When winter gives way to spring, life begins to reemerge. As your pastures begin to green up with fresh new growth, horse owners need to exercise caution.

First, horses can be destructive to pastures and the forage needs to be established to ensure it can withstand grazing. Most importantly, new growth is high in non-structural carbohydrates (NSCs) and a horse’s digestive system needs time to adjust to its new diet. If a horse is not properly transitioned onto a spring pasture, it can lead to digestive disorders such as colic, bloat, contribute to equine metabolic syndrome, or even cause laminitis.

In the early spring, the cool-season grasses and legumes begin to emerge. Depending on your location, your warm-season grasses and legume plants will not begin to appear until late spring or early summer. As your spring pastures begin to establish themselves, it is always wise to allow the plants time to establish the new growth prior to grazing. You can review our Summer Pasture Management article for some general guidelines. For example, horses should not be allowed on a pasture until the plant reaches a minimum height of 6 to 8 inches (15 to 20 cm).

For further explanation on why you should exercise caution, grasses and legumes use the sun’s energy through photosynthesis to produce NSCs, or starch and sugar (fructans), during the day. The plants will then use these NSCs to grow or, if in abundance, store them for later use. The NSC content tends to be highest in the late afternoon, and once photosynthesis halts during the night, they decrease. However, this is complicated by the fact that when temperatures drop below 40° F (4 °C), which is common for many areas during the spring, plant growth stops and the NSCs accumulate in the plant.

Young growth also tends to be problematic for horses because it is so dense in NSCs and has much less fiber compared to a more mature plant. This is also challenging because young growth is more palatable to a horse compared to mature plants. Thus, horses usually eat as much as they can of the young growth to not only fill their stomachs, but also because it tastes so good to them. If a horse is left to graze uncontrolled on a lush, young pasture, it can lead to multiple and even dangerous health issues.

A horse that is not properly transitioned to a spring pasture is at risk for digestive disorders for a few reasons. First, the small intestine cannot absorb all the NSCs passing through it, therefore it will be passed into the hindgut of the horse. Second, when these large concentrations of NSCs reach the hindgut, it results in rapid fermentation and greatly alters the microbial population. This can lead to serious issues like bloat, which is a large buildup of gas in the colon. This is just one cause of large colon displacement colic. It can also lead to a mass die off of microbes, which in turn, can lead to laminitis or other health issues.

Typically, most horses in the winter have very little pasture to graze on and are fed hay. Even horses left out on pasture during the winter will need to be watched carefully. This is because the hindgut microbial population will need time to safely adjust to a new diet of green pasture forages. To prevent an overload of NSCs to the hindgut and to safely transition your horse to pasture, the following tips of limited grazing time are recommended:

  • Plant height should be at a minimum of 6 inches (15 cm) prior to grazing.
  • Begin by allowing horses to graze for 15 minutes for a few days.
  • Increase grazing time by 15 minutes per day, per the schedule below.
  • After this time, the horse’s hindgut microbial population should be adjusted and you can safely turn out your horses with no limits.
  • Exercise caution if experiencing periods of frost or temperatures drop below 40° F (4 °C). In that scenario, we recommend to reduce grazing time or only allow brief access to pasture (30 minutes).
  • Grazing muzzles can be used to extend the time a horse may spend out on pasture, as they can reduce pasture intake by as much as 75% in most horses.


Slowly transitioning your horses to spring pastures will allow the microbial population in the hindgut of the horse to safely shift to handle these new changes to the diet. It will also greatly reduce the risk of any digestive disorders. If you are concerned about your feeding plan, you can always contact us for advice or to answer any of your questions.
 

Chris J. Mortensen, Ph.D.