The origins of behavioural problems in the competition mare can be divided into reproductive and non-reproductive causes. This article will predominantly focus on reproductive and hormonal causes, however, it is important to resist the temptation to always blame ‘hormones’ as the cause of poor performance in mares.

Behavioural problems in competition mares and fillies can be frustrating and challenging to deal with. They often inhibit a mare from focusing on the task at hand, preventing her from reaching her full performance potential.

This is especially important on competition and race days. Owners, trainers and veterinary surgeons must work together in order to reach a diagnosis and an effective treatment protocol that adheres to any specific competition withdrawal periods.

“Oestrous” is the time period in the mare’s cycle when she will stand to be covered by a stallion (in season) unlike “dioestrous”, the period of sexual quiescence.

In order to make a diagnosis as early as possible and determine the correct management protocol, it is imperative that you provide your veterinary surgeon with as much information about the mare’s behaviour as possible.

Intermittent or persistent behaviour relating to poor performance and the nature of that behaviour can offer large clues to the potential source of the problem. Aid your veterinary surgeon by giving them as precise and detailed a history as possible, noting especially when the behaviour occurs.

POSSIBLE CAUSES

The possible causes can be divided into three categories: normal hormonal behaviour, abnormal hormonal behaviour and abnormal behaviour unrelated to the mare’s hormones.

1. Normal hormonal behaviour

The oestrous cycle normally lasts for approximately 21 days consisting of oestrogen dominant and progesterone dominant phases.

During the “oestrogen” dominant phase (roughly seven days in length) the mare will stand for the stallion. The “progesterone” dominant phase (roughly 14 days in length) overrides the oestrous phase, mimics pregnancy and results in the mare rejecting the stallion.

It is the oestrogen dominant phase that can affect performance, hence why a change in behaviour is often witnessed for approximately one week in every three week cycle.

A concise history as well as scanning the reproductive tract can determine if the normal oestrous cycle is the cause of the change in behaviour and subsequent poor performance.

2. Abnormal hormonal behaviour

When a mare is in season for more than a week (persistent oestrous behaviour) this can be due to her being in “transition”. This behaviour is typical of mares during Spring time. Increased daylight reduces the production of melatonin in the mare’s brain. Melatonin plays a pivotal role in the seasonality of reproduction.

Increased daylight and a decrease in melatonin levels awaken hormones in the mare’s brain initiating follicular growth on the ovaries.

At normal levels this will allow for ovulation of a dominant follicle, the production of progesterone and normal cycling. Until normal levels exist, the mare may well stay in transition.

Spring time and the transitional period can be very frustrating for owners and trainers due to the extended time the mare is in season and can cause poor performance unless managed correctly.

Endometritis (infection of the uterus) can cause a mare to “short cycle” meaning that she comes back into season quicker than the normal two weeks or so, sometimes remaining constantly in season.

This happens because the inflamed uterus produces a chemical called prostaglandin which acts to destroy the source of progesterone production, leaving oestrogen as the dominant hormone.

Veterinary surgeons can often see signs of infection on scanning of the uterus such as fluid and/or excessive uterine “oedema” (a pattern identified on scan that can be a sign of inflammation) and can perform a range of diagnostic tests to rule infection in or out. If infected, further antibiotic sensitivity tests are done to determine the most appropriate antibiotic treatment of choice.

Granulosa cell tumours (GCTs) on the ovaries can cause a range of different clinical signs all of which fall under the term “abnormal hormonal behaviour”.

They include failure to come into season or continuous signs of being in season, or even stallion like aggressive behaviour.

It is important to rule GCTs in or out on the clinical examination and/or blood tests.

On ultrasound your veterinary sugeon will be able to see and feel one very large GCT ovary and one very small ovary.

Treatment for GCTs is via standing surgical removal of the single affected ovary and these mares can be reproductively normal within a year after surgery.

3. Non hormonal abnormal behaviour

A range of non hormonal problems can lead to a change of behaviour in the mare and should be considered especially if no hormonal explanation has been found.

Orthopaedic problems (lameness or back disease), dental problems, tempero-mandibular joint abnormalities, gastric ulcers and psychological abnormalities as well as a natural lack of talent and ability are some of the issues which should be considered as possible causes of poor performance.

SUPPRESSING OESTROUS

BEHAVIOUR

There are a range of options available for managing mares with hormonal behavioural issues.

It is important to know the rules and withdrawal periods for oestrous suppressing drugs outlined by your relevant competition governing body.

The FEI and IHRB have different rules and guidelines which regularly change. It is up to the owner, trainer and individual veterinary surgeon to adhere to the rules for each individual case.

Putting a mare in foal is sometimes used as a means of suppressing oestrous behaviour. Mares can normally compete until 120 days of pregnancy or not after their 4th month of pregnancy, depending on the regulating body. While pregnant, the mare normally won’t show signs of oestrous.

Pregnancy and its subsequent termination has also been described as a method for keeping a mare out of season. However this is not a reliable technique for managing behavioural issues and should not be pursued.

In cases where the mare’s oestrous cycle has been diagnosed as the cause of the problem oral altrenogest “Regumate” is recommended. It is considered the gold standard for supressing oestrous behaviour.

Regumate is a synthetic progesterone analogue which overrides oestrogen and keeps the mare out of season. It is one of only a few methods that work in controlling mares in early transition.

Regumate has a withdrawal period in the thoroughbred racing industry, but can be used without restriction under FEI rules. There are negatives to using Regumate. It is messy, expensive, requires the use of gloves and needs to be given daily.

Injectable altrenogest is available and works to suppress oestrous for five to seven days.

ALTERNATIVES TO

REGUMATE

Inserting a sterile marble into the uterus offers a good alternative to regumate since it has no withdrawal period.

The marble is subject to varying opinions amongst the veterinary community. Studies show varying reports of efficacy ranging from 40% to 75%.

This is a popular method of oestrous suppression but it does not always work. It requires appropriate knowledge of the timing of ovulation and therefore often requires ultrasonography and sometimes the use of ovulation drugs as well.

The marble should be removed from the uterus when it loses effect. Owners should consider taking note of when the marble is inserted, possibly writing it in the mare’s passport in order to avoid it being overlooked, especially if the mare goes on to become a broodmare.

Prolonged and unnecessary retention of intra uterine marbles has been associated with increased complications. This technique also requires the mare to be cycling and therefore is of no use for mares in transition.

Plant oils offer a cheaper alternative to the marble and have less chance of causing complications. Similarly to the marble plant oils do not work on transitional mares.

Peanut oil or coconut oil oestrous suppression involves the sterile instillation of one of these oils into the dioestrous uterus on day 10 post ovulation. Some studies have shown a 92% success rate with this technique. Like the marble it requires ultrasonography, ovulation drugs and when it works it is highly effective but it does not always work.

There are positive reports of a low dose oxytocin protocol being used to suppress oestrous behaviour. This technique works well in mares that are cycling but because it needs to be performed when the mare is in dioestrous, it is of no value in the transitional mare.

Some studies have shown that this technique works in 100% of cases for at least 30 days while others have shown a 60% to 70% success rate in keeping mares out of season for approximately two months. This is an easy method of oestrous suppression and maybe cheaper than the use of marbles or plant oils with as good if not better success rates.

A double dose of ovuplant/GNRH analogue will suppress a mare’s oestrous behaviour for 30 days or more. One study reported mares not coming back into season until the year after following this oestrous suppression protocol. Unlike other techniques, deslorelin and other GNRH analogues can be used in the transitional mare.

It has been suggested that mares who suck air into their vagina can find this uncomfortable and irritating. If this is a true diagnosis in an individual mare then it could be that she needs a Caslick’s surgery performed rather than hormonal manipulation. It is highly recommended that owners and trainers discuss this surgery with their veterinarian before it is preformed.

Any investigations to determine if oestrous behaviour is the cause of poor performance should start with a detailed history and a thorough clinical examination to investigate all possible causes of behaviour change and poor performance.

Be aware that hormones are not always the cause of all problems. However, when hormones are the cause of the problems there are a range of treatment protocols, techniques and management options which can be employed and should be considered judiciously with respect to the rules and guidelines of the relevant governing bodies.

Oral altrenogest is the gold standard for suppression of oestrous in both the normally cycling mare and the transitional mare. The drawbacks associated with its use have given rise to other techniques.

A lot of these techniques focus on prolonging dioestrous; thus keeping the cycling mare out of season. There are only a few treatments which suppress signs of oestrous in early transition, before the mare is cycling normally.

For further questions regarding the content of this article you can email Susan at suevet16@gmail.com.

The typical clinical signs that a mare that is in season or has abnormal hormone levels can be: