We all know a horse's primary food is pasture grass and/or hay (forage). The quality of the forage is, thus, a major factor affecting his health. Do you know if your horse's forage meets his needs? Truly, most of us don't--but we should.
Forage analysis can tell you whether your forage alone will provide the nutrition your horse needs, or whether he needs a supplement or a grain concentrate mix to balance the diet. This is doubly important for horses with problems that can be affected by certain nutrients in the feed. Some of these include hyperkalemic periodic paralysis (HYPP) and exertional rhabdomyolysis (tying-up). A recent focus on forage carbohydrate content comes from the combination of the human low-carb diet craze and the realization that excess carbohydrates can cause or worsen problems such as colic, laminitis, and Cushing's disease.
Normal horses benefit from knowledge of forage quality as well. Kathleen Crandell, PhD, of Middleburg, Va., an equine nutritionist for Kentucky Equine Research (KER), says a nutrient deficiency is a subtle thing you might not notice in normal horses because they are generally not "unhealthy." But they might have subtle problems such as a poor-quality hair coat, lower reproduction rates, or slightly impaired immune systems, and you might see more illness or developmental problems in foals. Toxicity from nutrient levels that are too high can be subtle, or painfully obvious.
Location, Location, Location
Soils in some regions are deficient in certain minerals (such as selenium, iodine, or copper), or might have excessive amounts. Crandell says it's wise to find out whether hay crops grown in your area are high or low in some of the trace minerals, and whether you should give or avoid certain supplements because of that. If you buy hay from another region, you need to know the mineral content of that hay; it might differ quite a bit from what you've used from your area.
In arid Western regions of the United States, crops are grown with irrigation rather than depending on rainfall, and hay is cut at the most optimum time, retaining more of the nutrients. However, many Western soils are low in copper and zinc, so the hay might also be low. Copper deficiency can affect bone development. Many Western regions are also high in molybdenum, which ties up copper and makes it unavailable for use in the body.
Your local extension agent can tell you if your general region tends to have too much or too little of certain nutrients for horses, but only a forage analysis can confirm the quality of what's going in your horse's mouth.
When taking hay samples, it's best to use a core borer, which goes all the way to the center of the bale. A core borer can be borrowed from your county extension agent. "If you do a lot of samples, you can buy one," says Crandell. "Unless you are a big farm and will be sampling hay all the time, it's more practical to borrow one. The county agent will usually give it to you with a hand drill. If you do a lot of samples, however, it's easier and quicker to use an electric drill--but just make sure that when you are taking the samples it doesn't get too hot and burn the hay."
Take a random sample from a number of bales. "If you don't have a core borer, grab a couple of handfuls from the middle of about 20 bales," she advises. "Then cut the hay wisps into one-inch lengths; that makes it easier to ship and for the lab to handle. If you have the core borer, take a sampling from 10 to 20 bales. Combine the samples and put them in a Ziploc bag (gallon size); have it reasonably full. This will give a more accurate sampling of your hay." The reason you need to sample so many bales is that one bale from one part of the field might not be indicative of the whole field or load of hay; it might be weedy, or didn't have as much irrigation water, or it was on the edge of a swamp (with different soil and plants).
When taking hay samples, keep the samples dry and send them as soon as possible. After you take the sample out of a bale, it is also more exposed to oxidation.
Paul Sirois, laboratory manager of Equi-Analytical/Dairy One Laboratories in Ithaca, N.Y. (which does feed and forage testing), warns, "Although hay is a relatively stable product, condensation from heat and moisture may promote mold development."
"A grass sample should be a random sample of the field," Crandell advises. "If it's a square pasture, start in one corner and walk diagonally across, stopping every 10 steps to cut a sample (from the pasture that's right at your toe). Scissors are the easiest tools to use, but grass clippers can also be used. Then go to the opposite corners and walk across again, making a big X through the field. Sometimes I just crisscross it, like a W, so I am covering more of the field.
"If it's a huge field (such as 30 or 40 acres), I take 20 steps between cuttings, so I don't end up with a ton of grass," she says. "My technique is to look at the grass at every stop, see what the horses are actually eating, and sample that. Or if I know it's something they will eat, I take a sample. I try to cut what they eat, rather than just what's right there (it might happen to be a plant they won't eat). Try to fill a gallon bag full of cuttings."
Take the top portion of the plant, down as far as you think the horse will eat it--what a bite of grass would be. After you've collected the samples, seal the bag and send it to the lab as soon as possible.
"Pasture samples should be frozen
overnight prior to shipping," says Sirois. "This will halt plant respiration and prevent chemical changes in the forage. If the samples can't be frozen soon after collection, it's best to keep them in a cooler on ice until they reach the freezer."
With forage analysis results in hand, now you are ready to evaluate how that forage meets your horse's needs. But you're not alone if you think that report might be confusing--and what are those numbers ideally supposed to be? You might want to consult with a nutritionist (see last month's Nutrition column for more on that, online at www.TheHorse.com/ViewArticle.aspx?ID=6018), but here are some of the basics.
"When you get the results back, there will usually be two columns," says Crandell. "One will be 'as fed' or 'as sampled,' and the other will be 'dry matter,' what the nutrient levels are before and after all the moisture is taken out. On a dry matter basis, the crude protein of a sample might be 21%, whereas the original sample was only 4.8% because of all the moisture."
Look at the dry matter basis to determine nutrient levels; that puts forages all on the same playing field. It's the same with hay samples, although the dry matter of hay doesn't vary much. If you are comparing pastures, definitely look at the dry matter basis.
The next thing listed is usually protein. "Crude protein is determined by measuring the amount of nitrogen in the plant and multiplying it by a conversion factor," Crandell says. Protein level (dry matter basis) in green plants is usually 18-26%, she adds, and yet people worry about whether they have enough protein in the grain being fed. If a horse has (access to) a diet consisting mostly of green pasture, he won't be short on protein except in a drought situation (when grass is overly mature), in cold winters, or if the horse has a medical condition that interferes with protein absorption.
Another value on the report might be lignin, and that's the amount of absolute indigestible fiber. "That's not given on every report, but every once in awhile you'll see it," she says.
Fiber measures will also appear on the report. "Fiber content is primarily composed of lignin, cellulose, and hemicellulose, and increases with plant maturity," says Sirois. "Acid detergent fiber (ADF) is composed of lignin and cellulose and represents the least digestible portion of the plant. As ADF increases, digestibility decreases. Neutral detergent fiber (NDF) is made up of all three fiber components and is associated with the bulky nature of forages. Straw, for example, averages 72% NDF and serves as a good filler, but it is low in nutrient value.
"As plants grow and mature, protein and fiber levels move in opposite directions," he continues. "Protein decreases with maturity, while fiber increases."
Total digestible nutrients (TDN) and digestible energy (DE) are two estimates of energy content that might be included on your report. "DE reported in megacalories/pound (Mcal/lb) or kg (Mcal/kg) is preferred and used most often in evaluating forages and balancing diets," says Sirois. "Forages ranging from 0.90-1.10 Mcal/lb will meet the needs of most horses."
Sugar and starch analyses are also offered by some labs; together, sugar and starches are referred to as non-structural carbohydrates (NSC). "While overall NSC levels are important, sugar is the predominant component in forages, while starch predominates in grains," Sirois explains. "Although there are no set requirements for NSC at this time, field evidence suggests keeping NSC levels under 12% for sensitive horses (see "Understanding Sugars in Forages" below).
Another carbohydrate measure that might appear on your analysis is non-fiber carbohydrates (NFC). "This is a calculated value based on other nutrient measures in the forage, and it was used as an estimate of carbohydrate levels before sugar and starch became mainstream analyses," Sirois notes. "NSC is more accurate to use when evaluating carbohydrate status in the diet because it is an actual measurement as opposed to a calculation.
"Relative feed value (RFV) may also appear on your report," he goes on. "RFV is a score assigned to hay by the dairy industry. Digestibility and intake potential are calculated from fiber components and combined to determine the score. The system is based on a mid-bloom alfalfa hay having a score of 100. Grass hays will typically score 75-105. Hays testing in the 90s will usually meet the needs of most horses. High-quality alfalfa might score 150 or greater and is too rich for the majority of horses. A good quality grass or grass/ legume mixture is preferred."
Most horse owners offer trace minerals, either in the feed or in the salt. This often helps, but in rare cases could hurt, depending on what's in your forage.
The forage analysis will include the levels of macrominerals (calcium, phosphorus, magnesium, potassium, and sodium). "Calcium can range from as low as 0.2 up to 2%, depending on the type of plants," says Crandell. "Legumes like alfalfa and clover will have much higher calcium levels than grass hay. The phosphorus may be as low as 0.1 and as high as 0.5%. You want more calcium than phosphorus. A fresh grass sample in the spring might have more phosphorus than calcium, especially if a field was recently fertilized. If you take another sample three months later, it may normalize (with more calcium than phosphorus).
"Magnesium is usually between 0.1 and 0.2%, but in some areas of the country it's higher," she continues. "Make sure it's less than the calcium or it will start interfering with the absorption of calcium. Low magnesium may be an issue for horse with muscle-related disorders.
"Potassium in forage will vary from 1-3%," she says. "If you have an HYPP horse, find forages that are less than 1.5%. Most fresh grasses are over 2%, so the horse is better off on hay. Potassium is one mineral that most horses readily excrete." HYPP horses, however, have a genetic defect that keeps them from getting rid of the potassium.
"If you look at the potassium level in fresh grass and your sample has 300% of the horse's requirement, it's nothing to worry about because the normal horse can get rid of the excess," Crandell notes.
Sodium levels are low in forages (usually below 0.01%), and that's why horses need supplemental salt. You should always provide free-choice salt.
Iron levels might show higher than usual if you had a lot of dirt in your sample or the grass was muddy where you sampled it. A horse usually won't have an iron deficiency unless he had severe blood loss recently; forage usually contains enough iron to meet the horse's requirement.
"Copper is usually between 4-12 parts per million (ppm), and zinc can vary from about 12 up to 45 ppm," says Crandell. "These are normal ranges for forages, but they are not quite enough to meet the requirements for some classes of horses. An idle horse on pasture might have his requirements met, but a hard-working horse, broodmare, or young, growing horse will usually need more."
In areas short on iodine, this can be taken care of by offering iodized salt. Iodine helps control body metabolism and is important for growth. Deficiencies can result in issues such as thyroid and mental problems.
Other minerals might also be included in your report; these are just the major ones.
Most horse owners realize the value of good pastures and hay, but don't take them into the equation when feeding their horses. Without knowing the nutrients contained--or not contained--in your forages, you run the risk of feeding your horse an imbalanced diet and possibly causing or worsening problems.
About the Author
Heather Smith Thomas ranches with her husband near Salmon, Idaho, raising cattle and a few horses. She has a B.A. in English and history from University of Puget Sound (1966). She has raised and trained horses for 50 years, and has been writing freelance articles and books nearly that long, publishing 20 books and more than 9,000 articles for horse and livestock publications. Some of her books include Understanding Equine Hoof Care, The Horse Conformation Handbook, Care and Management of Horses, Storey's Guide to Raising Horses and Storey's Guide to Training Horses. Besides having her own blog, www.heathersmiththomas.blogspot.com, she writes a biweekly blog at http://insidestorey.blogspot.com that comes out on Tuesdays.
POLL: University Equine Hospitals