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The potential of Russian comfrey (Symphytum officinale) as an animal feedstuff in Uganda

F B Bareeba, W O Odwongo and J S Mugerwa

Department of Animal Science
Faculty of Agriculture and Forestry
Makerere University
PO Box 7062, Kampala, Uganda

ABSTRACT

A trial was established at the Makerere University farm, Kabanyolo, Uganda, to study the growth characteristics, dry-matter yield and nutrient composition of Russian comfrey (Symphytum officinale) to assess its potential for livestock feeding in Uganda.

Dry-matter (DM) yields increased from about 2 t/ha at eight weeks of growth to 3 t/ha at 12 weeks of growth Yields of 2-3 t DM/ha were sustained during four, five and six weeks of regrowth. Crude-protein (CP) production increased steadily from 344 kg/ha at eight weeks to 517 kg/ha at 12 weeks of growth. However, CP content remained constant at about 16% at all cuttings. This is comparable to CP values of good to medium quality forage legumes, but is higher than observed in most pasture grasses. Both macro- and micro-mineral contents of the plants were higher at all cuttings than normally observed in most Ugandan fodder plants. Amino acid analyses indicated that the protein quality of comfrey is comparable to that of good quality alfalfa leaf meal, but higher than that of Amaranthus leaf meal.

Russian comfrey thus has potential as a complement to forage legumes, grasses and crop residues for sustainable animal production in Uganda.

RESUME

Evaluation de la consaude voyageuse (Symphytum officinale) en vue de l'alimentation du bétail en Ouganda

Un essai a été réalisé à la ferme expérimentale de l'Université Makerere à Kabanyolo (Ouganda) pour étudier la croissance, la production de matière sèche et la teneur en éléments nutritifs de la consoude voyageuse (Symphytum officinale) en vue de son introduction dans l'alimentation du bétail en Ouganda

La production de matière sèche, qui était d'environ 2 t/ha à 8 semaines, passait à 3 t/ha à 12 semaines puis allait de 2 à 3 t/ha après 4, 5 et 6 semaines de repousse. Quant à la production de protéines brutes, elle augmentait régulièrement de 344 kg/ha à 8 semaines à 517 kg/ha à 12 semaines. Toutefois, la teneur en protéines brutes demeurait constante, s'établissant toujours autour de 16%. Ce taux est comparable à ceux enregistrés pour les légumineuses fourragères de bonne qualité ou de qualité moyenne, mais supérieur à ceux rapportés pour la plupart des parcours de graminées. En ce qui concerne les analyses minérales macroscopiques et microscopiques, les chiffres enregistrés étaient plus élevés que les valeurs correspondantes rapportées sur la plupart des plantes fourragères rencontrées en Ouganda. Enfin, une analyse des acides aminés a montré que du point de vue qualitatif, les protéines de la consoude voyageuse étaient comparables à celles des feuilles de la luzerne mais supérieures à celles des feuilles de l'amarante.

La consaude voyageuse peut donc être utilisée comme complément des légumineuses fourragères, des graminées et des résidus de récolte en vue d'une production soutenue des animaux d'élevage en Ouganda.

INTRODUCTION

The majority of ruminant animals in Uganda depend wholly on grazing unimproved natural pastures. These pastures are dominated by coarse and stemmy grasses with low dry-matter yield and nutritive value. Hence animal production is limited from such pastures. Very little attention has been given to the development of suitable forage species and/or establishment of pastures capable of sustaining high levels of animal productivity.

Cultivated comfrey (Symphytum officinale), often referred to as Russian or Quaker comfrey, was introduced in Uganda in the 1950s. It is a perennial herb with the arrangement of stems and leaves similar to that of the tobacco plant. The root system of a well-established comfrey plant is fleshy and extensive. The plant is semi-sterile and is propagated vegetatively mainly through root cuttings and root offsets.

Once comfrey plants are well established, plenty of vegetative material can be harvested by cutting several times during the year; the plants regenerate quickly because of the large food reserves in the roots. Comfrey could become a major source of fresh herbage for most of the year in Uganda where there is plenty of sunshine and rainfall. Comfrey is also the only known land plant that extracts vitamin B12 from the soil (Odwongo et al, 1987). It also contains alantoin which is used by herbalists for treating digestive disorders. However, comfrey contains at least eight pyrrolizidine alkaloids which cause acute necrosis of liver and lungs in cattle and horses (Culvenor et al, 1980). Administration of comfrey pyrrolizidine alkaloids to rats resulted in mortality and liver damage (Culvenor et al, 1980).

Because little is known in Uganda about the agronomy and nutritive value of comfrey, a study was carried out to study its growth characteristics and nutrient composition.

MATERIALS AND METHODS

The study was conducted at Makerere University Research Institute, Kabanyolo, 19 km north of Kampala (0° 28' N. 32° 37' E; altitude 1200 m). The upland soils of Kabanyolo are classified as ferralitic soils. The area has a moist tropical climate with mean maximum temperatures varying from 28.5°C in January to 26.0°C in July and minimum temperatures ranging from 17.4°C in April to 15.9°C in July. Mean annual rainfall is about 1300 mm, with peaks in April and November and two periods of low rainfall in January and July when the monthly mean drops to 60 mm.

Russian comfrey was planted as offsets with 8 cm of cut root buried into the ground at a spacing of 1 x 1 m in a 0.2-ha plot. Weeding was carried out every three weeks after planting.

Comfrey was harvested at weekly intervals from eight to 12 weeks after planting. (Harvesting was stopped at 12 weeks of growth because the plants had become very coarse. They were also heavily infested with blight caused by Cladosporium sp, indicating that bacterial blight is potentially a major disease of comfrey in Uganda.) Regrowth materials were harvested after four, five and six weeks of regrowth. For each harvest, 12 plants were randomly selected from each quarter of the field, cut about 2.5 cm above ground, weighed and subsampled. The subsamples were dried to constant weight in an air-draught oven at 65°C and then ground through a 1-mm sieve for chemical analysis (AOAC, 1980). Amino acid profiles were determined by high performance liquid chromatography (Waters/Millipore). Minerals were assayed by atomic absorption spectrophotometry.

RESULTS AND DISCUSSION

Dry-matter (DM) and crude-protein (CP) yields of the comfrey plants are shown in Table 1. These DM yields are lower than that obtained from a comfrey field planted at a spacing of 0.9 x 0.9 m in Kenya - a total of about 40 t/ha from 12 monthly harvests, equivalent to a monthly yield of 3.4 t/ha (Anon, 1960). The differences in the yields may be due to variations in spacing, soil fertility, stage of plant establishment and plant variety. Most of these factors remain to be defined for comfrey production in Uganda.

There was a steady increase in CP yield during both growth and regrowth (Table 1), but CP content stayed constant at about 16%. This is comparable to CP values of good to medium quality forage legumes but higher than for most pasture grasses (Soneji et al, 1971; Sabiiti and Mugerwa, 1990).

Table 1. Russian comfrey dry-matter and crude-protein yields and contents during cutting trials

Cutting time

Dry matter

Crude protein

Yield (t/ha)

Content (%)

Yield (kg/ha)

Content (%DM)

Weeks of growth

8

2.11

13.74

343.93

16.30

9

2.48

13.27

409.94

16.53

10

2.60

12.89

440.70

16.95

11

3.64

14.96

591.86

16.26

12

3.34

14.44

516.70

15.47

Weeks of regrowth

4

2.06

12.87

339.49

16.48

5

2.88

12.38

419.04

14.55

6

2.58

12.48

408.67

15.84

During all harvests, the comfrey plants had higher contents of both macro-and micro-minerals (Table 2) than are usually observed in many fodder crops (Kabaija and Smith, 1988). Similar results have been reported from studies in Britain and New Zealand (Anon, 1960). The potassium content is very high, which may indicate that comfrey plants have a high requirement for potash fertiliser. However, Hart (1972) attributed the high potassium content of comfrey plants to soil clinging to the hairy leaves during harvest. It was not possible to estimate the contribution of such contamination to the values observed in the present study.

Table 2. Mineral content of Russian comfrey during cutting trials

Cutting time

Content (%DM)

Calcium

Phosphorus

Potassium

Magnesium

Iron

Copper

Sulphur

Weeks of growth

8

1.94

0.51

8.07

0.41

0.27

0.0019

0.26

9

1.90

0.44

7.11

0.45

0.45

0.0021

0.23

10

1.95

0.45

6.47

0.42

0.42

0.0017

0.23

11

1.86

0.45

7.03

0.45

0.45

0.0016

0.22

12

1.56

0.41

6.11

0.38

0.38

0.0016

0.21

Weds of regrowth

4

1.80

0.48

7.00

0.39

0.39

0.0018

0.22

5

1.90

0.43

7.40

0.40

0.39

0.0018

0.22

6

2.24

0.45

6.90

0.55

0.55

0.0012

0.22

Table 3. Amino acid profiles of Russian comfrey during cutting trials a

Amino acid

Content (%DM)

Weeks of growth

Weeks of regrowth

8

9

10

12

4

5

6

Mean

Alanine

1.30

1.22

1.44

1.21

1.16

0.85

0.84

1.15

Arginine

1.13

0.99

0.95

0.90

0.94

0.64

0.57

0.87

Asparagine

1.95

1.95

-

1.85

1.94

1.59

1.74

1.84

Glutamine

2.09

1.86

1.92

2.17

2.38

1.95

2.26

2.09

Glycine

1.17

1.13

1.15

1.03

1.10

0.84

0.50

0.99

Histidine

-

-

-

0.30

0.28

0.23

0.23

0.26

Isoleucine

-

-

-

-

0.86

0.88

0.60

0.78

Leucine

-

-

-

0.86

1.38

1.12

0.98

1.09

Lysine

-

-

-

-

0.63

-

0.54

0.59

Proline

0.99

0.95

1.00

0.90

1.01

0.87

0.89

0.94

Phenylalanine

-

-

-

-

0.96

0.74

0.65

0.79

Serine

0.85

0.80

0.82

0.75

0.79

0.65

0.59

0.75

Threonine

0.95

0.92

0.90

0.75

0.84

0.65

0.57

0.80

Tyrosine

-

-

-

0.58

0.66

0.63

0.50

0.59

Valine

1.33

1.23

1.26

1.07

1.10

0.83

0.79

1.09

a Assays for methionine and tryptophane are not available

Amino acid profiles of comfrey are shown in Table 3. Amino acid content tends to decrease as the plants mature. A comparison of essential amino acid profiles (Table 4) indicates that the protein quality of comfrey is comparable to that of good quality alfalfa but higher than that of Amaranthus leaf meal. These observations need to be confirmed through direct animal studies.

CONCLUSIONS

The results of this study suggest that comfrey could provide average monthly yields of 2 t DM/ha, containing over 300 kg high quality crude protein and high levels of minerals. It would therefore be worthwhile investing in comfrey production for livestock feeding because these yields are higher than those of most forage legumes and grasses available in Uganda.

Table 4. Comparison of essential amino acid profile of egg (standard protein) with those of leaf meals of Russian comfrey, Amaranthus hybridus and alfalfa a

Amino acid

Amino acids as % crude protein

% deficiency compared with egg protein

Egg protein

Amaranthus (29% CP)

Alfalfa (23% CP)

Comfrey (16% CP)

Amaranthus

Alfalfa

Comfrey

Arginine

6.60

5.86

5.65

5.44

11.2

14.4

17.6

Histidine

2.40

1.45

1.74

1.63

39.6

275

32.1

Isoleucine

6.60

2.79

4.35

4.88

57.7

34.1

26.1

Leucine

8.80

5.45

6.52

6.81

38.1

25.9

22.6

Lysine

6.60

4.03

4.78

3.69

38.9

27.6

44.1

Phenylalanine

5.80

3.69

4.35

4.94

36.4

25.0

14.8

Threonine

5.00

3.82

3.48

5.00

23.6

30.4

0.0

Valine

7.40

3.52

4.78

6.81

52.4

35.4

8.0

a Assays for methionine and tryptophane of comfrey are not available

Sources: Amino acid profiles: egg protein and alfalfa leaf meal, NRC (1982); Amaranthus leaf meal, Olaboro (1975)

REFERENCES

Anon. 1960. Comfrey report. The story of the world's fastest protein builder. Ministry Of Agriculture, Nairobi, Kenya. 15 pp.

AOAC (Association of Official Analytical Chemists). 1980. Official methods of analysis. 13th edition. AOAC, Washington, DC, USA. 1018 pp.

Culvenor C C J. Clarke M, Edgar J A, Frahn J L, Jago M V, Peterson J E and Smith L W. 1980. Structure and toxicity of the alkaloids of Russian comfrey, a medicinal herb and item of the human diet. Experientia 36:377.

Hart R H. 1972. Comfrey yields and forage value. United States Department of Agriculture, Plant Physiology Institute, Beltsville, Maryland, USA. 21 pp.

Kabaija E and Smith O B. 1988. Effect of season, fertilizer application and age of regrowth on mineral content of guinea grass (Panicum maximum Schum) and giant star grass (Cynodon nlemfuensis Chedda). In: Dzowela B H (ed), African forage plant genetic resources, evaluation of forage germplasm and extensive livestock production systems. Proceedings of the third workshop held at the International Conference Centre, Arusha, Tanzania, 27-30 April 1987. PANESA (Pasture Network for Eastern and Southern Africa). ILCA (International Livestock Centre for Africa), Addis Ababa, Ethiopia. pp. 458-467.

NRC (National Research Council). 1982. United States-Canadian tables of feed composition. National Academy Press, Washington, DC, USA. 150 pp.

Odwongo W O. Bareeba F B and Mugerwa J S. 1987. The potential of Russian comfrey as a feedstuff in Uganda. In: Sabiiti E N and Henderlong P (eds), Proceedings of the first Uganda Pasture Network workshop. Makerere University, Uganda. pp. 30-40.

Olaboro G. 1975. Amaranthus leaf meal as a protein source in diets for broiler chick. MSc Thesis. Makerere University, Kampala, Uganda. 71 pp.

Sabiiti E N and Mugerwa J S. 1990. Forage research and development for livestock production in Uganda. In: Dzowela B H. Said A N. Asrat Wendem-Agenehu and Kategile J A (eds), Utilization of research results on forage and agricultural by-product materials as animal feed resources in Africa Proceedings of the first joint workshop held in Lilongwe Malawi, 5-9 December 1988. PANESA/ARNAB (Pasture Network for Eastern and Southern Africa/African Research Network for Agricultural By-products). ILCA (International Livestock Centre for Africa), Addis Ababa, Ethiopia. pp. 186-206.

Soneji S V, Musangi R S and Olsen F J. 1971. Digestibility and feed intake investigations at different stages of growth of Bracharia ruziziensis, Chloris gayana and Setaria sphacelata. East African Agricultural and Forestry Journal 37:125


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