As a producer of beef, wool or lamb there are many stock feed supplements and additives to choose from, but how do you decide on the products that will benefit your stock and profit?
The following checklist can be used to assess the usefulness and economic benefit of stock feed additives and supplements.
This information sheet does not attempt to cover all mineral and vitamin requirements of grazing or intensively fed ruminants. Recommendations and values listed should be considered as a guide only. The analysis of all sources of feed and the use of independent nutritional advice are highly recommended.
Vitamins, minerals and requirements
As many as 14 different minerals are needed 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.
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.
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 the following table. Values shown are a guide only.
The Primefact Mineral content of common ruminant stockfeeds, crops and pastures outlines mineral composition data for a range of concentrates, mineral supplements, pasture, silage, roughages and by-products. It can be accessed at www.dpi.nsw.gov.au/primefacts
While it is beneficial to know a feed’s mineral and vitamin content and availability 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.
Macro and micro mineral requirements for ruminants
Macro minerals – roles and availability
Pasture and fodder crops usually contain sufficient minerals and vitamins for normal ruminant production. Minerals and vitamins are generally not the first limiting factor that negatively impact on intake and performance. Dietary energy and protein must first be addressed and consumed in quantities appropriate for the class of stock being fed.
The following are those minerals and vitamins considered essential for normal rumen function and animal performance.
Calcium (Ca)
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.
Calcium deficiency can occur in stock grazing oat crops in winter but this is often best treated using vitamin D due to the interaction between Ca:P balance and vitamin D (see the section on Vitamins). This phenomenon may account for the commonly held belief that animals grazing cereal crops in winter will do better if fed hay since most sun-ripened hay is sufficiently high in vitamin D.
Deficiency symptoms include milk fever, lethargy, weak bones and (in concert with low vitamin D) poor growth.
Phosphorus (P)
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, 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. The role of vitamin D is covered later.
Magnesium (Mg)
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.
CausMag is generally considered a suitable supplement when magnesium is deficient.
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.
Sulfur (S)
Sulfur, along with nitrogen, is essential for protein synthesis and growth of rumen microbes. In general, if dietary protein is adequate dietary sulfur 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) sulfur can often become the factor most limiting rumen microbial growth.
Sulfur amino acids (SAA) are particularly important in sheep nutrition as wool comprises about 4% sulfur. Adding extra sulfur 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.
