Recent advances in trace mineral deficiencies and their control.

Abstract

Recent advances in trace mineral deficiencies and their control B.W. Norton Department of Agriculture, llniversity of Queensland, St. Lucia, Qld, 4067. The study of trace element metabolism has intensified in the last 20 years due mainly to the availability of highly purified diets and to the development of sophisticated instrumentation capable of detecting minute amounts of elements in tissues and feeds. Since 1957, Se, Cr, Sn, V, F, Si and Ni have been isolated as essential nutrients for animal metabolism (Schwartz 1974). The recommended requirements for established trace elements have also changed. It is now recognised that the Zn requirements of Zn for chicks is greater than that originally proposed by ARC (1963). Preston and Willis (1974) have also suggested that the Zn requirements of cattle may be lower than initially proposed. It is also clear that precise requirement for many trace elements has not yet been determined, as shown by .the absence of recommendations for bin, I, Cu, Zn, M O and Se in laying poultry. (See ARC, 1963 and NRC). In the following paper, I wish to discuss some selected aspects of advances in trace element metabolism, with emphasi.s on findings which may be of local practical importance. Three areas are considered, the distribution of trace element deficiency in the livestock industries of Australia, the significance of diet-trace element interactions and some recent studies of Co deficiency in Queensland. Trace Element Deficiencies in Australia Fig. 1 shows an approximate distribution of Cu, Co, Se and I deficiency in grazing animals in Australia. It is interesting to note from this distribution that deficiencies have been recorded mainly where intensive animal production is practised, and it is not clear whether the more extensive areas would show similar deficiencies given an intensive research input. Trace element deficiencies in the pig and poultry industries are rare due mainly to addition of requirements during ration formulation. Copper axd Nelybdenwn Ataxia in young pigs in Queensland has been associated with low liver copper levels (EIcCavin et al. 1962). Cu deficiency of sheep and cattle has been reported in all states of Australia presenting a variety of symptoms from `depigmentation' and'steely wool' in sheep to anaemia, temporary sterility and profuse diarrhoea in cattle (Bennetts et aZ. 1941). In all Australian studies, Cu supplementation alone prevented deficiency . In the studies of Dick (1956)) high levels of MO and sulphate induced Cu deficiency providing an explanation for the symptoms of Go toxicity. Piore recently, Suttle (1974) has reported that !!o interacts with organic as well as inorganic S in limiting Cu utilization by sheep and these findings may have practical importance. Suttle calculated that for a feed containing 0.5 mg Ko/kg, increasing the concentration of S in 101 the feed from 2 to 3 g/kg (- 13 -+ 19% crude protein) decreased the availability of dietary Cu by 50%. Where Cu levels in pasture are marginal it is possible that fertilizer application (N and P) may result in induced Cu deficiency. In the U.K. survey studies indicate that Cu deficiency may be more prevalent than previously suspected (Davies and Baker 1974). It is also likely that from the low levels of MO and S in cereals, Cu toxicity could also be a problem, and on all concentrate rations small supplements of MO may be indicated. The significance of these interactions in Australian feeds is not known. The interaction between Cu, MO and S differs in ruminants and non-ruminants. In ruminants, dietary S is rapidly reduced toS- and favourable conditions exist for the formation of an unavailable form of Cupric thiomolybdate when diets are rich in MO (Suttle 1974). High MO intakes have been shown to decrease ruminal S- concentrations (Bryden and Bray 1972) and to decrease the soluble copper flowing from the rumen (Bird 1970), thereby inducing Cu deficiency. In non-ruminants, dietary sulphate competes with MO for a common absorptive pathr*:ay (Huisingh, Comez and blatrone 1973), and exerts a protective effect against MO toxi.city. Payne (1976) has reported a misfeathering syndrome in day old chicks which is responsive to MO supplementation, and has demonstrated 102 that Elo deficiency may be induced by copper sulphate. Apart from this study MO deficiency has not been recorded under practical feeding conditions, although Ellis et a2. (1958) found that increasi.ng dietary M O in sheep from 0.36 to 2.36 ppm increased cellulose digestibility in the rumen and lamb growth rate. Since ruminants in Austra1j.a graze pastures with Fio contents in this range, further studies in this area may be warranted. Manganese and Zillc There is little information in Australian literature to suggest that either Zn or Mn deficiency is a problem of practical importance in pigs and poultry. Occasional minor outbreaks of parakeratosis have been reported in Queensland piggeries (Anon 1972/73). The Mn requirements of pigs and Foultry vary with species, criteria of adequacy and the nature of the rest of the diet. Australian wheat appears adequate in Fin (Underwood et al. 1947; Murphy and Law 1974), although diets based on sorghum or maize may require additional Pin (Underwood 1971). The Zn content of Australian wheat is also low, and supplementation is indicated. The requirements of non-ruminants for Zn are influenced by the protein source used; plant proteins with their high phytic acid content render Zn less available for absorption. It has also been reported that high Ca levels in pig diets may increase the dietary requirement for Zn, (lloekstra et aZ. 1967). It is only recently that a response of grazing sheep to Mn/Zn supplementation has been reported in Australia. Egan (1972) found that fertility in ewes was markedly increased by dietary supplements of Mn, Zn or Mn and Zn. Pasture levels of these elements were not particularly low and provided little indication of a likely deficiency. As was shown with Cu and Co, trace element levels in pasture may be useful to detect severe deficiency, but provide little information on conditions where marginal deficiency is a problem. Foetal death occurs in rats where the dam suffers a brief exposure to low intakes of Cu or Mn (Hurley and Schrader 1972) and it is well known that the Zn requirements of rams for testicular development and spermatogenesis are greater than those growth, (Underwood and Somers 1969) suggesting that transient deficiencies of Vn or Zn may be of significance where poor reproductive performance of stock is observed. Iodine Endemic goitre, due to iodine deficiency, has heen recorded mostly in Eastern Australia. Underwood (1971) has comprehensively reviewed the field of iodine metabolism in animals. However, recent studies cf goitre incidence in Tasmania by Stratham and Bray (1975) and King (1976) deserve comment. Both studies suggest that the incidence of congenital goitre in sheep may be under-estimated -if thyroid enlargement detected by palpation is the sole criterion. King found that 27% of lambs without palpable thyroids apparently died of iodine deficiency, suggesting that the incidence of iodine deficiency based on thyroid enlargement may be under-estimated. In Northern Queensland, Fopkins and Pratt (1976) found that Supplementation with iodine (and the provision of shade) significantly improved the fertility of Merino ewes. From this experiment, it was not 104 barley diet. The efficacy of Se or vitamin E supplementation B.as not tested, but the generally low Se content of plant products should be recognised when plant proteins areused to replace animal proteins in rations. Selenite uptake by plants is inhibited by both sulphate and phosphate (Asher 1977)) and with continued cropping of low Se soils, the Se content of feed grains will decline. Since the addition of Se to feedstuffs is illegal in most states, future trends in the content and availability of Se in grains should be monitored. of grazing animals to Se supplementation. In sheep, Se therapy has prevented nutritiona. muscular dystrophy (MD) in lambs, incrca.sed both body weight gain and wool growth (McDonald 1975)) and has enhanced reproductive capacity (Wilkins 1977). In cattle NbE (cardiac form) has been diagnosed in calves, but body wei.r,ht response to Se was absent (Gabbedy et aZ. 1977). The recent development of Se pellets for intraruminal administration (Handreck and Godwin 1970) are a. practical solution to the provision of Se to deficient animals on a continuous basis. Se deficiency is most often found in high rainfall areas where pasture improvement has been undertaken and is therefore in areas of high animal production potential. There is a need for further study on a national basis to define the factors responsible for both high risk and marginal areas of Se deficiency. responses All states of Aust.ralj a (excepting Queensland) have recorded Cobalt The detection cf Co deficiency in sheep and cattle has had a major effect on animal production in Australia, particularly in Western Australia, South Australia and Tasmania (Underwood 1971; Alhiston 1975). Co deficiency is of little significance in non-ruminants. The symptoms of Co deficiency are generally those associated with malnutrition and pft:pn conrlicated by Cu deficiency and a high incidence of intestinal `Unthriftiness' is a term applied to the symptom of sporadic IJ3raSit.C.C. or marginal deficiency. It is only recently that Co deficiency has been described in sheep (Norton and Hales 1976) and cattle (Winter et aZ. 1977) grazing improved tropical pastures in Queensland. With the introduction of new tropical grass species into Australia, there has been a rapid expansion of improved pasture planting in soils generally deficient in most trace elements essential for plant growth. Roth Co and Cu deficiency in these areas have been suspected for some time (Donaldson ct aZ. 1964). Tropical pastures are low in nutritive value compared with temperate Fastures, but little attention has been given to the significance of trace element content of these pastures on animal production. The results in Table 1 are from a supplementation trial with breeding ewes grazing N- fertilized (200 kg N/ha) Pangola gra.ss (Digitaria deCWXbC?YtS, Stent .) in south-eastern Queensland. Co supplementation, either applied to the pasture or by direct administration as a pellet incrca.sed lamb birth weight, wei.ght gain to weaning and survival compared with unsuFplementcd ewes. In this la.tt.er group, 24% of lambs born were either born dead or survived less than a day. Milk production in unsupplemented ewes was only 303, of that in the supplemented groups and was t.he major contributor to poor lamb growth. Ewes on all treatments lost weight Fast-weaning suggesting that further supplementation was required. Despite supplementation cf lambs, post-weaning growth was also poor. Continuing studies are examining the 106 need for more frequent and/or high levels of Co supplements and the possibility of further trace element deficiencies being present. These studies may have wider applicati.on than a simple description of a regional deficiency (250,00@ ha) particularly where animals are grazed on tropical pa.stures. The pastures in thi.s study contained apparently adequate levels of Co (0.11?0.02 ppm), but total intake was clearly inadequate. The low feed intake usua.lly associated with the low digestibility of tropical pastures may be responsible, which indicates that current requirement recommendations in terms of pasture concentrations are of little value in assessing adequacy for animals grazing pastures of low Eutritive value. Pregnancy and lactation hastened the onset of severe cobalt deficiency and it is likely that the Co requirements of lactating ewes may be higher than dry ewes. l!igh calf mortality and lactational failure has been reported in young breeding cattle near Rockhnmpt.on (Anon 196X/ 64) . This condition was not responsive to Cu, and it would seem from results with sheep, that Co supplements may be required. Tropica 1 pastures have many charac.terist.j c, which increase the l.ikelihood of = trace mineral deficiencies occurring in grazing animals. They are usually grown on infertile soils in high rainfa.11 areas, and after a ra.Fid growth phase produce a bulk of low quality feed underlain by a deep litter of dead plant material. Grazing animals are not on1.y presented with a feed of low qualjty, but are denied a.ccess to the soil as a source of tra.ce element. Little is known about the Co status of tropical sojls or the capacity of new pasture species to accumulate trace elements under field conditions. Tlze `never ' trace eZments Schwartz (1.974) has reviewed recent develcpmcnts on the essentiality of Cr, Sn, V, F, Si and Ni. l'iTj.th the exception of Cr, defi.ciency symptoms are found at dietary concentrations \rTell below those found in conventional rations. Cr deficiency has been detected in malnourished children, where its absence interferes with normal carbohydrate metabolism (IIertz 1974). The significance of these trace elements in practical rations is unknown, although induced deficiency through interaction with other trace elements and dietary factcrs must be considered as a future Fossibility. Inte2~act:ions between trace e Zements The significance of interactions between some essential trace elements has been discussed in previous sections. Increasing levels of heavy metal contamination in the environment demand an understanding of their effects on animal and human health. Fig. 2 shows some interactions which may occur between trace elements in biological systems. Davies (1974) has classified interactions between trace elements into two types. Competitive interactions are an isomorphous replacement of one element by another and are characterized by mutually negative effects between elements. For example, high dietary Zn inhibits Cu utilization in pigs (Campbell and Mills 1974) and high dietary Cu inhibits Zn utilization (Richie et al. 1963). The action of the toxic metals IJg, As and Cd act as competitive inhibitors of essential trace elements. Non-competitive inhibition occurs where the absence or presence of one element determines the subsequent metabolic fate of another 107 The &Lrecticn. of an arrow betueen two elements inciieates direction of interaction from antagonist to agonist (-I represents a n.egative interaction (inhibition) and (+) represents a positive interaction (stimuZation). After Cavies (1074). Fig. 2. RiologicaZ interactions between trace eZements. element. Dietary Cu stimulates haenatopoesis through its role in mobilizing Fe from Fe stores for haemoglobin synthesis, thereby increasing Fe availabi.lity. Whilst there is considerable information available now on interactions between trace elements, less is known about the availability and form of trace elements in feeds, particularly in pastures. 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