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Rumen degradation of elephant grass supplemented with graded levels of perennial peanut by West African Dwarf sheep

B. Tchinda, D. Wegad and R. M. Njwe

Department of Animal Production INADER, Dechang University Centre, Cameroon


Abstract
Introduction
Materials and methods
Statistical analysis
Results and discussions
Conclusion
References


Abstract

The effect of 0, 10, 20 and 30 per cent supplementation of elephant grass (Pennisetum purpureum) with perennial peanut (Arachis glabrata) on rumen degradability of dry matter was investigated in a factorial trial involving 4 treatments, 5 incubation periods, 3 animals and 2 nylon-bag samples per animal per incubation period. Three rumen-fistulated West African Dwarf ewes of 24 months of age and weighing an average of 18 kg were used. Samples were incubated in the rumen of sheep for 6, 12, 24, 48 and 72 hours.

Dry and organic-matter degradation (DM and OM) increased significantly (P<0.05) when the legume fraction in the ration was raised from 0 to 20 per cent. Further increase in legume fraction to 30% of the ration did not result in significant increases in DM and OM degradability. There was also a significant (P<0.05) increase in DM and OM degradability of all rations when incubation time in the rumen was increased from 6 to 48 hours. Degradability of DM was 34% for elephant grass alone and 42,43 and 46%, respectively, for rations containing 10,20 and 30 percent legume after 48 hours' incubation. After 72 hours' incubation, there was no significant increase in DM and OM degradability.

The estimates of the immediate soluble fraction (a) and the rate of degradability © increased with increase in the level of legume in the ration. The lag time necessary for the microbial population to invade the feed also reduced as the level of legume in the diet was raised.

Dégradation de l'herbe à éléphant complémentée avec niveaux croissants de fourrage d'arachide pérenne dans le rumen de moutons de la race naine d'Afrique de l'Ouest

Résumé

L'effet de la complémentation de 0, 10, 20, ou 30% d'herbe à éléphant (Pennisetum purpureum) avec du fourrage d'arachide pérenne (Arachis glabrata) sur la dégradabilité dans le rumen a été étudié dans une expérience factorielle avec quatre traitements, cinq périodes d'incubation, trois animaux et deux échantillons dans des sacs en plastique par animal et par période. Trois brebis de la race naine d'Afrique occidentale dont le rumen a été fistulé, âgées de 24 mois et pesant en moyenne 18 kg ont été utilisées. Les échantillons ont été incubés dans leur rumen pendant 6, 12, 24, 48, et 72 heures.

La dégradation de la matière sèche et de la matière organique augmentait significativement (P<O,OS) avec l'accroissement de la proportion de légumineuse de la ration de O à 20%. L'augmentation de cette proportion à 30% n'entraînait aucun accroissement significatif de la dégradabilité de la matière sèche et de la matière organique. Toutefois, celle-ci augmentait significativement (P<O,OS) dans toutes les rations lorsque le temps d'incubation passait de 6 à 48 heures. Après 48 heures d'incubation, la dégradabilité de la matière sèche était de 34% pour l'herbe à éléphant seule puis de 42, 43 et 46% pour les rations contenant respectivement 10,20 et 30% de légumineuse. Après 72 heures d'incubation, il n'y avait pas d'augmentation significative de la dégradabilité de la matière sèche et de la matière organique.

Le taux de la fraction immédiatement soluble (a) et la dégradabilité © augmentaient avec l'accroissement de la proportion de légumineuse dans la ration. Enfin, le temps nécessaire pour permettre à la flore microbienne d'envahir les aliments diminuait avec l'augmentation de la proportion de légumineuse dans la ration.

Introduction

The most widely available low-cost feeds for ruminants in most tropical countries are usually native pasture, crop residues and, to a lesser extent, agro-industrial by-products. Legumes in the farming system may constitute an important feed resource of fermentable nitrogen and of by-pass protein. When fed to ruminants, legumes tend to increase the efficiency of utilisation of the basal diet, which is usually a low nitrogen pasture or a crop residue, at low levels of supplementation. Legume supplements given at levels below 30 per cent of dietary dry matter have a catalytic effect on feed utilisation. They ensure a more efficient environment for digestion of cell-wall carbohydrates, perhaps by providing micronutrients such as peptides, amino acids, minerals and vitamins which increase fungal biomass and/or the rate of bacterial colonisation of the fibre. The potential of the diet to meet the requirements of the animal for amino acids, glucogenic precursors and long chain fatty acid depends on the pattern of fermentation and on dietary protein lipids and starch that escape fermentation and are digested in the intestines. The extent to which the protein in a supplement escapes the rumen is partly a function of its rate of degradation in the rumen (Preston and Leng, 1987). The objective of this trial was to study the effect of graded levels of perennial peanut (PP) supplement fed with elephant grass (KG) on the degradability of dry and organic matter by West African Dwarf sheep.

Materials and methods

Three female West African Dwarf sheep fitted with rumen cannulae were used for the study. Their average age and body weight were 24 months and 18 kg, respectively. The animals were fed four experimental rations consisting of fresh EG (Pennisetum purpureum) only, or supplemented with PP (Arachis glabrata, ax-Florida) at 10, 20 and 30 per cent.

Table 1. Composition (%) of dried forages used in constituting rations incubated in the rumen.

Proximate components

PP

EG

Dry matter

92.03

92.10

Organic matter

86.18

86.25

Crude protein

17.80

12.50

Crude fibre

22.13

32.50

Ash

3.82

13.75

Table 2. Composition of experimental diets incubated in the rumen of sheep.

Proximate components

EG:PP ratio

100:00

90:10

80:20

70:30

Dry matter

92.10

92.06

92.04

92.05

Organic matter

86.25

86.20

86.19

86.20

Crude protein

12.50

13.03

13.57

14.11

Crude fibre

32.50

31.35

30.10

29.22

Ash

13.75

13.80

13.79

13.80

Fresh EG and PP were dried in a forced air laboratory oven at 60°C for 48 hours, milled separately to pass through a 2 mm screen, and mixed in the following gramineae/legume proportions, 100:0, 90: 10, 80:20 and 70:30. Four grams of ration was placed in a nylon bag (11 x 7 cm, 20 micron porosity) and sealed. The composition of KG, PP and their combinations incubated in the rumen are shown in Tables 1 and 2, respectively. The method of incubation in the rumen of sheep was as described by Ørskov et al (1980). Nylon bags were incubated in the rumen for 6, 12, 24, 48 and 72 hours after which they were withdrawn and washed in cold water for 25 minutes and dried to constant weight at 60°C in a forced air laboratory oven and weighed. Six nylon bags containing samples of each ration were soaked in water for 30 minutes and washed in the same manner and dried to constant weight.

The difference in weight of dry matter in nylon bag before and after rumen incubation represented material degraded in the rumen. Similarly, the difference in organic matter weight before and after incubation was equivalent to OM degraded in the rumen.

The degradation characteristics of each ration were described using the following exponential equation (Ørskov and McDonald, 1979),

P=a+b(1-e-ct)

where a, b and c are constants

a = intercept or immediate soluble fraction
b = insoluble but potentially degradable material at time t
c = rate of degradation per hour
P = level of degradation at time t

Statistical analysis

The experiment was a 4 x 5 x 3 x 2 factorial design (4 rations, 5 incubation intervals, 3 sheep and 2 nylon bags per animal per incubation period). Statistical analysis was carried out according to the procedures of Snedecor and Cochran (1976) for analysis of variance. The Duncan's multiple range test was used to test significant differences between treatments.

Results and discussions

The degradation of dry matter of the rations (Table 3) increased significantly (P<0.05) as a result of supplementation of EG with PP. Total dry matter degraded increased from 56.75% in the ration consisting of EG only to 69.47% in the 30% PP ration.

These results confirm findings by Mosi and Butterworth (1983) that the addition of 30% legume forage to a grass basal diet increased total dry matter degradability from 40-50% to 60%.

A comparison of DM degradation of the three rations containing legume supplement after 6 and 12 hours' incubation in the rumen indicated a significant difference (P<0.05) between the rations containing 10 and 20% legume; but no significant difference between those having 20 and 30% legume. DM disappearance was similar for all rations having legume supplement at 24,48 and 72 hours of incubation.

After 72 hours of rumen incubation more than 57 per cent of potentially degradable amount of DM in the control ration had disappeared, whereas for the rations containing legume more than 70 per cent had disappeared.

OM degradation in all rations is shown in Table 4. After 12, 24, 48 and 72 hours of rumen incubation all rations with legume supplement had significantly (P<0.05) higher OM degradation than EG alone.

Table 3. Effect of level of supplementation on dry-matter loss in the rumen of sheep (g/100g DM).

Treatment PP

Washing loss (g/100g DM)

Incubation period (hours)

a

b

c

Residual mean sq.

a+b

Time lag

Supplementation rate

6

12

24

48

72

0%

7.20

2.08

3.75

9.83

29.09

30.46

2.06

51.25

0.0182

18.76

53.03

5.79

10%

7.90

6.18

8.36

20.20

36.63

39.52

4.64

52.14

0.261

9.46

56.78

2.47

20%

8.00

12.21

14.97

25.31

37.16

40.70

12.47

42.56

0.0281

3.00

55.03

0.00

30%

10.00

12.54

20.88

23.76

38.08

40.17

17.31

38.57

0.0286

9.08

55.88

0.00

NB: a, b and c are constants in the equation P=a+b(1-e-ct) where P is the level of degradation at time t; a is the intercept or immediately soluble fraction; b is the insoluble but potentially degradable fraction et time t; c is the rate of degradation per hour while a+b is the maximum degradable fraction (assymptote).

Table 4. Effect of level of supplementation on organic-matter loss in the rumen of sheep (g/100g DM).

Treatment PP

Washing loss (g/100g DM)

Incubation period (hours)

a

b

c

Residual mean sq.

a+b

Time lag

Supplementation rate

6

12

24

48

72

0%

8.46

2.48

4.43

11.65

34.18

35.68

2.43

59.62

0.0185

25.83

62.05

5.75

10%

9.33

7.27

9.80

23.65

42.18

46.30

5.89

61.05

0.253

10.87

66.94

2.29

20%

10.29

13.44

18.60

28.75

42.77

46.83

15.63

48.39

0.0286

1.84

64.01

0.00

30%

11.75

13.46

21.17

27.85

45.53

46.90

17.00

48.30

0.0308

9.42

65.30

0.00

NB: a, b and c are constants in the equation P=a+b(1-e-ct) where P is the level of degradation at time t; a is the intercept or immediately soluble fraction; b is the insoluble but potentially degradable fraction at time t; c is the rate of degradation per hour while a+b is the maximum degradable fraction (assymptote).

OM degradation attained a maximum increased value of 13 per cent especially with the ration containing 30% PP. Similar results were reported by Dixon et al. (1979) when supplements of Leucaena leucocephala and rice polishing were fed with sisal pulp to cattle. This was associated with increased microbial synthesis.

There was no significant difference between the OM degradation of the control ration and the one containing 10 per cent legume after 6 hours of rumen incubation. Similarly' there was no significant improvement in OM disappearance in the rumen when the level of legume supplement in the ration was raised from 20 to 30 per cent. A significant improvement in OM degradation was evident after 24 and 48 hours incubation of feed samples in the rumen. Extending incubation time to 72 hours did not result in a significant increase in OM degradation.

It was also observed that estimated maximum potential degradable OM in the rations increased with increase in the level of legume supplement in the ration. After 72 hours of rumen incubation 58% of maximum degradable amount of EG organic matter in the control ration had disappeared whereas for the other treatments more than 69% had been degraded.

In the present study supplementation of EG with graded levels of legume resulted in an increase in the rate of DM and OM degradation in the rumen. For DM it increased from 0.0182 to 0.0286 per cent per hour as the level of legume in the ration was raised from 0 to 30 per cent, whereas for OM it increased from 0.0185 to 0.0308 per cent per hour. Also, it was observed that as the level of legume in the diet was raised there was a reduction in the lag time necessary for the microbial population to attack the feed.

Conclusion

It may be concluded from this study that inclusion of PP in the diet of sheep fed EG up to a level of 20 per cent results in a significant improvement in DM and OM degradation in the rumen.

References

Dixon R M, Priego A, Eliot R and Preston T R. 1979. Studies on the digestion in the forestomachs of cattle of a diet based on sisal pulp supplemented with Leucaena leucocephala and rice polishings. Tropical Animal Production 4(3):281-286.

Mosi A K and Butterworth M H. 1983. Utilisation de Trifolium tembense pour compléter les rations des ruminants abase des résidus agricoles. CIPEA actualités 2(4):5-6 CIPEA (Centre international pour l'élevage en Afrique), Addis-Abeba (Ethiopia).

Ørskov E R and McDonald L 1979. The estimation of protein degradability in the rumen from incubation measurements weighted according to rate of passage. Journal of Agricultural Science (Cambridge) 92:499-503.

Ørskov E R. Hovell E D de B and Mould F. 1980. The use of the nylon bag technique for the evaluation of feedstuffs Tropical Animal Production 5:195-213.

Preston T R and Leng R A. 1987. Matching ruminant production systems with available resources in the tropics and sub-tropics. Penambul Books, Armidale, Australia. 245 pp.

Snedecor E W and Cochran W G. 1976. Statistical methods. Sixth edition. Iowa State University Press, Ames, Iowa, USA.


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