Over the past couple months Horse Tales has discussed the importance of hay as being key in your horse’s diet, as well as information on deciphering the basic parameters used in analyzing hay and what they mean. In addition to hay being used to give horses ‘something to do’ during the long winter days and periods of confinement, your hay should ideally be providing much if not all of your horse’s nutritional needs. Horses fed solely forage-based foods (dried hay in cold weather) are felt to have a safer, more predictable feed intake because they will be satisfied (gut-filled) sooner and more easily than those fed predominantly on concentrated feeds.
This month we’ll look into why these various vitamins, minerals, proteins are important and in some instances might need to be supplemented in your horse’s diet.
Figuring out what are the best values for each of the parameters included in a horse’s diet is best done by a qualified nutritionist or veterinarian; however we can start by learning a bit about how each of the components found in a hay sample affects the horse.
Here in the United States, the National Academy of Sciences established a group of scientists involved in the National Research Council (NRC) who have spent many years researching nutritional requirements of animals. In 2007 they published the 6th and current revised edition of their voluminous report on Nutrient Requirements of Horses, which can also be accessed online, and provided requirements known for horses according to weight, age, work and reproductive status. The tables included in the book establish the minimum requirements necessary to sustain normal health, production, and performance of horses based on available research. These guidelines are the standard to use in determining how much energy, nutrients and minerals should be fed and in what ratios or proportions they should be fed to horses worldwide — for example, a horse in the United States of America would have the same nutritional requirements as one in Australia or elsewhere.
Protein is a major component in most tissues in the body, second only to water. Protein is made up of chains of amino acids (20 of which are considered the primary amino acids) and therefore the requirement for protein is actually a requirement for amino acids. All the essential amino acids necessary to create a protein must be present in the body at the same time. And as these essential amino acids cannot be synthesized by the body in sufficient quantity to meet the demand for them, the challenge in feeding horses is to provide adequate quantities of protein to enable sufficient concentrations of amino acids in the blood for the body to draw upon for various bodily functions.
The quality of the digestible protein is important to consider for the horse’s diet. The higher the digestibility of the protein, the higher the absorption of the amino acids to contribute to the horse’s health.
The essential amino acids, Vitamins such as A, C and Biotin; and minerals, such as copper, zinc, calcium, phosphorus and sulfur, are responsible for the structural integrity of the body, many metabolic processes, energy production, immune health and the general health your horse’s hooves.
Specific nutrients that affect your horse’s hoof health include:

  • Copper, which is an important component of many metabolic functions. Copper deficiency leads to defects in the pigmentation and strength of the hooves. Forages grown in areas of high rainfall can be deficient in copper.
  • Zinc, a mineral required for the healthy maturing of keratin, which is a major component of the outer layers of skin tissue: Proper keratin formation is important for wound healing, skin health, and hoof structure. The highest concentration of zinc in the body is found in the eye as well as in the skin, liver, bone and muscle. Zinc can also be deficient in forages.
  • Calcium and Phosphorus: About 99 percent of the calcium in the body is found in the teeth and bones; Calcium makes up about 35 percent of equine bones. It also plays an important role in muscle contraction, function of cells, blood coagulation and the regulation of many enzymes. There is a delicate balance between calcium and phosphorus in the body; nutritionists recommend that a Ca:P ratio between 1:1 to 2:1 should be provided by the total diet. Even if a diet contains adequate calcium, excessive phosphorus intake can interfere with calcium absorption and may cause skeletal abnormalities. Calcium deficiency can results in crumbly hoof horn. Like calcium, phosphorus is also a major component of bone, making up about 17 percent of the skeleton.
  • Sulfur: Sulfur is required to build the strong cross links necessary for healthy hoof horn. However, excessive sulfur interferes with copper metabolism leading to weak connective tissue structure and poor hoof quality. Sulfur plays a major role in the structural component of almost all proteins and enzymes in the body.

Of course each class of horse — age, size, degree of work/performance, reproduction status, even breed — will have slightly or predominantly different requirements, and you’ll need to tailor nutritional requirements accordingly. And, not surprisingly, whether you are feeding horses in cold or hot weather will also present its own challenges.
For example, the NRC reports show a disparity in feeding between recommendations for adults and growing horses in cold weather; as young, thin, or aged mature horses are less cold-tolerant than mature horses, and diet changes must be made much sooner for these susceptible horses when cold weather occurs than for adult horses in good condition.
In hot weather, water consumption is markedly increased to compensate for water lost through rapid respiration and sweating. If coupled with exercise during hot weather, this rapid water loss results in a substantial loss of electrolytes, primarily sodium, chloride and potassium. To compensate for this, free-choice salt should be available to all horses during hot weather.
According to the NRC’s study on Nutrient Requirements of Horses, the amount and type of electrolyte supplementation depends on the amount of heat stress and physical stress/activity that has been imposed.
Let’s take a closer look at electrolytes:
An electrolyte is defined as any mineral not attached to a protein in a free or ionized form. The major electrolytes in the bloodstream and in the space surrounding cells are sodium, chloride and (in much smaller amounts) potassium and bicarbonate, calcium and magnesium.
Electrolytes are essential for ensuring:

  1. The production and secretion of sweat, saliva, intestinal tract fluids, urine and mucus
  2. Skeletal muscle and heart contraction
  3. Intestinal and other involuntary smooth muscle contraction
  4. Absorption of nutrients across the intestinal wall and into the body cells
  5. Nerve function
  6. Maintenance of normal acid-base balance (pH)
  7. Maintenance of normal hydration (the body contains roughly 70 percent water)

Breaking down the electrolytes individually, we find that sodium is involved in many cellular processes including muscle contraction. If sodium is deficient then impaired performance will occur.
Sodium is also the major controller of water balance in tissues; In addition to ‘holding’ water in the tissues, sodium is what the brain ‘reads’ in determining when to trigger thirst and when to regulate the amount of sodium and water the body excretes in the urine.
Chloride helps maintain normal pH, fluid volume and electrical conductivity of cells.
Potassium is the major mineral inside the cells; the difference in sodium and potassium concentrations outside and inside the cells is responsible for the ability of a muscle or nerve tissue to respond rapidly to a stimulating agent. If potassium is deficient, symptoms can include fatigue, heart rhythm irregularities, muscle weakness, and nerve irritability.
The NRC proposes that the minimum standard of Sodium and Chloride for an ‘average’ adult horse is computed out to: for Sodium, 0.02 x the horse’s body weight (BW), and for Chloride, 0.08 x BW. A 1000-pound horse requires 9 grams of sodium and 36 grams chloride per day. Remember that these are minimum levels; not taking into account sweat losses on a hot day or exercise. One level tablespoon of salt contains approximately 9 grams of sodium and 14 grams of chloride.
Having your hay analyzed will provide you with important information on all the above mentioned requirements and a better knowledge of what you are feeding your horse; and a discussion with your veterinarian or a nutritionist will be helpful in determining not only how much hay to feed each day, but also whether your horse requires concentrated feeds or supplements in order to be in the best condition it can be.