In 350 B.C.E, Aristotle, in his work
The History of Animals makes one of the earliest written references to the use of castration in domestic animals.
It is not known with any certainty whether castration began with animals or men. Whatever, if it began as a method of pacifying captured enemies or slaves for safe domestic service around the captors womenfolk it is little wonder that the practice spread to male animals – particularly in the more difficult and dangerous species such as cattle, which we know were being castrated 6,500 years ago in Eastern Europe. For, while female cattle are considered domesticated, bulls are generally not. And, as one needs only one bull to serve many cows, it would have been a case of either killing those that were surplus to breeding requirements or finding some way of rendering them more passive and predictable during their growth toward slaughter. The effects of human castration were well known to include these characteristics. Anyone that has had dealings with bulls will know just how unpredictably dangerous they can be – even when hand reared and totally socialized to people. Nor, in the case of meat animals, would it have taken long to discover that those castrated at a sufficiently early age produced a greater weight of tender meat – whereas those left entire were liable to be somewhat stringy and tough. In fact the early Carib Indians had made the same grisly discovery about the preparation of their captives for the table!

Perhaps stallions may have survived as entires for somewhat longer than bulls, for unlike the male bovine the stallion is a domesticated animal that, when well reared and socialized, can make not only a pliable servant but also a brave and loyal friend. For this reason many of the early armies preferred the use of stallions to that of geldings for warfare. While geldings may have entered battle as mere transport the war stallion was quite capable when trained to not only carry his warrior master but to fight with him using teeth and hooves also!

With developments in agriculture and the use of donkeys and horses for field work there is little doubt that castration became yet more popular. The slow tedium of ploughing and seed-bed preparation is ill suited to any temperament other than passive – plus there being need for only a small handful of particularly good stallions to sire working horse replacements for quite a large local area. The picture that emerges from all this is of a practice that very likely has its first roots in human social behavior, followed closely by politics, commerce, agriculture and, last but most of all, convenience.

As with so much to do with the horse, politics and warfare had a massive effect on the practice of gelding. A good example of the way in which cultural standards were soundly established is that of medieval England. The political state of England between 1455 and 1485 was one torn apart by generalised lawlessness and, over and above that, the warring of two power factions; the House of York and House of Lancaster. Both determined to secure sovereign rule for their faction. Horses were central to the waging of any such war, and during the conflict numerous raids were made, by both sides, on breeding herds and, in order to protect their studs, owners exported large numbers of horses across the channel to the continent. So drastic an effect did this have that King Henry Vll (1457-1509) passed an enactment forbidding the export of horses (the word was then used to mean stallions – which, in itself, is an indicator that culturally the entire was considered the norm at that time), and of any mare whose value was six shillings and eight pence or over. This, in its turn, caused horses to become so numerous that there were large herds grazing in the common-land pastures, and breeding to such an extent that, to prevent the lowering of the standard of height, the operation of cutting, or gelding, was introduced. Matters continued in this way until, in 1535, Henry Vlll (1491-1547) is recorded as having made the following comments:

"for that in many and most places of this Realm, commonly little Horses and Nags of small stature and value be suffered to depasture and also to cover Mares and Felys (fillies) of very small stature, by reason whereof the Breed of good and strong Horses of this Realm is now lately diminished, altered and decayed, and further is likely to decay, if speedy Remedy be not sooner provided in that Behalf".

Henry stipulated that:

"all owners or Fermers (farmers) of parks and enclosed grounds of the extent of one mile in compass, shall keep two Mares, being not speyed, and able to bear foals of the altitude of height of thirteen handfulls (132cms, ed) at least upon pain of 40s."

Forty shillings, or two pounds sterling, was a considerable sum of money at the time and shows the seriousness with which the matter was viewed, but further fines were also introduced. A fine of 40s was inflicted on owners:

"who shall willingly suffer any of the said Mares to be covered or kept with any stoned Horse (stallion or entire colt) under the stature of fourteen handfulls." (142cms)

Later a further enactment was added for entires running in:

"any forest, chase, moor, heath or waste..... where Mares and Felys are used to be kept..... "

A minimum height of 15 hands high (152cm) or greater was set. Rather than face the consequence of such a crippling fine, owners were forced to the wholesale castration of colts under the proscribed size by means of a sharp knife.

These events were to carry gelding along on the wave of new technology that accompanied a new and vigorous historical era in the country’s development. What entered into British culture as an established agricultural practice with the Tudor dynasty, remains one in the culture of Britain today, almost 500 years later.

But is surgical castration as necessary now as it was then? And even if it is, is it ethical?

Given that we now have a far better understanding of horse behavior we should, in theory at the very least, be able to tolerate a far greater number of entires than in the past – should we choose. But many owners simply don’t want the bother generally associated with entires. The days of horses being pastured on ‘common-lands’ is long over in most countries, so a decrease in the size of the ‘national herd’ is not the problem it was.

So while there may not be the need that there was, convenience dictates that it will continue. Another difference is that surgical castration is not the only method available now, various forms of chemical castration being possible; a range of Progestin drugs providing control of male characteristics through antiandogens has been developed, although no doubt their use requires a more complicated process than the one single visit from a Vet’ required for surgical intervention.

As far as the ethical considerations go it could be considered better in utilitarian terms to subject horses to either the discomfort of a surgical procedure or chemical treatment, and the loss of the ability to breed, than to leave them entire but poorly managed. Of course this assumes that good management is unlikely to be available in the majority of cases. It is also arguable that since the horse has no clear awareness of possessing the ability to breed it cannot suffer emotionally as a result of losing it. Religion also has something to say on the matter, Orthodox Judaism, for example, proscribes castration in either man or animal.

The possible arguments both for and against castration are so numerous that it would be impossible to list them all in an article such as this, so let’s leave such decisions to the individual owner and move on to looking at what the affects are on the horse.

If castration is going to be carried out it is best done at 2 weeks to 6 months of age, when the procedure is least painful, and recovery the simplest. At this age there is limited blood and nerve supply to the testicles, which have not begun to produce sperm at that stage, and are quite small. At this stage surgery can be almost bloodless. Research suggests that gelding at this early age may produce a horse up to 10cms taller than if left entire.

Left later than 6 months there is greater associated trauma, and there will be some development of male behavior and shape. And, as time goes on, the relative ‘maleness’ in terms of both shape and behavior will increase.

Once male behavior patterns form it is pointless to expect castration to ‘put the clock back’ in any reliable sense. It may have some beneficial effect, and, just as likely, it will not. If the horse in question has learnt that it is far stronger than handlers and is able to dominate them by aggressive behavior it is extremely unlikely that its behavior will be changed – and it may become worse.

Some years ago I came across the case of a 10 year old carriage stallion that was purchased for a tourist run around a Southern Spanish town. The stallion came very well trained, and as quiet as could be wished for. The new owners were somewhat ignorant regarding stallions and decided that, for tourism, it would be better if the stallion were castrated – despite its age and the fact that it had served mares. The end result was that on one of the first occasions when the stallion pulled the carriage after recovering sufficiently he became quite furious, kicking the carriage to pieces, and depositing the driver and hapless tourists on the road. He never worked safely in shafts again.

No one should take on a stallion without having the knowledge and facilities to do so, and even then many of the environments in which stallions are kept by those with some knowledge fall far short of being supportive of their nature.

There is no doubt that pre-pubertal castration produces an animal whose behavior is rather ‘smaller’ and less complex than that of the entire. Stallion behaviors such as herding, mounting and biting associated with play-fighting are either absent or very greatly reduced, and the potential for displays of aggression is greatly lowered. Intolerance for other male horses, one of the most troublesome and potentially dangerous aspects of stallion behavior, is also very greatly reduced. Other more subtle and less well understood male behaviors are also eliminated, such as that of ‘out-breeding’ or exogamy. Stallion behavior toward female progeny is a complicated issue with a number of triggers. Size of group is an important factor, as is resource level.

Animal groups need to contain more than a minimum number of individuals in order to be biologically sustainable and, in conditions where groups are larger than this minimum, stallions are evolutionarily programmed to eject daughters as a protection against inbreeding. In small groups of 4 or 5 or less, which are below the minimum size, behavior changes – the stallion now has a new imperative – that of increasing the size of the group to a sustainable size. At this point he will mate with his own daughter/s – it being preferable under such conditions to take the risk that progeny will not survive than for number of individuals to remain too few for the dependable survival of the group.

Accurately predicting the point at which environmental triggers cause such changes of behavior to occur is far from easy, with differences to be expected from one sire to another and other issues, such as stallion’s age and range size also having an impact.

Resource levels also act as triggers, producing changes in both herding behavior and in rejection of females.  Should resources such as food, water, space or shelter fall below that which the stallion subconsciously senses is adequate he may eject members of the harem group by force. It is most likely that he will first eject post pubertal colts, followed by daughters – but if this does not offer a sufficient reduction he may well also eject lower status mares in favour of retaining a smaller group of higher ‘quality’.

The complications increase as stallions are kept in confined and unnatural conditions of isolation. Isolation tends to produce psychological aberrations in the stallion, with an associated reduction in the degree to which behavior can be predicted. At this point other horses, animals or people may be wrongly perceived as a threat, with the result being that they are driven forcibly from the area – through or over gates and fences if necessary. Confinement by itself can have a powerful effect, with some stallions showing a degree of tolerance and others far less so.

Geldings can be housed in lower cost buildings, and smaller grazing areas, and with a greater density of population than stallions. They are far less likely to exhibit the extreme and potentially dangerous aggression in support of triggered change to the immediate environment that characterise normal levels of testosterone in the entire horse. They are also far simpler to manage, being free from reproductive urges and associated behaviors – although there are notable exceptions.

Mixed groups of geldings and mares always offer possibilities for behavior problems, the worst, and perhaps most common, being that a gelding will become ‘herd-bound’. In this scenario the gelding becomes fixated, most usually on just one mare, but sometimes on a small group. Removing such a gelding for ridden work can become increasingly difficult, but the worst element of the ‘condition’ is that they may experience a type of separation anxiety while working, causing a panic attack during which desperation to return to the object of their fixation can act as an over-ride to considerations of safety – both their own and the rider’s. The simplest answer to such problems is to separate the gelding from the mare, which generally sets matters right after a remarkably short time. But even where the problem of possessiveness never gets so bad it can very easily provoke unpleasant, and potentially dangerous, kicking – particularly during oestrus. Very often mares will also prefer a gelding’s company to no male company at all, yet during oestrus, when the mare’s interest naturally peaks the poor old gelding simply does not smell right, look right in terms of body language, or behave right. With such a biological mismatch it is not surprising that frustration can build, tempers fray and kicks fly. So even when a horse has been gelded it is far simpler, in social terms, to keep them with other geldings than in mixed groups. 

Given that space is such an important factor in stallion behavior, and that we live in a world under extreme pressure for such space castration is a choice that will logically continue to be taken. And as space pressure continues to increase it may well be that its incidence will increase – rather than decrease because we have become better at managing stallions so that they are not problematic.

Ethically, if we wish to castrate, it is clear that sooner is better, and that gelding is preferable to slaughter for behavioral reasons. The question of castrating after a stallion has served a mare, or mares, is less clear. We can not ‘know’ with any certainty what the stallion feels, or whether, having been bred, it is ‘aware’ of what has been lost. But from anecdotal evidence it seems possible that there is an element of psychological injury. Even then it may still be argued that the horse is better castrated and alive than entire but destined for slaughter.

The final judgement is the concern of the owner, who must weigh the various considerations, and make a decision in keeping with their conscience. 

(c) AD Beck 2006