01 Mar 2016

Tweedie & Associates – Myth Busters Series

She’s gone marbles!

After a lifetime as a horse owner and many years as a veterinarian, I have seen, heard, learnt and occasionally used, many of the word of mouth tips and tricks that circulate within the equestrian community. Some are great but others really need to be consigned to the history books!

It is on this note, that I welcome everyone to the first article in our ongoing Myth Busters series. For this series, I will examine the current veterinary literature on various topics and use it to disprove some of our long held ideas about horse management. Let’s get started!

Intrauterine Glass Balls for the Suppression of Oestrus Behaviour

Anyone who has ever dealt with a mare ‘in season’ will understand that oestrus behaviour will often adversely affect performance activities. The most common method of suppressing oestrus behaviour is the daily administration of a synthetic oral progestin called altrenogest (Regumate). This course of management is not without it’s downsides, and its expense coupled with the potential safety risks for people (particularly women) administering the drug mean its use requires careful consideration.

The insertion of sterile glass balls (marbles) into the uterus of a mare one day after ovulation has been suggested as an alternative method of suppressing oestrus behaviour. I will explain the proposed mechanism by which this works as follows;

When a mare is approaching her ovulation date, she experiences hormonal changes that do a couple of things, firstly, they stimulate the growth of follicles on her ovaries, one or two of which will go on to ovulate and secondly, they make her sexually receptive to a stallion. During the period in which the mare is sexually receptive to a stallion, she will demonstrate ‘in season’ behaviour that is considered undesirable in a riding horse. These behaviours include but are not limited to, tail swishing, kicking, squealing, urination and winking of the vulva.

Once the mare has ovulated, the follicular tissue re-organises and becomes a corpus luteum (CL). The CL functions as a temporary endocrine gland and secretes progesterone. In a non-pregnant mare, the CL will secrete progesterone for approximately 2 weeks until the endometrium (lining of the uterus) secretes prostaglandin F2α (PGF2α) which causes regression of the CL, a subsequent drop in progesterone levels and a return to oestrus. When a mare becomes pregnant, the embryo blocks the secretion of PGF2α and the CL continues to function and secrete progesterone, which prevents the mare from coming back into season.

So, the thinking behind the insertion of a marble into the uterus the day after ovulation is that the mare’s uterus will be tricked into thinking she is pregnant and the endometrium will not secrete PGF2α. Without the secretion of PGF2α, the CL will remain functional and continue to secrete progesterone, thus acting to suppress oestrus and it’s associated oestrus behaviour.

Ok, so this sounds like a great idea, but does it actually work? Is it even safe?

Does it work?

Nie et al (2003) conducted a study where they placed 25mm glass balls (intrauterine device or IUD) into the uterus of horse and pony mares the day after ovulation. In this study, 50% of the glass balls were spontaneously expelled.

In the Nie et al (2003) study, they also found that CL function was prolonged in only 39% of mares. The prolongation of CL function was on average 87 days. Interestingly, they observed that the efficacy of IUDs was better in younger mares.

Other researchers, Argo and Turnbull (2010) conducted a similar study and found no difference in the inter-ovulatory interval between the mares with an IUD and control mares without an IUD.

So, the results of these two studies are not supporting the efficacy of IUDs as a technique to suppress oestrus in mares. This brings us to our next question.

Is it safe?

The short answer is, no, not really. Turner et al (2015) published a case study on complications associated with the presence of two intrauterine glass balls used for oestrus suppression in a mare.

In this case, an 8 year old quarter horse mare was presented for removal of 2 intrauterine glass balls, one of which had fragmented. The intact glass ball was removed and the fragmented pieces were eventually removed with great difficulty. The two subsequent attempts to breed the mare were unsuccessful.

Other serious complications have been reported secondary to insertion of an IUD, indeed Klabnik-Bradford et al (2013) reported a mare with pyometra secondary to this procedure.

There is also a chance that an IUD could become lodged between the endometrial folds and may then become impossible to remove.

Can we consider this myth officially busted?

Yes, I think we probably can. In my opinion, the efficacy of this procedure has not been proven. Since the reported complications have serious implications for the health and future fertility of the mare, the risks with this procedure do not outweigh the benefits.

Katila, T. (2015) Techniques to supress oestrus in mares. Equine Vet. Educ. 27, 344-345.
Klabnik-Bradford, J., Ferrer, M. S., Blevins, C. and Beard, L. (2013) Marble-induced pyometra in an Apaloosa mare. Clin. Theriogenol. 5, 410. (Abstr).
Nie, G.J., Johnson, K.E., Braden, T. D. and Wenzel, G. W. (2003) Use of an intra-uterine glass ball protocol to extend luteal function in mares. J. Equine Vet. Sci. 23, 266-273
Turner, R. M., Vanderwall, D. K. and Stawicki, R. (2015) Complications associated with the presence of two intrauterine glass balls used for oestrus suppression in a mare. Equine Vet. Educ. 27, 340-343.

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