WHAT IS LAMINITIS?

Laminitis is a painful condition of the tissues that bond the hoof wall to the pedal bone. These tissues are the laminae. Laminitis can lead to tearing or separation of the laminae, progressing to tissue death and subsequent rotation of the pedal bone. Laminitis is more common in the front feet and does not usually affect just one foot.

WHAT IS THE DIFFERENCE BETWEEN LAMINITIS AND FOUNDER?

Both terms are often used to describe Laminitis conditions. Laminae are the structures within the hoof that connect the external hoof wall to the internal coffin bone. When the laminae are inflamed, the horse is said to have laminitis. When the bond between the bone and the hoof wall is damaged severely the bone starts to move inside of the hoof capsule, it moves downward or sinks. When that happens, the horse is said to have foundered.

DIAGNOSIS

A diagnosis of laminitis can often be made from observable symptoms such as:

• Difficulty walking and marked difficulty when turning.
• A “stiff” gait.
• Rocking back onto the heels in order to spare the toe region.
• Strong “bounding” pulses to the feet indicating increased blood flow and inflammation of the area.
• A marked reluctance to pick up feet.

Another important test is the use of hoof testers on the sole of the hoof. Usually this will indicate sensitivity in front of the frog in the region of the tip of the pedal bone. Percussion (tapping) of the sole or shoe may also demonstrate increased sensitivity.

CAUSES

One of the more common causes is carbohydrate overload. Existing research suggests that the starch and water-soluble carbohydrate of a horse’s diet is the main contributing factor in the development of laminitis. Current theory states that if a horse is given grain in excess or eats grass that is under stress and has accumulated excess non-structural carbohydrates (NSC, i.e. sugars, starch or fructan), it may be unable to digest all of the carbohydrate in the foregut. The excess then moves on to the hindgut and ferments in the cecum. The presence of this fermenting carbohydrate in the cecum causes proliferation of lactic acid bacteria and an increase in acidity. This process kills beneficial bacteria, which ferment fiber. The endotoxins and exotoxins may then be absorbed into the bloodstream, due to increased gut permeability, caused by irritation of the gut lining by increased acidity. The endotoxaemia results in impaired circulation, particularly in the feet. This results in laminitis.

LAMINITIS AND GRASS

Grass plants, through the process of photosynthesis produce simple sugars (carbohydrate) to create an energy source for the plant.  When sugars are produced in excess of the energy requirement of the plant for growth and development, they are converted into storage, or ‘‘reserve’’ carbohydrates.

Pasture grass in the UK accumulate fructan as their reserve carbohydrate, which is stored in the stem of the plant, until required as an energy source.  Therefore short, stemmy, tightly grazed pastures are likely to have an increased fructan content.

The grass plant requires a number of nutrients to develop and grow.  Applying controlled amounts of fertiliser will encourage the plant to grow effectively. If the plant has insufficient nutrient levels to aid growth the fructan is stored, as opposed to being used throughout the plant to aid growth.

Cold, frosty mornings are a particular time when fructan content can be extremely high.  The sunshine is still causing the plant to photosynthesise and produce carbohydrate.  However, because of the cold temperatures the plant will not be actively growing, causing the plant to store the fructan as reserve carbohydrate.  Grazing horses during frosty mornings should be avoided for these reasons.

The fructan content of grass can change from day to day and even within a single day.  Light, temperature, water availability and the species of grass are all factors, which will affect both the production rate and use of fructan by the grass.

GRASS management tips

• Apply sufficient fertiliser to keep the grass plant healthy.  This should be done after a soil analysis to determine nutrient availability.
• During high growth periods monitor grass intake carefully, and restrict grazing if necessary by strip grazing.
• Don’t turnout on frosty grass, particularly on a sunny morning, when fructan levels can soar.
• When applying grass seed select low fructan grass species, specifically designed for equestrian pastures.  Do not use agricultural grass mixtures which are high in fructan content.