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==What is Magnesium?==
==What is Magnesium?==
Magnesium is a mineral that is the second most common cation (positive ion) in '''intracellular fluid''', after [[Potassium - Nutrition|potassium]]. Its other main site of storage is in '''bone''', where about 50% of the body magnesium is found. Like other minerals, magnesium is a reactive metal that is not found in its free state in nature but combined with other elements to form salts.
Magnesium is a mineral that is the second most common cation (positive ion) in '''intracellular fluid''', after [[Potassium - Nutrition|potassium]]. Its other main site of storage is in '''bone''', where about 50% of the bodys' magnesium is found. Like other minerals, magnesium is a reactive metal that is not found in its free state in nature but combined with other elements to form salts.
==Why is it Important?==
==Why is it Important?==
==Roles in the Body==
==Roles in the Body==
Although large amounts of magnesium are stored in bone, it is '''not readily mobilised''' as a reserve for the animal when the supply of dietary magnesium is insufficient. The absorption of magnesium is via an active transport process but passive diffusion from the digestive tract can occur if there is a concentration gradient from the gastrointestinal lumen to the extracellular space. Extracellular magnesium is vital for normal nerve function. A common sign of magnesium deficiency is hyperexcitability caused by a reduction in the resting potential of the nerve membrane, which allows the [[Neurons - Anatomy & Physiology#Nerve Impulse Propagation|action potential]] to be triggered prematurely.
Although large amounts of magnesium are stored in bone, it is '''not readily mobilised''' as a reserve for the animal when the supply of dietary magnesium is insufficient. The absorption of magnesium is via an active transport process but passive diffusion from the digestive tract can occur if there is a concentration gradient from the gastrointestinal lumen to the extracellular space. Extracellular magnesium is vital for normal nerve function. A common sign of magnesium deficiency is hyperexcitability caused by a reduction in the resting potential of the nerve membrane, which allows the [[Neurons - Anatomy & Physiology#Nerve Impulse Propagation|action potential]] to be triggered prematurely.
==Consequences of Magnesium Deficiency==
==Consequences of Magnesium Deficiency==
Studies evaluating magnesium deficiency in dogs have had to rely on using purified diets containing artificially low magnesium content, as a naturally-occurring deficiency in magnesium is not achievable.
Studies evaluating magnesium deficiency in dogs have had to rely on using purified diets containing artificially low magnesium content, as a naturally-occurring deficiency in magnesium is not achievable.
====Recognised Syndromes Related to Magnesium Deficiency====
#'''Joint problems and paralysis:''' Weaned mongrel puppies fed a purified diet with no added magnesium developed hyperextension of the carpal joints and hind-leg paralysis. The animals recovered on a diet containing 0.024% magnesium on dry matter (DM)<ref>Vitale, J, Hellerstein, E, Nakamura, N, Lown, B (1961). '''Effects of magnesium-deficient diet upon puppies'''''. Circ. Res. ''9:387-394.</ref>. Similar signs were seen in puppies fed dietary magnesium at less than 0.014% DM<ref>Bunce, G, Jenkins, K, Phillips, P (1962a) '''The mineral requirements of the dog. 3. The magnesium requirement. '''''J. Nutr. ''76:17-22. </ref>, in adult beagles fed 0.017% DM magnesium<ref>Cronin, R, Ferguson, E, Shannon Jr, W, Knochel, J (1982). '''Skeletal muscle injury after magnesium depletion in the dog'''''. Am. J. Physiol. ''243:F113-F120.</ref> and in beagle puppies fed a dietary magnesium content of 0.014% DM<ref>Stahlman, R, Kuhner, S, Shakibaei, M, Flores, J, Vormann, J, van Sickle,D (2000). '''Effects of magnesium deficiency on joint cartilage in immature beagle dogs: Immunohistochemistry, electron microscopy and mineral concentrations'''''. Archives of Toxicol.'' 73:573-580.</ref>.
#'''Joint problems and paralysis:''' Weaned mongrel puppies fed a purified diet with no added magnesium developed hyperextension of the carpal joints and hind-leg paralysis. The animals recovered on a diet containing 0.024% magnesium in dry matter (DM)<ref>Vitale, J, Hellerstein, E, Nakamura, N, Lown, B (1961). '''Effects of magnesium-deficient diet upon puppies'''''. Circ. Res. ''9:387-394.</ref>. Similar signs were seen in puppies fed dietary magnesium at less than 0.014% DM<ref>Bunce, G, Jenkins, K, Phillips, P (1962a) '''The mineral requirements of the dog. 3. The magnesium requirement. '''''J. Nutr. ''76:17-22. </ref>, in adult beagles fed 0.017% DM magnesium<ref>Cronin, R, Ferguson, E, Shannon Jr, W, Knochel, J (1982). '''Skeletal muscle injury after magnesium depletion in the dog'''''. Am. J. Physiol. ''243:F113-F120.</ref> and in Beagle puppies fed a dietary magnesium content of 0.014% DM<ref>Stahlman, R, Kuhner, S, Shakibaei, M, Flores, J, Vormann, J, van Sickle,D (2000). '''Effects of magnesium deficiency on joint cartilage in immature beagle dogs: Immunohistochemistry, electron microscopy and mineral concentrations'''''. Archives of Toxicol.'' 73:573-580.</ref>.
#'''Effect of phosphorus:''' Bunce ''et al.''<ref>Bunce, G, Chiemchaisri, Y, Phillips, P (1962b). '''The mineral requirements of the dog. 4. Effect of certain dietary and physiologic factors upon the magnesium deficiency syndrome'''''. J. Nutr.'' 76:23-29.</ref> showed that the adverse effects of magnesium deficiency were exacerbated by increasing dietary [[Phosphorus - Nutrition|phosphorus]] from 0.4% to 0.9% DM. As the nutritional recommendation for phosphorus in puppies is around the higher of these two values<ref name="FEDIAF">FEDIAF. '''European Pet Food Industry Federation Nutritional Guidelines, '''July 2013; FEDIAF website.</ref>, it is particularly important to ensure that the dietary contents of phosphorus and magnesium are in the correct balance.
#'''Effect of phosphorus:''' Bunce ''et al.''<ref>Bunce, G, Chiemchaisri, Y, Phillips, P (1962b). '''The mineral requirements of the dog. 4. Effect of certain dietary and physiologic factors upon the magnesium deficiency syndrome'''''. J. Nutr.'' 76:23-29.</ref> showed that the adverse effects of magnesium deficiency were exacerbated by increasing dietary [[Phosphorus - Nutrition|phosphorus]] from 0.4% to 0.9% DM. As the nutritional recommendation for phosphorus in puppies is around the higher of these two values<ref name="FEDIAF">FEDIAF. '''European Pet Food Industry Federation Nutritional Guidelines, '''July 2013; FEDIAF website.</ref>, it is particularly important to ensure that the dietary content of phosphorus and magnesium are correctly balanced.
===Cat: ===
===Cat: ===
As with dogs, studies of magnesium requirement in cats have used semi-purified diets in which the concentrations of magnesium and other minerals have been controlled.
As with dogs, studies of magnesium requirements in cats have used semi-purified diets in which the concentrations of magnesium and other minerals have been controlled.
====Recognised Syndromes Related to Magnesium Deficiency====
#'''Muscle weakness''': Clinical signs of magnesium deficiency in kittens include muscle tremors, lack of muscle tone and muscle weakness, initially in the hind limbs. There was also depressed food intake<ref name="Howard">Howard, K, Rogers, Q, Morris, J (1998). '''Magnesium requirement of kittens is increased by high dietary calcium'''''. J Nutr. ''128(suppl.):2601S-2602S.</ref>.
#'''Muscle weakness''': Clinical signs of magnesium deficiency in kittens include muscle tremors, lack of muscle tone and muscle weakness, initially in the hind limbs. There was also depressed food intake<ref name="Howard">Howard, K, Rogers, Q, Morris, J (1998). '''Magnesium requirement of kittens is increased by high dietary calcium'''''. J Nutr. ''128(suppl.):2601S-2602S.</ref>.
#'''Effect of calcium:''' In the same study<ref name="Howard" />, the effect of increased dietary [[Calcium - Nutrition|calcium]] on magnesium deficiency was also investigated. The deficiency signs described above in section (1) occurred only when kittens were fed 0.01% magnesium and a high calcium level of 2.3% calcium (both on a dry matter (DM) basis). However, kittens receiving 0.01% magnesium and a normal dietary calcium of 0.6% DM showed a lower serum magnesium than those on higher magnesium levels. Kittens receiving magnesium at 0.02% DM or higher and a normal dietary calcium showed no adverse effects. As observed in the dog studies, it is important that the balance of magnesium and other minerals is appropriate. This effect on magnesium requirement may be due to the formation of insoluble calcium-magnesium-phosphorus complexes that lower the bioavailability of magnesium<ref>Brink, EJ, Beynen, AC, Dekker, PR, Van Beresteijn, ECH, Van der Meer, R (1992). '''Interaction of calcium and phosphorus decreases ileal magnesium solubility and apparent magnesium absorption in rats'''''. J. Nutr.'' 122:580-586.</ref>.
#'''Effect of calcium:''' In the same study<ref name="Howard" />, the effect of increased dietary [[Calcium - Nutrition|calcium]] on magnesium deficiency was also investigated. The deficiency signs described above in section (1) occurred only when kittens were fed 0.01% magnesium and a high calcium level of 2.3% calcium (both on a dry matter (DM) basis). However, kittens receiving 0.01% magnesium and a normal dietary calcium of 0.6% DM showed a lower serum magnesium than those on higher magnesium levels. Kittens receiving magnesium at 0.02% DM or higher and a normal dietary calcium showed no adverse effects. As observed in the dog studies, it is important that the balance of magnesium and other minerals is appropriate. This effect on magnesium requirement may be due to the formation of insoluble calcium-magnesium-phosphorus complexes that lower the bioavailability of magnesium<ref>Brink, EJ, Beynen, AC, Dekker, PR, Van Beresteijn, ECH, Van der Meer, R (1992). '''Interaction of calcium and phosphorus decreases ileal magnesium solubility and apparent magnesium absorption in rats'''''. J. Nutr.'' 122:580-586.</ref>.
==Toxicity/Excess==
==Toxicity/Excess==
===Dog: ===
===Dog: ===
There is no direct information on dietary toxicity of magnesium in dogs. It has been reported that diets containing up to 0.2% DM magnesium (providing 3 to 5 times their requirement)<ref name="FEDIAF" /> has no adverse effect in adult dogs.
There is no direct information on dietary toxicity of magnesium in dogs. It has been reported that diets containing up to 0.2% DM magnesium (providing 3 to 5 times their requirement)<ref name="FEDIAF" /> have no adverse effects in adult dogs.
===Cat:===
===Cat:===