Benefits and shortfalls of forage for horses
Horses have evolved over millions of years to live on a diet of fibrous plant material,
or forage. They have become forage specialists, extracting nutrients from the tough,
structural part of plants that other animals and humans cannot digest. Given the
choice, almost three quarters of a horse’s time is spent foraging for its plant material
feed. Eating large quantities of a low nutrient quality diet in a ‘trickle feeding’ fashion
has been the horse’s evolutionary strategy.
Foraging behaviour
In nature, horses will forage for a variety of plant material, both grazing on grass and
browsing on herbs, shrubs, hedges and trees. Their highly mobile muzzles and sharp
biting incisors allow them to precisely select the plants they choose. Research trials on
stabled horses showed they spent longer browsing and less time on other behaviours
when given a variety of different forages rather than just one type. The taste sensation
of horses is highly developed and they will often refuse mouldy or stale feed, or feed
that they previously ingested just before feeling ill, e.g. with colic.
Horses have to spend long periods foraging in order to get the nutrients they require,
because their natural diet is relatively low in energy and protein and high in fibre. The
result is they have a high motivation to search out food and chew - behaviours that
will be directed towards less appropriate material such as wooden stables doors if they
are not allowed to be expressed. Forage is tough and requires more time chewing than
concentrate feed such as grain. Horses fed inadequate forage may wood chew or even
develop oral stereotypies (previously called vices) such as crib-biting and eventually
wind-sucking.
Despite the fact we think of our horses as domesticated creatures, we should not
forget that their behaviours and motivations are similar to those of wild horses.
Feeding your horse plenty of forage allows it to express a more normal repertoire of
behaviour; therefore ensuring good welfare.
Forage composition and digestion
As explained above, horses need to spend most of their time gathering and eating
forage because each mouthful of natural forage is low in nutrients. The structural parts
of plants contain tough material that is indigestible to mammalian gut enzymes.
However, horses and other herbivores e.g. cattle and sheep have developed a different
way of digesting this tough material. Herbivores have an enlarged gut compartment
that houses millions of beneficial fibre-digesting microorganisms including bacteria,
which break down the ‘indigestible’ fibre, releasing nutrients the animal can absorb.
Cattle and sheep are ruminant herbivores, because their ‘fermentation vat’ is one of
their stomachs (the rumen) within their foregut. Horses have adapted their hindguts
(their caecum and colon) into a fermentation vat, where fibre is broken down. The
beneficial micro-organisms are often called the gut microflora, and their health is
important to the overall health of the animal.
Fibre is a type of carbohydrate, just like starch and sugar. The difference is in its
structure, which is complex and bound together using bonds that only bacteria such as
those present in the horse’s hindgut, can break. In addition, more mature plants
contain a woody component called lignin bound to their fibre. Not even gut bacteria
can digest lignin, so the more lignified a forage, the less nutritious it will be. Straw is
a highly lignified forage.
Of course, not all forage is equal. The nutrient composition of straw is very different
to that of growing spring grass. The ideal forage for most horses is moderately high in
fibre, with a moderate protein and energy content. Too rich e.g. spring grass, and the
forage will not supply sufficient fibre while oversupplying protein and energy for
most horses. Too woody and fibrous, e.g. straw, and the forage will not supply
sufficient nutrients for most horses.
Benefits of forage
It is clear that horses have both a psychological and physiological need for adequate
dietary forage, which is a source of fibre. If not allowed to express their normal
foraging behaviour, many horses will redirect this urge into abnormal behaviour such
as wood chewing and the development of oral stereotypies such as crib-biting. If fed
insufficient fibre, horses suffer gut disorders from a disturbance of the beneficial
hindgut microflora. Feeding plenty of forage helps to reduce the risk of stomach
problems including gastric ulcers. Horses produce stomach acid almost continuously
and this builds up if the horse fasts for any length of time, increasing the risk of ulcer
formation. Forage should always be the foundation of every horse and pony’s diet,
with extra feed added only to balance out nutrients that may be in short supply from
the forage.
The benefits of feeding plenty of forage to horses include:
 A source of all-important fibre
 Keeps the hindgut microflora balanced and healthy
 Takes a long time to chew; therefore fills the horse’s time, reducing the risk of
abnormal behaviour development
 Allows a normal behaviour repertoire
 Supports normal digestive system function, reducing the risk of gastric ulcers
 Maintains a certain level of gut fill, which aids gut function
 Causes a more natural wearing of the teeth than a concentrate-based diet,
especially when fed from ground level
Feeding forage
Ideally, horses should be allowed to graze and browse naturally at pasture. But here in
the UK where space is short, and grass and plant growth slows to a stop over the
winter, this is not always convenient. In addition, many horse pastures have been
developed for production farm animals such as dairy cattle, and are too nutritious for
our horses. Pasture grazing may need to be restricted in the spring and summer and
supplemented with preserved forage in the winter. Strip grazing using mobile fencing
e.g. electric fencing is a useful method of restricting intake of rich spring/summer
grass, which is relatively low in fibre, high in protein, sugars and other hydrolysable
carbohydrates including fructans. The high moisture content of such grass allows
horses to eat large quantities very quickly, which can lead to gut disturbance, colic
and/or laminitis. Pasture that is particularly rich may need to be supplemented with a
lower nutrient quality forage such as high fibre haylage to ensure the horse’s fibre
requirements are fulfilled.
During winter, preserved forage should be fed to horses turned out on grazed-down
grass. Stabled horses should ideally have free-choice access to forage (ad lib). Ad lib
forage means there is always a little left when the next portion is fed. It is particularly
important to fed adequate forage overnight to ensure long periods of fasting are
avoided. A horse bedded on shavings and fed one haynet at 7pm, who finishes this by
11pm, may have 9 hours of fasting if he is fed again at 8am the next morning. This is
a recipe for gastric ulcer formation and an uncomfortable, grumpy, hungry horse.
In a few cases it may be appropriate for forage to be restricted; these include for
racehorses prior to racing and for very greedy horses that eat above 3% of their
bodyweight per day given the choice. But in these cases, forage should be given in
portions spread out over a period of time, and never in any circumstances less than
1% of their bodyweight per 24 hours e.g. 7.5kg/16.5lb fresh weight of average
haylage.
The consumption of forage can be slowed by feeding it in a small holed haynet, which
is useful for horses on restricted rations. Ideally horses should be given all feed
including forage from ground level because this simulates a natural feeding posture
and causes a more even wearing of the teeth. However, for horses who must have
their forage limited, haynets can help slow intake rate and avoid unhealthy periods of
fasting.
Haylage versus hay
Forage tends to be preserved in two ways in the UK – by cutting and drying as hay, or
by cutting, wilting then wrapping or bagging as haylage. The nutrient content of hay
and haylage depends on the grass species used, the time of year it is cut and the
environmental conditions at the time. Despite this, most haylage is more nutritious
than hay in terms of protein and energy. Haylage tends to contain more micronutrients
due to its preservation process – more nutrients are ‘sealed in’.
The often inclement weather in the UK means that making good hay is difficult. Good
hay is dried quickly and thoroughly. Rain on hay leaches out nutrients and increases
the risk of moulding on the field. If hay is baled at too high a moisture level,
moulding will occur in storage. Research has shown that all hay contains some dust
and mould spores, which are a health risk to horses. Horses – especially those stabled
- are very susceptible to respiratory irritation from inhaled dust and moulds, which
causes increased mucus production and airway constriction. Long term, the irritation
and inflammation cycle may lead to the development of allergic airway disease or
recurrent airway obstruction (RAO, previously called COPD). All hay should be
soaked for half an hour prior to feeding to horses, to reduce airborne particles. Bear in
mind that the liquid left over after soaking hay is basically contaminated water that is
a stronger pollutant than sewage; therefore it should be disposed of with care.
The haylage preservation process involves the forage being wilted rather than dried,
then baled and wrapped or bagged to exclude air. Naturally occurring beneficial
bacteria ferment the soluble carbohydrates in the grass, preserving it and creating a
palatable, dust-free product that is ideal for feeding to horses. No moulding occurs in
well-made haylage after wrapping, so total mould count is very low providing haylage
is fed within several days after opening. Nutrient losses from haylage as it wilts are
much less than those lost from hay during drying, so the end product is more
nutritious. Haylage was developed from silage made primarily for cattle, which is a
protein-rich forage that is often low in fibre. Nowadays, haylage made specifically for
horses is a more suitable higher fibre, lower protein and energy product.
Horse owners often feed less haylage than hay, but this is a mistake. To maintain an
appropriate fibre intake in your horse, you need to feed more haylage than hay
because haylage has a higher water content i.e. for every kilo of haylage, there is more
water and less actual haylage than a kilo of hay. If a horse puts on weight when fed ad
lib haylage, then a lower energy, higher fibre haylage should be fed instead.
Haylage tends to be more expensive than hay, but get good value by looking for a
higher dry matter haylage, preferably over 65% dry matter (35% moisture). In this
way you will get more forage for your money, and your horse will get more fibre per
mouthful of forage.
Shortfalls of forage
If forage is the ideal feed for horses, why do we need to feed anything else?
Forage can vary widely in nutrient content, as explained in the section on forage
composition. Feeding a hard working horse even the best quality hay will not supply
enough energy (calories) to support the work; therefore the horse would lose weight
without supplementary feed. Haylage tends to be higher in energy and protein than
hay, and therefore is a more suitable feed than hay for working horses. Horses do best
from a diet based on forage, with extra feed only added if the forage cannot supply
enough nutrients, therefore finding the most nutritious forage available makes sense.
On the other hand, for horses and ponies with low nutrient requirements who are good
doers and in light or no work, a high fibre haylage or soaked hay will supply all the
energy and protein they need.
Bear in mind that there is more to a balanced diet than simply meeting energy and
protein requirements. Even if an ad lib forage-fed horse maintains his condition - i.e.
is receiving enough energy and protein - he may not be receiving enough
micronutrients (vitamins and minerals). All forages, even the best quality grass,
haylage or hay can be short of minerals for horses, including sodium, zinc, copper,
iodine and selenium. In addition the process of preserving hay and haylage depletes
some of the vitamin E. Every essential nutrient plays an important role in healthy
body function and a balanced diet supplies all the essential nutrients in required
amounts every day. Horses fed only forage should always be fed a balanced source of
minerals and vitamin E. Some preserved forages will also be short of vitamin A
precursors, betacarotenes, so extra vitamin A might need to be fed.
It is not possible to determine which nutrients are in short supply from looking at
forage. The forage can be analysed, and this can help to formulate a balanced ration
for your horse. Reputable preserved forage manufacturers will supply a nutrient
analysis so do ask before you buy. Macronutrient (protein, fibre, energy) analysis is
relatively inexpensive, but micronutrient (vitamin and mineral) analysis is more
expensive. If in doubt, use either a broad spectrum or specific forage balancing
supplement to ensure your horse receives all the nutrients he needs for optimum
health.
Conclusions
In conclusion, horses have evolved over millions of years to survive on a fibrous
forage diet, and both their natural behaviour and healthy digestive function relies on
adequate supplies of fibre and forage. If you want to keep your horse healthy and
happy, feed plenty of forage – preferably ad lib. Choose the type of forage with care,
and ensure you maintain your horse’s respiratory health. Finally, make sure you
balance your horse’s diet with relevant supplementary feed or vitamins and minerals
because forage alone rarely provides a balanced diet.
© Clare MacLeod 2005