Beautiful to look at, wonderful to smell and if you’re a horse there is nothing you would rather be eating and arguably nothing more natural you should be eating. On the other hand, there are a few precautions.
First, the good stuff! Very young, succulent growths of pasture have lower percentages of fiber, higher percentage of easily digestible or fermentable carbohydrates and significantly higher levels of protein than older growth stages. Protein level may reach 20+% even in grasses that typically test around half that when put up as hay.
This is terrific news for heavily pregnant or foaling mares with high nutritional demands for milk production. Other horses will reliably gain weight on spring growths of pasture when access is not restricted. The lower fiber and higher levels of other nutrients make it more digestible.
In addition to the weight gain, horses on ample spring pasture typically literally glow with good health. I’m sure we don’t know all there is to know about what is behind this bloom but among known factors other than the protein are high levels of antioxidant vitamin E and vitamin C compared to hay, and peak levels of fat which is predominantly in the form of omega-3 fatty acids. Grasses also contain a full complement of B vitamins and many of the same metabolic cofactors as horses use.
On the side arguing for caution it is important to realize that a switch from baled hay to spring pastures is just as much a significant diet change as putting a horse on grain. It should be done gradually to avoid digestive upset such as bloating and diarrhea. Even horses accustomed to being turned out 24/7 may need their access restricted somewhat if grass begins to green up very rapidly. If that is not possible, be sure to continue to offer hay. Many horses will instinctively go for the higher fiber as a “supplement” to the grass.
The biggest caution is for the 10% or so of horses known to be insulin resistant or with a history of pasture related laminitis. They may not develop full blown laminitis every year but the higher levels of simple carbohydrate in these grasses is a major risk factor. Even when not blatantly laminitic there are likely pathological changes in the feet. There is no way to protect from this, including no grazing time limit that is reliably safe, so the best approach is simply to keep these horses off early growths of pasture.
Finally, in some areas early spring green growth is predominantly onion grass. Onion grass is a darker green and grows taller than typical pasture grasses. Blades are rounded compared to other grasses and have a distinct onion odor if opened. When pulled out of the ground you will find a small bulb just below ground level. Horses eating large amounts of onion grass because little or nothing else is available can develop Heinz body anemia. Both the prevention and the cure is to provide supplemental feed/hay until other grass types come up.
Understand the pros and cons, manage accordingly, then go ahead and enjoy!
Eleanor Kellon, VMD