apart. With iron, iodine and copper, some of the disadvantages of oral dosing can be overcome by the use of injectable organic complexes of the minerals.
Such complexes are more expensive, but, when injected subcutaneously or intramuscularly, they are translocated slowly to other tissues and provide protection against a dietary deficiency of the injected element for lengthy periods. For instance, a single intramuscular injection of iron-dextran, supplying 100 mg Fe, at 2–4 days of age can control piglet anaemia (Chapter 13).
The efficacy and costs of administering minerals to individual animals can be improved by using large doses in relatively inert, slowly mobilized forms. The administration of heavy pellets (Millar and Meads, 1988), glass boluses (Millar et al., 1988) or particles of the mineral (e.g. copper oxide: Chapter 11), which are retained in the gastrointestinal tract, all act as slow-release sources. The problem of cobalt deficiency can be solved by use of heavy cobalt pellets, as described in Chapter 10, which lodge in the reticulorumen and yield a steady supply of cobalt for many months, unless they are regurgitated or become coated.
The choice of a mineral supplement is determined by: (i) cost per unit of the element or elements required; (ii) the chemical form in which the element is combined; (iii) its physical form, especially its fineness of division; and (iv) its freedom from harmful impurities, particularly fluorine. With calcium and phosphorus supplements, these factors can greatly influence the choice of material used, but, with the trace elements, because of the small quantities required and the relatively low costs involved, such considerations are generally of minor significance and the choice of supplement widens.
Molybdate-containing salt-licks have been highly effective in preventing chronic copper poisoning in sheep and cattle in certain areas. There is a remarkable range in the composition of proprietary free-access mineral mixtures, which is influenced by factors such as cost of ingredients and colour, as well as nutritional need, and care is needed in choosing appro- priate mixtures (e.g. Suttle, 1983). The mineral supplements commonly employed are given in detail in Appendix Table 2 on p. 600 and the optimum methods of treatment discussed in more detail in the following chapters.
The provision of extra minerals beyond the animal’s needs is economically wasteful, confers no additional benefit on the animal and can be harmful.
Excesses of phosphorus and magnesium can cause death from urinary calculi (Hay and Suttle, 1993), while an excess of copper soon causes toxicity in Slow-release methods
Mineral sources
sheep. Commercial mineral mixtures often contain minerals which, although basically essential to the animal, are already present in adequate amounts in the pastures and feeds the animals will consume. There can be no automatic justification for the purchase and use of such ‘shotgun’ mixtures of minerals, which are designed to cover a very wide range of environments and feeding regimens and which often contain an unnecessarily wide margin of safety as an insurance against deficiency. The shotgun approach can be dangerous because of a possible disturbance of the overall dietary mineral balance and the consequent adverse effects on the absorption and utilization of certain minerals by the animal. Numerous examples of the importance of mineral balance are given in the chapters that follow. Furthermore, the surplus minerals are largely excreted and some (notably phosphorus and copper) are causing increasing concern as pollutants of the environment.
The manufacture and sale of ready-mixed mineral supplements by responsible firms is a legitimate and desirable business of considerable value to individual farmers. However, every farmer and stock-raiser should be on guard against exaggerated claims of advertising propaganda and salesman- ship and should critically examine claims in the light of the particular mineral needs of stock under local conditions. Claims that the use of chelated forms of trace elements are more cost-effective than simple inorganic sources should be ignored until there is published evidence in reputable scientific journals that such benefits are consistently attainable. Such complexes must be strong enough to resist natural dietary antagonists and yet deliver the complexed element to the tissues in a usable form. There is no evidence that such complexes are superior as copper sources for ruminants (Suttle, 1994).
While benefits of chelated minerals might be expected in non-ruminant diets, where phytate is such an important antagonist, these expectations have yet to be fulfilled and it may be better to attack the antagonist with phytase (see Chapters 5 and 16). Evidence that chelation alters the form or distribution of the complexed element at an early stage of digestion (e.g. in the rumen) is not proof of nutritional benefit. Evidence that chelation increases tissue element concentrations for elements whose uptake is normally regulated by need (e.g. zinc) may indicate a bypassing of the homeostatic mechanism and again provides no proof of nutritional benefit. The fact that chelation may be useful for one element (e.g. chromium, see Chapter 17) does not mean that it will be useful for others.
Contrary to popular belief, an appetite for minerals is not a reliable measure of the animal’s needs (Pamp et al., 1976). The voluntary consumption of mineral mixtures or ‘licks’ is determined as much by palatability as by physio- logical need. Sodium-deficient ruminants will consume sodium sources, such as sodium bicarbonate (NaHCO3), which are normally aversive, and the relish with which livestock consume mineral deposits around receding water
False claims
False concepts
sources may have selective nutritional benefit. Pullets approaching lay will self-select diets rich enough in calcium to meet the needs of medullary bone deposition and onset of shell calcification and the laying hen continues to show preference for calcium-rich diets on egg-laying days (Chapter 4), but these are exceptions. Experiments by Cunningham (1949, personal communi- cation) showed that grazing sheep dosed orally with minerals to overcome deficiencies in the pastures ate as much lick as similar undosed animals.
Furthermore, observations in many countries have shown that animals will regularly consume considerable quantities of licks supplying minerals in which they are not deficient and yet they will not always voluntarily consume minerals in which they are deficient.
Arthur, J.R. (1992) Selenium metabolism and function. Proceedings of the Nutrition Society of Australia17, 91–98.
Bowman, J.G.P. and Sowell, B.F. (1997) Delivery method and supplement consump- tion by grazing ruminants: a review. Journal of Animal Science75, 543–550.
Chesters, J.K. and Arthur, J.R. (1988) Early biochemical defects caused by dietary trace element deficiencies. Nutrition Research Reviews1, 39–56.
Clark, R.G., Wright, D.F. and Millar, K.R. (1985) A proposed new approach and protocol to defining mineral deficiencies using reference curves: cobalt defi- ciency in young sheep used as a model. New Zealand Veterinary Journal 33, 1–5.
Combs, D.K. (1987) Hair analysis as an indicator of the mineral status of livestock.
Journal of Animal Science65, 1753–1758.
Ducker, M.J., Kendall, P.T., Hemingway, R.G. and McClelland, T.H. (1981) An evaluation of feed blocks as a means of providing supplementary nutrients to ewes grazing upland/hill pastures. Animal Production33, 51–58.
Fordyce, F.M., Masara, D. and Appleton, J.D. (1996) Stream sediment, soil and forage chemistry as predictors of cattle mineral status in northeast Zimbabwe.
In: Appleton, J.D., Fuge, R. and McCall, G.H.J. (eds) Environmental Geochemistry and Health. Geological Society Special Publication No. 113, London, pp. 23–37.
Greger, J.L. and Sickles, V.S. (1979) Saliva zinc levels: potential indicators of zinc status. American Journal of Clinical Nutrition32, 1859–1866.
Hay, L. and Suttle, N.F. (1993) Urolithiasis. In: Aitken, I.D. and Martin, W.B. (eds) Diseases of Sheep, 2nd edn. Blackwell Scientific, London, pp. 250–253.
Henkin, R.I., Mueller, C.W. and Wolf, R.O. (1975) Estimation of zinc concentration of parotid saliva by flameless atomic absorption spectrophotometry in normal subjects and in patients with idiopathic hypogeusia. Journal of Laboratory and Clinical Medicine86, 175–180.
Johnson, P.J., Freeland, J. and Ebangit, M.L. (1978) Saliva: a diagnostic tool for evaluating zinc status in man. Federation Proceedings37, 253.
Jumba, I.O., Suttle, N.F., Hunter, E.A. and Wandiga, S.O. (1995) Effects of soil origin and mineral composition on the mineral composition of forages in the Mount Elgon region of Kenya. 2. Trace elements. Tropical Grasslands29, 47–52.
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The discovery during the 18th century that bone consisted primarily of calcium phosphate led to the use of calcium in the prevention of rickets, a childhood disorder of bone development which had plagued humans for centuries. Similar disorders in farm livestock were quickly linked to calcium deficiency, induced by feeding pigs and laying hens diets low in calcium and prevented in calves by feeding calcium-rich diets. As animal production intensified, energy-rich, grain-based diets were increasingly fed to livestock in protected environments and the incidence of bone disorders multiplied.
Unwittingly, livestock were being fed diets naturally deficient in calcium while simultaneously being ‘starved’ of vitamin D3, essential to the efficient utilization of calcium, by cutting them off from sunlight. Animal breeders ensured that interest in calcium nutrition was maintained by selecting for traits which had high requirements for calcium – growth, milk yield, litter size and egg production. By encouraging reproduction while skeletal growth is still incomplete, producers have ensured that bone disorders in poultry remain commonplace. In the high-yielding dairy cow, an acute calcium deficiency still strikes many animals at calving with no sign of bone disorders and controversy still surrounds the optimum level and pattern of calcium provision for averting such problems.
Forages are generally satisfactory sources of calcium (Ca) for grazing live- stock, particularly when they contain leguminous species. Minson (1990) gives the average published values as 14.2 and 10.1 g Ca kg21 dry matter (DM) for temperate and tropical legumes and 3.7 and 3.8 g Ca kg21 DM for the corresponding grasses. The average temperate grass sward will meet the
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© CAB International 1999. Mineral Nutrition of Livestock (E.J. Underwood and N.F. Suttle)