FORAGE is the most important ingredient in equine nutrition and all equines need at least 1% of their body weight in forage dry matter per day.

This equates to an average 500kg horse eating at least 5kg of forage on a dry matter basis, i.e. excluding the moisture content.

This is the minimum amount necessary to ensure a healthy digestive system and help prevent episodes of colic and ulcers as well as oral vices and dental problems.

In Ireland, grass does not grow all year round so it is necessary to preserve some for the winter months and also not every horse owner has enough land to graze all their horses so it may be necessary to purchase preserved forage.

TRADITION

The traditional method of grass preservation for horses is hay making.

This method involves drying the grass, thus lowering the moisture content to such an extent that stops decomposition.

However, this relies heavily on weather conditions, and ideally requires at least five days without rainfall and excellent drying conditions. Irish summers do not always provide such conditions and, if they do, it may be late July or early August when the nutritional value of the grass has passed its peak.

Silage, on the other hand, has become the most popular method of grass preservation for bovines.

It does not require such an extended period of sunny weather and the grass can be preserved at its optimum state of maturity, usually around the middle of May.

ENSILING FORAGE

The process of ensiling forage involves freshly-cut grass packed tight and sealed with plastic to exclude air thus allowing anaerobic fermentation of the sugars in the grass to produce acid, mainly lactic acid. These acids prevent further decomposition of the grass somewhat similar to the pickling process.

Silage pits or clamps are used where the fresh grass is packed tightly and sealed with plastic. It may often be covered with old tyres or soil to exclude air. Freshly-cut grass can also be baled and wrapped with layers of plastic to produce silage also. Silage produced from May grass is an ideal forage source for lactating dairy cows during the winter months as it is high in protein and energy and is very digestible.

The bovine digestive system is different from equines as they are ruminants and their digestive system consists of four stomachs that digest the grass through chewing the cud and fermentation. These large fermentation vats are not conducive to athletic performance due to their size and bulk. However they are more efficient than the equine digestive system. The equine has a smaller and simpler digestive system which has a specialised caecum and colon that facilitate the digestion of forage.

HAYLAGE

Haylage is in between hay and silage, as it is wilted or dried but not as much as hay.

It is then wrapped like silage which allows a partial fermentation of the grass sugars.

Therefore, sugar or sweetness remains, which some horses seem to prefer.

Most haylage resembles hay more so than resembles silage, and is normally harvested at the same time as hay. It provides an alternative method of preserving grass for the winter especially if the weather is not good enough to make hay.

Haylage requires one or two days less good weather than hay.

Due to the fact that it is not as dry as hay, there may not be as much dust, therefore making it suitable for performance horses that require 100% lung function.

THE SILAGE DEBATE

Feeding grass silage to horses has been a subject of debate. In some countries such as Finland and Sweden, many yards feed silage to all types of horses such as broodmares, young horses and even performance horses.

When compared to average hay it has superior nutritional value and lack of dust. The disadvantages would include difficult handling due to the extra weight of the bales, and the short shelf-life once a bale is opened and the silage is exposed to air. Ideally silage should be fed on the day the bale is opened as it starts to decompose rapidly on exposure to air. The silage should be golden brown and smell relatively pleasant, no hint of ammonia or smell of rotten grass.

PALATABILITY

Palatability may be an issue with certain horses, as all the sugar in the grass is converted to acid which takes the horse a little bit of time to get used to.

Therefore the horse may not consume enough for several days, thus causing concern for the owners. However, some studies have shown a preference for silage by some horses over hay or haylage.

BOTULISM

The main issue of feeding silage to horses would be the fear of botulism. This is caused by the introduction of a bacterium to the grass as it’s being cut and its incorporation into the silage. This bacterium can be introduced by cutting the grass too low, especially over rough ground, and contaminating the silage with soil.

It can also occur by accidental incorporation of a carcass (e.g. rabbit, sea-gull etc.) or poultry manure. The toxin that causes botulism can spread through the silage bale, not just where the contamination occurred.

Having said this, the reported incidences of botulism in horses due to silage contamination is very low, probably due to the fact that normally the silage is not fed from feeder wagons or other machines, but forked from a wheel barrow.

Therefore any black or foul smelling silage can be removed before it is offered to the horses. Also, silage intended for feeding to equines is wrapped with up to 12 layers of plastic to ensure exclusion of air, whereas silage intended for cattle may be wrapped with six layers of plastic.

This is due to the fact the in the bovine, the rumen acts to buffer some of the toxins making cattle far less susceptible to the effects of botulism and other possible toxins.

STOMACH ACID

The fibre content of silage is low in comparison to hay or haylage that is cut when the grass is more mature.

For a racehorse in training the main function of forage is often as a fibre source as the protein and energy is mostly supplied by concentrates.

Also silage is often chopped to allow compact-packing thus excluding all air, therefore there is less chewing required and less buffering of stomach acid. This excess acid leads to gastric ulcers which occur in the majority of racehorses in training. Therefore feeding of hay or haylage is preferred due to higher fibre content and more chewing required.

OLDER HORSES

The protein content of silage is usually higher than hay or haylage due to harvesting the grass in May rather than July. This protein level often exceeds the requirement of most horses, but does not cause problems in normal animals with normal liver and kidney function.

Older horses may not be able to cope with such a high level of protein over an extended period of time.

SPORES AND DUST

The main advantage of feeding silage is that there are no airborne fungal spores or dust that can occur in both hay and, to a lesser extent, haylage.

This means it’s an excellent forage source for horses with respiratory allergies or to horses in general if dust-free hay or haylage are not available.

OTHER ISSUES

  • A sudden change of diet may also disrupt the flora in the caecum and colon and lead to softer faeces, but this is normally resolved after a week or so. Gradually introducing horses to silage over a week normally overcomes this issue.
  • During very cold conditions, silage may freeze due to its high moisture content, and may lead to colic if consumed in large amounts.
  • Other crops may also be ensiled, such as whole crop maize to produce maize silage. This also may be fed to horses once it is of top quality with no spoilage. However, it is low in protein and higher in energy so would not be suitable for young growing animals or ponies prone to laminitis.

    • Dr Vivian Gath, BSc, HDipEd, MVB, PhD, MRCVS,

    UCD School of Veterinary Medicine