I just purchased a two year old appendix quarter horse filly (three in Feb) at auction. She's drop dead gorgeous and a real pretty mover, but her temperament leaves a lot to be desired--and that's being polite! She has what the seller calls progesterone implants in her chest. No one I've asked seems to know much about them, and our vet doesn't either, because he doesn't use them. We've assumed it's instead of daily Regu-mate to mellow her out, but if this is mellow, I'd hate to see her before! And she's also come into heat since we've bought her. Does anyone have any information that they could share with me? Thanks!
Here's a research document about the use of Synovex-S implants in the mare. It's generally considered that they are not a reliable tool for suppression of estrus, but some people still swear by them!
Efficacy of Synovex-S® implants in suppression of estrus in the mare
P.M. McCue, DVM, PhD; S.S. Lemons, BA; E.L. Squires, PhD; D. K. Vanderwall, DVM, PhD
Author's address: College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Ft. Collins, CO 80523.
Summary The objective of this study was to determine if administration of Synovex-S® implants, approved for use in cattle to promote weight gain and feed efficiency, would suppress the expression of behavioral estrus and/or alter follicular development and ovulation in the mare. Twenty- four clinically normal adult horses were randomly assigned to one of four treatment groups (6 mares per group) which received a total of 0, 8, 32 or 80 Synovex-S® pellets 5 days after ovulation. An implant dose of 8 Synovex-S® pellets contained a total of 200 mg of progesterone and 20 mg of estradiol benzoate. Mares were monitored daily by teasing and ultrasonography of the reproductive tract per rectum for 45 days. A blood sample was collected daily for progesterone analysis. All mares receiving Synovex-S® implants returned to estrus at the predicted time. No differences were noted in duration of estrus, interovulatory interval or ovulation rate. In conclusion, subcutaneous administration of 8, 32 or 80 Synovex-S® pellets did not suppress the expression of behavioral estrus or block ovulation in mares.
Introduction Exogenous progesterone or synthetic progestins have been used for many years for suppression of estrous behavior in mares.1 Recently, steroid implants containing progesterone and estradiol have been used in an attempt to suppress estrus in mares.2 These implants are intended for use in steers and heifers, where they have been shown to promote weight gain and feed efficiency.3 The most common cattle implants consist of either 4a or 8b pellets per cattle treatment dose. An implant dose comprised of 8 pellets contains a total of 200 mg of progesterone and 20 mg of estradiol benzoate. Controlled studies evaluating the efficacy of progesterone/estradiol implants, such as Synovex-S®, for suppression of estrus in the mare have not been reported. The purpose of this study was to determine if administration of Synovex-S® implants would suppress the expression of behavioral estrus and/or alter follicular development and ovulation in mares.
Materials and Methods Twenty-four mares were randomly assigned to 1 of 4 treatment groups of 6 mares each. Group 1 mares were administered subcutaneous placebo implants of polyethylene glycol (PEG), the carrier vehicle in the Synovex-S® implants. Groups 2, 3 and 4 mares received subcutaneous implants of 8, 32 or 80 Synovex-S® pellets. Mares were monitored daily by teasing and ultrasonography of the reproductive tract per rectum for one estrous cycle and the day of ovulation was determined. The implants were administered 5 days after ovulation. Mares were again monitored for 2 estrous cycles after implantation. Blood samples were collected daily beginning on the day of the initial ovulation and continuing until 3 days after the subsequent ovulation was detected to monitor serum progesterone concentrations.4 The intra- and inter-assay coefficients of variation for the progesterone assay were 1.4 % and 1.6 %, respectively. The sensitivity of the progesterone assay was < 0.05 ng/ml. Comparisons between treatment groups were made by one-way analysis of variance and a value of P< 0.05 was considered significant. All values are expressed as the mean ± SD.
Results There were no significant differences (p>0.05) in the duration of estrus, interovulatory interval, size of the preovulatory follicle or ovulation rate for mares receiving 0, 8, 32 or 80 Synovex-S® pellets (Table 1). All mares receiving Synovex-S® implants returned to estrus at the predicted time. Two mares receiving 32 Synovex-S® pellets were in heat for 15 and 21 consecutive days, respectively. These mares both came back into heat 15 days after the previous ovulation had been detected, which was 10 days after implantation of the Synovex-S® pellets. The duration of heat during the estrous cycle prior to treatment for these mares were 8 and 5 days, respectively.
Serum progesterone concentrations for all mares declined to less than 0.5 ng/ml following a luteal phase of 14.0 ± 0.9, 13.8 ± 1.6, 13.6 ± 1.3 or 14.2 ± 2.2 days, respectively, for mares receiving 0, 8, 32 or 80 Synovex-S® pellets (Figure 1). The luteal phase was calculated as the period during which progesterone levels were elevated above 1 ng/ml following an ovulation during estrus. Mean peak serum concentrations of progesterone following implant administration for mares receiving 0, 8, 32 or 80 pellets were not significantly different (8.7 ± 2.8; 6.4 ± 0.4; 7.2 ± 2.0 and 5.7 ± 2.1, respectively). After implantation, the number of days from the end of the luteal period until the next ovulation was significantly greater (p <0.05)> 0.05) between mares receiving the placebo treatment and mares receiving 8 pellets (7.4± 3.8 days).
Discussion Progesterone therapy has been used in mares for management of the spring transition period, uterine involution, maintenance of pregnancy and in the suppression of estrus.5 The types of progesterone shown to be effective in the suppression of estrus in mares are injectable progesterone-in-oil6,7 and an oral synthetic progestin, altrenogest.c,1 An implant or repositol form of progesterone that is effective in suppression of estrus would be of value to horse owners and veterinarians as it would eliminate the need for daily treatments over a prolonged period of time. An implant containing the synthetic progestin norgestomet has been reported to be ineffective in suppressing estrus in the mare.8 Anecdotal reports by practitioners have suggested that Synovex-S® implants marketed for use in cattle may be effective in suppressing estrous behavior in some mares. However, in the present study every mare treated with Synovex-S® implants returned to estrus at the expected time when teased with a stallion. All mares developed preovulatory follicles of normal size and ovulation rates were not significantly different. Although mean interovulatory intervals were not significantly different between groups, the rate of follicular development may have been slower in mares receiving higher implant doses as indicated by the increased interval from the end of the luteal phase until the subsequent ovulation. Follicular development has been reported to be suppressed in mares administered daily injections containing 150 mg progesterone and 10 mg estradiol-17b.9,10 Previous studies have shown that daily administration of 50 mg of progesterone-in-oil is required to prevent the expression of estrus in the mare.7 It is therefore unlikely that an implant which contains a total of only 200 mg of progesterone and is designed to release product over a period of several months will result in blood progesterone levels that are high enough to inhibit estrus. Measurement of serum progesterone concentrations in the present study indicated that progesterone levels were not maintained above 0.5 ng/ml, even when 80 pellets were implanted. Progesterone concentrations less than 1 ng/ml are not sufficient to suppress estrus. In conclusion, these results indicate that subcutaneous administration of Synovex-S® implants, at a rate of 8, 32 or 80 pellets per treatment dose, does not suppress the expression of behavioral estrus or block ovulation in mares. aSynovex C®; Syntex Animal Health, West Des Moines, IA 50266. bSynovex S®; Syntex Animal Health, West Des Moines, IA 50266. cRegumate®; Hoechst-Roussel Agri-Vet, Somerville, NJ 08876
References 1. Squires EL: In: McKinnon AO, Voss JL, (eds). Equine Reproduction. Philadelphia: Lea and Febiger, 1993;311318. 2. Paul JW, et al.: Equine Practice 1995;17:2122. 3. Hancock RF, et al.: J Anim Sci 1994;72:292299. 4. Niswender GD: Steroids 1994;22:413424. 5. Squires EL, et al.: Proceedings of the 27th Annul Conv Am Assoc Equine Practnr, 1981;221231. 6. Hawkins DL, et al.: J Reprod Fert, Suppl 1979;27:211216. 7. Loy RG, Swan SM: J Anim Sci 1966;25:821826. 8. Scheffrahn NS, et al.: Theriogenology 1982;17:571585. 9. Evans MJ, et al.: J Reprod Fert, Suppl 1982;32:205211. 10. Loy RG, et al.: J Reprod Fert, Suppl 1982;32:199204.
Posted on Wednesday, February 01, 2006 - 09:27 am:
Thanks for the info, Jos! Here's what's happened with my filly:
She did come into heat with the implants in, and seemed to be very uncomfortable--looked a bit colicky like a mare in labor. This was in October, and being that she was only 2, it might have been her first heat. We had a repro vet evaluate her and remove the implants. There was nothing remarkable on exam, but the implants were massive--one was the size of a quarter, and the other the size of a dime. They were white and waxy, and looked like maybe they were a bunch of Ovuplants stuck together. We put her on Bio-Release, which is an injectable, long lasting progesterone, for four weeks, and it mediated her behavior a bit. When she's not on anything, she's awful. I've taken both Ohio State's and Colorado State's short courses on breeding management, and they both recommended ReguMate, so that's our next plan of attack.
Posted on Wednesday, February 01, 2006 - 03:33 pm:
It is quite possible that they were indeed Ovuplant implants - I have heard rumours of that process being used, but there is no research that has been done to establish effectiveness or safety. Ovuplant is not progesterone though, it's Deslorelin, a synthetic GnRH - but that's not to say the seller wasn't misleading or misled!
P4-LA (from BET Pharm has actually been proven to be as effective as Regumate in elevating progestin levels for 7 days (Vanderwall D., et. al.), and may be more convenient to use as long as it reduces the symptoms as efficiently as Regumate, because of it being a single injection each 7 days rather than the requisite daily dosing with Regumate.
It is quite possible that what you are seeing is a response to the follicular growth and ovulatory process - some mares get very sensitive ovaries right before ovulation.
I have two mares on the synovex progesterone implants, these are both shown nationally in Reined Cowhorse Events and the difference is amazing. Of course we did not put them in until their three year old year. They arent being hauled anywhere at 2 so the trainer just puts up with them until their show year.
We have one that was so irritable she wouldnt work, but we put her on the implants, little teeny yellow BB looking things, takes about 2 months to start noticing a huge difference as they disolve slowly. Then they last a total of about 6 months, just thru the show season then they are off for the winter months and spring. I wont feed regumate, I have tried it and its so dangerous if you touch it, that I was just going to live with mine being moody till I found the implants.
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