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GENETICS
Just
as people of different ethnic origins have diverse languages, body
shape, colour, stature and disparate tastes in food, so horses have
sizes, shapes and behaviours that are exhibited to a greater degree
in one breed than in another. Genes, in conjunction
with environmental influences, determine how our horses look and
behave. This interaction between genetics and the environment
occurs naturally; it is known as natural selection and is the basis
for evolution, as we shall see when we
consider horse types. The term artificial selection describes
the process by which man can influence the genetic make-up of
animals. By selectively breeding for favoured bloodlines, we
can speed up the process of developing different groups of horses
that breed true. These groups are the breeds. just as with
people of a different nation, horses of different breeds show
characteristics that are common to a family group.
Type
Environmental features of
a region, such as the climate and the landscape, foster the
development of certain behavioural traits and conformational
features which improve the survival chances of resident animals. We
can see this effect in the two recognised horse types: the so-called
'hot-blooded' horses (such as the
Thoroughbred) and the
'cold-blooded' ones (such as the Clydesdale). These terms do not
actually refer to the horses' blood heat but are general labels for
their body shapes, temperaments and climatic origins. In fact, it
is known that the skin can be maintained at a constant temperature
even though the climatic temperature may vary. Hot-bloods can
tolerate changes in the air temperature in the range +5°C
to +30° C (37°F
to 86°F), while for cold-bloods the range
is from -IO°
C to +20° C (15°F
to 68°F).
The cold-bloods developed
in the cooler habitats of Europe and Northwest Asia, while the
hot-bloods have their ancestral homes in hot, dry regions close to
the equator. Thus, an archetypal cold-blood is equipped with a
chunky body in order to reduce heat loss, a tendency to increase
body weight in times of plenty by the deposition of subcutaneous
fat, and the capacity to grow a very thick winter coat. He is the
one with a phlegmatic temperament. The hot-blood, on the other
hand, is behaviourally more reactive, or flighty, in that he tends
to respond to more subtle stimuli. He has a thinner skin than his
cool country cousin and his athletic physique more rapidly turns to
a bag of bones when exposed to hard times.
The build of a cold-blood
befits the terrain that his ancestors encountered in the wetter
northern territories such as the steppes of Russia. Having to plod
through bogs and marshes demanded the strength of heavy-boned legs
and muscles to match. However, in habitats such as the semidesert,
at the other end of the climatic spectrum, the long distances
between water sources and areas of good grazing meant that sheer
endurance was more of an aid to survival. just as the narrow tyres
of a racing bike maximise performance in a velodrome while those
fitted to a mountain bike are more suitable for variable terrain,
the finer legs and smaller hooves found in hot-blooded horses are
more efficient for sustained work on the harder ground of semidesert
habitats.
The debate continues as to
when the process of domestication first began for the horse, and
fresh archaeological evidence is continually being uncovered to add
to the discussion. Bit wear on the molars of horse skulls that date
back to 6000 BC, is thought by some to mark the first use of horses
as riding animals. However, this assumption fails to address the
possibility that before that time horses were ridden in bitless
bridles. Whatever the date of the first-ever riding lesson, as
herbivores with large muscle masses early domesticated horses
probably first found their way into man's domain by virtue of their
appeal as meat animals. It is also possible that, rather than being
simply harvested from the wild, these animals were penned up or
housed. Evidence of their having been housed dates back to 2000
BC,
since skulls front this time have been shown to bear signs of
crib-biting, which is thought to arise only in confined animals.
So, starting with hot-
and cold-blooded types that had adapted the species
to different
habitats, man has selectively bred horses for a variety of
behavioural traits. Taking any indigenous type , as his raw
material, he was also able to select different sizes and shapes for
different kinds of work. The Arab and the shire perfectly
illustrate the diversity in the origins of the domestic horses we
see today. Both breeds have been finely selected by man, thereby
grossly exaggerating conformational differences. It is said that
the Shire was initially the product of intensive breeding for a
massive warhorse capable of carrying heavily armoured knights into
battle, while the cultural importance of the Arabian horse in the
Middle East highlights the value to Bedouins of an animal that had
been bred to cope with extended journeys from one camp to another.
The numerous breeds are
usually described as being either horses or ponies. Before
considering the differences between the two, it is worth emphasising
that they are more or less variations on the same theme, except that
there is a height limit of 14.2 hands (148 cm (58 ins) from the
ground to the withers) below which an equine is referred to as a
pony. Between ponies and horses we find 'cobs', which are often
regarded as combining the best features of both ends of the market.
Being over 14.2 hands but having the sturdy build that one expects
in a pony, as occupants of the middle ground between horses and
ponies cobs help to confirm that the distinction between the first
two is largely a semantic one. As if to highlight the fact that
14.2 hands is only, an arbitrary cut-off point, aficionados of
certain breeds completely ignore the distance from the animal's
withers to the ground. Hence one never encounters such a thing as
an Arab pony or a Polo horse. Similarly, we are told that the
Falabella breed is technically a horse even though it stands, on
average, around 75 cm (30 ins) high.
The main differences found
in ponies when we compare them with horses are to do with the body
shape and metabolism that accompany being short-legged. The equine
digestive system relies on a glorified rotting process involving
bugs in the large bowel. This decomposition is called 'hind-gut
fermentation'. Because the hind-gut is so important for the
breakdown of food, it is especially large in pony breeds that have
had to make the most of limited resources, such as the Shetland pony
which in its Scottish homeland often resorts to seaweed for
nutrition. This comparative increase in the ratio of gut volume to
body size makes the pony more efficient as a digester of plant
fibre; and it may be this efficiency that makes it more likely to
suffer from disorders such as laminitis and hyperlipaemia when it
has access to food that is too rich. That these problems are
especially common in the smallest of the ponies serves to confirm
that they are directly linked to the diminutive size of these
specimens of Equus Caballus (the Latin name for the domestic
horse/pony/cob).
At the other end of the
equine forecourt, horses have their own set of problems that are
specifically linked to being tall. For example, diseases like
whistling and roaring, which involve a lack of control of the
larynx, occur almost exclusively in horses and are particularly
prevalent in exceptionally tall individuals. Because disorders of
the respiratory tract are so common in really tall horses, the
ceiling has more or less been reached in terms of breeding the
biggest horse. Beyond 17.2 hands, wastage due to problems of this
sort means that further breeding efforts are uneconomic.
Physical differences
between horses and ponies rarely have repercussions when it comes to
behaviour. Even when we take into consideration their smaller
frames, ponies have particularly small heads, and especially tiny
ears, when compared with horses, and to the human observer this bas
the effect of making a threatening grimace from a pony less dramatic
than the equivalent from an aggressive Thoroughbred. Humans are
generally not very good at reading equine body language. No doubt a
horse would interpret such a gesture from a pony quite correctly,
and perhaps this is why examples of domineering equine dwarfs are
fairly thick on the ground.
My favourite bas to be
Seamus, who was the resident Shetland pony owned by the Australian
ranch on which 1 used to work. At feeding time, all the working
horses would be penned up individually and given their concentrate
rations in recycled twenty-litre (5 gallon) metal containers. But
the sides of the pens were not low enough to curb the advances of
the little emperor, who would march from one pen to the next
pillaging food from the occupants, who were often three times his
size. As if to embellish his image, he would often have his head
stuck in the feed tub from the previous pen as he moved to his next
conquest - such was the intensity of his feeding frenzy. Images of
Ned Kelly, the Australian outlaw famous for his taste in metallic
millinery, would spring to mind.
Breed
The types of horse
available to early man for domestication were products of natural
selection and thus of the climate and terrain of the locality in
which they evolved. It is from these original types that man has
developed the different breeds. Thus the behaviour and conformation
that we see in them are also products of the environmental
conditions which moulded their ancestral types. Naturally, through
artificial selection, man enhanced certain physical and behavioural
characteristics which would increase a horse's usefulness. These
are called breed-dependent characteristics.
The ability to find
shelter in response to the need for it is a good example of a
breed-dependent behaviour. As representatives of a hot-blooded
breed, Thoroughbreds are more likely to stand still in cold weather
and look miserable, while native ponies plump for the far more
sensible option of continuing their search for food or finding
shelter. Naturally, sheltering strategies involve a degree of
learning - as in the New Forest foal that follows its mother under
the cover of holly bushes when the rain sets in. However, learning
is just part of the story, since these animals'
genes have only
survived by demanding that shelter be acquired. The genes of
Thoroughbreds, on the other hand, with their more glamorous Persian
origins, have not had to meet so many challenging winters and so are
less well attuned to the advantages of shelter.
Similarly, in mountainous regions, the landscape
has favoured the selection of animals with innate sure-footedness,
and this comes with the ability to keep one's head in a
crisis - which is really another way of describing
an animal with a low reactivity score. Traditionally it is
maintained that the Highland pony was developed for bringing game
down from the hills after a day's shooting. Clearly, a horse that
showed a tendency to tear off at speed every time a grouse broke
cover from underneath his feet would not survive long in this tricky
terrain.
Man can enhance Mother
Nature's work by selecting genes which influence behaviours that he
favours. This means more than simply selecting quieter horses,
which are predictably easier to ride. For instance, in parts of the
world where livestock are still mustered from the back of a horse,
the ability to pursue an errant herd member is an extremely
desirable equine behavioural trait. And it can be bred for, along
with the short back and low centre of gravity which enhance a
horse's ability to turn on the proverbial sixpence and manoeuvre
cattle back into or away from the herd. The American Quarter-horse
demonstrates these herding and manoeuvring traits beautifully.
Another behaviour that is
breed-specific is homing ability which, while present in other
breeds, is legendary in Icelandic ponies. Why the equines of a
northern island should have a refined talent for finding their way
home is not clear. A similar characteristic is a feature of
Hardwick sheep, who are adept at finding their way back to their
birthplace. As a result, farmers with this ancient breed have to
rely less on fencing to keep their stock in the locality. So
perhaps this same ability bas appealed through the centuries to
Icelandic pony breeders. Indeed, the idea is by no means
unattractive to me whenever I weigh up the merits of being able to
ride back from the pub of an evening. Equally, having worked for a
horse dealer as a child, I find the mischievous side of me
speculating that this trait would be an excellent way of
ensuring
that you could sell the same horse many times over! Interestingly,
the behaviour of Icelandic ponies is also breed-specific when it
comes to gait, since they display the amble' which is somewhere
between a walk and a trot.
The development of draught
animals necessitated the selection of heavy creatures that could
start to shift a wagon just by leaning into the collar. 1 have great
affection for these characters, but I have to say that their ability
to drag things along the ground is not confined to vehicles. Hungry
carthorses have considerable pulling power, as anyone who has
attempted to prevent a Sire mare from getting to her evening meal
will testify. That lady is certainly not for turning! Heavier
horses are not only the most awesome when it comes to barging but,
similarly, they are notorious for leaning on the bit when being
ridden. Also called 'working on the forehand', this offers another
example of how breeding can influence behaviour.
The ways in which a
horse's breed affects its behaviour can even involve body language,
since the tools used for sending signals can differ from one breed
to another. For instance, Arabian horses and their crosses are very
demonstrative with their tails, rather like Pointer dogs are with
their forepaws. An Arabian raises his tail with tremendous
frequency but, most of the time, this is simply part of his way of
balancing himself when moving. In contrast the same elevation of
die tail by a Dartmoor pony would indicate a display of amazement or
exuberance.
Family
group
Every time a horse owner
decides to breed from an animal because of a particular physical or
behavioural attribute, he is doing what horse breeders have done
throughout the centuries. Any horse breeder will tell you that
certain family groups display certain mental characteristics. This
can influence the choice of stallion when the time comes to select a
mating partner, for instance - a gentle stud will be favoured for
use on a particularly talented but aggressive mare. Temperament is
known to be under genetic influence, and it follows that behavioural
problems like weaving and crib-biting have also been shown to arise
in individual Thoroughbred families.
Naturally, we breed from
horses which have performed successfully because we know that, quite
apart from selecting for good physique, we have to select bloodlines
which have the temperament to excel in particular disciplines. This
sort of psychological feature can be as simple as the family's
attitude to the type of work required. For example, the dams of top
police horses are likely to have been more suited to crowd control
than to winning the Two Thousand Guineas. |
