Will fresh grass make my horse colic or founder?

After a solid week of sunshine and temperatures reaching mid 70's, it certainly feels like spring is just around the corner!  This also means many of us are eagerly anticipating our pastures greening up again.  However, would my horse suffer any negative side effects - such as founder, colic, diarrhea - from grazing pastures full of lush, spring grass?

Well, like so many times when it comes to horses, it depends.

Lush spring growth, for both grasses and legumes, not only has a higher moisture content (75-85%), but is also higher in protein, vitamins, and minerals on a dry matter (DM) basis as opposed to any other time of the year.  Horses have a very delicate microbiome (think probiotics in yogurt) in their cecum that plays a crucial role in their digestion.  If suddenly introduced to fresh pasture, the higher nutrient content can wreak havoc on the microbiome, causing cases of colic and diarrhea.

In addition, early spring pastures are higher in simple sugars and starch.  These are an excellent source of energy, but in large quantities can cause horses with any metabolic disorders, such as Equine Metabolic Syndrome or insulin resistance, to founder.

However, these problems mostly occur if horses have been stalled overwinter without any access to pasture.  Horses are incredibly adaptable and can adjust to changes in pasture quality (i.e. its nutritive value - how much protein, sugar, and minerals it has) over long periods of time.  If your horse was stalled overwinter, or if you know you are concerned your horse has a metabolic disorder, here are a few management practices you can do to help them slowly adjust to fresh pastures:

1. Restrict grazing time: Allow horses 20 minutes of grazing time the first day out on fresh pasture, then increase grazing time by 5 minutes each day over a 2 week period, or until they have fully adapted to fresh pastures.
2. Supplement with hay: Before turning horses out, feed hay to help fill their stomachs and prevent overeating.
3. Avoid grazing early spring pastures altogether: You can avoid problems associated with grazing early spring growth by waiting 4 to 6 weeks - or when the grass is 6 inches tall - before introducing horses to pasture.  It is good practice to still restrict grazing time and supplement with hay if you do this.
4. Use a grazing muzzle: If your horse is susceptible to founder, but must be turned out on pasture, use a grazing muzzle to limit pasture consumption.

For more information on spring pastures and founder, see our previous article: Spring Pasture, Fructans, and Founder

For more information on how to make sure your pasture is ready for spring, see: Spring Pasture Checklist