by, Steffany Dragon

Although I’ve always taught the impact and risks of sugar content in grass, feed and hay, the dangers of Spring grasses have even more  importance to me now that my horses and I have moved from Florida to North Central Tennessee. Sadly, I discovered that many people on the Cumberland Plateau had experienced laminitis or founder at some point owning horses here. After assisting with the nutritional care of two acute cases and partnering with the local veterinarians, it became evident that due to the climactic changes and stressors in the area, there was a heightened threat from grazing for potentially sugar-sensitive horses. Wherever you are located, knowing under which conditions grazing (which usually provides nutrition and sustenance) may pose a threat to your horse’s health is worth understanding.

There are many articles written about sugars, starches, and fructans in grasses that pop up every Spring, but the rules of thumb always get convoluted because of the exceptions. I decided to come up with a concise resource and some simple graphs that horse owners may refer to when determining turnout schedules during the most common Spring scenarios.

Before presenting these scenarios, I would like to point out that many horses do tolerate and thrive on pasture turnout. In fact, there is nothing more natural and satisfying to see than horses out grazing on good grass!  My quarter horse gelding, for example, is a hard keeper and shows no signs of metabolic abnormalities so he gets to do this quite often. Even with him, I pay close attention and take the weather and stressors on the pasture into consideration as I manage his turnout. I do not want to find out through an episode that any horse of mine is more sensitive to sugar than I had thought, so I use this information to determine to the best of my ability, how much and when they can safely graze.

If your horse is an easy keeper, has any patchy fat or the slightest cresty neck; has been diagnosed with PPID (Cushing’s Disease), Insulin Resistance or Equine Metabolic Syndrome, or has had an episode of laminitis or founder in the past, you most likely know the importance of a dry lot or removing your horse from pasture. I will be referring to horses that fall into any of these categories as ‘sensitive horses.’ Knowing when pasture grass can become dangerous is the most important part of prevention.

I am a huge advocate of the benefits of “chew time” in keeping a horse healthy so I cannot stress enough that when removing your horse from grass pasture onto a dry lot, still provide him enough of a low sugar, low starch hay for him to eat it “free choice” throughout the day and night. I recommend using hay nets, slow feeders, and placing hay in various areas in the lot to encourage movement. My gelding is a ‘dunker’ and while I love that he is always hydrating while eating hay, I only provide a 5-gallon bucket where he dunks next to his hay while making sure the water trough is in a different part of the lot so he has to walk to it! A grazing muzzle also works great on my mini, allowing him the freedom to be with the herd while decreasing his grass intake anywhere from 50-80%.

If you pay attention to the following scenarios and factors, you may be able to manage your horse’s turnout to mitigate risk that Spring environmental factors combined with metabolic sensitivity may create.

Scenario 1: Mild Night before Sunny/Partly Sunny Day.     Graze sensitive horses any time after 3 am until 10am. (Fig. 1)

Scenario 2: Cold Night before Sunny/Partly Sunny Day.
Do Not allow sensitive horses to graze pasture on these days. It’s just not worth it. These are the most dangerous conditions because photosynthesis makes more sugar that accumulates on top of what was stored the day before since the nighttime temperatures were not warm enough for the plant to mobilize the sugar for growth overnight.  (Fig. 2) A Cold Night is defined as reaching freezing or near freezing temperatures. My guideline is 38°F.

Scenario 3: Cold Night before Cloudy Day. If there is little to no sunshine, photosynthesis cannot occur, so more sugar is not being made on top of the prior day’s sugar. However…temperatures are still too cold for respiration so for sensitive horses, it is still advised to wait to turn out until the next day AFTER a mild evening where respiration can take place and the sugar is used up for growth overnight.

Scenario 4 (SAFEST):  Mild Night before Cloudy Day.
Your horse and you will love these days!  If there is significant cloud cover, you can extend grazing by a few hours since sugar was used up during the mild night before during respiration for plant growth and photosynthesis will occur more slowly during this day since limited sun results in less photosynthesizing of sugar!

 Now that you understand the common scenarios and their effects on the concentrations and timing of sugar in pasture grass, it’s time to pay attention to the weather forecast! There are a few other factors worth mentioning, some in our control and others not.  As inflammatory as it sounds, a stressor of any type on grass has irrefutably led to higher concentrations of sugar and laminitic episodes and founder in otherwise safe pastures and healthy horses. Stressors include drought, over grazing, colder temperatures in general, an abundance of sunshine, too many weeds competing with the grass, abrupt temperature changes, or poor soil health. One misconception is that very short, overgrazed pastures are safer, but they fall into the category of being very stressed for survival and the sugar content in that grass is concentrated in the bottom 3 to 4 inches. Removing horses from grazing pasture before it is below 3-4” inches has multiple benefits. It reduces sugar intake per bite that is stored in the short blades but also prevents horses from chewing below the growing points of the plant, allowing the pasture to grow and become restored more quickly and fully. Proper liming, fertilizing, weed management and even irrigation if in a drought can reduce stress on your grass pasture providing safe grazing for your horse.

 Hopefully this simple recap of plant physiology and practical ideas for when and how to reduce grazing risk on Spring pastures will be of use this year as you manage your horse’s turnout. As always, please use this information in conjunction with routine veterinary care.