Grazing dangers

MAKING HEALTH A PRIORITY

Grazing is an important part of a horse’s daily routine, but it isn’t entirely without risk. For some horses, grazing on too much rich grass can lead to laminitis, a painful, life-changing hoof disease that can be fatal in more severe cases. It occurs when the laminae – the tissues that suspend the coffin bone within the hoof capsule – become damaged and inflamed.

WHY IS GREEN GRASS A PROBLEM?

So, what is it about green grass that proves such an issue for certain horses and ponies? It all comes down to the density of the nonstructural carbohydrates (NSCs), which are the sugars (glucose, fructose and sucrose), starches and fructans that grasses produce during photosynthesis. When a horse digests NSCs, his body breaks them down into glucose and fructose, which the small intestine absorbs. This results in an increase in blood glucose concentration that causes the insulin levels to rise.

NOTE: In horses that are predisposed to metabolic disorders, the baseline level of insulin circulating is already high. If, on top of this, these horses ingest a high amount of NSCs they will secrete very large amounts of insulin. Abnormally high baseline insulin levels can also be a feature of pituitary pars intermedia dysfunction (PPID), formerly known as equine Cushing’s disease.

SO CAN MY HORSE GRAZE?

To determine how to manage horses on grazing, you must first identify which horses are most at risk of laminitis. The four factors that most predispose a horse to develop pasture-associated laminitis are:

• Being an overweight good-doer

• Being a pony

• Having high circulating levels of insulin (a metabolic disorder)

• Having had laminitis previously

NOTE: Some signs of high circulating insulin levels include hooves that grow faster than normal, abnormal fat deposits and ridges on the hooves.

Some vets are suggesting to proactive owners that all horses over the age of approximately 15 get tested annually for metabolic conditions as most epidemiological studies are showing that it is the undetected metabolic disease that is implicated in most of the new cases of laminitis. Therefore, testing to accurately assess risk allows management of that risk.

TIPS FOR LOW-RISK HORSES

If your horse has been tested for metabolic conditions and is negative, is getting plenty of exercise and isn’t on lots of concentrate feed, then managing his health is going to boil down to monitoring his body condition so you can make sure he isn’t consuming too much grass. However, even in this category of low-risk horses, you still need to watch out for those who never take a break from grazing or those who have suddenly moved into paddocks with grazing after the winter shortages. These are the horses who are likely to encounter issues, despite their low-risk profile.

TIPS FOR SUSCEPTIBLE HORSES

Susceptible horses should have limited access to grazing or no grazing at all to be completely safe. At the very least, it is important that they only graze when forages are low in sugar. Sugar content is highest:

• In immature grass (early spring and during re-growth)

• During periods of cool nights and warm sunny days (spring)

• After a hard freeze

• During drought conditions

• In the afternoons (typically)

• When the grass has been stressed (for instance, by overgrazing)

However, a key point to note is that whilst it is necessary in these equids to limit the amount of grazing and be careful about the time and type of grazing, the amount of movement should not be reduced. One option for achieving this is a grazing muzzle, as this restricts intake but allows the horse to keep moving. Other options include track systems, which can incorporate some pasture but also some dry areas with soaked hay. This limits the amount of grass the horse is given access to but keeps up their movement levels.

PASTURE MANAGEMENT

Managing your horse’s pasture is another key way to reduce their risk of developing laminitis. Consider these steps:

• Keep your pasture fertilised. There is a lot of research to show that grass deficient in nitrogen is higher in sugar, so if there isn’t enough nitrogen to create protein, the grass uses sugar to grow. Fertilise your pasture as often as needed, but of course, make sure to only re-introduce horses to the fertilised pasture once it is safe to do so.

• Manage weeds. Weeds can be high in sugar. Clover, dandelions, thistles and other broad-leaf weeds are particularly problematic.

• Don’t let the grass go to seed, or don’t allow grazing on grass that has gone to seed. The growth points where the seeds develop is where the sugar accumulates. As the grass starts to form seed heads, the portion of the plant that is highest in sugars is now elevated and easy for the horse to ingest.

• Plant warm-season grasses if you have mild winters. Bermuda grass and teff don’t tend to accumulate as much sugar as cool-season grasses such as fescue.

• Strip graze or divide your pasture into smaller areas or ‘strips’ that reduce the horses’ risk of overeating. As you move horses from one strip to the next, you can maximise the pasture usage without impacting its nutritional value.

• Only allow susceptible horses to graze in ‘averagely mature paddocks’. It is important that horses predisposed to laminitis are only allowed to graze on mature grasses, but not those that have gone to seed.

THE PROBLEM WITH PONIES

Ponies should all be considered at risk of laminitis, whatever their metabolic status. Ponies evolved in harsh environments and often have higher insulin levels and metabolic rates as a starting point. Furthermore, they can eat twice as much as a horse can per unit of body weight, so even grass with a relatively low sugar content can be problematic for the pony.

Immature grasses are high in sugar, and overgrazed (stressed) grasses are also high in sugars, so should both be avoided.

FINAL THOUGHTS

If you’ve determined that your horse is at low risk for developing laminitis, and you can manage pasture quality and quantity, then, by all means, give him access to it. Grazing is important for horses and can fulfil almost all their protein, calorific, and vitamin requirements.

With high-risk horses, on the other hand, it is vital to remember that grazing risks are not only present in certain seasons and in very green grass. Every horse must be managed as an individual. If they have serious metabolic issues, it is better for their health to heavily restrict their grazing access or remove it altogether. Whilst this may feel ‘harsh’, it is certainly better than laminitis in the long run. Just remember to keep the horse moving and give him access to low-sugar forage 24/7 to meet his other needs.