-release P&E preparation on the market, but anecdeotal evidence indicates that the pinpointing of follicular development to a 3.5 cm follicle by day 18 is not as reliable as with the daily treatment.
The use of the vaginal implant CIDR-B however is a little different, and has been experimented with in the equine. It has been found to be workable and produce reliable results if removed at the right point. Problems seen have included premature loss of the implant from the vagina, and transient cervical and vaginal inflammatory response, which resolved once the implant was removed. This research has been performed primarily in Australia and New Zealand.
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