Mineral Requirements for Ruminants
Ruminant Mineral Requirements
As many as 14 different minerals are required by ruminants to maintain sound health and production. Some are required in relatively large amounts and form a significant proportion of the body. Such minerals are often classed as macro minerals. Others are required in much smaller amounts and are known as micro minerals or trace elements. Micro minerals generally assist or increase the rate of chemical reactions within the animal’s body.
Table 1. Macro and micro mineral requirements for ruminants.
|Macro minerals (g/kg DM)|
|Calcium||1.4 – 7.0||2.0 – 11.0|
|Phosphorous||0.9 – 3.0||1.0 – 3.8|
|Chlorine||0.3 – 1.0||0.7 – 2.4|
|Magnesium||0.9 – 1.2||1.3 – 2.2|
|Sodium||0.7 – 1.0||0.8 – 1.2|
|Micro minerals (mg/kg DM or ppm)|
|Cobalt||0.11 – 0.15||0.07 – 0.15|
|Copper||4 – 14||4 – 14|
|Manganese||20 – 25||20 – 25|
|Zinc||9 – 20||9 – 20|
*ppm = parts per million
*Lower values – maintenance
*Higher values – growing, pregnant or lactating animals
Difficulty in recommendations
There are significant interactions between minerals and vitamins and differences in availability can be unpredictable. It is therefore difficult to clearly define recommendations for supplementation.
The unavailability of pasture feed
In most circumstances, grazing ruminants will obtain the bulk of their requirements from pasture. The concentration and availability of minerals and vitamins depend on pasture composition, soil type, climatic conditions and stage of maturity, as well as the grazing selectivity of the animals.
The range of minerals considered necessary for maintenance through to rapidly growing, pregnant or lactating stock (higher values) is shown in Table 1 (above). Values shown are a guide only. Feed analysis determines the mineral content for feed concentrates, pasture, silage, roughages and while it is beneficial to know, but you should also consider requirements and differences due to foraging behaviour, age, genetic variability and stage of production effects. For example, Merinos are considered to be more susceptible to iodine and selenium deficiencies but less susceptible to copper deficiency or toxicity than some British breeds.
With respect to age-related issues, adult or mature animals may have sufficient reserves of many vitamins and minerals, allowing them to tolerate periods of deficiency, whereas young stock may have inadequate reserves and may require supplementation.
Micro mineral requirements
The most important micro mineral deficiencies are generally thought to be selenium, cobalt, copper, iodine and zinc.
The only known role of Se is in the destruction of peroxides and consequently protecting tissues against oxidation (damage). Vitamin E acts by preventing peroxides forming and both have a role in preventing white muscle disease, muscular dystrophy, ill thrift and infertility in ewes. Symptoms may include poor growth rates, decreased wool production and scouring.
Selenium is not required for plant growth, so conditions that favour increased pasture growth in selenium deficient soils will predispose animals to deficiency, since the uptake of selenium by plants is incidental to their uptake of nutrients essential for plant growth. Clover-dominated pasture and highly fertilised pastures in general tend to lead to lower concentration of selenium in plant tissue and potential deficiency in grazing animal diets. The syndrome can occur on both basalt and granite derived soils, acid sandy soils, high fortified super-phosphate or gypsum use and clover dominant pastures may induce a selenium deficiency.
While cobalt is not directly utilised by ruminants, its dietary requirement relates to its role as a precursor for synthesis of vitamin B12 by rumen micro-organisms. The effect of deficiency is manifested as a vitamin B12 deficiency.
Coastal, calcium rich or sandy soils are commonly low in cobalt but ill thrift due to deficiency of cobalt/vitamin B12 has also been observed on the tablelands. Excessive lime and lush pasture growth may also lead to deficiency symptoms. Symptoms include ill thrift, weepy eyes, anaemia, scaly ears, and infertility and poor mothering in ewes.
Cobalt / vitamin B12 deficiency is also associated with phalaris staggers and it has been found that chronic forms of staggers can be prevented through treatment with cobalt or vitamin B12 directly trigger on grass tetany as an effect of secondary ketosis.
Copper (Cu) and Molybdenum (Mo)
Copper is an essential part of several enzymes and is required for body, bone and wool growth. Grasses tend to contain more copper than clover-based pastures and availability is higher from dry feed than green herbage. High intakes of sulphur, zinc, iron, cadmium and calcium can decrease the availability of copper, although it has been shown that excess molybdenum is the main factor linked to copper deficiency.
Care must be taken to ensure that copper toxicity does not occur from supplementation since toxic levels are only slightly above the upper end of the target dietary intake range. Toxicity effects may be exacerbated where liver function has been compromised by intake of alkaloids from plants such as Paterson’s curse, senecio spp (fireweed/groundsel/ragwort) and blue heliotrope. This condition also interacts with supply of cobalt since high rumen concentrations of vitamin B12 can serve to detoxify these alkaloids before they can cause any damage.
Zinc has a role in enzymes and their involvement in carbohydrate metabolism and protein synthesis. It is constantly required in the diet as the body does not have significant mobilisable reserves. Deficiency symptoms may include excessive salivation, loss of wool crimp, loss of hair or wool around mouth and eyes, stiff joints, scaly and dry skin, slow wound healing and in appetence leading to reduced growth rates. Poor testicular growth and infertility are also symptoms commonly found with zinc deficiencies.
Macro minerals – roles and availability
The following are those minerals and vitamins considered essential for normal rumen function and animal performance.
Found in bones (about 99% of total body Ca), teeth and intracellular fluids, calcium is important for nerve function, muscle contraction, blood clotting, activation of a number of enzymes and bone formation. It is found in stems and leaves of herbage and is seldom deficient in soils. Availability does not decline with maturity of plant but deficiency can occur on acid or sandy soils when animals are grazing forage consisting of rapidly growing grasses or cereals or when grain supplementation is high.
Deficiency symptoms include milk fever, lethargy, weak bones and (in concert with low vitamin D) poor growth.
Phosphorus is found predominantly in the bones (about 80%) saliva and major metabolites (e.g. nucleic acids) and is important for cell membranes, energy production, and muscle contraction, appetite and bone formation. While phosphorus deficiency in sheep is uncommon, it is relatively common in cattle grazing pastures growing on low-P soils, particularly when pastures are dominated by low quality dead grass with little or no legume. Deficiency signs include slow growth rates, decreased appetite, listlessness and poor fertility. Adequate dietary vitamin D is essential for the correct metabolism of calcium and phosphorus.
Approx. 70% of a ruminant’s magnesium is stored in the skeleton. Growing lambs can use this stored magnesium to offset a Mg deficient diet but it is generally poorly remobilised, particularly in older animals. Magnesium is an activator of over 300 enzyme systems and is involved in the metabolism of carbohydrates, lipids and protein. It has roles in nerve conduction and muscle contraction.
Deficiency symptoms often include muscular spasms, trembling and nervousness manifest in the condition known as hypomagnesaemia or grass tetany. Adequate fibre, sodium intake and energy within the diet will aid in reducing deficiency issues. Proportionally high intakes of potassium (K), Ca, P and organic acids may decrease Mg availability. High K found in Lucerne stands growing in high K soils may induce a magnesium deficiency and supplementation may be required. Excess dietary Mg may cause damage to the rumen, scouring, reduced feed intake and lethargy.
Potassium (K), sodium (Na) and chlorine (Cl)
These all have roles in maintaining acid:base balance and the control of body fluids. Potassium is essential for plant growth and so available herbage is usually at least adequate in K even when grown on K deficient soils. Deficiencies of sodium and chlorine are possible, however, particularly in arid areas where pastures, grains and seeds may be abnormally low in sodium. Deficiency symptoms may include ill thrift, pica (bone chewing) and anorexia. Salt licks are generally the primary means of correcting deficiencies.
Sulphur, along with nitrogen, is essential for protein synthesis and growth of rumen microbes. In general, if dietary protein is adequate dietary sulphur is also likely to be adequate. However, if dietary protein deficiencies are overcome by the use of a non-protein nitrogen source alone (e.g. urea) sulphur can often become the factor most limiting rumen microbial growth. Sulphur amino acids (SAA) are particularly important in sheep nutrition as wool comprises about 4% sulphur. Adding extra sulphur to the diet of sheep will not necessarily increase SAA supply for wool growth and for best response SAA should be fed directly to the animal in a form which will bypass breakdown in the rumen. Deficiency symptoms in sheep include reduced wool production, lack of crimp and poor fleece characteristics.
Vitamins – roles and availability
Vitamin A is needed for normal bone development, maintenance of epithelial cells (cells which line the body cavities) and night vision. It is produced via conversion from beta-carotene which is found in green feed and is stored in the liver. Deficiencies, although rare, may occur during a prolonged period of drought or grazing dry, matured pasture.
Young stock are more susceptible to a vitamin A deficiency as their meagre liver reserves are more quickly depleted. Deficiency signs include night blindness, eye discharges and ill thrift, and are more common during periods of high grain feeding or in shedded animals.
Green pasture, leaves, green hay and yellow maize are good sources of beta-carotene and ultimately vitamin A.
Vitamin B12 is produced for ruminant animals by the action of rumen microbes using cobalt as a precursor. It is needed for cell growth, energy metabolism (glucose production) and wool production (metabolisation of methionine). Production of vitamin B12 in the rumen is enhance by increased concentration of cobalt although the efficiency with which cobalt is converted to vitamin B12 declines. The rate of absorption is inhibited if the rumen or small intestines are damaged (e.g. by worms).
Colostrum contains some vitamin B12 but milk and cereal grains contain limited amounts. Supplementation with vitamin B12 may be useful if you have a known cobalt deficiency or for young stock that may not have fully functional rumens (e.g. lambs <30 kg) and are not synthesising adequate B12. In adult animals a slow release cobalt bullet is likely to be more effective and economic than direct injection with B12.
Vitamin D is contained in sun-cured hay and is produced in the skin of animals through irradiation. It is stored in the liver and helps with calcium absorption by acting to regulate the Ca:P balance. Deficiencies are rare in extensively grazed animals; although in more southern latitudes a vitamin D response has been recorded in animals grazing oats during winter (see the section on Calcium).
Deficiency signs include ill thrift, anorexia, hunched back and rickets (swollen joints, bow legs, knock knees). Hypocalcaemia may also result from vitamin D deficiency.
Vitamin E is an antioxidant needed for unsaturated fatty acid metabolism and maintaining cell membranes. Deficiencies may occur occasionally in weaners which have had no green feed for several months. Symptoms may include lameness, muscle weakness and ill thrift and white muscle disease (diagnostically different from that caused by selenium deficiency).
Read more about the Benefits of Mineral Drenches.