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Nutrient quality of forages in Ethiopia with particular reference to mineral elements

E. Kabaija and D.A. Little

International Livestock Centre for Africa
P.O. Box 5689, Addis Ababa, Ethiopia


Introduction
Methodology
Results and discussion
Conclusion
References

Abstract

Hays, range grasses, crop residues and browse trees from different parts of Ethiopia were analysed for nitrogen, fibre components and mineral concentrations. Pasture grasses and crop residues studied had very low crude protein contents, while the browse on the average had more than 15% crude protein. Almost all the forages had sufficient levels of K, Ca, Mg, Mn and Zn to meet requirements of ruminant animals, but the occurrence of marginal to deficient supplies of Na, Cu and P appear very likely. There is an urgent requirement for experimentation on supplementation regimes involving these minerals, so that appropriate recommendations can be formulated.

Introduction

In Ethiopia, as elsewhere in Africa, malnutrition impairs livestock production. Ethiopia's overall livestock productivity is below average. Although 12.7% of Africa's 524.61 million cattle, sheep and goats are found in Ethiopia, the country produces only 7.3% and 5.1% of Africa's total meat and milk production respectively (FAO, 1985). Grazing animals in Ethiopia subsist mainly on poor quality feedstuffs in the form of poor quality pastures in arid and semi-arid areas and hays and/or crop residues in the arable areas. In a few of the animal production centres where improved management is undertaken, the main supplements are energy and protein in the form of agro-industrial by-products such as cereal brans, molasses and oilseed cakes. Scant attention is given to the mineral content and nutritional balance of such diets. It has been widely established that available energy and protein of a feed are of primary importance to any animal but optimal performance is only possible if there is an adequate supply of minerals and vitamins (McDowell, 1985).

In Ethiopia, cattle rarely receive mineral supplements except occasionally common salt. Pastures are thus the main source of minerals, and only rarely can forages completely satisfy all mineral requirements of livestock (Miles and McDowell, 1983). Mineral status of grazing animals in Ethiopia and other African countries has received very little attention. This may be due partly to the fact that the methodology of mineral nutrition studies, especially of trace elements, is rather complicated and signs of marginal mineral deficiencies are not easily detected but frequently it is mistakenly assumed that the grazing animal will obtain its mineral needs from the pasture. Mineral deficiencies, even if marginal, can result in depression of animal performance. Subclinical mineral deficiencies are often widespread and are responsible for as yet unestimated, but probably great, economic losses in livestock production.

An earlier mineral study in Ethiopia (Faye et al., 1983) indicated probable widespread copper and zinc deficiencies, and although much more information on the supplies of essential minerals for livestock is required, it is very likely that mineral deficiencies contribute to the poor performance of livestock in Ethiopia. Before measures can be undertaken to correct these deficiencies, it is necessary to assess the mineral status of forages and of the grazing animals as well as their production responses to mineral supplementation. This study was undertaken to investigate the nutrient status, with special regard to minerals, of the common crop residues, pasture grasses, grass hays and browse trees used as livestock feeds in Ethiopia.

Methodology

Samples

Samples of meadow hay were collected from an ILCA site in Addis Ababa and from two other sites at Debre Berhan (an ILCA-station 120 km east of Addis Ababa and a Government sheep breeding station 132 km from Addis Ababa). Samples were also taken from a commercial source in Addis Ababa, whose supplies came from the Addis Ababa region. All the samples were from the highlands (2500-3000 m) and were obtained by pooling core samples from ten positions within the stack. Samples of oats hay (whole plant with grain), ryegrass hay and improved pasture hay (mostly ryegrass and native Trifolium species) were taken as described above from stacks of hay at ILCA sites in Debre Berhan harvested between September and November, 1986.

Sesbania sesban grown at ILCA, Addis Ababa and in Yabello in the southern Ethiopian rangelands of Sidamo were harvested in February, 1987. Samples were taken by pooling leaves from mature trees (50 in Addis Ababa and 15 in Sidamo). Leaves from the trees in Addis Ababa were further separated into young (first ten leaves on twig) and old. Pods with seeds on trees from Addis Ababa were first air-dried and then separated into pods and seeds. Samples of Leucaena leucocephala cv Peru were taken in February, 1987 from a lowland area at a Government research station (Institute of Agricultural Research, Melka Worer) in eastern Ethiopia using the same procedures as for Sesbania.

Grass and browse species were collected from the Sidamo southern rangelands in February, 1987 by hand plucking during grazing observations over three days. The species collected included: Cenchrus ciliaris, Themeda triandra, Chrysopogon aucheri, Pennisetum mezianum, Acacia brevispica and Acacia nilotica. The Acacia samples were of the species mainly browsed by camels and goats.

Samples of crop residues were taken using the same procedures as for hays. The crop residues were of highland origin, and most of them were being used in feeding experiments at ILCA, Debre Zeit and ILCA, Addis Ababa.

Chemical Analysis

Dry matter was determined after drying in a microwave oven at 60°C for 24 hours. The dried samples were ground using a one-mm sieve and stored in plastic bottles ready for analysis. Neutral-detergent fibre (NDF), acid-detergent fibre (ADF), lignin and ADF ash were determined with a microfibre apparatus using the procedures of Goering and van Soest (1970).

Samples were prepared for mineral analysis by the wet digestion method using concentrated sulphuric acid in presence of hydrogen peroxide. Nitrogen (N) and phosphorus (P) concentrations in the extracts were determined with the autoanalyser which uses ascorbic acid as a reducing agent for P determination. The concentrations of potassium (K), sodium (Na), calcium (Ca), magnesium (Mg), iron (Fe), manganese (Mn), zinc (Zn) and copper (Cu) were determined by atomic absorption spectroscopy. Sulphur (S) in the samples was quantified using the turbidimetric method of Cottenie et al. (1982).

Results and discussion

The analytical results for hay and range grasses are shown in Tables 1 and 2, for crop residues in Tables 3 and 4 and for leguminous trees in Tables 5 and 6.

Table 1. Dry matter, crude protein, NDF, lignin, ash and ADF ash of some hays from Ethiopian highlands and range grasses from southern Ethiopian rangelands.

Sample description

DM

CP

NDF

ADF

Lignin

Ash

ADF ash

%

Highland hays


Meadow hay, DBSBS

93.4

5.3

69.7

37.9

4.0

7.5

2.4


Meadow hay, ILCA-DB

93.1

4.4

69.2

37.9

4.9

7.9

2.8


Oats hay, ILCA-DB

91.2

5.1

71.0

38.1

4.5

4.6

1.5


Rye grass hay, ILCA-DB

92.5

6.2

57.5

35.7

5.0

7.4

2.6


Improved pasture hay, ILCA-DB

92.0

5.3

58.7

32.7

4.0

6.5

3.1


Meadow hay, ILCA-Addis

94.1

4.6

72.2

43.7

5.7

8.7

3.4


Meadow hay from commercial centre

91.9

3.7

77.0

41.1

5.1

8.4

3.4

Range grasses


Cenchrus ciliaris

58.8

7.5

66.2

37.2

5.1

11.3

4.06


Themeda triandra

84.7

5.0

77.2

50.2

8.0

10.9

7.61


Chrysopogon aucheri

59.1

6.0

71.2

36.0

5.2

11.5

5.80


Pennisetum mezianum

78.0

6.3

74.1

46.0

8.5

10.7

4.60

Table 2. Mineral content of some hays from Ethiopian highlands and range grasses from Ethiopian Sidamo southern rangelands.

Sample description

K

Na

Ca

Mg

P

S

Fe

Mn

Zn

Cu

g/kg

mg/kg

Highland hays












Meadow hay, DBSBS

17.6

0.4

3.4

1.6

1.6

3.0

695

207

45

5.9


Meadow hay, ILCA-DB

18.4

0.3

4.4

1.6

1.4

2.6

974

274

39

6.1


Oats hay, ILCA-DB

12.6

0.9

1.6

1.0

1.8

1.8

192

96

30

7.0


Ryegrass hay, ILCA-DB

16.3

1.1

3.8

1.7

2.2

2.1

397

214

32

7.9


Improved pasture hay, ILCA-DB

20.8

1.2

3.7

1.7

1.6

2.6

358

206

28

7.1


Meadow hay, ILCA-Addis

17.5

0.6

4.9

1.7

1.4

2.4

191

246

29

6.2


Meadow hay, from commercial centre

13.1

0.5

4.6

2.1

1.6

3.0

589

322

37

7.9

Range grasses












Cenchrus ciliaris

23.5

1.0

2.0

1.6

1.5

2.1

830

45

24

3.6


Themeda triandra

12.0

0.1

4.1

1.5

1.2

1.0

625

72

31

3.5


Chrysopogon aucheri

1.0

0.08

2.2

1.6

1.0

1.1

882

63

32

5.6


Pennisetum mezianum

12.0

0.1

3.2

2.0

1.4

1.1

452

72

40

4.7

Table 3. Dry matter, crude protein, NDF, ADF, lignin, ash and ADF ash of some crop residues from Ethiopian highlands.



DM

CP

NDF

ADF

Lignin

Ash

ADF ash

(%)

Wheat straw

90.5

1.6

70.7

50.6

11.1

10.8

5.5

Barley straw

88.2

1.8

65.4

56.2

7.0

7.7

1.7

Teff straw

89.7

1.7

71.3

49.1

7.9

7.8

3.7

Oats straw

88.9

1.5

57.2

41.9

6.0

8.3

2.1

Linseed straw

93.0

3.0

68.7

-

-

8.4

3.1

Maize stover

87.2

1.5

68.1

47.1

7.9

9.2

3.1

Table 4. Mineral concentration of some crop residues from the Ethiopian highlands.



K

Na

Ca

Mg

P

S

Fe

Mn

Zn

Cu

g/kg

mg/kg

Wheat straw

14.8

0.3

4.1

1.5

1.3

1.4

325

78

11

3.0

Barley straw

10.7

0.5

4.6

1.4

1.9

1.2

1175

90

12

5.0

Teff straw

11.7

0.3

4.3

1.9

1.6

1.6

170

59

26

6.5

Oats straw

17.7

0.4

3.9

1.8

1.7

1.7

196

191

17

14.0

Linseed straw

10.7

0.6

7.7

2.2

1.3

1.6

103

71

24

14.0

Maize stover

17.8

0.5

3.3

2.5

1.7

0.9

408

61

24

5.9

Table 5. Dry matter, crude protein, NDF, ADF, lignin, ash and ADF ash of Leucaena leucocephala, Sesbania sesban and Acacia species.

Sample description

DM

CP

NDF

ADF

Lignin

Ash

ADF ash


%

Leucaena:


Young leaves

20.7

31.2

25.1

10.6

0.3

6.5

-


old leaves

34.1

28.6

23.4

13.4

2.4

8.9

-


Pods

79.1

7.9

67.8

61.1

19.6

5.7

-


Seeds

97.3

34.8

33.9

21.2

2.1

4.2


Sesbania:


Small twigs with leaves

29.0

27.5

14.0

12.4

2.8

12.4

0.3


First ten leaves

31.3

28.5

13.3

9.2

2.4

6.3

0.2


Old leaves

30.4

28.5

12.7

9.8

2.6

7.8

0.4


Pods with seeds

27.5

21.0

50.4

40.4

6.6

2.7

0.5


Pods alone

90.8*

10.6

60.9

52.6

13.9

6.4

0.3


Seeds alone

89.8**

34.6

33.0

22.4

2.6

3.7

0.3


Old and young leaves*

33.6

25.9

13.0

9.9

1.7

13.6

0.8

Acacia:









Acacia brevispica

38.9

26.3

47.3

29.0

13.0

8.4

0.60


Acacia nilotica

40.1

15.0

30.7

28.1

11.0

5.9

0.60

* Taken from the low-mid altitude southern Ethiopia rangelands.
** First air-dried.

Table 6. Mineral content of Leucaena leucocephala, Sesbania sesban, and Acacia species.

Sample description

K

Na

Ca

Mg

P

S

Fe

Mn

Zn

Cu

g/kg

mg/kg

Leucaena:


Young leaves

20.4

0.3

3.7

1.9

3.1

3.4

181

31

39

10.0


Old leaves

16.7

0.3

18.4

3.9

2.1

2.5

214

53

19

11.8


Pods

13.6

0.4

15.4

0.6

0.4

-

198

43

11

3.4


Seeds

15.6

0.3

3.4

1.9

3.8

4.9

131

29

40

11.0

Sesbania:


Small twigs with leaves

13.0

1.2

21.3

2.8

2.1

2.3

274

165

41

9.5


First ten leaves

10.9

1.2

23.4

2.7

2.1

2.3

285

200

48

8.1


Pods with seeds

19.9

1.0

6.3

1.2

2.6

1.7

109

45

37

5.2


Pods alone

12.8

1.1

12.0

0.9

1.1

1.2

581

63

31

5.3


Seeds alone

9.3

0.8

3.7

1.4

4.6

1.9

181

52

52

7.6


Old and young leaves

13.2

1.0

28.3

4.9

2.4

3.2

280

410

62

6.4

Acacia brevispica

16.9

1.04

7.7

2.9

2.0

3.4

151

137

46

6.9

Acacia nilotica

8.1

0.5

18.0

1.9

2.2

2.3

664

66

31

9.0

* Taken from the low-mid altitude southern Ethiopian rangelands.

All the pasture grasses and crop residues studied had very low crude protein contents which is characteristic of mature tropical forages whose protein content declines rapidly following the rapid growth of the rainy season. Those figures were all below the level of 7.5% considered to be required for optimum rumen function (van Soest, 1982).

For reasonable levels of production, animals subsisting on these forages will therefore require supplementary protein which may be in the form of oilseed cakes and/or NPN sources such as urea which could be easily obtained locally. While use of such sources is practicable on smallholder units, it is not easy to do so for cattle on range in pastoral areas. In such situations it is possible to achieve some success through the use of high protein browse and tree crops such as Sesbania, Leucaena, Gliricidia and Acacia species (Table 5). On smallholdings in the highlands, where feeding hay is practised, effort could be made to improve the quality of the hay by practising early cutting, although the problem here is to compromise quantity with quality. Since hay is now being marketed in Ethiopia, a degree of quality control could be achieved if analyses were carried out and a system of price premium for good quality was introduced. The high levels of ADF ash in most of the grasses indicates the presence of large amounts of silica which may seriously reduce digestibility (van Soest, 1982).

In relation to the essential mineral elements, the level of K in all the forages was above the level of 8 g/kg recommended for grazing animals (Underwood, 1981). It has, however, been suggested (McDowell, 1985) that weaned calves and high producing dairy cows under stress, such as heat stress, may require K level above 10 g/kg, but since only the straws of barley, teff and linseed approached this figure, it seems most unlikely that problems of K deficiency are likely to arise. The same conclusion appears valid for S, Fe and Mn, the contents of which in almost all the forages studied were above the levels of 1 g/kg, 50 mg/kg and 40 mg/kg respectively proposed as adequate for grazing animals (McDowell, 1985). The requirement for S is basically related to that for N and S-containing amino acids, such that the ARC (1980) suggested that an N:S ratio of 14:1 is indicative of adequacy of S; in this regard, all of the materials examined are satisfactory.

With reference to Na, there is some debate in the literature concerning the dietary concentration required. While Underwood (1981) recommended 1 g/kg for most grazing animals, the findings of Morris (1980) and Little (1987) indicate that 0.7 g/kg is adequate for non-lactating cattle, and the ARC (1980) suggested that a level of 1.4 g/kg is required by sheep. The present data show that with the exception of Sesbania, most of the materials examined were very poor sources of Na, such that routine supplementation is likely to be necessary. This characteristic of Sesbania has been recorded elsewhere in the tropics (Little, 1986).

While dietary Ca concentrations of 2-6 g/kg, with higher requirements for lactation have been variously recommended for cattle and sheep (NRC, 1978, 1984, 1985: ARC, 1980), the findings of Sykes and Field (1972) suggest that levels of 2.53.0 g/kg are adequate in most circumstances. The results indicate that problems of Ca deficiency would not be expected. It is still widely believed that a large excess of Ca over P. resulting in Ca:P ratios approximating 10 or more, is deleterious to ruminants, although much conflicting evidence occurs in the literature (reviewed by Little, 1970). In this context it is noteworthy that the ARC (1980) concluded that "...it is not possible to state the optimal ratio of calcium to phosphorus for animal performance or whether such a ratio actually exists." Where wide ratios occur, the dietary concentration of P per se is almost certain to be inadequate.

Underwood (1981) considered a dietary P level of 1.7 g/kg to be marginal for grazing animals, in essential agreement with work of Little (1980, 1985) which indicated that a figure of 1.4 g/kg should be regarded as minimal for growing cattle. The data in Tables 2 and 4 show that most grasses and crop residues examined were marginal to deficient in P. and supplementation with P is likely to be beneficial. For animals grazing on range, this would best be supplied through incorporation into complete mineral licks or in mixtures with common salt and bone meal. Animals on smallholder units, which may receive some concentrate feeds, may receive adequate P if offered high protein oilseed cakes such as cotton seed cake and noug cake.

McDowell et al (1978) considered 30 mg/kg to be a critical level of dietary Zn, although the ARC (1980) has suggested that concentrations of 12-20 mg/kg are adequate for growing cattle. The crop residues may thus constitute a marginal supply of Zn (Table 4); the necessity for supplementary Zn needs to be kept under review particularly for sheep, which require some 35 mg Zn/kg diet (ARC, 1980).

It is commonly accepted that the dietary requirement of cattle for Cu lies in the range 8-14 mg/kg (ARC, 1980; NRC, 1978, 1984). Clearly most of the materials examined will provide a marginal to deficient supply of this mineral. This situation may be even further complicated by high levels of dietary Fe which can be elevated by soil ingestion during grazing. Humpries et al. (1981) showed that dietary concentrations exceeding 1 g Fe/kg can profoundly reduce the availability of ingested Cu; relatively slight and doubtless common levels of dietary soil contamination can produce Fe concentrations of this order (Healy, 1973), necessitating the serious consideration of - supplying supplementary Cu. either by injectable preparations, oral dosing with copper oxide needles or providing mineral licks containing Cu. In this context it should be remembered that the Cu requirement of sheep is only about 5 mg/kg however, so that the provision of supplementary Cu to this species is much less likely to be required.

It should be stressed that data of the type presented here can provide only an indication of the existence of potential mineral deficiency problems, since animal selectivity usually results in the consumption of material of somewhat higher quality than that of the total available, and conclusive diagnosis must be based on the occurrence of a positive response to supplementary supply of the mineral in question. However, such data are vital in the formulation of critical supplementation experiments, upon which recommendations for practical supplementation regimes should be based.

Conclusion

The pasture and crop residues examined had very low crude protein contents, and for increased levels of animal production the primary need is for supplementary protein. The most appropriate means of providing this will vary with local circumstances; protein-rich oilseed cakes or urea-containing blocks are valuable sources where they are available. But there is great potential for encouraging the use of leguminous trees, as well as the establishment of forage legumes as crops or oversown in the pasture.

The minerals most widely present in inadequate amounts are Na, Cu and P. and supplementation regimes involving these elements are very likely to produce beneficial results. There is an urgent need for appropriate experimentation so that soundly-based supplementation packages can be devised.

References

ARC. 1980. The nutrient requirements of ruminant livestock. Commonwealth Agricultural Bureaux, Farnham Royal, U.K.

Cottenie, A., Veroo, M., Jiekens, L., Velgha, G. and Camerlynch, R. 1982. Chemical analysis of plants and soils. I.W.O.N., Ghent-Belgium.

FAO. 1985. Production yearbook 39. FAO, Rome.

Faye, B., Grillet, C. and Tessema, A. 1983. Report on survey of trace element status of forages and blood of domestic ruminants in Ethiopia. National Veterinary Institute, Debre Zeit, Ethiopia.

Goering, H.K. and van Soest, P.J. 1970. Forage fibre analysis, Agric. Handbook 379. Agricultural Research Service, USDA O ARS, Beltsville, MD.

Healy, W.B. 1973. Nutritional aspects of soil ingestion by grazing animals. In: G.W. Butler and R.W. Bailey (eds), Chemistry and biochemistry of herbage. Vol. 1. Academic Press, London. pp. 567-588.

Humpries, W.R., Young, B.W., Phillippo, M. and Bremner, I. 1981. The effects of iron and molybdenum on copper metabolism in cattle. Proceedings of the Nutrition Society 40:68A.

Little, D.A. 1970. Factors of importance in the phosphorus nutrition of beef cattle in northern Australia. Australian Veterinary Journal 46:241-248.

Little, D.A. 1980. Observations on the phosphorus requirement of cattle for growth. Research in Veterinary Science 28:258-260.

Little, D.A. 1985. The dietary mineral requirements of ruminants; implications for the utilization of tropical fibrous agricultural residues. In: P.T. Doyle (ed.), The utilization of fibrous agricultural residues as animal feeds. IDP, Canberra, Australia. pp. 34-43.

Little, D.A. 1986. The mineral content of mineral feeds and the potential for mineral supplementation in South-East Asia, with particular reference to Indonesia. In: Ruminant feeding systems utilizing fibrous agricultural residues, 1985. IDP, Canberra, Australia. pp. 77-86.

McDowell, L.R. 1985. Nutrition of grazing ruminants in warm climates. Academic Press, New York.

McDowell, L.R., Houser, R.H. and Fick, K.R. 1978. Iron, zinc and manganese in ruminant nutrition. In: J.R. Conrad and L.R. McDowell (eds), Latin American symposium on mineral nutrition research with grazing ruminants. University of Florida, Gainesville, Florida. pp. 108-116.

Miles, E.H. and McDowell, L.R. 1983. Mineral deficiencies in the Llanos rangelands of Colombia. World Animal Review 46:2-10.

Morris, J.G. 1980. Assessment of sodium requirements of grazing beef cattle: a review. Journal of Animal Science 50:145-152.

NRC. 1978. Nutrient requirements of domestic animals. Nutrient requirements of dairy cattle. 5th edition. National Academy of Sciences, Washington, D.C.

NRC. 1984. Nutrient requirements of domestic animals. Nutrient requirements of sheep. 6th edition. National Academy of Sciences, Washington, D.C.

NRC. 1985. Nutrient requirements of sheep. 6th edition. National Research Council, National Academy Press, Washington, D.C.

Sykes, A.R. and Field, A.C. 1972. Effects of dietary deficiencies of energy, protein and calcium on the pregnant ewe. I. Body composition and mineral content of the ewes. Journal of Agricultural Science (Cambridge) 78:109-117.

Underwood, E.J. 1981. The mineral nutrition of livestock. 2nd edition. Commonwealth Agricultural Bureau, London.

Van Soest, P.J. 1982. Nutritional ecology of the ruminant. O and B Books, Oregon.


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