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» Zinc
» Selenium
» Cobalt
» Copper
» Basic Cations (1)
» Basic Cations (2)

 


Zinc - Animal Nutrition

Written by John Turner Consultancy © for Agrifert
 
Zinc is an essential trace element for the nutrition of all ruminant animals.
For many years zinc deficiency in NZ agriculture has been masked by the fact  that zinc is a significant impurity in superphosphate fertiliser.  Zinc treatments for prevention of facial eczema symptoms have raised soil and pasture herbage zinc levels in some areas throughout the northern half of the North Island.

Zinc contamination of soil is common on land previously used for horticulture, particularly avocado orchards, however, elevated soil zinc levels are not always reflected in pasture and forage crop herbage.


Symptoms of deficiency:
Deficiency of zinc typically results in reduced growth rates of young stock, reduced feed consumption, reduced efficiency  of conversion of feed energy to milk or live-weight gains, dermatitis or scaley skin, swollen tissues around the hooves and foot problems. Development or growth of testicles and sperm production is likely to be affected as is the quality of wool, particularly fine wool. Young Animals are typically listless and lack energy.
 
Zinc is also thought to be required for the excretion of mucus from the gut lining, this is a barrier to attack by gut parasites so zinc deficiency may be linked to low resistance to intestinal worms. Healing rate of injury of wounds is reduced and more likely to become chronic infections for zinc deficient animals.


Different Classes of Livestock have different requirements for zinc:
Calves and Lambs are most susceptible to zinc deficiency and increase the mortality rate of young animals.


Factors that influence the zinc contenet of pastures:
There is a weak correlation between soil zinc levels and the zinc content of pastures so soil testing for this element is used as a general indicator of zinc status and to predict if application of this element to the soil may be worth considering. Plant uptake of zinc from the soil is reduced by cold soil temperature, high pH of recent lime application and high levels of phosphorus. Zinc absorption by animals is reduced when the copper level is high, copper supplementation is not recommended at the same time as high rates of zinc are being supplemented for facial eczema control.  Zinc absorption is reduced when dietary iron and manganese levels are high, soil ingestion in wet muddy conditions will have this effect.


Level of Zinc required in pasture or feed:
The desired range of zinc levels considered adequate in pasture and animal feeds is 30 to 50 mg/kg however for young stock and where symptoms linked to zinc deficiency are a concern, 40 mg/kg is the suggested target level.  To quantify this amount  of zinc, 40 mg.kg is th same as 40 grams per 1000kg dry feed.


Options for Zinc application:
Zinc is still an impurity in superphosphate and fertiliser blends containing this fertiliser, so where there is a long history of application of 'super', soil zinc levels are likely to be acceptable. Where pasture or forage zinc levels are low, foliar application is a good option.
The distribution of zinc over an area fertilised with a bulk blend where zinc sulphate is added to base fertiliser may also be uneven and the timing of application may not be ideal for meeting the spring requirements of sensitive classes of stock.  Zinc applied as a foliar treatment is effective on all pasture types and there is no  time lag between application and when the element is available to grazing animals. The rate required for effective tretment is much lower than for soil application. Application may be targeted onto pastures for young stock in the spring and rams or bulls pre-mating.
Multimineral additives to salt blocks or to stock drinking water may be beneficial however the amount of any one element included is usually not adequate for 'deficient' stock. Zinc addition to drinking water tastes bad to sheep and they tend to avoid drinking from treated troughs.
 


Selenium - Animal Nutrition

Written by John Turner Consultancy © for Agrifert
 
Selenium is an essential ultra-trace element essential for the nutrition of all animals. Care must be taken when applying selenium as this element is also potentially very toxic.
 
Symptoms of deficiency:
The classic sympton of selenium deficiency is "white muscle disease" of lambs, the muscle most affected is the heart. This results in heart failure or paralysis of the hind limbs and resulting in a high mortality rate for new born animals. Slight deficiency is associated with ill-thrift and scouring, female animals have reduced fertility and cows that get into calf typically have increased incidence of "retained placenta" at calving time. Retained placenta can result in minor infections that also reduces fertility.
 
Different classes of livestock have different requirements for selenium:
As for most essential nutrients, selenium deficiency affects young animals more than fully grown livestock. Adequate selenium is also important for cows and ewes from before mating to the end of the gestation period.
 
Factors that influence the selenium content pastures:
There is reasonably good correlation between the soil selenium test level, the plant tissue selenium status and animal status. One problem with selenium treatment of soil has been the fact that sodium selenate (the most common selenium compound used) is very water soluble and has a short effective life in the soil unless incorporated into a slow release product such as "Selcote".  Where the soil ph is low, plant uptake of selenium will be reduced and soil applied selenium products become "less effective". In parts of the world where selenium toxicity is an issue, it is referred to as "alkali disease" due to increased uptake of selenium from soil minerals when ph is high.
 
Sulphur at high levels in the diet will reduce selenium absorption by grazing animals. Brassica leaf tissue often has high sulphur levels.
 
Level of Selenium required in pasture or feed:
The level of selenium that is considered adequate in pasture and animal feeds is 0.10 mg/kg however some consultants recommend levels up to 0.30 mg/kg for dairy cows. The threshold of toxicity depends on dietary factors that influence selenium absorption however 5.0 mg/kg is likely to be toxic.  To quantify this amount of selenium, 0.10 mg/kg is the same as 0.1 gram per 1000 kg dry feed, a very small amount.
 
Options for Selenium treatment:
Addition of selenium prills to base fertiliser blends is the standard approach to providing selenium for grazing animals. Usually the rate is 1 kg of a 1% selenium product per hectare per year, manufacturers of these products (such as Nufarm) produce information about release patterns and pasture Se levels.  Selenium has also been added to animal drench products however the rate added may not be effective where stock are "deficient". Vets have often advised farmers not to use selenised drench if they have applied prills to the soil however as there is a 30 to 50 fold margin of safety between deficiency and toxicity, this is very cautious advice.

Injection products are marketed, particularly for young lambs and calves, which contains selenium and vitamin B12 (cobalt metabolite). This is intended as a dose to reduce mortality and ill-thrift due to sub-clinical deficiency of both elements.  Treatment of drinking water and inclusion of selenium in foliar treatment products are possible treatment options however caution is essential to avoid the possibility of selenium poisoning. A foliar treatment product to provide 0.30 mg/kg to 2000 kg DM requires 0.6 grams of selenium per hectare.

 


Cobalt - Animal Nutrition

Written by John Turner Consultancy © for Agrifert

Cobalt is an essential trace element for the nutrition of all ruminant animals.
Rumen microbes produce vitamin B12 of which cobalt is an essential component.
Vitamin B12 is required for the absorption of some products of rumen fermentation so deficiency produces symptoms rather like starvation of the animal.


Symptoms of deficiency:
These include reduced growth rate, decreased appetite, decreased milk production, rough hair coat, weight loss, weak animals, increased susceptibility to parasites, increased risk of disease or infections and increased mortality of young animals. Reduced conception rates can be expected from cobalt deficiency during the period (2 months) before mating.  All female animals will be affected however the worst affected will be heifers, ewe hoggets and 2-tooth ewes.


Different Classes of Livestock have different requirements for Cobalt or Vitamin B12:
Lambs have the highest requirement followed by calves, adult sheep and adult cattle. For any species young animals are more likely to be affected by cobalt deficiency than fully grown animals. In a dairy farm situation, an indicator of cobalt deficiency is slow growth rate of weaned calves.


Factors that influence the cobalt content of pastures:
There is a reasonable correlation between soil cobalt levels and the cobalt content of pastures so soil testing for this element is used as a general indicator of cobalt status and to predict if application of this element to the soil is a reasonable treatment option. The composition of pasture is a significant factor that influences animal uptake of cobalt. Ryegrass has roughly double the cobalt content of low fertility grass species such as browntop and clover has about 1.5 times the content of ryegrass.

Management aimed at increasing the clover content of pastures and reducing the content of "low fertility" grass species will be beneficial. This includes increasing the soil pH and levels of nutrients such as phosphorus.


Level of Cobalt required in pasture or feed:
Although adult cattle may not be afected by levels as low as 0.06 mg/kg in the pasture if fully fed however a safe minimum level is considered to be 0.10 mg/kg to cater for the requirements of all ages of cattle on a property. To quantify this amount of cobalt, 0.10 mg/kg is the same as 0.1 gram per 1000 kg dry feed.  Sheep, goats and deer pastures should also be maintained at a level of between 0.10 and 0.15 mg/kg especially for young animals being weaned onto pasture.


Options for Cobalt application:
For many years, cobalt has been included in solid fertiliser blends however the efficiency of uptake may be low (possibly less than 5%) and there is a time lag between soil application and uptake by pasture plants. The distribution of cobalt over an area fertilised with a bulk blend may also be uneven and the timing of application may be targeted onto pastures for young stock.

Vitamin B12 injection directly into stock is a good option but the beneficial effect is not long term.
 
Multimineral additives to salt blocks or to stock drinking water may be beneficial however the amount of any one element included is usually not adequate for "deficient" stock.
 


Copper - Animal Nutrition

Written by John Turner Consultancy © for Agrifert
 
Copper is an essential trace element required for both plant growth and animal nutrition. The minimum requirement for animals is slightly higher than the minimum requirement for plant growth so symptoms of copper deficiency are observed in grazing animals before the deficiency is clinical in pasture plants.


Symptoms of deficiency:
A wide variety of symptoms may arise from copper deficiency. In young animals, deformed leg bones, fractures of leg bones and high mortality rate due to anaemia and heart failure are common symptoms. In order animals, reduced growth rate, reduced production, scouring, light or faded hair/coat colour and general unthriftiness are common symptoms. Copper deficiency may be associated with increased incidence of metabolic disorders, particularly in dairy cows around calving time.


Different Classes of stock have different requirements for Copper:
Sheep have a lower requirement for copper than cattle or deer and are more likely to suffer from copper toxicity due to a relatively low ability to excrete excessive dietary copper. Copper is required for the normal growth of bone, hair and skin so animals that are growing rapidly and female animals in late pregnancy are most likely to show copper deficiency.


Factors that influence the copper content of pastures:
There is some correlation between soil copper level and the copper content of plants however use of a soil test alone is not good enough to base copper treatment recommendation on. Soils with low copper status in general are sandy soils and peat soils. Application of high rates of lime will reduce copper availability to plants and alkaline soil (pH greater than 7) is also associated with low copper levels in plants. Low soil temperature will reduce the copper content of pastures.
Herbs such as chicory and plantain may have copper levels up to 3 times that grass growing under the same conditions.


Factors that affect copper absorption by animals:
Molybdenum is well known as a trace element that reduces the absorption of copper by animals and the factors thet increase the molybdenum content of pastures are similar to those that decrease the copper content. These are high pH and wet soils including peat. The molybdenum level in pastures grown in late winter may be up to 3 times the level grown on the same site during hot dry summer conditions.  There is some debate about what is the desired level of molybdenum in pastures. Levels of between 1 and 2 ppm are not considered to have a severe effect on copper absorption by cattle however where the level is close to deficient for clover growth (0.15 ppm in summer), copper absorption may be slightly enhanced and "mask" a simple deficiency in copper. The logic of running low Mo levels which compromise clover growth and pasture production as an alternative to supplementing copper to livestock is questionable. Sheep may actually suffer from "molybdenosis" due to lack of molybdenum leading to copper toxicity (symptoms are black liver and liver failure) despite the diet having a normal copper level.
Dietary sulphur and iron at high levels (due to soil or mud ingestion) also affect the absorption of copper from forage. Forage brassicas generally have high levels of dietary sulphur.


Level of Copper required in pasture feed:
Sheep have adequate copper at levels between 6 and 10 ppm which is a typical ryegrass based pasture level.
Cattle require about 10 ppm however in controlled feeding situations, levels of up to 20 ppm are recommended for cows during late pregnancy and for rapidly growing yearlings. Deer have at least as high a requirement for copper as cattle, the production of antlers/velvet from stags is likely to mean that they have a similar copper requirement  to hinds.  To raise the copper level of pasture by 5ppm, 5 grams of copper is required per 1000 kg of dry feed.


Testing for Copper status:
Soil test data is of limited value in determining copper status of pastures and stock however where pasture herbage levels are low and the soil test level also appears low, soil application of copper as a solid fertiliser may be an option.  Blood test of animals or liver biopsy is used to determine the copper status of animals. Copper is stored in the liver and this reserve is used to mantain blood copper levels. The problem with the blood test is that it will not indicate low until the liver reserves are very low, but it is a convenient test to conduct. The liver biopsy is the best test but it is very invasive.


Options for Copper application:
Copper may be included in soil applied fertiliser as either copper sulphate (water soluble) or copper hydroxide (low solubility - slow acting) however raising the copper level in ryegrass to about 10 ppm for cattle or deer is not easily achieved.
Application of more than 5 kg copper sulphate/ha may reduce pasture growth.
Environmental factors affect the efficiency of uptake of soil copper by plants, particularly in winter/spring for dairy cows.  Mineralised salt blocks and drenches may contain copper but the amount is generally not sufficient to overcome copper deficiency. Copper addition to drinking water may be beneficial however this may not be effective for dairy cows during winter/early spring when pasture water content is high.  Injection of stock to treat copper deficiency is effective but this is a shock dose and ideally the copper supply to animals should be mantained at an adequate level. Bolus treatment provides a steady supply of copper but this may not be sufficient during peak demand periods such as late pregnancy in dairy cows.
Foliar application to pasture or feed is a good option. Application timing for dairy cows after zinc treatment for FE is completed and 1 to 2 months prior to calving. For deer, hinds in late pregnancy, stags at the start of horn growth and young stock after weaning. Be very careful about recommending copper for sheep, they have a low requirement and there is a risk of toxicity.

 


Basic Cations - Animal Nutrition

Written by John Turner Consultancy © for Agrifert

Potassium, Calcium, Magnesium and Sodium
Basic Cation major nutrients are all essential for animal nutrition and also for plant nutrition with the exception of sodium. The problem is that these nutrients inter-act with each other in the soil, plant tissue and in the animals' digestive system, the content of each of these nutrients in lush pasture is different to ruminant animal dietary requirements.
 
Calcium, Magnesium and Sodium are required for metabolic (energy) processes such as nerve function, muscle function and electrolyte balance in blood. Clinical deficiency has severe effect on animal productivity and is a common cause of cow death. Calcium and magnesium deficiency at sub-clinical level (no obvious symptoms) can reduce lactation performance by 10% and conception rates at mating.


Comparison of typical pasture levels with animals requirements


The reason why calcium and magnesium deficiencies are problems in dairy cow nutrition is due to the antagonistic effect of high potassium in the diet and marginal levels of these nutrients in winter/spring grown pasture.


Potassium:
Potassium deficiency is not an issue for rumiants fed on a green forage based diet. The issue is that the pasture potassium content must be about 3% during late winter and spring for optimum plant growth. This is about 3 times the animal requirement and this reduces the absorption of dietary calcium and magnesium by ruminant animals. When a grass plant is defoliated, potassium and nitrogen is mobilized from the crown of the plant and the roots so that replacement growth of new leaf tissue is rapid and the potassium content reduces as the calcium content increases. The typical appearance of grass leaves that are expanding is light green compared to a deeper green colour of fully expanded leaves.  A grazing rotation length of less than 3 weeks in spring is likely to be associated with increased metabolic stress to stock.
When fertiliser potassium is applied to the soil, luxury uptake and a rapid increase in pasture potassium content is common. Application of potassium fertilisers should be timed to avoid seasonal times when animals are prone to metabolic stress.


Calcium:
Calcium deficiency is generally referred to as "milk fever" due to the increased incidence of this metabolic problem the start of lactation. Affected ruminant animals have impaired muscle function, particularly smooth muscles associated with the uterus and gut. Symptoms include difficulty with calving (cows), retained placenta and associated infections. The rate of passage of forage through the gut may be reduced which reduces feed intake and energy supply.
Bone calcium may be mobilized to mantain blood calcium levels however this process requires up to 3 weeks from the start of calcium stress to become effective. If the dietary calcium content is chronically low, bone strength will reduce and the incidence of bone fractures and arthritis will increase.

 


Basic Cations - Animal Nutrition (2)

Written by John Turner Consultancy © for Agrifert

Magnesium:
Magnesium deficiency is "hypomagnesaemia" (low blood/body fluid magnesium) or "grass tetany" (convulsions and profuse salivation or frothing at the mouth).
Subclinical deficiency tends to affect animal behavior with increased excitability. Death can be rapid for clinically affected animals.
 
Hypomagnesaemia can occur quickly (within a couple of days) because bone magnesium reserves are not able to be quickly mobilized to mantain blood magnesium levels. Mature lactating cows grazing low magnesium content feed with a high potassium level are most likely to be affected.
The magnesium content of pastures is affected by soil temperature, pasture content reducing by 0.01% per degree reduction.


Sodium:
Sodium deficiency is often overlooked because the effect is not as dramatic as milk fever or hypomagnesaemia. However it has been estimated that up to 30% of Waikato dairy herds have reduced milk production due to sodium deficiency. Dominion Salt published information on salt application to pastures during the 1970's and 1980's.  Low sodium levels (less than 0.1%) are typical of pumice soils in the central North Island. Northland, Taranaki, Manawatu and the South Island West Coast often have high pasture sodium levels due to salt spray being carried on the prevailing westerly wind.

Plant growth research has shown that many plants can utilise sodium as a nutrient, especially where soil potassium level is low. Sodium is thought to reduce luxury uptake of potassium by plants where soil potassium levels are high. Excessively high levels of sodium in the diet has the same effect as high potassium as a predisposing factor for the incidence of milk fever. Dietary Cation Anion Difference (DCAD) is used to estimate the combined effect of dietary potassium and sodium on dairy cows.


Comparison of typical pasture levels with animals requirements
Where pasture treatment is considered, it is interesting to calculate the requirement to raise the concentrations from low to adequate:
 


These calculated rates represent "worst case" scenarios, several factors influence the proportion of dietary calcium and magnesium that is absorbed through the ruminant gut. Do not use this information as a recommendation.


Seasonal Changes in Ryegrass Pasture Nutrient Levels:
Ryegrass based pastures have some growth stage variations due to seasonal growing conditions, the seasonal changes could be similar to the table below



 
Calcium deficiency is generally referred to as "milk fever" due to the increased incidence of this metabolic problem the start of lactation. Affected ruminant animals have impaired muscle function, particularly smooth muscles associated with the uterus and gut. Symptoms include difficulty with calving (cows), retained placenta and associated infections. The rate of passage of forage through the gut may be reduced which reduces feed intake and energy supply.
Bone calcium may be mobilized to mantain blood calcium levels however this process requires up to 3 weeks from the start of calcium stress to become effective. If the dietary calcium content is chronically low, bone strength will reduce and the incidence of bone fractures and arthritis will increase.