1. Vitamin A

Function: Major component of photopigments in retinal rods, important for vision, especially at night. Vitamin A also promotes cell differentiation and regeneration, playing a key role in growth and healing.

Risk of Imbalance: Deficiencies are rare in mature horses fed adequate forage. Foals born without defects may be weak, grow slowly and/or develop night blindness. Excess can only be achieved through oversupplementation; pasture and hay cannot provide toxic levels. Toxic reactions may occur in dull coat, weak bones, poor liver and kidney function.

2. Vitamin B1 (thiamine)

Function: Helps metabolize carbohydrates and extract energy from diet.

Risk of Imbalance: Horses receiving high-quality forage are less likely to be deficient in nutrients. However, intestinal diseases or parasites can interfere with the synthesis of vitamins in the gut. Some poisonous plants, such as bracken, also inhibit absorption. Signs of deficiency include lethargy, loss of appetite, and nervousness. Overdoses are almost always due to injections to improve horse performance, signs include excitement, dyspnea, and convulsions.

3. Vitamin C (ascorbic acid)

Function: Promote the synthesis of collagen, which is the main component of connective tissue

Risk of Imbalance: The body controls production so a deficiency is less likely. Toxicity through supplementation has not been documented.

4. Vitamin D

Function: Both forms D2 and D3 bind calcium and magnesium to maintain electrolyte balance and bone formation. Also regulates excretion of phosphate in urine.

Risk of imbalance: Defects are only seen when induced experimentally. Overdose occurs only through oversupplementation, signs of which include calcification of the heart muscle and other soft tissues.

5. Vitamin K

Function: Necessary for coagulation and utilization of various proteins throughout the body

Risk of imbalance: Deficiency can only occur when the gut cannot synthesize vitamin K or the liver is damaged so that the body cannot absorb vitamin K. Some medications can also interfere with vitamin K production. Signs of deficiency include internal and external bleeding. Overdose only occurs as a direct result of injecting K2 when the horse is not deficient. Signs of toxicity include kidney damage, laminitis, and death

6. Vitamin E

Function: Works with the mineral selenium to counteract the potentially harmful effects of oxygen byproducts of normal cellular metabolism called free radicals.

Risk of Imbalance: Horses who are deprived of fresh forage may develop a deficiency. Signs of deficiency in young horses include rapid degeneration of cardiac and skeletal muscles. In adult horses, certain muscle disorders such as equine motor neuron disease are associated with relative deficiency. No overdose observed

7. Calcium

Function: Makes up approximately 35% of the horse's skeletal structure and is involved in blood clotting, muscle function and heart rate regulation. The balance between calcium and phosphorus is critical for bone development.

Risk of imbalance: Insufficient absorption due to insufficient intake or unbalanced diet. Foals deficient in calcium can develop rickets, a disease that weakens long bones and enlarges joints. In mature horses, calcium deficiency can cause a brief lameness. Excess has been associated with epiphysitis, a disorder in the conversion of cartilage to bone; however, this has not been observed when calcium is in balance with other minerals.

8. Iron

Functions: Oxygen transport and hemoglobin production - Iron is vital to a horse's endurance potential. Although it is common practice to give horse athletes iron supplements to enhance performance, the extra iron provides no benefit unless the horse is deficient.

Unbalanced Risk: With rare exceptions, iron deficiency usually occurs in horses with chronic or severe blood loss or long-term parasitic damage. When iron stores in the liver, spleen and bone marrow are depleted, horses become anemic and exercise tolerance is significantly reduced. Iron poisoning is almost exclusively caused by injectable supplements that bypass the normal absorption process. Horses with high iron levels in their blood are more susceptible to bacterial infections. Foals that ingest too much iron may become comatose and die.

9. Phosphorus

Imbalance risk: Phosphorus deficiency resulting from insufficient intake or an unbalanced diet can lead to bone demineralization and, in extreme cases, spontaneous fractures. The greatest damage from overfeeding phosphorus is its interaction with calcium. At one time, "big head" disease, in which the bones of the horse's head became enlarged, was common in horses fed large amounts of wheat bran, which was high in bran and low in calcium.

Function: Contributes to the metabolism of carbohydrates, fats and sugars, the utilization of vitamins, as well as kidney function and cell repair

10. Selenium

Function: Synergize with vitamin E to remove destructive free radicals and help muscle development.

Imbalance risk: Selenium-deficient diets can lead to reproductive problems, immune deficiencies and, especially in foals, leukmyosis, in which muscles become weak and useless. Selenium toxicity usually occurs when horses eat plants that contain high levels of the mineral. Horses with acute selenium intoxication may exhibit colic-like discomfort and increased heart and respiratory rates. Long-term grazing on plants high in selenium can cause chronic toxicity and associated anemia, lameness, rough and brittle, misshapen hooves. Untreated chronic toxicity can be fatal.

11. Sodium chloride (salt)

Function: Essential for regulating body fluids and conducting electrical impulses to nerves and muscles.

Risk of Imbalance: Without supplemental salt, horses can quickly become starved, especially if they are sweating profusely or lactating. A slow-onset deficiency can lead to decreased sweating efficiency, loss of appetite, weakness and dehydration. A rapid drop in the body's salt supply can lead to uncoordinated muscle contractions. Horses can tolerate high salt levels if they have access to fresh water. Signs of salt poisoning include colic, diarrhea, and paralysis of the hind limbs, which can be fatal in extreme cases.