minerals

what two groups are essential dietary minerals split into?

• macro minerals (major elements) - g/d

• micro minerals (trace elements) - mg/d

why is knowledge of minerals important?

• some deficiency states occur commonly

• all are treatable (by provision of the mineral in the appropriate form

• all are preventable (by correction of dietary or physiological imbalances

• some can induce toxicity states if given in excess quantities

why are both calcium and phosphorus important?

• most important mineral constituents of bone and teeth:

  • bone = 46% ash

  • ash = 36% calcium and 17% phosphorus (2:1)

• physiological regulation of Ca and P uptake, storage, function and excretion are interrelated

what are the functions of calcium?

• structural component of skeleton

• controls cell excitability (nerve and muscle)

• regulates muscle contraction

• regulates blood coagulation

• many enzyme actions

there is rigid homeostatic control of plasma calcium ion concentrations via vitamin D and hormones

what are the different sources of calcium?

must take Ca:P ratio into account (ideally 1:1 to 2:1)

• leafy greens

• hay/silage

• animal products (milk, meat, eggs)

• some food contain more P than Ca and require artificial ration balancing:

  • bran

  • cereals

  • roots

  • legume and oil seeds

what are some corrective sources of calcium?

• limestone flour

• in poultry: soluble grit (e.g. limestone/oyster shell)

what factors affect calcium absorption?

• much plant Ca is bound as phytates (prevents absorption in monogastrics but rumen microflora can release (phytases))

• oxalates: bind to Ca to form insoluble salts so Ca can’t be absorbed by animals - significant quantities in spinach, sugar beet tops etc

• total absorption of dietary Ca and P decreases as dietary conc. becomes excessive

• high fat diets: excess dietary free fatty acids bind to Ca (and Mg) to form insoluble salts

• enteritis: inflamed mucosa will not absorb Ca

what are signs of calcium deficiency?

hypocalcaemia:

• occurs if sudden decrease in blood calcium concentration - homeostatic control sluggish to correct

• acute form:

  • can occur in female mammals at onset or peak of lactation as high demands of mammary gland for calcium to synthesise milk

  • can occur in laying hens due to high calcium demands for eggshell production

when does hypocalcaemia often occur in dairy cows?

also called milk fever:

• commonly from 1 day before calving to 3 days post-partum - high demand for Ca from lactation

• high-yielding cows in their third and subsequent lactations

• slow homeostatic adaptation in combination with increased Ca demand - mechanisms unable to prevent a sudden decrease in blood Ca level

what are signs of hypocalcaemia in dairy cows?

• flaccid paralysis (progressive)

  • general uneasiness

  • dullness

  • paddling/shifting of hind legs

  • dry muzzle

  • constipation

  • inability to stand

  • coma

  • death

• recumbency (‘downer cow’)

• rumen stasis

• pupil dilation

what are signs of hypocalcaemia in bitch, sow, and beef cattle?

eclampsia (lactation tetany - involuntary, sustained muscle spasms)

what are symptoms of hypocalcaemia in growing animals?

• high rate of skeletal growth (high Ca and P demand)

  • beware of breeds/species with high growth rates

• osteodystrophy = abnormal bone growth

  • deficiencies of Ca, P, and vitamin D

  • nearly always accompanied by osteoporosis: loss of Ca and P from bones making them thinner and weaker, increasing incidence of fractures

• rockets = failure of bone to ossify

  • vitamin D deficiency (classically)

  • in ruminants a deficiency of either vitamin D or P can cause rickets

what are the causes of osteodystrophy in different species?

• puppies/kittens: excessive P (secondary Ca deficiency)

• foals: poor artificial rearing, gut parasites, low hay and high cereal diets (secondary deficiency)

• calves and lambs: unsupplemented high cereal/straw diet

• piglets: failure to supplement dietary Ca, P, vitamin D

treatment = correct dietary Ca:P balance

what are the symptoms of chronic hypocalcaemia in adult animals?

skeletal Ca and P reserves are high and can be withdrawn upon if temporary imbalance (except in late pregnancy and early lactation)

• mobilisation of skeletal Ca and P long term leads to osteomalacia (due to lack of provision of Ca and P):

  • weakened, thin bones = easily fractured

  • increased incidence of osteoarthritis

• decreased milk yields

• urethral caliculi in entire and castrated male lambs fed high concentrate diet

• in horses, goats, and pigs: demineralisation of bones of skull and compensatory collagen deposition causing thickening of the bones (bran disease - excessive P)

what factors affect phosphorus absorption?

• oxalates and phytates: much plant P is organically bound as salts of phytic acid - in simple stomached animals little of the phytate is available

• excess dietary Ca or P inhibit the absorption of P or Ca

what are signs of phosphorus deficiency?

hypophosphataemia:

• abnormal bone growth and osteomalacia

• reduced growth rate

• ‘pica’ (abnormal appetites) e.g. bone/wood chewing

• infertility

what are the functions of magnesium?

no body reserves and no homeostatic regulation - dependent on dietary intake to maintain function

• around 70% total body magnesium is present in bone

• most common enzyme activator

• muscle contraction

• propagation of nerve impulses

what are the different sources of magnesium?

• all green plants (chlorophyll)

• meat and bone

• colostrum

• magnesite and calcined magnesite

how much magnesium do animals absorb from diet?

• 20-30%

• decreased by high copper and high phytate P intakes

what is hypomagnesia?

lack of/not enough magnesium

what are the 4 major presentations of hypomagnesia?

• calves fed unsupplemented all-milk diets are at risk (2-3 months)

  • milk is a poor source of Mg

  • Mg absorption decreases with age

• beef cattle and sheep fed on low quality roughage (straw) or fodder crops (kale, beet)

  • symptoms may occur over several days

  • dullness, hyperaesthesia, convulsions, death

• lactating cattle and sheep

  • grass staggers = emergency

  • signs:

    • hyperaesthesia (hyper-sensitive to stimuli)

    • incoordination

    • muscle tremor

    • recumbency

    • convulsions

    • death

  • frequent cause of sudden deaths - treatable by giving magnesium

• sub-clinical hypomagnesaemia

  • possibly a cause of reduced fertility and milk production in dairy cattle

what are predisposing factors for grass staggers?

• in spring:

  • rapid grass growth = Mg uptake by plant

  • grass diarrhoea = faster passage of digesta through the gut decreases Mg uptake

  • bad weather = grass intake reduced as cows shelter

  • fertilisers:

    • nitrogen fertilisers - increase rumen NH3 which depresses Mg uptake

    • potassium fertilisers - increase Mg excretion

    • liming - decrease grass Mg concentration

• in autumn:

  • gradual decrease in grass Mg

• year round:

  • stresses which decrease food intake (e.g. bad weather/dog worry)

how is hypomagnesaemia controlled or prevented?

• provide shelter

• introduce to spring grass slowly (prevents diarrhoea)

• use fertilisers with care and avoid potassium fertiliser in spring

• provide mineral (Mg) licks

• top dress pastures (calcinated magnesite)

• increase clover in swards

• supplement diet or water with Mg

• Mg rumen boluses

• avoid stress

what are the major/macro minerals?

• calcium

• phosphorus

• magnesium

• sodium

• potassium

• chloride

• sulphur

generally deficiency is uncommon or rare

what are the trace/micro elements?

• copper

• molybdenum

• iron

• zinc

• selenium

• iodine

• manganese

• cobalt

what are the functions of copper?

• important in formation of some plasma proteins (e.g. ceruloplasmin)

• component of other blood proteins and plays a role in oxygen metabolism

• vital role in many enzyme systems e.g. component of cytochrome oxidase in oxidative phosphorylation

• essential for normal hair, wool, and feather pigmentation and crimp in wool

• essential for immune function

how well is copper absorbed?

• CuSO4 is the most readily absorbed copper salt

• metallic copper is poorly absorbed

how is copper transported and used in tissues?

• loosely bound to albumen in the plasma

• stored and released from the liver to meet body requirements

• if too much is stored, the liver explodes

what are signs of copper deficiency?

in all species:

• anaemia (impaired RBC formation)

• abnormal bone growth

• abnormal hair, feather, and wool growth

• loss of hair pigmentation

• cardiovascular disease

in practice:

• most common in sheep and cattle

what are signs of copper deficiency in sheep?

• swayback:

  • affects lambs born to Cu2+ deficient ewes

  • failure or degeneration of normal neural development in the lamb

• congenital (from birth)

  • stillborn, weak - ataxia, paresis, unable to stand, death

  • irreversible

• delayed onset (few weeks old)

  • normal at birth

  • depressed growth rate, rapid onset hind limb weakness, ataxia then paresis and death

  • can be prevented/reduced in Cu deficient lambs by parenteral injection of small doses of Cu complexes

how does copper deficiency in cattle present?

• common 3-9 months of age

• especially in suckler calves where the dam may not be Cu deficient

• failure to thrive

• poor growth

• stiff gait/lameness

• loss of hair pigment

what is copper thiomolybdate?

• rumen microbes form sulphides which combine with Mo to thiomolybdate

• thiomolybdate binds to copper to form copper thiomolybdate

• it decreases Cu absorption and causes signs of Cu deficiency despite adequate dietary Cu provision

how does tolerance to copper toxicity vary by species?

pigs > horses > cattle > sheep

what does copper accumulation in the liver cause?

cell necrosis

what are signs of copper toxicity?

• jaundice

• appetite loss

• hepatic come and death

what is important about copper toxicity in sheep?

tolerance varies between breeds e.g. north ronaldsay sheep are less tolerant to copper toxicity than the scottish blackface breed (would only show copper deficiency)