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Effect of pasture mineral levels on extensive cattle production in Kenya

Aggrey Abate

Department of Animal Production
University of Nairobi
P.O. Box 29053, Nairobi, Kenya


Introduction
Earth licks as sources of minerals
Borderline to sufficient minerals
Deficient minerals
Mineral levels in the rangelands
Meeting mineral requirements of grazing animals
References

Abstract

Mineral levels of Kenyan pastures were examined with the objective of determining whether they were sufficient to meet the requirements of grazing cattle. Potassium (K) was found to be adequate in the herbage while grazing animals are likely to meet their requirements for iron (Fe) through incidental ingestion of soil. The status of magnesium (Mg) and calcium (Ca) needs resolving because adequacy and deficiency have both been reported. Other minerals were, however, found to limit extensive cattle production because they were deficient particularly in the dry season. These included phosphorus (P), sodium (Na), copper (Cu) and cobalt (Co). There was little information on minerals in the rangelands and further research in this area was suggested. Of the preventive measures recommended, provision of mineral supplements was found most appropriate. It was, however, emphasised that for effectiveness of any mineral nutrition programmes, adequate energy and protein nutrition has to be maintained particularly in the dry season.

Introduction

In Kenya, as in many developing countries natural pastures are the main source of nutrients for cattle. As a consequence, seasonality in quantity and quality of available herbage has a marked influence on animal productivity. Poor animal performance has usually been interpreted in terms of low dry-matter (DM) intake and inadequacy of energy and protein in the DM (Grover and Dougall, 1961; Abate et al., 1981; Abate, 1985; Abate and Abate, in press). Little mention is made of the effect essential elements have on production mainly because under controlled experimental conditions mineral supplements are normally fed. Yet surveys carried out in the country have revealed mineral deficiencies in Kenyan pastures (Burdin and Howard, 1963; Howard, 1969; Mwakatundu, 1977) with obvious consequences on animal development and reproduction (Todd, 1954; Howard et al., 1962).

This paper aims to examine mineral levels in Kenyan pastures with emphasis on the effect of deficiencies on cattle production.

Earth licks as sources of minerals

Early indications of mineral deficiency in Kenyan pastures followed observations on earth eating and oesteofagia by cattle and wild ruminants (Todd, 1954; French, 1955; Howard, 1963). Table 1 shows the composition of two such natural licks. Hudson (1944), French (1955) and Howard (1963) concluded from other similar analyses that natural licks contained insufficient sodium (Na) while the levels of phosphorus (P) and calcium (Ca) were too low to alleviate a deficiency. Concentrations of as high as 15.1 and 78.1% of sodium chloride (NaCl) have, however, been reported in the DM of natural salt licks in parts of North Eastern Province (Hudson, 1944). The availability of mineral elements from earth licks is also probably low since only up to 6% of the organic matter is soluble in dilute acid (Table 1). In spite of their unlikelihood as sources of minerals, cattle owners still regarded such salt licks as essential to the well being of their animals (Hudson, 1944).

Table 1. Mineral composition (% DM) of salt licks from two different areas in Machakos District.


Emali

Koru

Total organic matter, %

98.6

96.8

Inorganic matter soluble in 0.125N HCl, %

1.8

6.5

Percent DM


Calcium

0.03

0.80


Magnesium

0.40

0.10


Sodium

0.02

0.10


Potassium

0

Trace


Phosphorus

Trace

0.01


Iron

0.04

0.18


Copper

0.0008

0.001

Source: Hudson (1944).

Borderline to sufficient minerals

Potassium (K) concentration in Kenyan forages are quite high (Abate, 1984; unpublished data); levels compare well to those in productive grasses elsewhere in the world (Howard, 1963) and are adequate in meeting the requirements of grazing livestock (Howard et al., 1962). Because of large quantities in the soil, animals are also likely to augment their iron (Fe) supplies through direct ingestion of soil or from soil-contaminated herbage (French, 1955; Hodgson et al., 1962) and would, therefore, suffer no deficiency. For some minerals, the risk is either little or there is no evidence of deficiency in grazing animals (French, 1955; Mwakatundu, 1977). Depending on the area, other minerals may be borderline to sufficient. Thus, Howard (1963) has indicated that there may be a need to topdress Kenyan pastures with magnesium (Mg) fertilizers because levels of the element in grazings were similar to those that predispose animals to grass tetany. But Mwakatundu (1977) maintained that Mg was not limiting in Kenya because the element was sufficient in soils, pastures and bovine plasma. Also a suspected case of hypomagnesemia in the Naivasha area was not confirmed by serum analysis (Howard, 1963). The position with regard to Ca equally requires defining. Howard (1963) found Ca levels in Kenyan pastures satisfactory but Mwakatundu (1977) reported that areas in Central and Rift Valley provinces were deficient in the mineral. A national average value of 0.53$ has been quoted (Howard, 1963) although a lower concentration of 0.39% has also been reported for ley and natural pastures at Muguga, Central Kenya (Howard et al., 1962). On account of a comparatively lower productivity, a Ca deficiency is unlikely to occur in beef herds because of the ability to mobilise body depots. A proper Ca:P ratio is, however, physiologically desirable for high fertility and adequate rate of growth irrespective of level of production. Results of studies carried out in Baraton, Egerton, Kabete and Molo suggested that the Ca:P ratios of the grazings were satisfactory for ruminants (Mwakatundu, 1977).

Deficient minerals

Based on the available literature, the minerals most likely to limit cattle production in Kenya are P. Na, copper (Cu) and cobalt (Co). Certain trace minerals like selenium (Se) and zinc (Zn) could, however, also be limiting.

Phosphorus

In a mineral survey Howard (1963) reported that 36% of natural pastures analysed contained less than 0.3% P while the average value for the country was 0.41%. Levels were lower in the dry than in the wet season. Todd (1954) analysed samples of Chloris gayana, Bothriochloa insculpta and Brachiaria dictyoneura and found them to contain as low as 0.13% P in the DM in the dry season. These results were similar to those of Howard et al., (1962) who reported a range in P content of 0.072-0.252% in grazed pastures in the high potential areas of Kenya; at the lower level P was deficient and this occurred during dry spells. Mwakatundu (1977) also confirmed that in Kenya P deficiency was widespread as shown by low levels in soil, pasture and bovine plasma. The concentration of P depended largely upon the extent of recent precipitation and was highly correlated (r = 0.72**) to CP levels in the pasture (Howard et al., 1962). Mwakatundu (1977) has reported similar results.

The requirements for P by grazing Kenyan cattle are not known. It is probable, however, that pasture levels of P are sufficient to maintain slow maturing and low producing indigenous animals but is inadequate for high producing improved breeds (French, 1955). Suboptimal P levels in grazings have resulted in the following in Kenyan cattle: loss of appetite hence reduced feed intake, retarded growth, interference with regularity of heat hence reproductive rates, lowered milk production and, in extreme cases, depraved appetite or pica (Howard, 1963).

Sodium

The concentrations of Na in pastures throughout Kenya are very low (Howard, 1963), particularly in the dry season (French, 1955). Wet season grass may, however, also contain Na levels that are insufficient in meeting animal requirements (French, 1955). This is because rapid gain in weight by animals during the wet season induces high mineral requirements (McDowell et al., 1984). Of all pastures analysed in Kenya, 77% contained 0.01% or less Na; levels which are inadequate to cover the demands of dairy and improved beef cattle. A range of 0.007-0.022% Na has been reported for samples obtained from ley and permanent pastures of Cynodon dactylon and Chloris gayana in Muguga, Central Kenya (Howard et al., 1962). Severe symptoms of Na deficiency have not been reported in Kenya mainly because most farmers feed salt to their animals.

Copper

Disorders such as stilted gait, rusty coat colour and, in severe cases, fragility of bones in calves have been identified in Kenya as due to Cu deficiency (French, 1955; Howard, 1963). Copper concentrations in Kenyan pastures seem to lie between 4.0 and 12.2 ppm (Howard et al., 1962). Deficiency normally shows itself at levels lower than 5.0 ppm, and this has been shown in about 35% of pastures analysed in Kenya (Howard, 1963). Shortage of Cu has been recorded in grazings along the Rift Valley and in parts of Central and Rift Valley provinces (Howard, 1963) because of a Cu deficiency in the soil (Pinkerton et al., 1965). Soils in which the underlying rock is ash and pumice may be expected to be deficient in Cu (Nyandat and Ochieng, 1976). Mwakatundu (1977) also found subclinical Cu deficiency widespread in Kenya as a result of Cu deficiency either in the soil or pasture or bovine plasma and is more pronounced in dry periods (Nyandat and Ochieng, 1976). The functioning of dietary Cu can be inhibited by excess molybdenum (Mo) resulting in a conditioned Cu deficiency. Animals consuming forages with Mo concentrations above 15 to 20 ppm showed Cu deficiency symptoms even though the Cu levels in the forage were higher than 5 ppm (Hodgson et al., 1962). Conditioned Cu deficiency does not seem a problem in Kenya because Mo was found deficient in several areas surveyed (Mwakatundu, 1977).

Cobalt

Cobalt is a serious mineral limitation to livestock because even when grazing is abundant deficiency will lead to chronic starvation or wasting which is often indistinguishable from energy and protein malnutrition (French, 1952; Howard, 1963; McDowell et al., 1984). It is rare for grasses to contain Co in concentrations that meet the demands of grazing animals (Hodgson et al., 1962). When the content in the pastures herbage is 0.10 ppm or less (Hodgson et al., 1962) grazing animals are likely to suffer from Co deficiency. In Kenya, the condition is known as "Nakuruitis" (French, 1952; Howard, 1963) or as "Narurasha" among Maasai herdsmen (Hudson, 1944; French, 1952). Cobalt deficiency is common along the Rift Valley and is seasonal in character with symptoms usually appearing after the rains when grazing is plentiful and green (Hudson, 1944). Mwakatundu (1977) also confirmed Co deficiency in the Egerton, Kabete and Molo areas of Kenya. Animals suffering from Co deficiency lose appetite and condition, may abort if in calf or may have difficulty to conceive again, the condition seems to affect lactating cows more than any other type of stock (Hudson, 1944; French, 1952).

Mineral levels in the rangelands

The literature cited above refers mainly to mineral deficiencies in the high potential areas of Kenya which are characterised by about 1200 mm of rainfall per annum. Reports on the effects of minerals on animal production in the rangelands of Kenya are lacking.

About 85% of the total land area of Kenya is rangeland unsuitable for arable cropping because it receives only 500-750 mm of rainfall per year. The rangelands are, however, important because they contain about 50% of the total livestock population in the country. The cattle population here consists mainly of low production indigenous stock. In these areas grazing forms the only source of feed and the natural vegetation is dominated by Commiphora, Acacia and Themeda associations with a carrying capacity of 4 ha to a stock unit.

In Table 2 are given lists of preferred grass species in the rangelands of Kiboko (Hatch et al., 1984) and around Isiolo (Schwartz, H.J. pers. comm.). For most of the year the quality of the herbage is low. Karue (1974) stated that the level of digestible energy for most of the grasses in the dry zones of Kenya is inadequate to meet the demands for maintenance of grazing stock in the wet and dry seasons. Tessema (1986) reported that the grasses of the semi-arid areas of Eastern Province had high proportions of structural carbohydrates which were deposited in the plant tissues at an early vegetational stage; the protein content on the other hand dropped from 11 to 4% at six months of age.

Table 2. Composition of the most important grass species in the rangelands around Kiboko and Isiolo.

Kiboko

Isiolo

Digitaria macroblephara

Setaria verticillata

Cenchrus ciliaris

Sporobolus nervosa

Themeda triandra

Aristida adscensiomis

Chrysopogon plectostachyus

Eragrostis ciliaris

Chloris roxburghiana

Cynodon dactylon

Eragrostis caespitosa

Tetrapogon cenchriformis

Panicum maximum

Pennisetum mezianum

Enteropogon macrostachys

Chrysopogon plumulosus

Sporobolus fimbriatus


Sources: Hatch et al (1984); Shwartz (unpublished data).

The mineral composition of wet season grasses around Isiolo is given in Table 3. This is compared to the data from high potential areas of Mwakatundu (1977) given in Table 4. The mean values for the range area are comparable to those reported for the high potential areas. The data suggest that wet season grasses in the rangelands of Isiolo contain adequate levels of minerals to meet the demands of grazing animals. Consumption of sufficient quantities may, however, be limited by herbage intake since in the rangelands, CP levels fall to about 7% in only 8-10 weeks (Tessema, 1986).

Table 3. Mineral composition (% DM) of some grass species in the Isiolo rangelands.



P

Mg

Na

K

% M

Pennisetum mezianum

0.17

0.19

0.10

0.62

Setaria vertilillata

0.27

0.41

0.10

2.62

Aristida adscensionis

0.14

0.15

0.11

0.51

Tetrapogon cenchriformis

0.24

0.22

0.14

1.22

Cynodon dactylon

0.44

1.10

0.11

1.86

Eragrostis ciliaris

0.39

0.28

0.10

1.44

Chrysopogon plumulosus

0.16

0.21

0.06

0.69

Sporobolus nervosas

0.40

0.28

0.08

1.21

Mean ± S.D.

0.28±0.12

0.36±0.31

0.1±0.02

1.27±0.27

Table 4. Average mineral composition in the DM of pastures from selected areas of Kenya.

Ca

P

Mg

Cu

Co

Season


Station


% M

ppm

0.32

0.24

0.17

7.0

0.142

Wet

Baraton

0.59

0.28

0.24

11.0

0.210

Dry


0.53

0.35

1.18

14.0

0.061

Wet

Egerton

0.55

0.27

0.17

9.0

0.036

Dry


0.37

0.45

0.26

7.0

0.142

Wet

Kabete

0.39

0.26

0.10

6.0

0.098

Dry


0.38

0.16

0.18

8.0

0.086

Wet

Molo

0.53

0.20

0.18

11.0

0.027

Dry


Source: Mwakatundu (1977).

Meeting mineral requirements of grazing animals

An adequate supply of energy and protein are no doubt important in the maintenance of high productivity in any animal production system. In the rangelands of Kenya benefits would be even greater if in addition, appropriate strategies were adopted to meet the mineral requirements of the grazing animal. McDowell et al. (1984) have observed that cattle grazing forages in severe P-Co- or Cu-deficient areas are even more limited by lack of these elements than by lack of either energy or protein.

In the past the practice has been to move cattle to natural earth licks at certain seasons of the year (Hudson, 1944; Howard, 1963), but as has been indicated earlier, the value of such licks as sources of minerals is low since they are devoid of reasonable quantities of either salt, Ca or P. Movement of animals to unaffected areas has been shown to cure Co deficiency (Hudson, 1944). This is unlikely to remain a solution in the future in view of the present increase in population which will take more land for food crop production. Use of mineral supplements on the other hand increased milk yields, produced heavier calves and maintained better animal condition than unsupplemented controls, particularly in the dry season (Howard, 1963).

It is evident from the above observations that there is need for increased attention to be paid to mineral nutrition. Farmers need to be informed that energy, protein and minerals are interrelated in body maintenance, growth and health. They should be made aware of the possible incidence of mineral deficiencies because parts of Kenya are lacking in a number of the mineral elements essential in animal nutrition. Periodic mineral surveys which should include analyses of soil, water, plant and animal tissue are necessary in order to detect inadequacies.

Inclusion of legumes in the pasture provides a mixture that ensures adequate intake of Co by grazing animals because legumes are efficient in accumulating Co in amounts above animal requirements (Hodgson et al., 1962).

A mineral deficiency in pasture herbage is often a result of a deficiency in soil. Thus, the potential role of fertilizers in meeting animal requirements for minerals needs to be studied so as to develop a fertilizer package that is location specific. For example, Cu deficiency in animals may be treated by top dressing pastures with copper sulphate (Hodgson et al., 1962). It should be noted, however, that inadequate or erratic rainfall may be dominant over soil effects in determining the mineral concentrations of the herbage. Individual minerals may be administered as a drench, injection or slow release pellets. The use of "copper bullets" has been recommended for range livestock (Hodgson et al., 1962), but this would require professional supervision.

By far the most important method of meeting requirements lies in mineral supplementation. Economic and physiological responses to mineral supplements have been recorded (French, 1955; Howard, 1963), and this should be encouraged through the widespread use of free choice compound mineral licks. Several ranches in Kenya are known to offer mineral licks to their animals although there is no guarantee that all animals will consume enough of the lick at all times. What is desirable, however, is that such mineral mixtures should ensure that levels of P. Na, Cu and Co are particularly adequate. Finally, it is important to note that the measures recommended above are only effective if the general level of nutrition with regard to energy and protein is maintained particularly in the dry season.

References

Abate, A. 1985. In vitro estimation of the energy content of some feeds commonly fed to livestock in Kenya. East African Agricultural and Forestry Journal 45:255-260.

Abate, A.N. and Abate, A. (in press). Cassava as a source of energy in supplementary rations for weaner beef calves. East Afric. Agric. For. J.

Abate, A., Kayongo-Male, H. and Karue, C.N. 1981. Dry matter, protein, energy and fibre intake by dairy heifers grazing a Rhodes (Chloris gayana) pasture. Animal Feed Science and Technology 6:15-26.

Burdin, M.L. and Howard, D.A. 1963. Mineral survey of Kenya. Kenya Veterinary Research Laboratories, Kabete, Kenya.

French, M.H. 1952. Mineral deficiencies in farm livestock. East African Agricultural and Forestry Journal 10:4-8.

French, M.H. 1955. Earth eating and the mineral needs of livestock. East African Agricultural and Forestry Journal 20:168-175.

Glover, J. and Dougall, H.W. 1961. Milk production from pastures. Journal of Agricultural Science (Cambridge) 56:201-204.

Hatch, S.L., Morden, C.W. and Woie, B.M. 1984. The grasses of the National Range Research Station, Kiboko (Kenya). S.M. Tracey Herbarium, Department of Range Science, Texas A & M University, Texas.

Hodgson, J.F., Leach, R.M. and Allway, W.H. 1962. Micronutrients in soils and plants in relation to animal nutrition. Journal of Agriculture Food and Chemistry 10:171-174.

Howard, D.A. 1963. Notes on animal diseases. XXIII. Mineral deficiency diseases. East African Agricultural and Forestry Journal 28:191-194.

Howard, D.A. 1969. Notes on animal diseases. Mimeographed report. Veterinary Research Laboratories, Kabete, Kenya.

Howard, D.A., Burdin, M.L. and Lampkin, G.H. 1962. Variation in mineral and crude protein content of pastures at Muguga in the Kenya Highlands. Journal of Agricultural Science (Cambridge) 59:251-256.

Hudson, J.R. 1944. Notes on animal diseases. XXIII. Deficiency diseases. East African Agricultural and Forestry Journal 10:51-55.

Karue, C.N. 1974. The nutritive value of herbage in semi-arid lands of East Africa. 1. Chemical composition. East African Agricultural and Forestry Journal 40:89-95.

McDowell, L.R., Conrad, J.H. and Ellis, G.L. 1984. Mineral deficiencies and imbalances and their diagnosis. In: F.C.M. Gilchrist and R.I. Mackie (eds), Herbivore nutrition in the subtropics and tropics. The Science Press.

Mwakatundu, A.G.K. 1977. A study of the nutritive value of East African pastures for ruminant livestock with special reference to mineral nutrition in grazing dairy cattle. Ph.D. thesis, University of Nairobi, Kenya.

Nyandat, N.N. and Ochieng, P.N. 1976. Copper content and availability in soils: a survey of arable and range areas of Kenya. East African Agricultural and Forestry Journal 42: 1-7.

Pinkerton, A., garret, M.W. and Guthrie, E.J. 1965. A note on copper deficiency in the Njoro area, Kenya. East African Agricultural and Forestry Journal 30:257-258.

Tessema, S. 1986. Chemical and in vitro dry-matter digestibility of herbage. In: R.M. Hansen, B.M. Woie and R.D. Child (eds), Proceedings of a conference on Range Development and Research in Kenya held at Egerton College, Njoro, Kenya, 1-5 April 1988. Winrock International Institute, Morrilton, Arkansas, USA. pp. 85-102.

Todd, J.R. 1954. The phosphorus status of cattle in parts of Central Province, Kenya. East African Agricultural and Forestry Journal 20:66-68.


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