Applying Pasture Analysis

Applying Pasture Analysis

Photo: Anne M. Eberhardt/The Horse

Collecting an accurate pasture sample is only half the battle; interpreting the results and putting them to good use is where owners often go astray.

Forage is the foundation. It's practically an equine nutrition mantra, emphasizing the role of pasture or hay as the basis for any horse's diet. To balance all aspects of your mount's diet, from forage to grain and concentrates, you must know forage nutrient levels. To this end, if your horse spends part or all of his time on pasture, your equine nutritionist or veterinarian might recommend a pasture analysis.

Such an analysis is also helpful if you want to assess a pasture's quality (nutrient value), learn how to improve it, or maximize its use, according to Bob Coleman, PhD, associate director for undergraduate education in equine science and management and extension horse specialist at the University of Kentucky. "There are two ways to analyze pastures," he says. "One is looking at the plants and how the pasture is managed, and the other is taking samples for nutrient analysis."

You'll want to solicit advice from your local extension agent or an equine nutritionist to interpret both pasture content and analysis numbers, says Paul Siciliano, PhD, an associate professor in North Carolina State University's department of animal science, who compares deciphering a pasture sample without an expert's help to trying to repair your car with just a manual. "Without some background and experience you may do more harm than good," he says. "The important things are to first get a good sample; second, get some help to interpret the result; and third, figure out how to apply that information."

Step 1: Take an Accurate Sample

To assess your pastures' content, you need to collect a mix of plant clippings. The number and type of samples you should gather for evaluation might vary.

"If (the pasture is) fairly uniform in species and similar for ground cover, slope, soil type, etc., you can walk through it in a random or zigzag pattern and gather several clippings," notes Krishona Martinson, PhD, equine extension specialist for the University of Minnesota Extension Service. "If your pastures are similar, you'll only need to send in one combined sample. But if your farm has several pastures, and one has different soils, more legumes (alfalfa or clover), a big hill, or lower (and wetter) ground, you'll need to send separate samples for different pastures to get a true analysis of each."

Simply knowing the plants you are sampling and how the pasture is managed can also tell you a lot about your forage. For instance, "we know legumes will have greater amounts of protein and energy and lower amounts of carbohydrates compared to grasses at the same stage of maturity," explains Martinson. "And if a pasture is overgrazed (less than three inches tall), a forage analysis will not be beneficial, as there is not enough plant material to get a quality sample."

Also take note of what plants your horses actually consume, so the sample you provide the laboratory accurately reflects the horse's pasture intake.

"In a research setting we typically walk amongst the horses and try to watch them eat and see what they are eating--and take samples of those plants," says Siciliano. "Then we cut the forage at the height the horses are eating."

Similarly, Coleman suggests, "If it's an area that's tall and rank that the horses aren't eating, move on another step or two (before taking a sample)." Be careful, however, to avoid including any dirt or fecal material that would contaminate the sample. If you pull up roots, for instance, the soil might cling to them.

Thus, Martinson recommends clipping samples no closer to the ground than three inches. "You can use scissors, taking a handful of grass and snipping it off," she says. "In an average size pasture I recommend taking about 15 to 20 samples at various places. Put all clippings together in a five-gallon bucket, and stir them around. Then put one or two large handfuls into a large Ziploc baggie and immediately freeze it. After it's frozen, get it to the lab without exposure to heat or sunlight, because that will alter the results."

Some laboratories report analysis values specific to dairy or beef cows that have minimal relevance for the horse. Thus, make sure you request an equine analysis when you send your sample to the lab. "The fiber, protein, vitamins, and minerals won't be any different, but the digestible energy is figured differently for individual species," says Martinson. "The ruminant analysis might give you an estimate of milk production per acre or milk per animal, and you wouldn't need that."

Step 2: So, What Does it All Mean?

When the report comes back from the lab, it will list levels of various forage components. But it's no good to the horse owner unless he or she understands what all those figures and abbreviations mean. Here's where your extension agent or nutritionist can help."Many feed companies have people who are well-trained in this area," says Sicilano. "If you don't have some background in equine nutrition, it can be hard to figure out what to do with the results ... almost every land-grant university has some of this information on their website or a brochure on interpreting forage analysis. There are also resources available that you can easily access online or from the forage testing labs."

"Fiber components are stated as ADF (acid detergent fiber) and NDF (neutral detergent fiber)," explains Martinson. The lower these two figures, the higher quality the forage. "With pasture grasses that are mostly vegetative (in early growth stages), those numbers will be relatively small--between 30 and 35 for ADF and 40 to 50 for NDF (in comparison with more mature pastures where ADF values can be greater than 40 and NDF greater than 60)."

A pasture's crude protein (CP) level also is important, as CP should make up 10-12% of an average idle adult horse's diet. "In a vegetative pasture, even if it's just grass with no legumes, CP can range from 10-20%," Martinson emphasizes.

Also check digestible energy--the amount of energy that can be absorbed by the horse. This might be listed on the report as equine DE. The main source of DE in a horse's diet is carbohydrates. "A mixed pasture, containing legumes, will be higher in energy and protein," explains Martinson. However, plant maturity is the greatest indicator of forage quality. Vegetative forages will be higher in protein and lower in fiber compared to more mature (i.e., flowering) forages that are lower in energy and protein and higher in fiber.

"Some nutrient levels will depend on how well the pasture is fertilized," she adds. "We see a correlation between nitrogen fertilizer and increased protein in plants," for example.

Using the DE level indicated on the lab report and information from an equine nutritionist or a resource such as the latest Nutrient Requirements of Horses, you can then determine how many pounds of pasture grass your horse needs based on his weight and activity level. "This figure is what a nutritionist would use to start with for balancing that horse's ration," says Martinson. "Most horses, however, that are on a good, well-managed pasture (not overgrazed, with a good forage stand, and fertilized according to soil test results), receive an excessive amount of energy."

Thus, one of the biggest challenges of keeping horses on high-quality pasture is preventing them from becoming overweight. While grazing, "most horses can eat what they need within four to eight hours, but many of them keep eating," Martinson says. If a pasture is not carefully managed, horses might overgraze their favorite plants.

You also can request that the lab evaluate the pasture's vitamins and minerals. "Unlike dried hay that's lacking in a lot of the vitamins and some of the minerals, most of the vitamins and minerals the horse needs, including vitamin A and E, will be sufficient in fresh pasture grass," says Martinson.

Step 3: Apply What You've Learned

It's important to be flexible in your pasture management and respond not only to analysis results but also to what you found in the physical evaluation of the pasture: what plants are there and how the horses are using that pasture. Regardless of the current plant species in a pasture, one of the most influential factors in quality is management. If a pasture is not carefully managed, horses overgraze their favorite plants and those die out, leaving a higher percentage of less preferred plants.

"They often prefer timothy and Kentucky bluegrass," says Martinson. "Our trials last year with 12 different varieties of cool-season grasses showed that timothy does not stand up well to frequent grazing." Maintaining healthy grass can be challenging unless you divide pastures and graze them rotationally, to give plants a rest so they can regrow.

Martinson notes that a healthy, well-managed pasture with fertile soil and ample regrowth time usually outcompetes most weeds. "The weeds won't establish as easily if the ground is already covered with a thick, healthy grass stand," which blocks sunlight to any weeds trying to take hold, she says. "This will also help keep poisonous plants from invading your pastures."

However, if your pasture is more weeds than desired forage, a full renovation might be needed. This would include removing the weeds with an herbicide or tillage and overseeding (if an herbicide is used) or replanting (if tillage is used). According to Martinson, the key to maintaining your pasture boils down to two key points: Avoid overgrazing and allow your pasture to rest (regrow). She also recommends ordering a soil test every three years. A soil test will indicate how much fertilizer is needed, as well as the soil pH level (acidity), which is important information to have if you are establishing a new pasture, as most forages grow best between a pH of 6.0 and 7.0 (basic). Apply lime to raise the soil pH, as soils tend to become acidic as they age.

You might make decisions regarding management based on nutrient analysis results, as well, to increase your pasture's quality. If a certain pasture is low in protein, for instance, you might want to consider fertilizing it or adding legumes (alfalfa or clover) to the plant mix. Your local extension agent or nutritionist can help you make these decisions.

Take-Home Message

Good-quality pasture alone should meet the average horse's nutritional needs, with some vitamin and mineral supplementation. But, in other instances--as with lactating mares, young growing horses, or hard-working horses--the animals might require dietary supplements of hay, grain, or other nutrient sources. In all scenarios a pasture analysis can be a helpful starting point to determine what the plants are providing and whether you need to add more energy, protein, or certain vitamins or minerals to your horses' diets.

About the Author

Heather Smith Thomas

