Trace Elements

General Mineral Information


Copper  Selenium  Cobalt  Magnesium  Iodine

These notes are designed to help understand and interpret mineral results and reports


Copper Deficiency - Deficiencies are widespread in NZ, especially on volcanic soils, peat soil, pumice and sandy soils. Deficiencies can generally be described as primary or secondary.  Primary deficiencies occur when stock are not ingesting enough copper.  Secondary deficiencies occur when Molybdenum (Mo) or other ions interfere with copper uptake and/or metabolism.

Deficiency is seen most commonly when:

·         when daily intakes are <5mg/kgDM.

·         when Mo is > 20mg/kg DM in diet (sometimes called Mo toxicity).

·         when Co:Mo < 2:1.

Uses in the body - Copper is required for the activity of enzymes associated with iron metabolism, the production of red blood cells, the formation of connective tissue, coat colour and immune function.  It is used throughout the entire body and signs of deficiency are often non-specific.

Clinical signs of deficiency;  poor conception rates, reduced growth rates, ill thrift and scouring faded coat colour (reddish tinge), rough coat, anaemia & red water, broken bones


Blood tests – Are useful if deficiencies are suspected.  Blood tests that come back in the normal range inform you that your herd is not suffering from deficiencies but give no indication about copper status in the near future.  Blood copper levels can be falsely elevated in sick animals.

Liver tests – Give the best information as informs as to the level of copper stores that the animal has to draw on.  This is especially valuable in autumn as winter and early spring are times when stores are heavily drawn on.

·         Liver biopsies taken from the live cow are most representative of your herd.  Live liver biopsies have an extremely low risk of complications.

·         Liver biopsies taken from cull cows are an acceptable estimate but bear in mind that these cows may not be representative – ie – non – pregnant, sick, old, empty carryovers or heifers.

Generally cows with liver samples less than 95 umol/kg are considered deficient.  Supplementing these cows will usually result in a measurable production response.  Prior to winter however, we may recommend supplementing cows that are above this level.  This is to ensure that reserves are high enough to carry through the winter and into spring.

Pasture/Soil tests – Pasture testing gives some information about what your stock are eating but give little information about the actual status of the cow.  These tests are important however, as they allow us to get a full picture of the copper cycle on your farm.  Levels of Mo, Fe and S should also be looked at as these may influence your approach to supplementation.


Injectable copper – Rapidly effective but relatively short acting (approx 3 months).  Should not be used on stock suffering from liver damage.  High risk of toxicity if liver levels are high and in sick animals.

Copper boluses – Very effective with longer duration of action (approx 6-9 months), safe in face of liver damage, however labor intensive to administer and slightly more expensive form of supplementation.

Copper via water troughs/drench – there is some evidence to suggest that a mixture of both sulphates and chelates are optimal.

Copper Sulphate – 25% bioavailable.  Requires daily supplement.  Relatively cheap.  Possible interactions with other supplements (eg Zinc during facial eczema season).

Copper chelates – Higher availability than sulphates, Requires daily supplementation.  More expensive than sulphates.  Not thought to interfere with zinc supplementation

Copper sulphate in fertilizer – may not the most efficient way of getting copper into stock – particularly in high Mo, S and Fe soils

Other points of interest

·         High use of palm kernel as a feed source may reduce the need for the copper supplementation previously required.

·         Liver damage from hepatic cirrhosis/FE will lead to less liver cells to store copper.

·         Silaging or drying (hay) of forages may increase the bioavailability of copper – therefore fast growing lush pastures have the lowest availability of copper (early spring) .

·         Lime on soil increases Mo levels and lowers copper in pasture.

·         Excess copper can be toxic.  This can be acute (ie – shortly after supplementation) or chronic (ie – build up in liver over time leading to liver damage).

·         Un-weaned calves are more efficient in absorbing copper.  Take care if they are drinking trough treated water.







Selenium deficiency




About 30% on New Zealand soils are selenium deficient, and selenium deficiency is still quite common despite the importance of selenium being known about for some time.  In Golden Bay the soils are generally deficient, and this is commonly reflected in low selenium levels in stock.




Uses in the body




Selenium’s most important role in the body is as part of the enzyme glutathione peroxidase which acts as an antioxidant which means that it acts as a mop to remove many of the free radicals (dangerous oxidative chemicals) that are produced in the body during day to day functioning.  Selenium is also involved in the functioning of the immune system.  However, there are at least 20 other enzymes (protein engines) that contain selenium in the body and the function of many of these is currently unknown.




Clinical signs of deficiency




Many clinical signs of selenium have been described, and these are very varied.  Supplementation in NZ has been seen to reduce the incidence of white muscle disease and ill thrift and improve fertility and milk production.  Other signs of selenium deficiency have been reported worldwide include; retained foetal membranes, metritis, poor uterine involution, pre-mature calving, abortion, sub-clinical mastitis, reduced fertility, abortion and premature calving.




Dietary requirements




Current NZ recommendations is for 3 – 5 mg/cow/day in dairy cows.








Selenium has no storage organ, so samples reflect current or historical intake, rather than reserves.  Selenium status is generally very consistent across the herd so only a small number need to be sampled.




Serum (blood) – quick and easy, reflects current intake




GSH-px (blood) – this enzyme is found in red blood cells (RBC), and reflects the selenium status of the animal in the past (ie – when those blood cells were formed).  RBCs can survive for several months, so may not be useful if there has been a recent change in the diet or supplementation.




Liver – reflects current intake well.  The same samples taken for copper can be used for selenium, so no extra cost in sampling here.








Fertiliser – cheap, convenient and easy, recommend autumn and spring application.  Usually fully effective, but in Golden Bay may not be due to high loss from soil.  Slow response, so not suitable has whole approach in deficient stock.




Oral supplementation – RSC mineral mix – specially formulated to combat the low soil levels in Golden Bay.  Can be given in water or mixed into feed.  Proven to be very effective in maintaining good levels year round.  Requires daily supplementation so if no mix in water over dry period may need top up method of supplementation during this time.




Short acting injection – Prolaject B12 + selenium – Cheap, good for rapid increase if low levels, but not much selenium so repeat injections required.  Packet recommendation is not to repeat injections less than every 3 months so not useful as a whole approach, but maybe useful as a top up (eg) prior to calving and mating.




Long acting injection – Selovin LA – relatively expensive, lasts about 12 months, good option for treatment for run off stock, or if no other selenium supplementation being undertaken. 




Pour on – Selpour – relatively cheap, easy to apply, but only lasts about 6 weeks so repeat applications required if only form of supplementation.












Acute – colic, diarrhea and difficulty breathing. 




Chronic – ill-thrift, anemia, rough coats, stiffness and hoof lesions. 




There is no specific antidote for either acute or chronic toxicity, supportive treatment is all that can be given.  Most cases of toxicity occur when more than one form of selenium is supplemented simultaneously.  Supplementation should only be undertaken after testing, and under advice from a vet.  








Other points of interest




Monensin concurrent administration of monensin and selenium increases the toxicity of selenium.




Sulphur – Selenium and sulphur are interchangeable in many compounds and high levels of sulphur may displace selenium.  Applications of sulphur fertilizers can slightly decrease available selenium.




Vitamin E – Selenium and Vitamin E have similar functions and high levels of either appear to result in a lower demand for the other.  Current recommendations for selenium in New Zealand pastures are typically a fraction of overseas recommendations, but the incidence of selenium responsive disorders is still relatively low.  It is thought that high levels of Vitamin E in New Zealand grass may reduce the selenium requirements.






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 Magnesium deficiency - The cost of magnesium deficiency to the dairy industry was estimated at 28 million dollars annually in 1991.  Even with the now widespread use of magnesium supplementation, 20-25% of herds are considered low in magnesium during the winter months.  Production responses of 10-15% can be seen in deficient herds when supplementation is given.  

Uses in the body - Magnesium has many roles in the body, particularly in enzyme systems.  It is essential for energy metabolism and protein and lipid metabolism.  Mg is also very important in the regulation of calcium in the body and low magnesium increases the risk of milk fever.

Clinical signs of deficiencyHypomagnesaemia (low magnesium) can occur in both acute and chronic forms.

Classical acute hypomagnesaemia tetany (grass staggers, grass tetany, lactation tetany) is relatively rare, but generally represents the “tip of the iceberg”, meaning there are likely to be other hypomagnesaemia animals within the herd.  Clinical signs are increased nervousness and over reaction to normal handling, with onset of convulsions when stimulated.  Champing of the jaws, frothing at the mouth, head thrown back and eyes rolling may all be observed during convulsions.  Heart and respiratory rates are elevated, and the heart sounds are greatly increased in intensity.  Temperature may be elevated to 40-40.5°C.  Death due to respiratory failure usually occurs in ½-1 hour if untreated.

Chronic hypomagnesaemia is characterised by an increased incidence of milk fever, poor body condition, low milk production and udder oedema.  It is thought that some of these animals may be predisposed individuals, as they sometimes occur in well supplemented herds.

Dietary requirements - Cows are almost totally dependent on daily absorption for their magnesium needs as there is little control of the utilization of magnesium stored in body tissues.  Absorption is relatively poor, ranging from 7-35% (average 17% in early lactation). 

Calving/early lactation – require 15-20g (average 18g) elemental magnesium/cow/day.  Pasture is generally 0.16 – 0.22% Mg, and the recommended ration composition for early lactation is 0.25% Mg (i.e. 2.5g/kg DM).  Therefore supplementation is essential.

Mid-late lactation -  In mid lactation the cows requirement in rations should still be 0.25% Mg, by late lactation 0.2% Mg.  At this time pasture Mg composition is increasing as grass becomes more mature, whilst cows requirements are decreasing.   There will be variation in grass maturity at different times between years, but in general cow requirements should be met by pasture supply at about mid November – mid December, and supplementation can generally be removed at this stage.

Dry Period - There is little scientific data on the requirement for and supplementation of magnesium during the dry period.  However, there appears to be an optimal magnesium concentration in the rumen for maximum plant digestibility.  Therefore, suboptimal magnesium levels in the dry period could theoretically affect feed conversion efficiency. Cow requirements are lower in the early dry period as a large part of magnesium requirements are due to magnesium loss in the milk.  Requirements rise late in the dry period and springers should always be supplemented.

Testing - Serum (blood) is the most commonly used test.   Ideally we test 10 animals.  Aqueous humour (from the eye) is used for post-mortem diagnosis. The reference range for serum magnesium is 0.62-1.15 mmol/l.  Individual cows with serum Mg concentrations <0.4 mmol/l are at risk of clinical grass staggers.  A calving cow with levels <0.85 mmol/l may be at increased risk of milk fever.  Note that results may be variable if daily intake is not consistent and results vary with timing of sample relative to supplementation (peak levels 1-3 hours after drenching).  Also the age of the cow affects result (0.03 mmol/l drop in serum Mg per year of age)

Supplementation  The same dose of elemental magnesium should be used for all magnesium products, as there appear to be only small variations in availability between oxides, chlorides and sulphates.  However the particle size (measured as mesh number) of oxides does affect availability, with finer particle sizes increasing surface area and therefore absorption.   50 mesh is coarse, with low availability.

1)    Drenching Magnesium Oxide (55% elemental magnesium) - Often referred to as “causmag” (an early brand name), magnesium oxide is the most commonly used of the supplementation options.  Some drenching systems can use the dusting mag oxide, but many will need a specific drenching mag oxide, which is a finer grade and may also have stabilising agents added to help keep it in suspension. All magnesium oxide drenches are compatible with bloat drenches.  Dose rate           30-35g (average 33g)/cow/day.  Best split into half doses morning and night, as more than 15g elemental magnesium (i.e. 27g magnesium oxide) in a single dose can in theory create a high enough Mg concentration in the rumen to kill some micro flora, and thus reduce feed conversion efficiency.  Duration of action  Maximum of 24 hours.  Gives most consistent intake so is method of choice for milking cows

2)    Dusting Magnesium Oxide (55% elemental magnesium)  Assume two-thirds loss rate on pasture, 50% losses on supplements.  80-100g/cow/day on pasture, 60-80g/cow/day on supplements.  Should be as evenly mixed as possible in supplements, may need to mix into slurry with water to help mixing and to adhere to dry supplements such as hay.  Duration of action - Maximum of 24 hours.  Loss rate means greater expense than drenching.  Heavy rain may wash off dusted pasture.

3)    Magnesium Sulphate (10% elemental magnesium) - Most commonly added to drinking water, can be used for drenching or adding to supplements, but this is rarely done.  Not compatible with bloat remedies if drenching due to potential oesophageal groove closure.  Dose rate is 180g/cow/day  (Although this is the dose to supply 18g elemental magnesium/day, very few farmers are using this rate for addition to water due to palatability issues.  The usual rates given are 80-100g/cow/day i.e. about half of the ideal dose.  Palatability may be improved by adding flavourings such as aniseed, apple or caramel to the water.)  Duration of action  Maximum of 24 hours.  Easy to use, slight DCAD effect if using precalving and more palatable than mag chloride but relatively high cost compared with drenching mag oxide and there must be no access to alternative water sources  The lack of palatability at high doses means that many herds are underdosing due to palatability problems, may need other supplementary magnesium

4)    Magnesium Chloride (12.5% elemental magnesium)  Also usually added to water supply, and occasionally drenched or added to supplements.  Also not compatible with bloat drenches.  Dose rate is 144g/cow/day (As for magnesium sulphate above, most farmers will use 60-80g/cow/day due to palatability problems.)  Duration of action  Maximum of 24 hours.  Advantages and disadvantages are similar to MgSO4 but MgCl is more soluble and slightly cheaper than mag sulphate, and mag chloride has poorer palatability.

5)    Intraruminal Magnesium Capsules  Rumetrace capsules contain 189g elemental magnesium and last 9-12 weeks.  They only delivers approx 2.5g elemental magnesium/day so other forms of supplementation may be necessary. They are relatively expensive but may be useful for high value animals or where other options not available

Other points of interest

·         Plant uptake of magnesium is reduced in soils high in potassium, meaning less available magnesium.  This is exacerbated when soil temperatures are low.  Herbage levels above 22.5g/kg DM are thought to have significant effects.  Most NZ dairy pastures are above 30g/kg.  These effects can be nullified somewhat by increasing magnesium levels.

·         DCAD (dietary cation-anion deficiency) levels can theoretically be manipulated to adjust magnesium levels by increasing magnesium availability on the rumen.   High levels of K and Na create a high DCAD level, and decreasing these cations or increasing anions such as Cl and S (present in mag chloride and sulphate) will produce a lower DCAD and theoretically improve availability of magnesium.  Ammonium salts can also be used to manipulate DCAD.  However, in New Zealand conditions it is often impractical to supply enough anions to have a significant effect on DCAD.
Low dietary sodium can also reduce magnesium availability.  This is thought to be due to an increase in potassium levels in saliva, and therefore an increased concentration of rumen potassium.

·         High pasture nitrogen can reduce magnesium levels, as high rumen ammonia levels depress magnesium absorption.  This effect is most noticeable in soils that have had both potassium and nitrogen applied at high rates – typically these are paddocks where effluent has recently been spread.  These paddocks should be avoided during calving where possible. 

·         Dry matter intake has a large effect on magnesium availability – underfed cows are more likely to become hypomagnasaemic.   Increasing feeding levels can sometimes be almost as beneficial as magnesium supplementation.  Readily available carbohydrates (such as soluble sugars) also increase Mg absorption.

·         Ionophores (such as Rumensin) increase magnesium absorption, presumably via positive effects on the Na:K pump.

·         Oversupplementation with magnesium can cause diarrheoa and “sleepy” cows.  There is little information on whether this is production limiting, but first principles would suggest there is likely to be at least some effect on production.  High serum magnesium levels suggest magnesium is being supplemented well in excess of demand.  Cows are able to excrete surplus magnesium in urine, so high serum levels indicate the kidneys are being faced with non-physiological amounts of magnesium. 

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