Acidosis

IN THE wild, horses consume an unchanging supply of fibrous, low energy forages for up to 17 hours a day. In order to deal with this feeding pattern, the horse’s digestive system has evolved to digest large quantities of fibre. The majority of starch, sugars, fats and proteins are digested in the stomach and small intestine.

The stomach is relatively small (about the size of a rugby ball) and digesta passes through the foregut fairly rapidly. It then proceeds into the hindgut where the fibrous fraction is digested by microflora, using the process of hindgut fermentation.

One core feature of the hindgut is the fragile population of micro-organisms that inhabit it. Anaerobic bacteria, fungi, and protozoa coexist contentedly in the hindgut when the system is working proficiently. Together, the microbes’ primary responsibility is to digest fibre.

Gut problems

Certain situations trigger the pH of the hindgut to drop sharply. The two most common causes are the overconsumption of high-starch concentrates or pasture grasses rich in fructan. In either of these situations, it is impossible for the stomach and small intestine to sufficiently digest and absorb the massive onslaught of starch. If undigested starch reaches the hindgut, it will be broken down and lactic acid will be produced, lowering the pH of the hindgut dramatically. This acid kills off the fibre digesters and inflames the gut wall (colitis).

With the fibre digesters depleted, the horse will not be able to digest fibre, the dung will become loose, the inflamed gut wall opens the way for the absorption of toxins into the bloodstream and the reduction in good bacteria allows bad bacteria to proliferate and take over.

Sudden changes in diet, stress, a course of antibiotics and wormers will also upset the delicate gut microflora balance.

Changes in the pH of the hindgut due to alterations in the microbial populations and acid profiles cause a condition known as subclinical acidosis.

Signs of sub-

clinical acidosis

One of the primary signs of subclinical acidosis is inappetence or decreased appetite. A horse is often reported to be ‘off his feed’. When the hindgut is overwhelmed with lactic acid, the intestinal lining becomes inflamed and irritated, causing the horse discomfort.

This irritation may be severe enough to induce behavior characteristic of colic. In a cruel twist, long-term exposure of the intestinal lining to a low-pH environment may negatively affect the absorptive capacities of these structures, limiting the amount of energy available for performance.

This is why no matter how much feed a horse requires, its meal size should never be larger than 2kg, the number of meals given, or the nutrient density of the feed, should be increased instead.

In addition to these health concerns, a link between subclinical acidosis and stereotypies, such as crib biting and weaving, has been suggested by researchers. Due to the precarious nature of the hindgut, it is less able to handle metabolic crises that healthy horses may be able to fend off. Therefore, horses with subclinical acidosis are more susceptible to colic and laminitis.

Buffer

A buffer is an agent that helps a target environment (in this case the horse’s hindgut and stomach) resist changes in pH.

Sodium bicarbonate is a well-known buffer used regularly in cattle and sheep feed. Because scientists know that changes in pH are unavoidable in these organs under certain feeding conditions, a buffer is used in an attempt to keep those changes to a minimum.

Even though the buffer may not be able to keep the environment at a constant pH, it is extremely effective in preventing tremendous shifts in pH.

Ultimately, it is these dramatic ups and downs that bring on subclinical acidosis. There are now many acid buffers on the market for horses.

Many of these are aimed at combating gastric ulcers and therefore are targeted at the stomach/foregut of the horse.

Subclinical or full blown acidosis occurs in the hindgut. This means that any supplement aiming to ease the effect of hindgut acidosis needs to survive the trip through the horse’s stomach in order to have an effect.

There are buffers available that work in a time release fashion which would be more appropriate; in the main these should at least contain calcified seaweed, as well as sodium bicarbonate and a yeast (eg Yea-sacc 1026). Check with manufacturers or a nutritionist.

Feeding

management

Of course the best way to combat this problem is by feeding appropriately. There are many things that we can do to help keep the gut healthy. Management changes can be implemented:

1, Assess if your horse really requires high starch concentrates or cereals; don’t give him them just because all his pals get them. If your horse keeps his condition and has enough energy levels for the job he is doing, then he does not require performance type feeds. Stick to leisure feeds with high oil and high fibre levels.

2, For performance horses requiring high levels of concentrate, make sure you split the concentrate portion into as many meals as it takes (remember no more than 2kg of concentrate per meal). Feed little and often. Feed along with alfalfa or chaff, this slows down the rate of passage of the feed and further aids digestion of starch.

3, Consider replacing some of the cereal portion with oil or sugar beet pulp.

4, Make sure any changes are made gradually, the gut microflora need time to adjust to the different type of feed or amount of feed.

5, Use products such as Yea-Sacc 1026 – particularly when changing feeds or feeding high levels of cereal. It promotes good bugs, increases digestion of fibre and reduces the effects of lactic acid on both the gut lining and the good bugs. Its stabilising effect on hind-gut fermentation means that cereal can be fed to provide energy with a lower risk of colitis, enterotoxaemia or laminitis.

6, If using performance feeds or high levels of cereal or if your horse is exhibiting signs of subclinical acidosis, then investigate the use of a buffer, speak to manufacturers and nutritionists to select an appropriate product.

There are, therefore, many things we can do to keep our horse’s gut healthy. The most effective is to feed as much fibre as possible (even to competition horses) and, also, not to overload the gut with starch by feeding concentrates little and often.