As you push your shopping cart down the aisle at the supermarket, it's likely become routine for you to do a quick scan of the nutritional analysis printed on the side of every cereal box and container of yogurt you select. Instantly, you know how much crude protein the product contains, how much fat, how many micrograms of manganese.

The same is true at the feed store, where grain bags all bear labels telling us their nutritional life stories. Or you can consult the National Research Council's publications on nutrition to tell you exactly how much copper and zinc are contained in oats, corn, flax seeds, or peanut hulls.

Many of us never think beyond those handy little charts and tables. But have you ever considered just how those plant products in your horse's feed come to contain those vitamins and minerals? Just like your horse, plants are a product of the environment they inhabit. They derive their substance from the soil, air, and water that help them grow. From the raw ingredients drawn in by their root systems and their leaves, plants manufacture some nutrients, such as vitamins, and store others. When they're ingested, those nutrients are broken down, processed, and used by your horse's many complex systems to support everything from basic everyday metabolism to reproduction and high-intensity exercise.

The soil in which your horse's feeds grow have an enormous impact on the nutrient content of the plants that result. Oats don't contain their "normal" levels of potassium, for example, if the soil in which they grow is depleted of that mineral. Excesses are just as possible, and just as problematic. In some pockets of the Rocky Mountain range, for example, soil concentrations of selenium are so high that the pasture growing there can be toxic to horses. Minerals are only part of the story. Levels of acidity or alkalinity (otherwise known as the pH level), concentrations of contaminants such as PCBs (or even radioactive elements), and percentages of organic matter also can have an impact on the growth of plants in soil.

Water can have an even more direct influence on your horse's nutritional well-being. In addition to being used by the plants your horse eventually eats, water also is taken in directly by the horse. Dissolved in that clear liquid are minerals absorbed from the environment the water flows through, as well as chemical contaminants and bacteria picked up along the way. Sometimes the levels are within safe limits, and sometimes they are not.

When you consider the soil and the water in your horse's environment, you're really going to the source of his nutritional health. Being better able to determine exactly what the nutrient contributions of your pastures are in his diet can put you significantly ahead of the game when it comes to balancing the entire ration, and it's particularly important if you're growing your own pasture, hay, and/or grain. Fortunately, testing your soil and water is a fairly simple procedure, from which you can reap a wealth of information.

Digging Into the Dirt

Of the 16 major elements that play a part in plant nutrition, all but three (carbon, hydrogen, and oxygen) come from the soil. Just like animals, plants need some of these elements in large quantities, and others in only microscopic amounts, but all are essential for correct growth. When it comes to pasture grasses and grains, nitrogen, potassium, and phosphorus are taken from the soil in generous amounts, while zinc, copper, boron, iron, manganese, and molybdenum (along with a few other trace minerals) contribute to a plant's growth in lesser ways. In order for a pasture to grow healthy and lush, or for a grain crop to yield well, all of these nutrients must be available in adequate and balanced amounts.

Just having these minerals lurking in the soil isn't enough for plants. They must be available for uptake by the root system--a factor that depends on the moisture content of the soil, its relative acidity, air and soil temperatures, and the distribution of the plant's roots. Extremes of pH, in particular, can dramatically affect how well plants can absorb soil nutrients. The vigor of the plant growth (or the lack thereof) generally will tell you whether there are serious imbalances afoot, but really to know what you're dealing with, you need to do some soil testing.

Getting a soil analysis is a pretty simple process, fortunately. Your local or county agricultural extension service, your closest agricultural university, or your feed store or local fertilizer company should be able to perform the testing for you, often for less than $20. They'll ask you to take 20 or more two- to five-centimeter diameter (one-half inch to 1") core samples of the top 10 centimeters (four inches) of your soil, excluding surface litter, plant roots, and foliage. (A core sampler usually can be borrowed from your testing agent--or you can use a stainless steel pipe. In a pinch, you can use a shovel.)

Try to take the samples from several different locations in your pasture or field. The larger the field, the more samples you should take to provide a really representative picture. Avoid sampling areas where fertilizer has been applied recently, dead furrows, areas next to gravel roads, or anywhere where lime, compost, or manure has been piled. Break up the lumps and mix all the soil samples together thoroughly in a plastic or stainless steel container, using clean, rustless tools. (The idea here is not to use metals that could contribute their own particles to the mix and throw off the accuracy of your results. Galvanized metal, for example, contains zinc and can skew the test's results for that element. Anything rusty could contribute a disproportionate amount of iron.) Let the soil mixture air-dry, being careful to keep dust and other contaminants out of the container; then send at least three to four handfuls of it to the lab for analysis.

A routine soil test--which should be performed every two to three years--can include analysis for the minerals potassium, phosphorus, calcium, and magnesium, as well as the pH and percentage of organic matter (a benchmark of how well the soil supports plant life). You also can request tests for sulfate, zinc, iron, manganese, copper, boron, nitrates or nitrogen, and even textural analysis and electrical conductivity (actually a measure of the concentration of salts in the soil). An organic carbon test can point to the soil's fertility, with levels of 1-2% considered normal.

The general idea behind generating these numbers is that once you know what your soil is short on, you can fertilize it to bring it back to optimal balance. Of course, that's not quite as simple as it sounds. Because there are so many variables, recommending appropriate fertilizing materials, times, and quantities is often a job left to an expert. Just as one example: boron deficiency in soils is rarely a problem for most plants, but it can affect the growth of alfalfa, and boron deficiency usually occurs only in dry weather, which can make responses to boron fertilization somewhat erratic. Applying extra boron to fields that are growing cereal grains, peas, or beans can be toxic. Remembering all these little details generally isn't something an average horse owner should be expected to do, so don't be afraid to consult a fertilizer specialist!

Soils tend to acidify as they age (the longer they're planted with a single crop), so a pH level can be one of the most valuable pieces of information your testing yields. There are two ways of measuring soil pH in the lab: as a water solution, or in a solution of calcium carbonate (CaCl2). Most soil scientists prefer the calcium carbonate test, but it will tend to generate a pH result that is 0.5 to 0.8 lower than in water. The preferred pH level for equine pasture is between 5.0 and 5.5 (in CaCl2), which is slightly acidic. A pasture that has a pH level lower than 5.0 is more strongly acidic, and that can limit the growth and vigor of your pasture grasses. In acid soils, minerals like aluminum and manganese can build up to toxic levels, while phosphorus, calcium, magnesium, and molybdenum become less and less available to the plants. Legumes in particular (such as clover and alfalfa) might struggle when trying to grow in acid soils because their symbiotic rhizome bacteria find it difficult to establish, although other types of pasture plants can be quite acid-tolerant.

Acidity usually is corrected by applying ground limestone, or "lime." Lime is composed largely of calcium carbonate--dolomitic limestone, or dolomite, is a combination of calcium carbonate and magnesium carbonate. Either can do a good job of returning soil pH to a more neutral level (closer to 7.0), although dolomite is the better choice if the soil also is magnesium-deficient.

Another common fertilizer applied to hay fields and pastures is common or garden-variety manure. Besides having the advantage of being cheap and plentiful, manure is an excellent source of nitrogen, phosphorus, and potassium. It also supplies micronutrients and organic matter, which can significantly benefit many soils (especially heavy, clay-based ones that can use some aeration). Corn and grass hay both are crops with high phosphorus requirements and thus often respond well to manure; legume pasture or hay, on the other hand, doesn't really benefit from the application of manure because it doesn't make efficient use of the nitrogen it contains. In fact, manure applied on a hay field or pasture that contains both legumes and grasses might encourage the grasses to flourish and crowd out the legumes. Crops grown on clay or clay/loam soils often don't need any supplemental potassium, so a more specific fertilizer than manure might be a better bet (it's quite possible for the soil to develop toxic levels of potassium).

Nitrogen fertilization might be all that's needed on many grass pastures in North America. In certain areas, however, the results of your soil analysis might point to a need for potash (potassium carbonate), magnesium, sulfur, or trace minerals like copper, manganese, or zinc (these elements might be particularly useful if you're growing pasture or hay for broodmares and babies, who have increased requirements). Interestingly, applying nitrogen to grass pastures not only tends to increase the amount of forage produced, but also increases its protein content--which can be a substantial economic advantage. It's often used to spur short-term increases in growth during times of feed shortage. But be cautious: sudden lush pasture growth can increase the risk of laminitis, especially in ponies, as well as the incidence of orthopedic growth disorders in foals.

Probing Plants

Testing your soils and treating them with appropriate fertilizers to correct imbalances can go a long way toward making sure the forage your horses eat contains a correct balance of nutrients. But even soil testing doesn't tell the whole tale; it won't tell you how well your plants are absorbing or utilizing the nutrients waiting for them in the soil. If you have unhealthy-looking crops, or if your horses are failing to thrive on the pasture, hay, or grain you're growing, you'll need to do a plant tissue analysis to get the complete story. Plant tissue testing can be helpful in diagnosing plant "nutrition" problems, many of which have very similar symptoms (deficiencies of nitrogen, potassium, and iron all can result in plants with stunted growth, yellow leaves, and die-back of new shoots). In addition, this type of analysis can help define the availability (to your horse) of trace elements in the plants; sometimes, it even can detect deficiencies before they become serious.

A plant tissue analysis might test for essential minerals such as nitrogen, phosphorus, potassium, calcium, magnesium, sodium, chloride, sulfur, manganese, copper, zinc, iron, and boron. You also can test for selenium, molybdenum, and even cobalt if you like. Unlike a hay analysis, plant tissue tests are usually done on 30 to 100 fresh leaves, collected from a pasture and mixed to make one composite sample of 100 g or more. Avoid soil contamination when you gather plant material for this test (if it occurs, wash the leaves lightly with water and pat dry). Place the leaves in a paper bag to minimize sweating, and send it off to the lab as quickly as possible.

What About Water?

Much as we'd like to believe the water we, and our horses, consume is "pure," the truth is that water completely untouched by chemicals or minerals doesn't exist. Water is, after all, the universal solvent, with a unique ability to pick up and dissolve virtually everything it encounters. The other substances contained in our drinking water aren't necessarily bad; minerals dissolved in water impart much of its flavor, after all, and many are beneficial (such as fluoride in city water supplies). Instead of worrying about purity, we ought to focus our attention instead on our water being safe to drink--which means that none of its contents have reached a toxic level.

If you live in suburbia, your barn might draw its water from a public or municipal system that provides extensive purification and filtration services. It also regularly tests the water for contaminants such as disease-causing bacteria, toxic chemicals, and radioactive elements such as radon. Worries are few with this sort of system, but that doesn't mean there's no possibility of contamination. The testing is done at the source, and if there is damage to the delivery line, or a problem with the plumbing on your property, your water could be compromised.

More diligence is required if, like the majority of horse people, you draw your barn's water from a well. Horses, after all, consume at least half a gallon of water for each 100 pounds of body weight every day, with demand increasing in hot, humid weather, with increased work loads, during lactation, and even when being fed coarse hay or pasture. That can add up to 16 gallons a day or more. So, water can be a significant influence on their overall nutritional balance, not to mention their health. Many wells provide perfectly clean water, but there also is the potential for contamination.

It's a good idea to test your well's water on an annual basis. A total coliform test checks the water for levels of bacteria that normally are found in the soil, in surface water, and in human and animal waste. Coliform bacteria are not, in themselves, considered harmful, but their presence in your water supply is an indication that your well might be contaminated either from run-off from your manure pile, or from a nearby septic tank or bed. Coliform levels can rise in drought conditions, when there's a sudden, heavy rainfall, or with any unusual change in weather patterns. It's also possible to have high coliform levels when the well has developed physical defects, such as a broken or missing cap, which could allow debris, surface water, insects, or rodents inside.

Generally, doing bacterial testing is a good idea whenever

  • There is a noticeable change in the color, odor, or taste of your water;
  • Any animal or person on your farm becomes sick from a water-borne disease (Potomac horse fever, for example, is suspected of being water-borne through freshwater snails);
  • The water supply system on your farm has been disassembled for repairs to the well, the pipes, or the pump;
  • Flooding occurs near your well;
  • The cap or the interior of the well has been damaged.

Wells which are drilled correctly, well-protected, and more than 50 feet deep generally have less chance of becoming contaminated with bacteria. If you have such a well and several previous bacterial tests have come back negative, you might be safe in testing only every two to three years. Water from an old or shallow well should be tested more frequently. Don't rely, by the way, on "clean" tests from a neighbor's well. Even two wells side-by-side can draw water from separate aquifers (underground water sources) and yield very different results.

In a 1998 study conducted by Leslie Huber, DVM; Gayle Ecker, BA, MSc; and Simone Payne, BSc, at the Equine Research Centre in Guelph, Ontario, 39 water samples from Ontario horse farms were examined for levels of bacterial contamination. The results showed that 61% of the samples were safe to drink, with no significant evidence of bacterial contamination. There were 18% that had high levels of coliform contamination, indicating they might be unsafe to drink (although animals often consume water containing coliforms over long periods of time with no apparent ill effects). Most alarmingly, 21% of the samples were definitely unsafe for drinking, due to contamination by the fecal coliform E. coli (an indication of recent sewage contamination, either from a septic bed on the property or from a poorly located manure pile). This study points to the importance of regular checking of your water supply.

Water testing for coliform bacteria can be done by your county or state health laboratory, your local agricultural extension agent, or the Environmental Protection Agency. When you contact them for information about water testing, make sure you meticulously follow their instructions for collecting your sample. Incorrect collection procedures easily can contaminate your water sample and lead to false results on the test.

Minerals, Algae, And Assorted "Stuff"

Bacteria aren't the only concern when you test your water. You also can check it for mineral content, the concentrations of which can influence the taste, smell, and palatability of your water. (The classic example is "sulfur water," which has that characteristic rotten-egg odor.) Your local lab should be able to test your water for levels of calcium, magnesium, manganese, iron, copper, zinc, sodium, chloride, and lead, as well as sulfates and nitrates. (Nitrate contamination is particularly common on horse farms; its likely source is your manure pile.) Concentrations of these minerals, if sufficiently high, can have an impact on your horse's dietary balance, since levels of one mineral in his gut can influence his ability to absorb another.

Iron is a mineral often found in high concentrations in well water. Below the ground's surface, it might be dissolved in the water in the form of ferrous bicarbonate, which is colorless. However exposure to air, or heating the water, can change it to ferric hydroxide, which can stain your water a red or rusty color and leave it with a metallic taste. Iron also is sometimes accompanied by "iron bacteria," which consume iron in the water and, in the process, exude a rust-colored slime that can coat the insides of your pipes and fixtures. If iron bacteria are present in your well, you might be looking at total, repeated disinfection procedures.

Calcium and/or magnesium salts are to blame if your water is "hard." Although hard water (up to a level of about 100 parts per million of salts) isn't a major problem in the barn, your horses might not enjoy much lather when they get a shampoo, and at high concentrations, magnesium salts have been known to trigger mild diarrhea.

Lead is another mineral that has caused grave concern with regard to the human water supply. Lead pipes and soldering have sometimes increased lead concentrations in water to dangerous levels. The effects of high lead levels are less well understood in horses than in humans, but it's definitely best avoided. Even though new copper pipes contain some small amount of lead in their soldering, the amount released into the water can be controlled by making sure the pH of the water doesn't become too acidic (which can cause pipes to corrode). A calcite filter is an effective way to decrease the corrosiveness of well water and thus lower the lead levels.

Speaking of pH, an acidity/alkalinity test is another frequently performed water analysis. Anything below pH 6.5 is considered acidic, and can contribute to the corrosion of your pipes. (Acidic water isn't necessarily as nasty as it sounds; a can of carbonated soda can be 10 to 100 times more acidic than water with a pH of 5.0.) On the other hand, if your water tests at pH 8.5 or higher, it's alkaline, which means you probably have crusty mineral deposits on your pipes and fixtures. (Alkaline water also is hard water, as a rule.) The pH levels in water usually fluctuate very little over time. A sudden change might indicate damage to your well, or below-ground corrosion.

Consider testing your water at least once every three years for pH, nitrates (which can be derived from local farmers fertilizing their fields), and total dissolved solids (TDS). TDS is a measure of the inorganic and organic solids dissolved in your water, and high levels (over 1,000 parts per million) generally are linked with water that has an offensive smell, taste, or color. It also can contribute to health problems. The ERC study noted that at levels over 1,000 parts per million, equine diarrhea was a common complaint.

Turbidity is a related water test that can help you identify the suspended solids in your water, which make it look cloudy. Mud, algae, and iron are three likely culprits.

Blue-green algae occasionally blooms in ponds in hot, dry weather, and can be a concern if your chief water source is above-ground, rather than a well. Blue-green algae poisoning can cause muscle tremors, labored breathing, liver damage, and even death. So, it's best to remove horses immediately from a contaminated water source with algal blooms.

Pesticides are another worry when it comes to water safety. Although testing for these chemicals is expensive, it might be worth doing if you have significant concerns about the amount of pesticides used in your area. It's important to recognize that it's virtually impossible (and financially prohibitive) to test for everything. Testing for bacterial contamination should be a given for most wells, but in addition to that, consider the following:

  • If you live in an agricultural area where crops and/or livestock (such as cattle or swine) are raised, test for pH, nitrates, and possibly pesticides;
  • If your water has an unpleasant smell, test for pH, copper, lead, iron, zinc, sodium, chloride, TDS, and hydrogen sulfide;
  • If your water is cloudy and frothy, test for turbidity, TDS, and detergents;
  • If you live near a road salt storage site, a street which is heavily salted in winter, or the ocean shore, test for sodium and chloride levels.

So what should you do if your water tests reveal an imbalance or contamination? Take action by doing the following:

  • Eliminate the source of the contamination (which might be as simple as re-locating the manure pile);
  • Improve the protection for your well by giving it a weather-proof, sanitary seal and eliminating access for debris, insects, and rodents;
  • Treat the water with chemicals or filtration to improve its quality, if that's what your lab recommends;
  • Or, if all else fails, consider drilling a new well.

The lab at which you have your water testing done probably is your best source for specific recommendations. Consult them with any concerns you might have.

About the Author

Karen Briggs

Karen Briggs is the author of six books, including the recently updated Understanding Equine Nutrition as well as Understanding The Pony, both published by Eclipse Press. She's written a few thousand articles on subjects ranging from guttural pouch infections to how to compost your manure. She is also a Canadian certified riding coach, an equine nutritionist, and works in media relations for the harness racing industry. She lives with her band of off-the-track Thoroughbreds on a farm near Guelph, Ontario, and dabbles in eventing.

Stay on top of the most recent Horse Health news with FREE weekly newsletters from TheHorse.com. Learn More

Free Newsletters

Sign up for the latest in:

From our partners