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Nutrition: minerals

ISSN 2398-2977

Podcast: Nutrition: minerals


Calcium and phophorus

  • Calcium   Calcium salts  and phosphorus   Phosphorus  : essential in crystal apatite   →   strength and rigidity of bones.
  • Approximately 99% of calcium and 80% of phosphorus in the body is in bones and teeth, so bone acts as a reservoir.
  • Calcium is also required for blood clotting, cell membrane functions and glandular secretion.
  • Soluble Ca++ ions in the plasma are essential for normal muscle and nerve function, they are also involved in regulating enzyme activity.
  • Vitamin D, parathormone and thyrocalcitonin together maintain a constant level of calcium in the blood by controlling intestinal absorption, renal excretion and mineralization of bone.
  • Phosphorus is necessary as a buffer and for energy   Nutrition: energy  metabolism.
  • Diets excessively high in calcium are largely dealt with by high urinary excretion.
  • Diets based on cereals and wheat bran are low in calcium and high in phosphorus - may   →   osteomalacia.
  • Alfalfa contains high levels of calcium although a proportion may be bound to oxalates and unavailable to the horse.
  • Oxalates in tropical grasses may bind calcium   →   nutritional secondary hyperparathyroidism   →   characteristic enlargement of the facial bones ("big head").
  • Nephrocalcinosis may also occur.
  • Excess intake of phosphorus binds calcium making it unavailable for absorption by the horse. Excess calcium intake has little effect on phosphorus absorption because calcium is absorbed in the small intestine and phosphorus is mostly absorbed in the large intestine.
  • Hypocalcemia   Blood: biochemistry - calcium  can occur   →    tetanic spasms and inco-ordination, as a consequence of metabolic alkalosis after strenuous exercise and not from dietary calcium deficiency.
  • Diets high in cereals and low in forages can   →   calcium deficiency; these diets may have a low base excess and the activation of the phosphate buffering system can   →    an increased excretion of calcium ions even when the diet has a marginally adequate calcium level.
  • Mobilization of bone Ca may   →   weak bones subsequent to fractures.
  • Ideally the calcium:phosphorus (Ca:P) ratio of the total diet should be between 1.5:1 and 2:1. However, the ratio of the nutrients is irrelevant if the horse's requirements for the minerals are not met.

Other essential elements

  • Required for regulation of body fluids, maintaining acid-base balance and neuromuscular function.
  • If sodium requirements are met as sodium chloride   Sodium chloride   there should be no deficiency of chloride.
  • Most losses via sweat.
  • Chromium is a component of glucose tolerance factor    which is thought to be involved in the regulation of insulin.
  • Not licensed in the EU, but widely used in rest of world.
  • Requirements are increased with exercise.
  • Chromium supplemented performance horses have been reported to respond better to exercise stress.
  • Small amount essential in the diet for synthesis of vitamin B12 which in turn is involved in cell replication, thus a deficiency interrupts erythrocyte formation.
  • Copper   Copper  is essential for several enzymes involved in synthesis and maintenance of elastic tissue, mobilization of iron stores and preserving mitochondrial integrity.
  • Deficiency may cause anemia   Anemia: chronic disease  , post-partum bleeding and erosion of cartilage in articular joints   Musculoskeletal: nutritional deficiencies  . Status assessed as leukocyte copper.
  • Mares   Nutrition: brood mare  and young stock   Nutrition: neonate  fed marginal or deficient diets may   →   greater incidence/severity of developmental orthopedic disease in young stock   Musculoskeletal: angular deformity  .
  • Copper is believed to interact with molybdenum. Elevated molybdenum levels can block the absorption of copper in ruminants, but are unlikely to do so in horses.
  • Essential in the formation of teeth and bones and maintaining their strength.
  • Deficiency unusual but toxic levels cause fluorosis Fluorosis in which softening and weakening of bones and pitting of teeth may occur due to polluted grazing, especially from brickworks and water contaminated by rock phosphate.
  • Iodine   Iodine  is required for the production of thyroxine and tri-iodothyronine-2 thyroid hormones.
  • Thyroxine controls cellular energy metabolism in the athletic horse.
  • Deficiency in mares causes abnormal estrus cycles.
  • Their foals tend to be weak with high mortality rates; some have goiter.
  • Excessive levels of iodine in the diet of pregnant mares, eg from seaweed, may also produce weak foals with goiter, severe bony abnormalities and high mortality.
  • Occurrence of low packed cell volumes (anemia) rarely associated with impaired iron status.
  • A deficiency   →    anemia may occur due to chronic blood loss   Anemia: blood loss  or nematode worm parasites.
  • Mare's milk has scant iron, however, foal is usually born with adequate stores, and normal grazing activity supplements this.
  • Dietary requirements - 50 mg/kg feed.
  • An electrolyte involved in maintaining fluid balance and neuromuscular function, a co-factor of several enzymes and a component of bone mineral.
  • Lost in sweat so exercise increases requirements.
  • Acute deficiency causes nervousness, sweating, muscle tremors, rapid breathing, poor performance and early fatigue.
  • Chronic deficiency may cause deposition of calcium and phosphate in the pulmonary artery.
  • Present in feed, particularly milk and legumes.
  • Required for oxidative phosphorylation, fatty acid synthesis.
  • Also involved in amino acid metabolism and cartilage formation of bone matrix.
  • Deficiency causes abnormal bone growth and interference with regular estrous cycles.
  • Severe deficiency may give rise to death at birth or resorption in utero.
  • Low levels have been found in USA.
  • Potassium   Potassium  is an electrolyte involved in maintaining fluid balance and neuromuscular function.
  • Deficiency   →   reduced appetite and growth, and impaired performance.
  • Lost in sweat so exercise increases requirements and replenished with electrolyte supplements.
  • Abundant in lush pasture and good roughage.
  • Significant losses occur in prolonged diarrhea.
  • Most blood potassium occurs in red cells, so status measured by red cell K, not plasma K.
  • Selenium   Selenium  acts with vitamin E as an anti-oxidant to protect polyunsaturated fatty acids from peroxidation.
  • It is a component of the enzyme glutathione peroxidase.
  • Deficiency causes white muscle disease   Nutrition: nutritional myopathy   in foals, weakness in adults   Muscle: myopathy - overview   and abnormal neutrophil function.
  • Status measured by plasma selenium level.
  • High levels are toxic - acute toxicity causes respiratory failure. Chronic toxicity may   →   loss of hooves   Farriery: raised heel boot  , mane, tail and skin disorders   Hair: alopecia - body  .
  • Excessive supplementation   →   increased secretion and pollution of the environment.
  • Selenium is highly toxic to persons handling the concentrated salt.
  • Sodium selenite or sodium selenate are inorganic sources of selenium used in horse feeds and supplements. Seleno-yeast is an alternative source of selenium that has been found to be absorbed more efficiently by the horse as it is bound to amino acids.
  • Required for regulation of body fluids, maintaining acid-base balance and neuromuscular function.
  • Diets providing 5-10 g/kg fed adequate.
  • Can supplement with salt lick if desired particularly for athletic horse where losses increased in sweat and replenished with electrolyte supplements. After a long ride in hot weather, losses of sodium chloride may amount to >50 g.
  • Constituent of several amino acids   Amino acids  and vitamins   Nutrition: vitamins  .
  • Also a component of some hormones and chondroitin sulfate   Chondroitin sulfate  , which is found in cartilage, bone, tendons and blood vessels.
  • Sulfur containing amino acids are found abundantly in hoof and hair.
  • Deficiencies have not been reported in horses. Causes depressed appetite, growth, hair/wool growth, weight loss and reduced milk production in other species.
  • Components of many enzymes involved in protein and carbohydrate metabolism.
  • Most feeds contain more than adequate amounts.
  • Excessive intakes may interfere with copper utilization.
  • High levels of calcium may affect zinc absorption.
  • Deficiencies can depress appetite and growth rate, abnormal bone development in several species, depressed immune function in young horses and may cause skin lesions.
Print-off the Owner Factsheet onNutrition - keeping your horse on top form  Nutrition - keeping your horse on top form  to give to your client.

Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Hintz H F (1992) Clinical nutrition. Vet Clin North Am (2).
  • Hintz H F (1991) Dietary cation-anion balance. Equine Pract 13.

Other sources of information

  • Frape D (2004) Equine Nutrition and Feeding. 3rd edn. Blackwell Publishing Ltd, UK. ISBN: 1405105984.
  • Pagan J D, Jackson S G & Duren S E (1995) The Effect of Chromium Supplementation on the Metabolic Response to Exercise in Thoroughbred Horses. In: Proc 14th Equine Nutrition and Physiology Symposium. Ontario, California.

Further Reading