To feed your horse the best forage for his needs, you have to understand the plants and what affects their nutrient content, said Jerry Chatterton, PhD, Research Leader of the USDA Agricultural Research Service, Forage and Range Research Laboratory in Logan, Utah. He spoke at the Equine Forage: Risks and Rewards Seminar and Summit held Oct. 22-23 at Rutgers University.

He explained that there are two types of carbohydrates in forages: Total non-structural carbohydrates (TNC), which are inside the cells and include sugars, starch, and fructan (a type of sugar); and structural carbohydrates in plant cell walls, which include cellulose and hemicellulose. The TNC are the ones that can cause problems in chronically laminitic and/or metabolically challenged horses.

A plant’s levels of TNC vary with its rate of photosynthesis and respiration. In a nutshell, Chatterton explained that photosynthesis is the plant’s creation of sugars from sunlight energy, water, and carbon dioxide; respiration converts those sugars into energy for growth.

“When the rate of sugar synthesis (photosynthesis) exceeds the rate of sugar utilization (respiration and growth), non-structural carbohydrates accumulate in many plant parts--leaves, stems, and roots,” he said. Conditions under which this can happen are very sunny days (driving lots of photosynthesis) and cool nights (slowing respiration’s utilization of the sugars).

Why is this important? The rates of photosynthesis and respiration, which are heavily dependent on environmental and climatic conditions, determine in large part the amount of TNC in your horse’s pasture and hay. Understanding how those processes are affected can help you select better forages, manage your pastures for optimum feed, and provide your horse with more suitable forages. For example, knowing that shade slows photosynthesis, you might choose to put your laminitic horse in a shady paddock instead of the sunny one so his diet isn’t as “rich.” Or if you want lower-sugar hay, ayou might choose to cut your hay field after a few days of cloudy weather. Lack of sunlight slows photosynthesis and thus the production of sugars that can be detrimental to these horses.

What else should you know about forages and carbohydrate content? Chatterton offered the following general comments:

  • Lower portions of stems are higher in TNC than upper portions (so overgrazed pastures tend to have higher concentrations of TNC than healthier plants).
  • Developing seed heads are very high in TNC.
  • Stems have more TNC than leaves.
  • TNC are often high in stem bases, stolons, and rhizomes (underground stems and roots) of mature plants.
  • Carbohydrates are usually high in spring and fall (cool temperatures and bright sunlight).
  • Fructans (which have been used to induce laminitis experimentally) occur on cool-season grasses under cool conditions, but not in legumes (such as alfalfa and clover).
  • Mature grasses generally have lower TNC.
  • Some TNC are lost from harvested hay during drying, especially if it has been rained on (the TNC are water-soluble).
  • Protein content is generally high when photosynthetic rates are high, and increases with nitrogen application.
  • Mineral content varies with many factors--plant part, stage of growth, soil moisture and soil fertility, and harvesting conditions.
  • Textbooks offer broad generalities about forage quality; real values must be measured.

Recommendations for Horses

Chatterton urged the audience to not 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. “Sometimes a little straw filler might be okay,” he said with a smile. In other words, lower-quality forage will keep your horse busy longer, is less likely to make him overweight and/or laminitic, and he’ll eat more of it to get energy--keeping his stomach full and at lower risk of ulcers.

He asked the audience to remember eight points regarding forages for horses:

  1. Much of the “organic hype” is a hoax. There is no scientific basis for a lot of it.
  2. Cool temperatures in spring and fall can result in forages with high carbohydrate content.
  3. Don’t be afraid to feed hay that isn’t a pretty bright green.
  4. High fiber is good for horses.
  5. Mineral content varies with the plant species, soil fertility, and plant maturity; few generalities are applicable.
  6. Cutting number (first cutting alfalfa) has little meaning; environment and plant growth stage are much more important considerations.
  7. Carbohydrate content is influenced by the environment--cold generally equals high carbs.
  8. Visual observation for judging forage quality is not a good indicator, forage analyses are best!

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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