Analyzing sugar content in pasture grasses (Column)
(Editor’s note: Carey A. Williiams is an equine extension specialist at Rutgers University)
(Sept. 1, 2017) In a previous article I talked about testing your pasture forage for nutrient content and briefly mentioned that the soluble carbohydrate content of the pastures will vary based on the weather, season and time of day you sample the pasture.
This can also mean that when your horses are out grazing they can also be consuming grasses that have very large changes in the amounts of sugars as well.
In this month’s article I want to explain these changes and maybe help you make decisions about your horse’s pasture turnout and care.
Last month I briefly mentioned non-structural carbohydrates can range from 6-20 percent in a mixed grass pasture (i.e. Timothy, Orchard Grass, Tall Fescue, Kentucky Bluegrass, etc.).
The NSC of a forage includes simple sugars, fructans and starch; starch being the smallest contributor to this total.
Fructans are a polymer of fructose, similarly to how starch is a polymer of glucose.
These components are produced in the grasses through sunlight triggering photosynthesis.
The grasses use these products as an energy source to help them grow.
Sunlight is the key! The more sunlight, the more NSC products produced.
The tricky part is that when the grasses are producing the sugars and starches they are not using them at the same time, but are storing them for future use.
They store them all day so when the sun goes down at night they can utilize them to help the plant grow.
Therefore on a hot sunny day the NSC will accumulate all day long being highest in the evening hours (about 4-6 p.m., depending on the season) before sundown, and will be used all night being lowest in the morning (about 6-8 a.m.) before having enough sunlight to start accumulating again.
Is it really that easy? Not exactly.
There are many other factors that go into how much sugar and starch is in the grass.
Take for instance the season: After winter the grasses are young and trying to grow as quickly as possible in the spring, therefore the amount of NSC is even higher because of the increase in photosynthesis producing the sugars.
Another factor is the type of grass.
In the Northeast we primarily have cool-season grasses in our pastures (those listed above).
These grasses grow best in the cooler climates, and have spikes in growth in the spring and fall, but go dormant in the hot summer months.
In the south, warm season grasses are most dominant and flourish in the hot climates year round, these include Bermuda grass, Bahia grass, crab grass and teff.
Cool-season grasses have been found to have typically higher NSC concentrations than warm season grasses.
Legumes such as alfalfa, on the other hand do not accumulate NSC at all.
They use starch as their primary form of energy, but they have a shut off mechanism that will not allow them to accumulate levels as high as those in cool-season grasses.
Cool season grasses also have a mechanism where when stressed and growth is compromised they will store even more sugars and starches to help them during these times of stress.
By stress I mean drought, frost, overgrazing, or lack of the proper nutrients (i.e. unfertilized). So during these times the NSC content is expected to be higher than if these conditions were not present.
So if you are managing a horse that is prone to metabolic conditions like colic, laminitis, insulin resistance and requires a low sugar or starch diet, it might be time to think about managing your pastures and turnout regime to help eliminate the possibility that you introduce your horse to a pasture full of sugary candy! Here are my recommendations:
• Do not overgraze your pastures. Rotational grazing is recommended. See Rutgers NJAES fact sheet #368 and #1271 for more information here (https://njaes.rutgers.edu/pubs/);
• Fertilize your pastures based on a soil test to ensure that your grasses have to proper nutrients for optimal growth;
• Avoid turning out on over-grazed or under-grazed pastures. Overgrown pastures with lots of seed heads are just as bad and also have a lot of NSC. Keep pasture mowed or around 6-8 inches and take the horses off the pastures when they reach 3-4 inches;
• Turn out horses in the very early morning and bring them in by 10-11 a.m;
• Do not turn out after a night of frost or when drought stressed;
• Turn out horses on a shady pasture or paddock or on a cloudy day; and
• Keep your horses’ body condition around a 5-6 on the Henneke Body condition scoring scale (for more information see https://www.youtube.com/playlist?list=PLS_j7MIcs2AE9of8ZJGrD4B-CiLvcSJjW).