23 Jan 2017
Madeleine Campbell explores lack of libido in stallions, the common clinical presentations and possible management methods.
Madeleine Campbell
Job Title
Figure 1: A flehmen reaction is one of the common behavioural signs of sexual interest exhibited by stallions. Image: © Fotolia/TOMsPiC.
Libido may be defined as sexual interest, which, in the case of a stallion, is usually exhibited as a series of well-recognised reproductive behaviours, culminating in gaining an erection and mounting the mare. Lack of libido in stallions is a significant problem for the equine breeding industry and is commonly related to psychological inhibition of normal reproductive behaviours. Stallions may present as novice “slow breeders”, as exhibiting erratic levels of libido or with a consistent lack of libido. Treatment depends on the underlying cause for the psychological inhibition and focuses on appropriate and sympathetic management, sometimes supported by pharmacological treatments. The risks to stallion, mares and personnel associated with undertaking such management or treatment must be assessed and addressed.
Lack of libido can limit a stallion’s breeding career and becomes rapidly frustrating for all involved, including the stallion itself. This article aims to review the causes of reduced libido in stallions, to describe common clinical presentations and to suggest possible treatment/management approaches to such cases.
The scope of this article does not extend to failures of penile erection (except as a symptom of lack of libido) or ejaculation. McDonnell (2011a) discusses this topic in Equine Reproduction.
Sexually mature stallions, when exposed to a mare in oestrus, normally display a range of precopulatory behaviours, which may include pawing at the ground, vocalising, approaching the mare, sniffing the mare’s external genitalia, licking the mare, nuzzling the mare, biting the mare, displaying a flehmen reaction (Figure 1), leaning against the mare, kicking out, rearing, extruding the penis, gaining an erection and mounting the mare (which sometimes initially occurs in the absence of an erection). This collection of behaviours – not all of which necessarily occur on any one occasion – together indicate sexual excitement or “libido” and normally occur rapidly after exposure to an oestrus mare.
Libido is usually maintained throughout the year, although it may be subdued in the winter season compared to spring/summer.
Failure to exhibit interest in a mare or become sexually excited can limit a stallion’s reproductive efficiency, particularly where a “natural cover” system is being used, and is recognised as being a significant problem in the equine reproduction industry (Alvarenga and Pap, 2009; Burger et al, 2012; Silva Rua et al, 2015).
In stallions, as in males of other species, gonadotropin releasing hormone (GnRH) from the hypothalamus promotes release of the luteinising hormone (LH) from the anterior pituitary gland. LH stimulates the Leydig cells of the testes to secrete testosterone. Testosterone is important for spermatogenesis and also plays a role in sexual behaviour. However, the relationship between circulating plasma testosterone levels and libido in stallions is not straightforward.
A study (Squires et al, 1997) suggested low plasma levels of testosterone (caused by treatment with oral altrenogest) were associated with low libido in stallions. The proposed mechanism was lack of circulating testosterone to be aromatised into oestradiol and, since oestradiol is associated with libido, this explained these findings.
Other studies have either failed to demonstrate a correlation between libido and plasma testosterone levels (Searle, 2009) or shown a negative correlation (Waheed et al, 2015).
An association seems to exist between a competitive, harem stallion with a high breeding effort and having higher plasma testosterone levels compared to bachelor stallions (McDonnell and Murray, 1995; Burger et al, 2012).
However, it may be the higher plasma testosterone levels are primarily a reflection of the competitive breeding effort needed to maintain his harem position, rather than necessarily the cause of the dominant stallion’s libido (Burger et al, 2012).
Apparent lack of libido in stallions commonly has a psychological cause. In part, this may relate to the ways in which domesticated breeding stallions are managed (Burger et al, 2012).
Typically, stallions are housed separately from mares and expected to engage in breeding activities up to three times a day (if in a “natural cover” management system) or daily (if a popular stallion in an artificial insemination management system) during the breeding season.
Such conditions differ significantly from those that occur in feral horse herds, when a harem stallion typically interacts continuously with its band of mares, and breeds fewer mares (McDonnell, 2000), typically no more than 20 per year (Burger et al, 2012).
Furthermore, the trend towards the use of artificial insemination and its acceptance by most breed registries means many stallions have semen collected using a “dummy mare”, sometimes in the complete absence of a live, oestrus mare.
The cumulative tiring effects of a long breeding season or the requirement to participate in competitive, as well as breeding, programmes can also negatively affect on stallion’s libido.
Successful treatment of lack of libido in stallions requires a very careful history taking, appreciation of the likely underlying cause, and appropriate, sympathetic, and patient management. The risks to stallions, mares and personnel associated with undertaking such management or treatment must never be forgotten, particularly given stallions frequently become frustrated.
Stallions should be appropriately bridled and handled by a competent, experienced and sympathetic handler; care should be taken to ensure footing is good and space adequate, and appropriate protective clothing (for example, headgear, back protectors, suitable footwear) should be worn by personnel.
It is not uncommon for inexperienced stallions to exhibit an apparent lack of libido when first expected to participate in a breeding programme.
Management of novice “slow breeders” should focus on encouraging them to show normal sexual interest and providing a calm, safe environment in which they can do so. Initially, it may be best to ignore any part of the usual breeding routine that might distract or upset the stallion, such as washing the penis or dressing the mare in protective gear.
Some novice slow breeder stallions can, with patience, be trained to use a dummy mare, using a “teaser” mare in oestrus positioned on the far side of the dummy. Many novice stallions will react favourably to being exposed to the mare and dummy in this way for a few sessions and will increasingly gain confidence and start to display normal libido.
As a rule, multiple short training sessions are more successful than a few long sessions. It is best to stop the session when the stallion shows progress in terms of exhibiting normal reproductive behaviours, before it starts to become frustrated. Very often, it will return to the breeding barn at the start of the next session more confident, with improved libido.
If the stallion fails to develop normal libido when presented with the dummy in the presence of an oestrus mare, or if a dummy mare is not available, it may be necessary to use a live mare for semen collection, at least initially.
The extra stimulus provided by being given full access to a live mare is often enough to disinhibit stallions that have not shown sufficient libido to mount a dummy mare. Once they have learned it is acceptable to exhibit normal libido and had semen collected using a live “jump” mare, it is often subsequently possible to train them to use the dummy mare, starting by positioning the live mare beside the dummy.
Stallions that persist in demonstrating a lack of libido when trying to collect semen from them using a live jump mare, or when trying to cover a mare “naturally”, may gain confidence if they are allowed to breed mares at pasture or at least given access to mares without human interference (for example, via a secure fence line between two fields).
Some variation in libido is, of course, normal. However, stallions that exhibit fairly normal libido on some occasions and then a lack of libido on others can present a real managerial problem, particularly if enrolled in a shipped semen programme.
Sometimes, transient loss of libido is associated with infrequent use and lack of familiarity with the breeding shed routine. Regular use (for example, scheduled semen collections, even if there is no requirement to breed a mare) can help restore libido in such cases.
Conversely, and more commonly, lack of libido is associated with very frequent sexual use, and consequent physical or mental tiredness. In such cases, it may be necessary to reduce the number of mares scheduled to visit the stallion, or the frequency of semen collections.
Where semen is being artificially collected, changing the teasing or jump mare, or using a second, unfamiliar mare to tease the stallion alongside the normal jump mare, can help to increase libido.
Sometimes, erratic loss of libido can relate unexpectedly to management factors. For example, the author dealt with one stallion in which its libido was manageably adequate if he was always the first stallion to have semen collected each day, but that suffered a complete loss of libido if another stallion had semen collected before him, even though the collection area was out of sight of the stables.
The relationship between exercise and libido in stallions is unclear. Some stallions seem to find it difficult to combine stud and competition careers. This may relate to being reprimanded for showing sexual interest during their competition career, or may be they are physically and mentally tired by training and competing.
A study (Dinger and Noiles, 1986) appeared to suggest exercise reduced libido. However, the interpretation of that study was confounded by the fact the “non-exercise” stallion group was kept confined in individual stables, meaning its apparently higher libido when taken to the breeding shed may have been an expression of exuberance at exiting the stable.
In the author’s experience, moderate exercise – for example, hacking or turnout at pasture – is likely to contribute to the mental well-being of breeding stallions and, therefore, have a positive effect on their libido.
Previous negative breeding-associated experiences can have a lasting impact on a stallion’s libido. Such experiences may have been directly related to breeding activity; for example, stallions may have been kicked by a mare, or may have an orthopaedic problem that makes it painful for them to mount.
In other cases, lack of libido may be associated with having been previously reprimanded for having shown sexual interest in mares.
Whatever the negative association, stallions may simply ignore the oestrus mare or display erratic behaviour, which is a mixture of starting to show sexual interest and then backing off or becoming frustrated (sometimes violently so) as they anticipate pain or fear.
Careful observation of the stallion’s behaviour may offer some clue as to the source of the psychological inhibition of libido. For example, stallions that were previously kicked may extrude the penis and gain an erection when there is a solid barrier, such as a stable door or teasing board between it and an oestrus mare, but then lose its erection and withdraw the penis if the barrier is removed.
In the author’s experience, older novice breeding stallions that have been disciplined for rearing during their competition careers are often scared to mount the dummy – they typically show good interest in the mare or dummy, strong teasing behaviour, and gain and sustain an erection, but refuse to mount. Such stallions are initially more likely to be persuaded to mount a real mare than the dummy. Some stallions clearly associate its usual rider/trainer with being reprimanded for showing sexual interest. In such cases, ensuring this person is not present in the breeding shed can have a remarkably prompt disinhibiting effect on the stallion’s libido.
Careful history-taking helps to elucidate the underlying problem, although commercial sensitivities sometimes deter owners/riders from being transparent about lameness issues.
Where an orthopaedic problem is suspected, the history may reveal the stallion initially had good libido, but exhibited difficulty mounting or maintaining its balance and subsequently, lost libido – because it learned to associate breeding activity with pain. A combination of NSAID agents and management tools may help to alleviate discomfort in such stallions and, therefore, combined with sympathetic handling and encouragement, restore libido.
Using a smaller mare, standing the mare downhill from the stallion or adjusting the height or angle of the dummy mare, can help.
In stallions with hock problems it may be more comfortable for the dummy to be higher rather than lower, as this opens the angle of the hock.
For some stallions with orthopaedic problems, “ground collection” may be more comfortable. A description of this technique is outside the scope of this article, but is provided by Brinsko (2011). Particular attention should also be paid to the safety of personnel when using ground collection.
Where management and retraining fails to restore libido, pharmacological manipulation may be appropriate.
No drugs are licensed in the UK for the treatment of lack of libido in stallions, meaning vets should prescribe under the cascade, with informed consent from stallion owners.
As mentioned previously, analgesics, particularly NSAIDs, have a role to play in managing stallions that have pain-related loss of libido. The use of gabapentin has also been suggested in cases where there is a neurogenic component to discomfort (McDonnell, 2011b).
Anxiolytic therapy with intravenous diazepam may be useful in stallions where lack of libido is related to a previous negative experience (McDonnell et al, 1985).
GnRH treatment may help to increase sexual arousal (McDonnell, 2011b), as may treatment with exogenous testosterone (McDonnell, 2011b). However, the potential for exogenous testosterone to have a negative effect on fertility by disrupting spermatogenesis via negative feedback mechanisms, and to potentially increase aggressive behaviours, means owners must be made aware of this and testosterone (and hormone therapies generally) should be used with great caution in breeding stallions (Dinger and Noiles, 1986; McDonnell, 2011b).
Lack of libido in stallions, whether sustained or intermittent, is a serious cause of inefficiency within the equine breeding industry, and can limit an individual stallion’s economic and genetic success.
Pharmacological treatments may sometimes be necessary, but generally successful treatment is focused on careful consideration of the underlying cause, retraining and sympathetic management.
