Why grass selection is a big question:
A common question I get is, "What should I plant in my pasture". This always is answered by a big inhale and a frustrating, "It depends". There are a lot (like a lot a lot) of factors that go into deciding which grass is the "best" for a farm- there isn't a simple answer. What works in South Eastern Virginia where I live, could be a disaster in Ireland or Iowa and vice versa.
Most research in and development of forages are done on behalf of dairy and meat livestock producers who are looking to create increasingly nutrient dense, hardy forages. Horses have vastly different digestive systems and dietary needs than cattle.The bits of equine related study are normally done on behalf of high performance horses. Few of us have horses working at the level of those athletes, we're just struggling to reduce NSC while keeping our hay bill out of the 6 figure range.
** In the name of readability and comprehension, some of these complex concepts are going to be summarized, (over)simplified, and generalized. If you'd ever like to get into a more detailed conversation about the intracacies of what we will cover below, I'd love to have that chat!**
How and Why Do Plants Make Sugar?
Plants use sugar/starch to sustain themselves in times of stress (and honestly who doesn't?). The more sugar a plant can store, the more resilient it will be.Keeping grass in its optimal state, will generally reduce its NSC production. So, what does grass find stressful? Again, it depends...
To really get into this conversation, you need to understand the two main types of grasses and knowing the types of grasses you're working with will help you make better choices on planting, grazing, etc.
Cool Season (C3) grasses - eg Fescue, Ky bluegrass, orchard, timothy, rye etc
Warm Season (C4) grasses - eg Bermuda, bahia, meadow bromegrass, indiangrass, switchgrass,
Why does climate matter?
Average temperatures, rainfall, cloud cover and more will impact what types of pasture grasses will give you the best results.
Generally speaking, plants create sugars via photosynthesis when the sun is shining and use that sugar overnight to grow and stay alive. Sunny days increase the amount of sugar a plant can produce and cloudy days lessen it.
Grasses grown in areas of high cloud cover will have less NSC production than the same type of grass grown under sunny conditions.
The cool and warm designation, as the names suggest, tell you when the plants grow best. Cool season plants have a greater tolerance to cooler temperatures (yay longer growing season), but they maintain this by creating sugar (dangerous for EMS ponies).
Cool season plants store their excess energy as sugar/fructose, they will hold on to these excess sugars to stay alive during frosts and droughts. Because of this, they generally tend to be higher in NCS than optimally grown warm season grasses.
Warm Season plants store their excess energy as starch and they they go dormant when temps get too low- around 50-55 F. Due to the lack of cold hardiness, they are generally lower in NSC than cool season grasses. However, this means that in times of high heat and no rain, starch accumulation (which allows the plant to survive) can increase, they also are late to green up and start producing in the spring
Temperatures below 40 degrees F, will cause cool season plants stop the respiration process and hold onto their sugar as frost protection. They will continue to photosynthize during the day (accumulating sugar) and holding it overnight as long as they have green leaves. During these times, common in the spring and fall, NSC can reach as high as 37% - Far beyond the 10% recommended for metabolic horses. Leading to concerns of "spring and fall laminitis". Warm season grasses are less problematic in this area, as they've been dormant since around 55 degrees.
Cool season grasses grown in areas where temperatures rarely dip below 40 degrees, will accumulate less sugar than areas where spring/fall/winter temps typically fall within 40-32 F where plants are still photosynthesizing but are unable to respire their sugars.
The takeaway is that cool season grasses are generally higher in NSC than warm season grasses, but the divide becomes increasingly concerning during cool, sunny conditions.
Considering Micro climates and sparse/overgrazed fields
Shade from trees (or even densely growing grass), warmth from sunny walls, wind breaks, water from overflowing water troughs, tops or bottoms of hills, etc will create microclimates that could make small impacts to the over all growing conditions and thus NSC of grasses. You may be able to take advantage of some of these micro climates when setting up your rotational grazing system. You should consider the impacts they can have on otherwise optimal grass species.
Preferred pasture grasses (fescue, rye, orchard grass, etc) grow in spite of the abuse and neglect (that is too often the case in horse pastures) due to the availability of NSC.
We know that plants need sunlight to create sugars/starches. When we consider a densely growing stand of grass, each tightly packed leaf has less exposure to the sun than if it was sparse and each leaf was fully available for photosynthesis.
A field that at the bottom of a hill, shaded in the afternoon and often "watered" by an overflowing/dumped water trough, could be a better option to graze than a field at the top of a hill in direct sun, that is overgrazed, and dry.
Rapidly growing grasses tend to be lower in NSC as the grasses are using the sugars to grow, leaving less in the plant. Grasses tend to store their sugars in the lower stems (bottom 3") of the plants rather than leaves, as such overgrazed pastures tend to have more NSC per bite than tall grass.
However, as NSC per bite decreases, NSC per acre tends to increase. This is where the use of strip grazing or limiting time on fields may come in to play to reduce access to large swaths of grass. To fully regrow an average "resting time" per pasture should be no shorter than three weeks. Increasing pasture height also allows us to produce more pounds of forage per acre than shortly grazed grasses. It's worth noting that overgrazed pastures can lead to competition from weeds, who are very hardy and thus (you guessed it ) high in NSC
Mature grasses tend to have lower NSC than short/new grasses however this can be heavily impacted by adverse growing conditions, and can't be accepted as a fact- Testing of pastures is still recommended. Seed heads on all grasses, tend to be high in starch (which should remain under 4% for metabolic horses).
How does NSC relate to hardiness:
It is easier to grow low-NSC grass in warm (not hot), cloudy climates, and more difficult in sunny, cool, dry climates. Cool season grasses, due to their higher sugar reserves, stand up better to high traffic, overgrazing.
Based on all of the above, the most commonly used grasses in horse pasture (particularly in regions with cold winters) must have a genetic potential for high levels of NSC in order to be productive throughout a long grazing season and to withstand the stress of intensive grazing, cold, and perhaps drought.
What do we do?
So, for those of us blessed to live in subtropical regions with fairly mild winters and hot humid summers (thank you SE Virginia) warm season grasses may be viable options to reduce NSC of our pastures. We can supplement with hay for the few months of the year that we are outside of our prime growing conditions (usually November - March for us) if we have the ability to properly rotate and manage pastures for optimal grazing.
One possible alternative for cooler weather is to grow native or warm season grasses as standing hay for grazing in the cool seasons- a project in its second year of experimentation at my farm. However, this requires the acreage to set aside for winter grazing. A luxury, I realize, not everyone has.
A more successful approach to growing low-sugar forage may be to choose grass species that are well-adapted to the growing area, and apply best management practices for minimizing stress and optimizing growth. Stress causes accumulation of NSC, and growth utilizes NSC. It's clear that rotational grazing, with ample time for grass to regrow (and thus use its energy stores) will be required for NSC management to work.
There will always be some trade-off between lower NSC and increased hardiness (the lower the NSC, the less resilient to stress/grazing). Knowing your grass and your current conditions should help you manage your pastures effectively, and restrict access as needed.
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Note: These are suggestions only and in no way guarantee the prevention of adverse effects of EMS. Also, this is meant to be a holistic approach. Choosing to follow only one piece of this advice may or may not deliver the intended result, as there are many variables involved. Work with your nutritionist, veterinary specialist to analyze each of your feed sources so that your horse’s diet may be optimized for its individual needs (and of course, to avoid harm to an animal).