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AQHA VET NEWS
by reducing the amount in the urine . It does this by swapping potassium for sodium in the kidneys – saving the sodium for the body . So , for horses with low blood potassium , the answer is often to increase salt ( ie sodium ) intake , not potassium !
For nonexercised horses , voluntary intake from salt / mineral blocks is usually enough to meet their sodium and chloride needs . In exercising horses , voluntary salt intake is highly variable and in one study , the intake of four out of six horses was well below even the maintenance requirement . To replace losses from hard work , horses need to consume 50g a day from a salt block - you can weigh blocks regularly to determine intake . Have a salt block in the stable , feed bin , yard or paddock , but monitor consumption and add extra salt to the feed .
PHOSPHORUS AND CALCIUM . About 99 % of total body calcium is deposited in bone . This gives bone its strength but also serves as a reservoir for calcium needed in blood clotting , muscle contraction , enzyme activities and digestion . Bone calcium stores ‘ feed ’ the mobile calcium pool in blood or muscle and the import and export of calcium into and out of bone is tightly regulated . It is sensitive to the amount of phosphorus in the diet . The calcium to phosphorus ratio in the diet needs to be at least 2 to 1 . It is not uncommon for diets to have a calclium-phosphorus imbalance such that the phosphorus intake is higher than calcium and this inevitably leads to a varying degree of generalised skeletal osteoporosis . Although historically known as ‘ big-head ’ only 5 % of horses with osteoporosis develop head swellings , the majority have vague and variable signs .
There is wide variation in the calcium content of grass and hay – most except lucerne , clover and teff are low . Grains and their by-products ( bran , pollard , millrun etc ) are low in calcium and high in phosphorus . Calcium supplementation or feeds higher in calcium than phosphorus is needed . However , even if the diet has a correct calcium to phosphorus ratio , there are several situations in which calcium absorption is reduced . Calcium absorption from the gut into the body requires an acid environment . Many anti-ulcer drugs that suppress gut acidity also reduce calcium absorption and the addition of extra calcium to the diet is necessary .
OXALATES – found in most sub-tropical grasses - bind the grass calcium so tightly in the form of calcium-oxalate that it is insoluble in the gut and can ’ t be absorbed by the horse . Other grass oxalates that are bound to potassium and magnesium are soluble in the gut and the potassium and magnesium is freed and can be absorbed . However the freed oxalates will bind to other calcium in the diet , further preventing calcium absorption .
Calcium supplementation is essential , especially for pregnant , lactating and growing horses . Calcium uptake in the horse is independent of vitamin D .
MAGNESIUM About 60 % of magnesium is stored in the skeleton and 32 % in muscle .
Deficiency is linked to bone weakness and abnormal mineralization in soft tissues , in particular the aorta . There are important interactions of magnesium with the immune system , brain function and memory processing . Insufficient magnesium affects bone strength and energy metabolism , but the dominant response is behavioural , poor performance , increased disease risk due to immune-incompetence and muscle weakness .
COPPER has multiple roles , helping with haemoglobin building , nerve function , hoof strength and bone development . Low haemoglobin levels are often attributed to iron deficiency when in fact it ’ s a copper deficiency or imbalance that is causing the low haemoglobin . Copper deficiency is thought to be involved in osteochondrosis in foals .
Most forages are low in copper and supplementation is often needed . Levels in feeds vary and supplementation is frequently required , especially for pregnant mares and growing horses . Liver is the most important site of Cu storage but , as a consequence , also the tissue most susceptible to toxicity .
ZINC nutrition is commonly linked with skin health although its biological function is distributed over all tissues . Zincdependent enzymes are involved in hoof strength and low zinc intakes have been associated with decreased horn strength and hardness . Most grasses and hays are marginal in zinc but because manufactured feeds usually have additional zinc , addition of a supplement or multiple supplements that all contain zinc can result in an oversupply . Excess zinc has the potential to contribute to the development of osteochondrosis in foals . Horses on restricted amounts of roughage in order to reduce body weight will be at risk of marginal or deficient zinc intake unless provided appropriate supplementation .
SELENIUM deficiency has a long history and was the impetus for use of selenium-enriched fertilisers in crop production . Selenium has a powerful role in the anti-oxidant defence system , hoof wall integrity and activation of thyroid hormones . Most of body Selenium is located in muscle , bone and skin . The liver and kidney serve as storage sites in situations of elevated Selenium intake , overload or toxicity . If the requirements for Selenium are covered by the basic diet there is no benefit in providing a supplementary source .
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