Fall and Winter Bring Forage Risks

Now that we've had our first frost in Central Kentucky (and many areas have had more than that), your pastures might be higher in carbohydrates and thus more dangerous for laminitic and/or metabolically challenged horses (such as Cushingoid ones). And while weather plays a significant role in forage carbohydrate levels, high levels often trace back to grass species that were bred for improved production (via higher carbs) in cattle. At the first Equine Forage: Risks and Rewards Seminar and Summit held Oct. 22-23 at Rutgers University, Katy Watts, BS, director of research for Rocky Mountain Research and Consulting, Inc., explained what factors cause carbohydrate accumulation in forages and how owners can manage their horses and pastures to keep carbs lower for horses that can't tolerate high-carb diets.

"A horse is not a cow, so why do we feed them the same?" asked Watts. Unfortunately, she says, many of the "improved" grasses in pastures were designed to maximize cattle weight gain and milk production and aren't good for horses, particularly horses that are laminitic and/or metabolically challenged. The high levels of carbohydrates can cause colic and laminitis in some horses.

"Forage scientists confer with dairy and sheep producers all the time, but when I went to see Dr. Jerry Chatterton (PhD, Research Leader of the USDA Forage and Range Research Laboratory Leader) in Utah, he told me, 'You are the first horse person ever to sit in that chair,' " Watts said. "The dairy industry has directed the forage industry by default." She noted that higher-carb forages generate better production in cattle, and they tend to be hardier and more palatable than lower-carb versions.

Until lower-carb varieties of pasture plants are developed, she said, horse owners need to do three things:

  • Understand how sugar is formed in grass;
  • Recognize the effects of environmental conditions on non-structural carbohydrates (NSC, the storage carbohydrates of plants that can be dangerous to horses in large amounts) content of forage; and
  • Use this information to make better decisions on hay selection, pasture management, and "safer" times to graze.

Just because forage looks bad doesn't mean it can't be rich in sugars.
(Left) This is a sample of fescue that caused two chronically laminitic ponies to relapse after two days of grazing in mid-December. It tested 29.6% of dry matter as non-structural carbohydrates (nearly twice the level of average fescue hay). This sample, collected Dec. 21, 2003, in Colorado under drought conditions, had not had any rain or snow to leach out sugars. Later, after a heavy snow that melted, the ponies grazed the same pasture without a problem.
(Right) This rye grass tested 39.7% NSC dry matter in January in Colorado, under drought conditions.


Carbs in Pasture Plants

To help attendees understand how sugars form in grass, Watts described several factors that affect NSC content in forages, including:

  • Type of grass (cool- or warm-season, or variety);
  • Temperature;
  • Water;
  • Light intensity;
  • Time of day;
  • Stage of growth;
  • Speed of hay curing;
  • Nutrient status; and
  • Plant part.

Cool-season grasses tend to have higher amounts of NSC than warm-season grasses, but not always. "The level of NSC at any given time for a given species cannot be taken out of context from the environmental conditions that produced it," she explained. "A certain species of grass may be low in NSC under one set of conditions, yet high under other conditions." (For more information on grasses and carbs, see also "Nutritional Value of Forages," www.TheHorse.com/ViewArticle.aspx?ID=5249.)

What are those conditions for high-carb pasture and hay? Sunny, cold, and dry, she says. "Photosynthesis (the plant's process of making of sugars from sunlight energy and carbon dioxide) can even occur under a thin layer of snow, and respiration (the process of using up sugars for growth) slows in cold temperatures and stops at freezing." Thus, cold temperatures and sunny weather stimulate lots of sugar production, but little sugar utilization, so the sugars build up in the plant. Frost isn't as big of a problem as the amount of time the grass was below 40ºF, she added.

Cloudy weather and shade result in lower sugar gain. So it might be a good idea to put a laminitic or metabolically challenged horse in a shady paddock instead of a sunny one, or limit his access to pasture in sunny, cold conditions.

Also, Watts noted that "starving" grass by not fertilizing or watering it doesn't help reduce carbs; in fact, it promotes the opposite. "Drought-stressed plants can be even higher in carbs than green, full, thick, gorgeous grass," she commented. Nutrient (nitrogen and/or phosphorus) deficiencies are known to trigger more accumulation of NSC--the utilization of sugars for growth stops if there isn't enough of these nutrients. Thus, she said, "organic" forages (i.e., all-natural) may be higher in NSC unless the plants' fertility needs are met by other methods.

In fact, fertilizing pastures can lead to lower NSC content. Watts reported a trial she did in which fertilizing pasture with 35 pounds/acre of nitrogen resulted in 29% lower NSC and three times the dry matter yield for the first cutting.

Time of day also affects NSC content. She reported that NSC content is lowest from 3 a.m. to 10 a.m. since the plant has spent all night using up sugars for growth (if conditions have been favorable, or warm enough), and hasn't yet synthesized more sugars using sunlight.

Watts did not list season as an important factor, as it's the weather conditions that are important, not time of year. The conditions that trigger high NSC accumulation can exist in spring or fall, although "lush, spring grass" is usually cursed as a culprit in laminitis attacks. But owners can't get complacent after spring has passed, she warned.

In trials of different forages following four to five nights of hard freeze in the fall, she has found that NSC contents can rise as high as 33.1% (perennial ryegrass in late afternoon). Even timothy, long considered by many to be a lower-nutrient forage than many other plants, tested at 26.4% NSC. "And perennial rye is the quintessential founder fodder," Watts stated. "It's three times higher in sugars than some other species. If you have an at-risk horse, avoid this grass like the plague."

Another trial tested "dead" grass (in Colorado in January, complete with snow) and found very high levels of sugars in various plants, after a fall with very little rain or snow to leach out sugars accumulated as the grass froze.  Tall fescue in these conditions had 31.9% NSC (twice the average of average fescue hay, she added) and perennial ryegrass had 39.7% NSC. 

The part of the plant grazed is also important. She explained that NSC content tends to be very high in developing flower parts (so mowing or grazing to avoid seed head formation can help keep NSC lower) and lower parts of stems (so overgrazing can actually be worse in terms of NSC than grazing good pasture).

Carbs in Hay

The best stage of growth for low-NSC hay is generally slightly over-mature, with fully developed seed heads, Watts said, although environmental conditions are more important. She notes that seed shatters in overmature hay (so high-NSC heads aren't usually in the hay), and the photosynthetic capacity of mature leaves (to make sugars) goes down. Humidity and any rainfall between cutting and baling play very large roles in NSC content as well.

"Cut grass is not dead; it will continue to make or use sugar until the moisture content is below about 40%," she explained. "The longer it takes to dry, the more sugar might change from when it is cut. Cloudy, high-humidity conditions create lower NSC hay due to respiratory loss (more moisture equals more time for sugars to be used for growth via respiration before full drying, but aren't synthesized as much with photosynthesis because of less sunlight). Conversely, quick-dried hay retains more NSC, and if it's very sunny, NSC content can even increase after cutting due to photosynthesis.

"And in hay (or standing dead grass) that's been rained on (or soaked), sugars (which are water-soluble) can be leached out also," Watts added. She reported the results of a hay soaking study in which soaking hay for 60 minutes in cold water or 30 minutes in hot water yielded an average 31% reduction in soluble carbohydrates. The range of carb cutting was 0-56% depending on the species of grass; she said more testing is needed to fully clarify the effectiveness of this carb reduction method. (For more information on this study, see www.TheHorse.com/ViewArticle.aspx?ID=4777.) Likewise, rain or melting snow will leach some of the carbohydrates out of dead grass in a pasture, so it will then be safer for at-risk horses.

Watts described "founder fodder" as hay with the following characteristics:

  • "Improved" cool-season grass;
  • Low soil nutrients;
  • Drought;
  • Intense sunlight;
  • Frost;
  • Flower stage;
  • Cut in the afternoon;
  • Fast drying.

    Her recipe for "Hay Lite" (low-NSC hay) is as follows:

    • Warm-season grass;
    • Optimum soil fertility;
    • Optimum temperature;
    • Optimum moisture;
    • Cloudy weather;
    • Cut in the morning;
    • Mature plants;
    • Slow drying.

    If you don't know the conditions under which hay was grown or harvested, can you still pick low-carb hays? Not by looking, Watts said, citing one example of a poor-looking hay on which an owner's pony had foundered, "thinking 'crappy looking' was safe--it had 3.5% protein, but 30% NSC.

    "Get it tested!" she urged. "With these sensitive horses, you can't just feed them whatever happens to be on the market that day. You have to know what's going in their mouths. Color is meaningless--don't guess, test."

    How well does this low-carb approach work for laminitic/Cushingoid horses? "People e-mail me after soaking their hay for awhile saying, 'He trotted today for the first time in six months!' This really does work," Watts said.

    Her take-home message follows:

    • Beware grazing during time with cold nights or under drought stress.
    • Manage pasture and hay crops for optimum, but not excessive, growth.
    • Fertilizer and irrigation are our friends.
    • Get hay tested for NSC for susceptible animals.
  • More on Forage Risks and Rewards

    Why Horses Need Forages--While many of us want to simplify nutrition for our horses, selecting the best forage for a horse isn't always simple, particularly if he is chronically laminitic and/or metabolically challenged. Diets for these horses require particular care; however, in order to optimize the diet, first you must understand the horse's need for forages.

    Nutrients in Forages--To feed your horse the best forage for his needs, you have to understand the plants and what affects their nutrient content. Don't base forage purchases on love for your horse (i.e., "only the best for my baby") or looks (the prettiest green forage you can find), but on the horse's actual needs and feed analyses.

    About the Author

    Christy M. West

    Christy West has a BS in Equine Science from the University of Kentucky, and an MS in Agricultural Journalism from the University of Wisconsin-Madison.

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