Stallion sexual behaviour can be considered in two broad categories:
As with the mare the expression of sexual behaviours is largely dependent on the effects of the sex hormones. In the stallion the main sex hormone is testosterone, which is produced in the testicles.
Such behaviours are not therefore as strong in a gelding (who has had his testicles removed). Some masculinisation does occur before a male foal is born, since a surge of testosterone is responsible for the development of male genitalia; this also has a permanent effect on the brain.
1. Behaviour to build and maintain a harem
Within a harem the oldest mare tends to travel at the head of the group and the stallion at the rear. By driving the mares the stallion can ensure no mares stray and that they are less vulnerable to being kidnapped by other stallions. The stallion drives the mob by running alongside but slightly behind an individual or snaking at her to move her on.
The snaking posture involves a stallion lowering and extending his head
whilst laying back his ears. The head is swung from side to side or
rotated like a threatening cobra.
Photo courtesy of U.S. National Parks Service
Stray mares may be gathered into the group and other stallions driven away using this behaviour. Stallion conflicts may be preceded by a ritual display of arousal including foot stamping and threats and only occasionally escalating to rearing boxing matches.
Aggression involves a risk of injury even if you are likely to win the fight. Accordingly, natural selection has favoured individuals who adopt strategies which avoid conflict. This involves assessing signals from the opposing stallion that give information on that horses fitness.
Let's have a look at those signals in a little more detail:
a) Direct signals include visual ones such as the arching of the neck, prancing, rearing and striking, as well as audible roars.
b) Indirect signals include the chemical ones left by the stallion over his territory. The harem may be considered to be a moving territory since he will tend to mark over the urine and faeces of the other members of his harem.
Faeces are particularly useful as a means of communication in your absence. A decent pile of faeces not only declares who you are, but also how recently you have been there. For this reason a stallion tends to defecate over his own faeces as this notifies others of his continued presence and avoids unnecessary conflict.
If the herd stays in the same area then these piles of faeces will accumulate in specific sites. These are referred to as stud piles and are commonly seen in stallion paddocks at domestic studs.
2. Courtship and mating behaviour
When a stallion detects that one of his mares is about to come into season he may become a real nuisance, though others may be less of a problem to manage. He may drive, snake and bite the haunches of such a mare for several days if necessary.
However, only if she stands still in response to this will he attempt the next stage of courtship. If the mare is receptive he will nudge and nip her along her body to her neck. Both animals may appear to behave quite aggressively to each other at this time, but this should soon settle down if the mare is in oestrus.
The stallion will sniff her vulva, flehmen in response to any secretion or excretion and call out with a long low nicker sound. Jerky movements increase the attention value of the display. Horses naturally focus on such movements since they have such survival value at other times, such as when a predator finally decides to make a decisive strike.
If the mare responds favourably with clitoral winks, the stallions penis is extended and will become erect. He will make several partial mounts before attempting a full mount, usually from behind but occasionally from the side. Penetration is normally achieved after a few exploratory thrusts.
Copulation does not take long and after a few pelvic thrusts, flagging of the raised tail signals ejaculation. The stallions head also tends to lower and the facial muscles relax at this time. During copulation the stallion may bite at the mares neck and mane.
Within 30 seconds the mare will normally move forward to allow the stallion to dismount. It is not uncommon for the stallion to squeal a little at this time. In the natural state the stallion does not have to step backwards to dismount.
The stallion will be willing to serve another mare within ten minutes or so, and is likely to show mated mares greater attention over the next few days. As a result a mare in oestrus may be served between five and ten times.
Effects of captivity
It is usually considered unsafe to keep stallions together but in the wild bachelor bands are a normal feature. Why is this?
Stallions will fight and possibly even kill each other when they are competing over possession of a group of females. Deaths are however not the norm, and even ultimately fatal injuries are not common in the wild.
A serious fight involves great risks for both parties and, as with other aggressive behaviour, an escalating series of threats is issued and physical contact only made when absolutely necessary.
Photo courtesy of U.S. Bureau of Land Management
This may be because the two stallions are unable to clearly determine who is likely to win a contest, or because the loser is unable to retreat.
Stallions kept for breeding purposes are often near mares and so there is the potential for competition when a female comes into oestrus.
Stallions living together in the wild have often grown up together or shared some adolescent life. During this time they can learn about each others strengths and weaknesses and so more fully evaluate and recognise their chances in any serious competition. In addition they learn the rules of living in a social group.
Such information or opportunities are rarely available to domestic stallions, and the captive environment may not allow some signals normally used in such evaluation to be transmitted efficiently. For example, the audible roar may be muffled or blocked by enclosed housing.
Moreover, should a fight take place, a paddock may not be large enough or provide sufficient cover for the loser to retire safely.
The aggression of stallions in captivity
is therefore behaviour that can be expected for such an abnormal
situation. The problem lies more in the management system than the
TAFE NSW Commission January 2002 Version - 1.0 (of this page)
U.S. Bureau of Land Management, [Online] http://www.blm.gov/nhp/index.htm
U.S. National Parks Service, [Online] http://www.nps.gov/
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