Geochemistry and the Mineral Nutrition of Agricultural Livestock and Wildlife

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Geochemistry and the mineral nutrition of agricultural

livestock and wildlife

Iain Thornton*

Environmental Geochemistry Research Group, T H Huxley School of Environment, Earth Sciences and Engineering,

Imperial College of Science, Technology and Medicine, London, UK

Abstract

Relations between the geochemical nature of soils and their parent materials and the occurrence of nutritional defi-ciencies and excesses in grazing livestock have been documented since the 1960s and earlier, with notable work in

Australia, New Zealand, United Kingdom, Ireland, USA and the Soviet Union. Studies at Imperial College London,

into the development of regional geochemical mapping techniques as a means of delineating nutritional problems

commenced in the 1960s and have continued to the present. Research has mainly focussed on deficiencies of Cu, Co and

Se in cattle and sheep, and the role of Mo and S in the soil/plant system in both clinical and sub-clinical hypocuprosis in

cattle. Exposure to heavy metals, in particular Pb, Zn, Cd and the metalloid As have also received attention in areas

contaminated by past mining and smelting activities. Soil and plant factors influencing the dietary supply of both essential

trace elements and toxic metals have been studied, including their speciation and bioavailability. Soil ingestion has been

recognised as an important exposure pathway of heavy metal contamination to grazing cattle, and as an antagonist of Cu

supply and a source of dietary Co in sheep. Relations between soil geochemistry and the mineral status of wildlife species,

in particular impala and black rhinoceros, have been established in Kenya and recent work, presented elsewhere in this

Symposium, has concerned the supply of nutrients to the Roosevelt sable in Kenya. The compilation of regional andnational multi-purpose geochemical atlases, based on the systematic sampling of soils or stream sediments, is now

recognised as a priority in many countries of the developed and developing world. This paper explores the opportunities

for future research into the application of geochemical maps for the optimisation of land use, efficient livestock produc-

tion, and improving conservation of wildlife.# 2002 Elsevier Science Ltd. All rights reserved.

1. Introduction

Mills (1979) reviewed the nature, pathological

response, metabolic defects, aetiology and detection of

trace element deficiency and excess in animals. He

emphasized the complexity of soil–plant–animal rela-tions with respect to trace element supply and noted

that the application of geochemical approaches to the

initial recognition of areas associated with a high risk

of anomalies in trace element supply to animals had

considerable potential value. Such an approach had

initially been proposed by Webb (1964), whose concept

of multi-purpose geochemical mapping was to instigate

wide-ranging studies in future years.

In a presentation entitled ‘‘Environmental geochemistry

and health in the 1990s: a global perspective’’ at the 2nd

International Symposium on Environmental Geochemistry

in Uppsala in 1991, Thornton (1993) reviewed the general

area of multi-purpose geochemical surveys and their

applications to agriculture and wildlife nutrition andmade some predictions as to priorities for future

research. The present paper draws attention to some of

the key features of early research, details progress over

the past 10 a and examines the outcome of these previous

predictions.

Studies have continued to focus on the same groups

of chemical elements relating to deficiencies of Cu, Co,

Se, etc., and excesses of Mo, Cd, Zn Pb and As

(Thornton and Webb, 1979; Thornton, 1983; Leech and

Thornton, 1987). The environmental geochemist has

continued to provide ongoing sources of information on

(i) background/baseline concentrations of elements in

0883-2927/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved.

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Applied Geochemistry 17 (2002) 1017–1028

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rocks, soils and plants; (ii) spacial information on ele-

ment distribution in the form of geochemical maps and

atlases; (iii) the development of analytical techniques,

particularly for the characterisation of chemical and

mineral forms of elements in soils and (iv) arising from

the above, the provision of geochemical data required to

understand the processes leading to the solubility, bio-availability, and pathways of nutritionally essential trace

elements and potentially toxic metals in the rock–soil–

plant–animal system. Such information continues to be of

value in understanding the sources and supply/exposure of

elements to both domestic livestock and wildlife species.

In recent years, data handling, interpretation and

application has been assisted by the development of

Geographical Information Systems (GIS) and by the

development of risk assessment strategies used as tools

for the prediction of element deficiencies and excesses

leading to animal ill-health.

2. Agricultural livestock

Research in the 1960s and earlier into applications of

geochemistry to agriculture was mainly undertaken in

Australia, New Zealand, United Kingdom, Ireland,

USA and the Soviet Union. In the 1960s, 70s and 80s

much emphasis was placed on the nutritional needs of

domestic livestock. In developed countries, intensive

farming methods aimed to realize the genetic potential

of different breeds of cattle and sheep for meat, dairy

and wool production.

Within this period, geochemical maps, based on a

systematic sampling and analysis of stream sediments

and soils, were used to delineate areas of potential

nutrient deficiency and metal excess. Their main appli-

cation was to indicate areas or regions within which

more detailed study of soil and pasture herbage could

then be concentrated. For example, early studies in

Counties Whicklow and Carlow, Eire, indicated a

correlation between the Co content of stream sediments

and the occurrence and severity of pine in sheep and

cattle on soils derived from granite (Webb, 1964). Geo-

chemical maps showed similar low Co patterns (<10

mg/g) on granites in SW England on which pine hadbeen recognized since the 1930s (Patterson, 1938), while

moderately low patterns (10–15 mg/g) on the Culm

Measures in Devon and on Triassic drift in Denbigh-

shire were related to soil and pasture of low Co content

on which unthriftiness and pine were found in sheep

(Thornton and Webb, 1970).

One of the best examples of the application of geochem-

istry to agriculture is shown by the combined geochemical

map for Mo and Cu in England and Wales (Fig. 1) (Webb

et al., 1978) which highlights the considerable extent of high

Mo and low Cu land which is thought to exceed 4105 ha.

The main patterns of elevated Mo concentrations are

found in areas underlain by marine black shales

(Thomson et al., 1972). This elevated Mo in soil under

certain conditions is reflected in raised Mo levels in

pasture herbage which causes a conditioned Cu defi-

ciency in grazing cattle. As indicated in Fig. 2, the wide

distribution of low blood Cu values (hyopocupraemia) in

cattle is mainly located in areas with molybdeniferous soils,in which over 1700 herds were found to be Cu deficient

(Leech et al., 1982). Molybdenum accumulation in saltings

(recent marine alluvium) reclaimed some 400 a ago for

agricultural use is thought to be due to the fixation of Mo

by soil sesquioxides and organic matter. Extensive coastal

areas in Norfolk, Suffolk and Essex are affected as shown

by the geochemical map. Vegetation growing on these soils,

withpH values ranging from 7.0 to 8.0, was found to have a

Cu: Mo ratio below 4:1 and to be potentially toxic to

ruminants, depending on dietary SO4 (Smart, 1991).

As indicated by Thornton (1993), similar marine

black shales and marine/estuarine alluvium are found inmany parts of the world, though, with the exception of

North America, have received little attention as yet. It is

confidently predicted that as extensive systems of live-

stock farming are forced to become more intensive due

to population pressure worldwide, natural limitations to

food production of this type will become of increasing

importance. It is surprising that over the past 9 a little

further attention has been given to this emerging problem.

Perhaps in Europe one reason may be that less emphasis

is now placed on intensive livestock rearing, due to sur-

pluses of dairy products and meat arising as a result of

the EU Common Agricultural Policy. However, less

intensive production with reduced supplementary feed

has meant that grazing livestock are now more dependent

on grass as their main source of nutrition and thus

become dependent on the mineral status of the farm and

its soils. It is no doubt true that research into trace element

deficiencies is no longer fashionable in Europe and has

received little funding since the early 1980s. Nonetheless,

in the future, a less intensive and more sustainable system

of livestock farming will predispose towards nutritional

deficiencies inherent in the land.

The disease swayback, known as Lamkrius in South

Africa, Kipsiepsiep in Kenya and enzootic ataxia in

several other countries, including the former USSR, is anervous disorder of lambs. It is characterized by lack of

co-ordination of movement and paralysis of the back

legs, and has been long recognized in many parts of the

world (Underwood, 1966). It can be prevented by giving

Cu supplementation halfway through pregnancy. This

disease has been studied by a large number of animal

nutritionists, veterinary scientists, biochemists and

pathologists. However, an actual cause has been difficult

to find and a Cu-deficient diet would not seem to be the

simple solution.

Research in New Zealand clearly showed that farm

animals accidentally ingest appreciable amounts of soil

1018 I. Thornton / Applied Geochemistry 17 (2002) 1017–1028



(Healy, 1968). Using Ti as a stable indicator of soil

ingestion, subsequent studies in the UK showed that

between 2 and 20% of the dry matter intake of grazing

cattle was soil, and up to 30 or 40% in sheep as they

graze closer to the ground (Thornton, 1974). This led to

an examination of the actual ingredients in soil that may

influence animal metabolism and nutrition.

Collaborative research with Professor Neville Suttle

of the Moredon Institute, found that 10% soil in the

diet of sheep reduced Cu absorption and utilisation by

Fig. 1. Combined element map for empirical Molybdenum (red), increasing colour contribution with increasing element concentration

and percentile Copper (blue), increasing colour contribution with decreasing element concentration.

I. Thornton / Applied Geochemistry 17 (2002) 1017–1028 1019



as much as 50%, and that as little as 2% ingestion sig-

nificantly reduced Cu use. The mechanism for this was

not immediately clear and it was not known whether the

soil particles occluded Cu in the diet, whether they sup-

plied Mo, or whether the effect was due to some as yet

unknown process (Suttle et al., 1975).

In some simple laboratory experiments, soil was sha-

ken with rumen liquor in a test tube. The large amounts

of Fe coming into solution from this soil gave a valuable

clue. This work was repeated on a larger scale using

artificial rumen systems at the Moredon Institute. The

Fe released from soil is a powerful Cu antagonist, and it

was proposed that accidentally ingested soil provides a

source of large amounts of Fe in the rumen of sheep.

This Fe interacts with dietary Cu and reduces the utili-

sation of Cu. Suttle et al (1984) strongly suggested that

the soilCu antagonism was dependent on soil Fe, and

Underwood and Suttle (1999) present data indicating

the magnitude of the Fe effect. It would seem thus that

this mechanism could make a significant contribution to

the aetiology of swayback (Thornton, 1983), though this

requires further investigation. In the UK, swayback is

found in years with warm winters and very little snow

cover. In warm weather, sheep are left to fend for

Fig. 2.




themselves on poor pasture with little or no extra feed.

This is when soil ingestion is at its highest and when

supplementary Cu is needed by the pregnant ewe

(Thornton, 1983).

Soil may also contribute to the supply of nutritionally

essential elements for the grazing animal under UK

conditions and, in particular, the trace element Co.Cobalt is an essential constituent and, indeed, comprises

some 4% of vitamin B12 the anti-pernicious anaemia

factor of liver which is produced by the synthesizing

abilities of the ruminants symbiotic gastro-intestinal

flora (Underwood, 1962). Nutritional deficiencies of Co

result in severe emaciation and listlessness. These may

lead to death in both cattle and sheep; milder forms are

usually described as ill thrift and respond rapidly to Co

supplementation (Underwood, 1962). Cobalt deficiency

in sheep has been recorded in several areas in the UK

underlain by arenaceous course-grained soil parent

materials and by acid igneous rocks which contain onlyvery small amounts of Co. It is normally treated by the

direct oral administration of ‘‘cobalt bullets’’ to the

animal or by the treatment of deficient pastures with Co

SO4. As there is 100 to 1000 times more Co in soil than

in pasture herbage, potentially, a little ingested soil

could provide the dietary requirements of the animal,

irrespective of how much Co is present in plants. Fur-

ther collaborative studies between Imperial College and

the Moredun Institute, showed that not only was Co

extracted from soil in the sheep’s rumen, but it was also

synthesized into Vitamin B12 as required by the sheep

(Brebner et al., 1987). The diagnostic practice of MAFF

for the past 20 or more years had been based on the

analysis of pasture herbage for Co. On the evidence of

this research, it was suggested that this may not have

been appropriate as sheep directly ingest appreciable

quantities of Co in soil.

One of the possible limitations of much of the

research into relations between geochemistry and live-

stock nutrition has been that the majority of studies have

been based on the determination of ‘‘total’’ rather than

‘‘bioavailable’’ concentrations of mineral elements in the

soil. The use of chemical extractants such as EDTA and

ammonium acetate to estimate plant available levels of

trace elements have met with limited success particularlywhen comparisons are made between contrasting soil

types with large variations in pH or organic matter

content. Indeed it has been suggested that ‘‘total’’ con-

tent in combination with soil pH may well be a useful

estimate of bioavailability and may be used to predict

levels of trace elements in the soil solution (Rieuwerts et

al., 1998).

The Soil Geochemical Atlas of England and Wales

(McGrath and Loveland, 1992) provides maps showing

the distribution of both ‘‘total’’ and EDTA—extractable

trace elements on a sub-regional scale, though limited to

a sampling density of one per 25 km2.

With the research focus and funding moving from the

recognition and remediation of trace element defi-

ciencies, the move over the past decade has been

towards environmental protection with the emphasis on

human health and the ecosystem. An example of this

new perspective is provided by recent research colla-

boration between the Veterinary Laboratories Agencyand Imperial College which has focussed on the possible

influence of geochemical factors on the susceptibility of

cattle to infection by bovine tuberculosis from badgers

which is of increasing prevalence in the UK at this time.

Research has aimed to predict areas where deficiency of

Cu in the diet results from excess soil Mo whose avail-

ability and uptake into pasture is influenced by soil pH

and other soil factors. The geochemical maps for Mo

and Cu together with information on soil pH and S has

been introduced into a GIS system to predict possible

nutritional stress and increased likelihood of suscept-

ibility to infection. (Drs. P.A. Durr and M. Ramsay,1999, pers. commun.). This work falls within a broader

programme funded by the Ministry of Agriculture,

Fisheries and Food (Phillips et al., 2000).

In April 2000, Part IIA of the Environmental Protection

Act came into force in the United Kingdom—com-

monly termed the ‘‘Contaminated Land Regime’’. This

introduced the concept of ‘‘pollutant linkage’’ in which

meat and dairy products from the grazing animal can be

seen as part of the pathway from contaminated soil to

the human receptor. Heavy metal contamination of

agricultural soils arising from past mining and smelting

activities provides an appropriate example. On such

land, it is accepted that the principle threat to livestock

is directly ingested soil and vulnerable animals are those

consuming soil while grazing or foraging on con-

taminated land (Underwood and Suttle, 1999). Lead

mining in the Southern Pennines over several hundred

years to around 1900 has resulted in contamination of

around 250 km2 of land, with concentrations ranging

from several hundred to several thousand mg/kg Pb and

as much as 1% or more in and around mineral wastes

(Colbourn and Thornton, 1978). Rarely, cattle are

affected by Pb, usually through straying onto waste tips

and eating brightly coloured galena (PbS). A survey of

grazing cattle on 11 farms with soils ranging from 150 to4000 mg/kg Pb showed blood Pb levels to broadly

reflect amounts of Pb in the soil, as a result of ingesting

contaminated soil and pasture (Fig. 3). Between 40 and

70% of the Pb intake was shown to be as a result of

directly ingested soil (Thornton and Kinniburgh, 1978;

Thornton, 1983). This study also showed a wide range

of blood Pb levels encountered at any one time within a

single herd, probably reflecting the different rates of

absorption, metabolism and excretion between individ-

ual animals, coupled with different grazing habits of

individual cattle. It has been suggested that the greater

response in blood Pb to soil Pb recorded in the early




part of the grazing season compared to the late season

may be due to the initial metabolic response of the animal

to Pb exposure and changes in the rate of Pb metabolism

resulting from continuing exposure, a phenomenon also

encountered in the human (D. Barltrop, pers. commun.,1983). Although Suttle et al. (1991) have clearly shown

that the majority of Pb ingested in soil is excreted in

faeces, it is evident that a small proportion is absorbed—

an important factor on heavily contaminated land. Later

studies showed that in this area Pb contaminated soils

also contained appreciable amounts of F (some exceeding

1% F) and that soil ingestion was a major pathway of

soil F into grazing cattle (Geeson et al., 1998). Indeed, it

is recognised that ingestion of F-rich soil on overgrazed

pastures can significantly contribute to F intakes

(Underwood and Suttle, 1999). However, neither exposure

to Pb or F would seem to result in losses in production

or in the contamination of products offered for sale,

including milk. In this respect, Oelschlager et al. (1970)

had previously shown that ingested soil F was poorly

absorbed by cattle.

Another example is provided by the metalloid As.Extensive contamination of agricultural soils in SW

England has been documented by Abrahams and

Thornton (1987). Within the Hayle/Camborne area the

concentrations of As and Cu found in surface (0–15 cm)

soils across the Cornish Peninsula ranged up to 730 ppm

As and 560 ppm Cu, confirming the widespread surface

contamination of the area during the course of mining

and smelting operations spanning several centuries, with

around 700 km2 of agricultural land in Cornwall and

Devon affected to varying degrees (Abrahams and

Thornton, 1987). The agricultural significance of these

findings was, in part, assessed by determining the uptake

Fig. 3.




of As and Cu into pasture herbage and the intake of

these elements by grazing cattle on 11 farms in the

region, selected on the basis of the As content of their

soils. Neither As nor Cu are readily taken up and

translocated to the aerial parts of grasses, and it has

been clearly shown that accidentally ingested soil com-

prises a major exposure route to the grazing animal(Table 1; Thornton and Abrahams, 1983). Further

studies showed that the amount of soil ingested (calcu-

lated on the basis of the Ti content of faeces) varied

appreciably between seasons of the year and in this

study ranged from 0.2 to nearly 18% of the animal’s dry

matter intake (Abrahams and Thornton, 1994). In the

spring when there is little grass cover, this could account

for around 90% of the As and 30–60% of the Cu intake

of grazing cattle. Even though some of the animals

would seem to ingest in excess of 50 mg of As per day,

no adverse effects on the health or production of cattle

have as yet been reported in this area. Anecdotally, ithas been suggested that local cattle and sheep have

developed some resistance to biological exposure to

these two potentially toxic elements. Scanning electron

spectroscopy and X-ray analysis has shown that much

of the As in surface soils and waste materials in this area

is present as the mineral scorodite, ferric arsenate, which

is highly insoluble and thus of low bioavailability/

bioaccessibility.

Other sources of heavy metal contaminants in agri-

cultural soils have been well documented and include

phosphatic fertilizers (Cd), sewage sludge and pig slurry

(Cd, Pb and Cu) and a wide range of industrial and

urban emissions. Their sources, exposure pathways,

absorption, retention and toxic effects on grazing live-

stock are discussed by Underwood and Suttle (1999).

To implement the new ‘‘contaminated land regime’’

guideline values for metals in soils, derived as a result of

strategies based on risk assessment, will soon be pub-

lished as a means of deciding whether land may be

regarded as contaminated or not. It is as yet uncertain

as to how these values will affect the quality and value

of agricultural land and whether these will be applied

regarding the suitability of land for livestock farming.

One problem with deriving guidelines is that they are

usually based on total metal concentrations in the soil and

do not take into account different chemical and mineral

forms which naturally influence the metal’s solubility,

mobility and bioavailability. Similarly, they do not take

into account the fact that metals present as contaminants

in soils may change their form and availability over time

as a result of ageing and transformation processes.The majority of the livestock-related research sum-

marised in this article refers to work undertaken in the

UK and the developed world. Appleton (1992) has

reviewed the use of regional geochemical maps, some

compiled for mineral exploration, in developing countries

to identify areas of potential mineral deficiencies and

excesses in cattle. Attention is drawn to (a) relations

between areas of low Cu, Mn and Zn indicated by

regional geochemical maps for Swaziland (Forgeron,

1979) and possible deficiencies of these elements in

grazing livestock previously proposed as a result of

analysis of soils, herbage, cattle liver and serum in themiddle veld topographic zone (Ogwang, 1988); (b)

broad agreement between soil and drainage geochem-

istry (Stephenson et al., 1983) showing the potential for

deficiencies of Co and Cu and for Mo-induced Cu defi-

ciency in a mixed farming region in the centre of northern

Sumatra; (c) areas in which geochemical maps for NE

Zimbabwe (Dunkley, 1987) indicate the likelihood of

deficiencies of Co, Cu, Mn and Zn; (d) possible animal

deficiencies in extensive areas underlain by Precambrian

crystalline rocks of low Co, Cu, Mn and Zn shown by

the geochemical atlas of eastern Bolivia (Appleton and

Llanos, 1985) and (e) extensive areas of northern Sierra

Leone with low levels of Co, Cu and Mn in drainage

sediments (MacFarlane et al., 1981), again mainly

underlain by Precambrian crystalline rocks, in which

cattle are reared by nomadic farmers but where cattle

could be reared more intensively in the future.

A follow up report prepared by the Centre for Tropical

Veterinary Medicine, Edinburgh (1992), provided a

review of published literature on the mineral status of

livestock and pastures in these tropical countries. Infor-

mation was found to be sparse for the specific areas

covered by the regional geochemical maps reported by

Appleton (1992), and it was recommended that sampling

Table 1

Mean contribution of soil to total daily intake of As and Cu in 11 herds of cattle in Cornwall, England

Farm type

(based on soil As)

Mean % soil

ingested

Soil (mg kg1) Total daily intake (mg d1) % element ingested as soil

As Cu As Cu As Cu

20–50 mg kg1 As 1.4 24 26 7 140 67 10

n=3

55–140 mg kg1 As 1.4 85 93 21 175 76 10

n=3

160–259 mg kg1 As 1.1 202 199 52 190 58 16

n=5




of soil, forage, animal fluid and tissue should now be

carried out in selected areas to further assess the usefulness

of geochemical maps to identify areas where trace element

deficiencies or excesses might affect cattle productivity

under tropical conditions. On the basis of limited

correlations between reported deficiencies in livestock

and data provided by the geochemical maps, the authorsproposed levels of Cu, Co, Mn and Zn in drainage

sediments below which deficiencies in unsupplemented

grazing ruminants might occur.

More recent research in East Africa has demonstrated

the role of geochemistry in identifying trace element

imbalances in pasture in Zimbabwe and Kenya (Plant et

al., 1996; Fordyce et al., 1996; Jumba et al., 1996a,b).

However, in NE Zimbabwe, where stream sediment

geochemical maps provided useful indication of levels of

Zn and Cu in soil and grass, there was no correlation

with levels in bovine serum. The authors concluded that

this was probably due to differences in the species andmaturity of forages sampled and in the gender and age

of cattle from which serum had been obtained (Fordyce et

al., 1996). In Kenya, mineral concentrations in pastures

frequently fall below published standards for grazing

livestock. However, it is suggested that levels of Zn and

P below these standards do not necessarily imply that

production will benefit by supplementation; requirements

for livestock production may well be met. It was noted

that there were large differences in Zn concentrations

between herbage species sampled (Jumba et al., 1996b).

3. Geochemistry and wildlife nutrition

Further to the successful application of geochemistry

to agriculture and the recognition that geochemical

maps can delineate areas in which food crop and farm

livestock production and health could be influenced by

trace element deficiencies and excesses, the People’s

Trust for Endangered Species commissioned research to

see if this approach could be applied to wildlife con-

servation areas in Kenya. Here, a potential problem had

been recognised by the Kenyan Department of Wildlife

Conservation and Management within the Lake

Nakuru National Park. It was designated as the firstsanctuary for the black rhinoceros, an animal in danger

of extinction as a result of poaching. In this region in

the Rift Valley there is a history of mineral deficiencies

of ranched cattle and both the impala and waterbuck

within the Park show signs of possible deficiencies. The

impala show weakness and stiffness of the back legs and

the waterbuck, emaciation and loss of coat colour

(Maskall and Thornton, 1989).

The problem is that, in order to support conservation

and encourage tourism, wildlife are now enclosed in

what can be described as island parks. Instead of being

able to roam over very large areas, the animals are now

dependent on herbage and browse plants in relatively

small areas. Lake Nakuru National Park is only 160

km2. Some 20 black rhinoceros have been moved into

the Park, which is also the home of the relatively rare

Rothchilds giraffe.

A reconnaissance geochemical survey was carried out

to establish the mineral status of soils and selected plantspecies and the results related to the health of the animals

(Maskall and Thornton, 1989). Soil and plant samples

collected on a one-kilometre grid were analysed for 25

elements using ICP-AES and blood samples analysed

for Cu and vitamin B12.

The total concentrations of Cu and Co in soils were

low, a geochemical feature shared by many of the Rift

Valley soils derived from volcanic ash sediments and

other volcanic rocks. Total soil Se and P levels were also

relatively low. Grass species contained higher levels of

Cu and Co and lower levels of Se compared to browse

plants. Molybdenum levels in all plants reached rela-tively high values and the availability of this element

appeared to increase in wetter soils of high pH near the

lake shore (Maskall and Thornton, 1991, 1996). Over

30% of impala sampled had blood Cu levels below that

regarded adequate for domestic animals and were sig-

nificantly lower than those typical for impala throughout

Kenya. The relatively high Mo content of grasses and

browse plants is believed to contribute to possible Cu

deficiencies of impala and water buck in the park. The

lack of data on the mineral requirements of other wildlife

species prevents an assessment of the risk of deficiencies to

these species, including rhino, at the present time. As a

result of this work, recommendations were made to the

Kenya Department of Wildlife Conservation and Man-

agement that mineral salts containing Co, Cu and Se

should be made available to wildlife in Lake Nakuru

Park.

Further geochemical studies showed similar low con-

centrations of Cu and Co in brown clay loams at the Ol

Ari Nyiro Wildlife Reserve and the dark brown clays

developed from lavas from Mount Kenya at Solio

Wildlife Reserve. Soils derived from basaltic lavas at

Aberdares Salient, Amboseli National Park and basalts

at Lewa Downs Wildlife Reserve had higher concen-

trations of trace elements reflecting the basic nature of the parent material (Maskall and Thornton, 1991).

Black rhino at Solio had lower blood Cu levels than

rhino sampled in Zimbabwe and may indicate Cu defi-

ciency in the former. Jumba et al (1996a,b) reported low

‘‘total’’ concentrations of Ca, Mg, P, Cu and Zn in her-

bage from the Mount Elgar region of Kenya. Recent

geochemical studies in the Shimba Hills National Park,

home of the endangered Roosevelt sable, are reported

elsewhere in this volume.

Bowell and Ansah (1993) studied soils and vegetation

in the Mole National Park, Ghana and found Fe, Mn

and Co to be mainly fixed in the mineral fraction of the




soil, while Cu, Mo and Se were readily extractable. They

also showed Cu, Co and Mn to be present in higher

concentrations in grasses and Mo and Se in browse

plants.

The low Cu status of soils found in a geochemical

reconnaissance survey of the Mkomazi Game Reserve in

Tanzania suggest a possible Cu deficiency problem inherbivores (Abrahams and Bowell, 1998). McNaughton

(1990) proposed that seasonal movements of migrating

grazers in the Serengeti National Park in Tanzania were

influenced by the need for minerals, and in particular

Ca, Na, N, Cu and Zn, together with Mg and P for

lactating females and young animals. Of course, there

are numerous other situations when this type of

approach could be applied.

However, it has long been recognised that wildlife

regularly and intentionally eat soil from specific loca-

tions, commonly referred to as salt licks (Ayeni, 1971).

The reason for this geophagia has remained obscurethough it has commonly been supposed that this soil is

ingested to supplement minerals deficient in the animal’s

diet. Studies aimed at identifying a common nutritional

feature of these lick soils have proven inconclusive,

though soil enrichment with Na has been noted (Kreulen

and Jager, 1984; Abrahams, 1999) and it has been sug-

gested that this mineral is the main attraction (Tracy

and McNaughton, 1995).

Osteophagia or bone consumption has also been

noted in giraffe at the Timbavati Private Nature

Reserve, South Africa (Langman, 1978) and in sable at

Shimba Hills National Reserve, Kenya (Sekulic, 1977)

as a probable source of Ca and/or P.

4. The future

Thornton (1993) referred to the fact that geochemical

maps and atlases continue to cover greater areas and

would provide an exciting opportunity to study the global

significance of many of the problems previously studied

on a local or regional scale. The group of European

Geological Surveys (FOREGS, 1996) has made con-

siderable progress in bringing together existing geo-

chemical survey information Europe-wide and planshave been drawn up for further sampling strategies to

complete the European picture. On a global scale, an

updated proposal for a geochemical reference network

has been published, with the prime aim of providing a

framework of systematic baseline data to facilitate the

preparation of a World Geochemical Atlas. Both the

European mapping programme and the worldwide

initiative would have obvious applications to agri-

culture, including animal health and production (Darn-

ley et al., 1995).

There is also obvious potential on a regional and

national scale for the consolidation and interpretation

of previous geochemical survey information based on

stream sediment, soil and vegetation sampling—fre-

quently undertaken for purposes of mineral exploration.

One of the unfortunate limitations of applying these

data for environmental purposes is that frequently the

analytical detection limits employed for exploration

purposes are too high to be meaningful at the levelrequired for the identification of animal deficiencies.

It has already been noted that there have been

encouraging developments in the application of regional

geochemical surveys to livestock nutrition in developing

countries. It is emphasised that there is an urgent need for

greater data sources on veterinary/agricultural information

for comparison with these geochemical maps/atlases in the

tropics. The opportunities for multi-disciplinary research in

the developing world are enormous and call for the

establishment of teams encompassing geochemists, soil

scientists, biologists and veterinary scientists together

with those agencies responsible for agricultural andwildlife development.

The enormity of the problems ahead were noted by

Mills (1985), who concluded that ‘‘despite increasing

experimental evidence that anomalies in trace element sup-

ply can influence the growth, reproduction performance or

immunocompetence of domestic animals, few data exist

from which the incidence and economic significance of

such problems can reliably be assessed. In particular,

difficulties are experienced in assessed economic losses

arising from disorders giving rise to non-specific effects

on growth, fertility and resistance to infection induced

by deficiencies of Cu, Co, Zn or Se or by Mo excess’’. If

one considers Cu deficiency alone, in the 1980s it was

estimated ‘‘that characteristic clinical evidence of Cu

deficiency probably develop annually in about 0.9% of

the UK cattle population’’. Mills (1985) suggested that

‘‘assuming very conservatively, that similar conditions

govern the frequency of this disorder worldwide, the

approximate magnitude of the problem could be that

11.3106 clinically identifiable cases of severe Cu defi-

ciency develop in cattle annually. This estimate takes no

account of losses in buffalo, goats and other ruminants’’.

The extent of the problem is illustrated in Table 2 which

lists those tropical countries in which Cu deficiency in

cattle and sheep was recognised as a serious problem inthe 1980s (Shorrocks and Alloway, 1985). Undoubtedly,

more information is now available. Mills further suggests

‘‘that losses from severe Co deficiency may be similar in

magnitude’’. Mills specifically draws attention to the

problems in developing countries and to the problem of

focussing on inorganic element nutrition in relation to

animal productivity when a complex interplay of multiple

deficiencies and infections confuses the clinical picture.

The situation in central and eastern Europe warrants

special consideration as, until relatively recent political

change, there had been difficulties in obtaining reliable

information on agricultural problems and their extent and




severity. A notable exception was work on biogeochemical

mapping in the USSR by scientists of the Vernadsky Insti-

tute, Moscow, based on extensive soil sampling. This lead

to the recognition of zones and zonal provinces in which

groups of trace and major elements were present at low,

adequate or high concentrations and in which animals

showed a biological response (Kovalsky, 1970, 1979;

Kovalsky and Andreanova, 1970). This valuable

compilation of data was regrettably not followed up by

more detailed investigations or, if so, these have not

been made available to the wider scientific community.

There is obvious potential for building on this geo-

chemical baseline.

The growing problem of contaminated land and the

development of regulations at a national, European and

international level has jointly focussed on the protection

of human health and of ecosystem as noted earlier in

this paper. In particular, the impacts of historical and

more recent mining and smelting activities have left a

legacy of extensive areas of agricultural and natural

land contaminated with one or more heavy metals,

sometimes at very high concentrations. An example of the worldwide relevance of this is illustrated by recent

studies in Korea (Jung and Thornton, 1996). The issue

of contaminated land and its potential impacts is again

of paramount importance in central and eastern Europe.

The use of land for livestock production will no doubt

be influenced by further developments in this regulatory

process, in that much land heavily contaminated by

potentially toxic metals is used for livestock rearing at

this time and could, in certain cases, lead to the pro-

duction and sale of livestock products, particularly liver

and kidney, that exceed recommended levels for human

consumption.

The applications of geochemistry to wildlife nutrition

and conservation is still relatively new and the recent

work in Tanzania and Kenya is encouraging. There is,

however, a huge potential to develop this type of inves-

tigation further, particularly in southern Africa and

Latin America. Funding such work must surely be the

responsibility of international and national developmentagencies with a view to supporting the future growth of

tourism based on successful wildlife management.

Finally, it is recognised that the geochemist and chemist

now have more sophisticated tools to facilitate the

understanding of processes in the soil–plant–animal

system that influence and control the supply of essential

nutrient elements and/or exposure to potentially toxic

metals. Recent developments in sampling and analytical

procedures have focussed on the speciation of elements

in the soil and soil solution as the first critical stage in the

source–pathway–animal receptor model. It is envisaged

that these analytical tools, coupled with modellingtechniques and the use of GIS will lead to improved

methods of applying geochemical maps to livestock and

wildlife nutrition and sustainability.

In conclusion, it is stressed that geochemists must not

work in isolation. If full use is to be made of geochemical

data, whatever the scale, collaboration with agricultural

and veterinary scientists and with those responsible for

wildlife management is essential if meaningful progress

is to be made.

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Table 2

Tropical countries in which Cu deficiency in grazing cattle and

sheep is a serious problem

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Brazil Mexico

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Costa Rice Peru

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Dominican Rep. Senegal

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Geochemistry and the Mineral Nutrition of Agricultural Livestock and Wildlife