Updated: Apr 13, 2020
As winter slowly slips away, it often leaves fresh green grass in its wake. As tempting as it may be to let your horse indulge, that green grass may actually do more harm than good. So, before you turn your horse out to fresh green pasture here’s some information worth considering.
Not all grass is the same. There are several different types and some are more rich than others, especially after they’ve been mowed or are grazed upon frequently which stresses the grass and causes it to be more rich in non-structural carbohydrates (NSC). That being said, grass certainly is a component of a healthy diet as it can be rich in nutrition and fiber which is beneficial to gut health. Even for horses without metabolic disorders, it is important to correctly transition them over to grass through incremental grazing. For those horses that suffer from metabolic disorders, come spring time, grass is notorious for causing more harm than good.
Dr. Juliet Getty (an equine nutrition expert with an international following) says that “Transitioning a horse from hay to pasture must be handled with care; this point is non-negotiable. For every horse, a gradual change from hay to grass is required to allow the digestive system to adapt, but for the insulin-resistant horse, grazing time and duration can make the difference between soundness and a disabling condition like laminitis.” As a horse owner, it is important to keep the health of the horse a top priority. With that in mind, incremental transition onto grass is key. If a horse who has a metabolic disorder, is overweight, laminitic or cushingoid is left to graze at free will their natural instinct to eat fresh grass will lead to a dangerous overconsumption of NSC’s.
For these extra sensitive horses, environment temperature and sunlight exposure on the grass should also be taken into consideration as these both play a role in how much NSC the grass accumulates. Dr. Getty recommends taking these points into account when turning your horse out to grass: “When the night temperature is below 40 degrees F, the grass is too high in NSC. Once it gets above 40 degrees F at night, the lowest NSC level is right before the sun rises. The NSC level is highest in the late afternoon, after a sunny day.” With these points in mind, it may be ideal to let your sensitive horse graze in the early morning or late in the evening if possible and not when temperatures drop too low at night.
There are two classes of grasses, either warm-season or cool-season, which is based off of their growing cycle and how they metabolize and photosynthesize sunlight into carbohydrates. Cool-season grasses (orchard, timothy and fescue) can gather higher amounts of carbohydrates due to the storage of their fructans outside of the chloroplast in vacuoles that do not limit their storage. Whereas the starch production in warm-season grasses (clover and alfalfa) is limited within the chloroplast. Come springtime, it is the cool-season grasses that cause trouble because the environmental conditions during that time favor NSC production. Sudden and long exposure to cool-season grasses during the spring months to a horse who has been kept on hay during the winter can wreak havoc on the horse’s metabolism and digestive system which can trigger a variety of ailments, some irreversible.
In summary, while your horse may seem to beg for pasture time remember that letting them overindulge can lead to health issues. It is important to attentively manage your horse’s pasture time and for some horses, the best option may be no pasture time at all. For the horses this situation pertains to, it is best to keep them in a drylot and fed a diet that is low in NSC, along with a ration balancer. For the average horse, a gradual transition out onto grass pasture is still ideal as a preventative measure for the development of health issues associated with the overconsumption of fresh grass. Gradual introduction to grass pasture will allow their digestive tract to adjust to the higher levels of NSC and reduce the risk of microbial upset. Introduce them to pasture in one hour increments and increase it 30 minutes every 3 days or so. Managing time on pasture can ensure that the grass does not become overgrazed as this can cause the grass to become even more rich in NSC. Sending a sample of the grass that grows in your pasture to a lab for insight on the type of grass that grows there can also help ensure that you are creating the most successful grazing routine for your horse.