Livestock Research for Rural Development 3 (2) 1991

Citation of this paper

Comparative rumen degradability of forages, browse, crop residues and agricultural by-products

O B Smith, O A Idowu, V O Asaolu and O Odunlami

Department of Animal Science, Obafemi Awolowo University, Ile Ife, Nigeria

Summary

In situ degradability experiments with forages, browse, crop residues and by-products in cattle, sheep and goats were carried out to assess nutritional value and potential use as feed. The 48hr dry matter degradability data suggest that many items available in large amounts in humid tropical Africa could be used as supplements to dry season forages of low nutritive value. Degradability ranged from medium for Leucaena and Gliricidia (68%), winged bean forage (65%) and green corn stover (68%) to high for cassava leaves (84%), cowpea husk (74%), foofoo residue (78%), plantain peels (74%), maize bran (81%), cassava peels (83%), yam peels (86%) and sweet potato peels (95%). Values for browse, crop residues and by-products were higher than those for 5 dry season forages (mean of 56%) and underline their potential nutritive value.

KEY WORDS: Rumen degradability, cattle, sheep, goats, crop residues, forage trees, browse, dry season grasses, byproducts, legumes

Introduction

The majority of ruminant animals in tropical Africa are raised on natural pastures which decline rapidly in quality during the dry season (Ademosun 1973). Changes in nutritional status result in very irregular growth and marked fluctuations in seasonal weights (Wilson 1987). Small-scale farmers cannot afford the investments required to establish improved pastures and feed concentrate supplements to alleviate dry season growth checks. From experience, and to a lesser extent from the extension of research results, small-scale farmers are increasingly relying on browse and on crop residues and by-products to supplement roadside grazing during the dry season. Some of these materials are potentially good feed resources which degrade readily in the rumen (Krishna 1985; Odunlami 1988). Others have shown poor degradability so that they may require some treatment before they can contribute to animal nutrition (Smith et al 1988).

There is, however, little information on the usefulness of the majority of these materials as feed resources. This study was designed to evaluate the potential nutritive value of browse plants, crop residues and by-products commonly fed to ruminants in the humid zone of Nigeria, using rumen degradability as a screening technique, in order to determine which materials can best be used in ruminant diets.

Table 1: Nutrient contents of Nigerian forages, browse, crop residues and by-products.
Common names

Dry matter (%)

Acid-detergent fibre(as % DM)

Crude protein (as % DM)

Forages      
Northern Gamba grass

24.6

44.5

9.6

Southern Gamba grass

25.6

45.6

7.9

Elephant grass

26.6

41.9

12.5

Stylo

30.5

58.7

9.5

Pueraria (kudzu)

21.3

51.3

16.5

Centro

30.1

--

--

Browse      
Oil palm leaves (with midrib)

43.4

48.5

17.0

Oil palm leaves (no midrib)

41.6

49.7

16.6

Plantain leaves

33.0

44.3

16.2

Leucaena

24.0

33.8

30.0

Gliricidia

23.5

29.4

28.4

Bamboo leaves

27.3

47.9

21.1

Cassava leaves

23.8

29.8

23.0

Ficus-1

22.0

36.8

18.0

Ficus-2

23.7

39.0

18.9

Crop residues/by-products      
Winged beans

--

44.1

26.3

Cocoa pod husk

42.5

59.1

8.0

Green corn stover

21.1

31.5

10.0

Mature corn stover

27.2

46.2

9.0

Cowpea husk

--

39.7

10.0

Foofoo residue

24.9

18.5

9.3

Corn bran (wet milled)

34.1

8.9

22.1

Yam peels

26.8

11.5

5.2

Plantain peels

26.0

31.8

7.7

Sweet potato peels

19.9

18.1

18.8

Rice bran

87.2

54.0

11.3

Cassava peels

--

15.9

4.8

Brewers dried grains

90.2

26.4

23.3

 

Materials and methods

Test materials

Test materials included herbaceous forages (3 grasses and 3 legumes), browse (9) and crop residues and by-products (13) (Table 1). All materials were collected during the dry season with the exception of winged bean and maize stover which were harvested during the growing period. All materials were dried at 70C to constant weight, ground through a 1 mm sieve and stored for subsequent analysis for acid-detergent fibre (Goering and van Soest 1970) and nitrogen (AOAC 1980).

Animals

Three Keteku cattle (150 kg initial weight), three West African Dwarf sheep (18 kg) and three West African Dwarf goats (12 kg) were fitted with rumen cannulae of 55 mm (cattle) or 40 mm (sheep and goats) internal diameter. During a 1 month recovery period, animals were dewormed (Panacur), sprayed against ectoparasites (Asuntol) and injected with a vitamin ADE preparation. They were provided a diet of Guinea grass (Panicum maximum), Gliricidia sepium and brewers grains ad libitum. A salt lick was permanently available.

Preliminary study

A preliminary dry matter degradability study was carried out to determine the optimum number of bags that could be inserted in the rumen. Gliricidia leaves were re-dried overnight in an oven at 70C and cooled in a desiccator. Samples were weighed into nylon filter cloth bags (195 mm x 105 mm, 40 pore size) each containing a marble. Sufficient bags were prepared to allow for a 10 d (cattle) or 12 d (sheep and goats) trial period. Dry matter degradability in 24 hr as well as the variability between bags in each animal were calculated and used to determine the optimum number of bags for subsequent incubation.

Main study

Test materials were re-dried to eliminate moisture absorbed during storage and 5 g (cattle) and 3 g (sheep and goats) of each weighed into nylon bags. Each of the 9 cannulated animals was provided with 1 bag of each material to give 3 replicates per sample. A total of 15 bags were incubated at a time in cattle, and 6 in sheep and goats. Bags were incubated for 48 hr, several runs being made to accommodate all 28 test materials. Materials incubated at any one run were chosen randomly. Bags were washed after withdrawal from the rumen and dried at 70C to constant weight. Dry matter losses and percentage dry matter degraded were calculated. About 100 ml rumen fluid was taken at the beginning, halfway and at the end of the trial from each animal prior to morning feeding. The pH was measured immediately on a sub-sample. The remaining sample, to which a few drops of concentrated hydrochloric acid were added, was filtered through 3 layers of cheese-cloth, centrifuged at 5000 rpm for 20 min at 10C and the supernatant analyzed for NH3-N (Preston and Leng 1987).

Statistical analyses

Dry matter degradability was analyzed within each class (forage, browse, crop residues) for feed type and animal species effects by 2-way analysis of variance (Steel and Torrie 1960). Differences between means were identified using Turkey's Omega test. A correlation analysis was also performed to examine the relationship between acid-detergent fibre content and degradability in the rumen.

Table 2: Mean squares from the analysis of variance for degradability of potential feeds in Nigeria
 

Feed type

 

Forage

Browse

Crop-residues

Source of variation

df

MS

df

MS

df

MS

Feed type (T)

4

430.2*

5

2971.5*

12

2627.1*

Animal species (S)

2

13.2

2

32.0

2

48.6*

T x S

8

18.3*

10

19.8

24

70.7*

             
Error

30

5.7

36

13.6

78

8.7

 

* P < 0.05

Results

Forages

The 3 ruminant species degraded the various forages to a similar (P > 0.05) extent (Table 2) with mean values of 55.1%, 54.8% and 56.6% ( 0.6% SE) for cattle, sheep and goats. Forage type, and forage type by animal species effects were significant. The variability observed for forage type (Table 3) seemed to be mainly due to differences in fibre content, as a high negative correlation coefficient (r = -0.93, P < 0.05) was obtained between acid-detergent fibre and dry matter degradability. Stylo, the least degraded, had the highest acid-detergent fibre content, while elephant grass, the best degraded, had the least. About 86% of the observed variation in forage dry matter degradability was due to fibre content (Table 4).

Browse

Dry matter degradability of browse was affected only by type; neither species nor species by browse type effects were significant (Table 2). Cassava leaves were the best (P < 0.05) degraded (84.3%), followed by Gliricidia and Leucaena which were degraded to the same extent but better (P < 0.05) than other browses except cassava leaves. The difference between the degradability of oil palm leaves with or without midribs was not significant. Bamboo leaves, with a low dry matter degradability of 36.6%, were the least (P < 0.05) degraded of all browses. As observed for forages, a high negative correlation coefficient (r= -0.94, P < 0.05) between acid-detergent fibre and dry matter degradability was obtained for browse, with fibre content accounting for about 88% of the variability.

Table 3: Mean dry matter degradability (48hr) of forages used in feeding trials in Nigeria

Forage

Dry matter degradability (%)

Acid-detergent fibre content (%)

Stylo

44.4a

58.7

Northern Gamba grass

55.6b

44.5

Pueraria

55.8b

51.3

Southern Gamba grass

58.6b

45.6

Elephant grass

63.1c

41.9

SE of mean

0.62

 

 

In the same column, values without a suffix letter in common differ (P < 0.05).

Table 4: Nylon bag dry matter degradability (48hr) of forages fed to ruminants in Nigeria
 

Ruminant species

Forage

Cattle

Sheep

Goats

Northern Gamba grass

54.5a

55.0a

57.4a

Southern Gamba grass

59.0ab

60.5a

56.3a

Elephant grass

64.9b

61.0ab

63.5ab

Stylo

41.9c

42.0c

49.2b

Pueraria

55.2a

55.6a

56.5a

SE

0.44

0.44

0.44

 

In the same column, and along rows, values without a suffix letter in common differ (P<0.05).

 

Crop residues and by-products

Animal species, residue type and the interaction between the two significantly affected dry matter degradability of crop residues and by-products (Table 2). Cocoa pods and rice bran had similar degradabilities and were the least degraded (P < 0.05) of all residues. Sweet potato peels had the highest degradability. The other residues can be grouped into 4 lots of decreasing degradability: corn bran, cassava peels and yam peels (80% to 86%); plantain peels, cowpea husk and foofoo residue (74% to 78%); green corn stover and winged bean forage (65% to 68%); and mature corn stover and brewers dried grains (56% to 58%).

An examination of species by crop residue type degradability (Table 5) shows that goats degraded foofoo residue and cassava peels better than both cattle and sheep, while sheep degraded winged bean forage better than both cattle and goats. Cattle degraded yam peels and brewers grains better than goats and sheep.

Table 5: Nylon bag dry matter degradability (48hr) of crop residues and by-products by ruminants in Nigeria
Residues

Cattle

Sheep

Goats

Winged bean forage

60.1a

71.7b

63.0a

Cocoa pod

35.5b

38.0b

41.9b

Green corn stover

70.3c

67.3c

65.1c

Mature corn stover

56.7a

55.2a

56.7a

Cowpea husk

71.9c

76.3c

73.3c

Foofoo residue

75.4c

76.0c

83.7d

Corn bran

77.2c

81.7c

83.5c

Yam peels

90.3d

81.7c

83.9c

Plantain peels

74.4c

72.0c

74.6c

Sweet potato peels

94.1d

93.1d

96.7d

Rice bran

43.4b

38.7b

37.0b

Cassava peels

82.3c

76.3c

90.2d

Brewers dried grains

71.1c

50.8a

52.9a

SE

2.1

2.1

2.1

 

In the same column, and along rows, values without a suffix letter in common differ (P < 0.05).

 

Crop residues and by-products had lower fibre (31.2%) than the other types of feed but fibre content still accounted for 76% of the variability in dry matter degradability.

Mean rumen pH during the trial was 7.1, 7.2 and 6.8 for cattle, sheep and goats. Levels of NH3-N were 33.0 mg/100 ml rumen fluid, 27.7 mg/100 ml and 29.0 mg/100 ml for the 3 species.

Discussion

Using the combined criteria of degradability and variation between bags, it was clear from the preliminary study that up to 25 bags in small tropical cattle, 7 bags in goats and 8 in sheep could be used without an appreciable reduction in degradability or extensive variability between bags. When more than 15 bags in cattle or 6 bags in sheep and goats were incubated, removal became difficult when using 55 mm cannulae for cattle and 40 mm ones for sheep and goats. If these diameters are used, it is recommended that 15 and 6 bags in the respective species not be exceeded.

It has been suggested that materials incubated in sacco should first be incorporated in the diet, in order to adjust the rumen microbes to the materials and ensure optimum degradability. It was not possible to follow this procedure because of the large number of materials tested but, as pointed out elsewhere, it is more important that the diet be similar to the materials being tested (Orskov 1982) as was achieved in this study. By a judicious choice of diet in the present study, a rumen ecosystem (pH and rumen NH3-N level) that ensured optimum conditions for fibre degradability was maintained (Preston and Leng 1987).

Data analyses and comparisons were limited to within, rather than across, material class because of the wide variation among the test materials. Degradability of forages thus ranged from 44% to 63% with a mean of 56%. The range (37% to 84%) and mean (58%) for browses and crop residues (39% to 95%; 69%) suggest that during the dry season, because of high cell wall contents, forage quality is too low to sustain animals and a balanced selection of browse and crop residues for use as supplements may increase productivity. Crop residues and by-products were well degraded with the exception of rice bran, brewers dried grains, mature corn stover and cocoa pods, which have also been shown to be poorly degraded in other studies (Krishna 1985; Smith et al 1988). Of particular interest are cassava and maize by-products. These two plants are widely cultivated in the humid zone of West Africa, and by-products and residues are available in large amounts. Recent studies (Odunlami 1988) suggest that these materials degrade quite rapidly and that the energy released may not be synchronised with the rate of degradability of the basal forage or browse diets available. For maximum benefit maize and cassava products may have to be fed 2 or 3 times a day, starting in the afternoon with animals that have grazed all morning. Alternatively, they can be fed with non-protein nitrogen sources that can match their rapid degradability.

Removal of oil palm midrib may not be necessary, as degradability with or without it is similar. Bamboo leaves may have been poorly degraded because of a high tannin content but further studies are needed to confirm this and to evaluate rumen by-pass potential. Both Gliricidia and Leucaena were well degraded as reported earlier (Minor and Hovell 1979; Kabaija 1985). The often stated superiority of goats over sheep and cattle in terms of fibre digestibility (Devendra 1986) was not confirmed in this study.

The results obtained indicate that a wide variety of browse species, crop residues and by-products have high nutritional value. These materials will be particularly useful as supplementary feeds during the dry season when forage quality is low. The in situ dry matter degradability values obtained will be useful in identifying the best materials for use in practical ruminant diets.

Acknowledgements

This study was jointly financed by the International Foundation for Science and the Obafemi Awolowo University, Nigeria.

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