O.B. Smith, O.A. Idowu, V.O. Asaoluand
O. Odunlami
Department of Animal Science
Obafemi Awolowo University
Ile Ife
Nigeria
Summary
Resume
Introduction
Materials and methods
Results
Discussion
Acknowledgements
References
In situ degradability experiments of 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 48 hr dry matter degradability obtained suggests that many items available in large amounts in humid tropical Africa could be used as supplements to poor quality dry season forages. 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 byproducts were higher than those for 5 dry season forages (mean of 56%) and underline their potential nutritive value.
La dégradabilité in situ des fourrages, pâturages aériens, résidues de culture et sous-produits agricoles fut déterminée pour estimer la valeur nutritive et les possibilités de les incorporer dans les rations animales. La dégradabilité de la matière sèche en 48 h obtenue suggère que beaucoup de produits disponibles en Afrique humide tropicale pourraient être utilisés en saison sèche pour complémenter des fourrages de mauvaise qualité. La dégradabilité était moyenne pour les pâturages aériens tels le Leucaena et le Gliricidia (68 p.cent), le Phosphocarpus (65 p.cent) ou les résidus de culture comme les tiges vertes de maïs (68 p.cent). Pour d'autres aliments, tels les feuilles de manioc (84 p.cent), les corses de niébé (74 p.cent), les résidus de foufou (78 p.cent), les épluchures de plantain (74 p.cent), le son de maïs (81 p.cent), les épluchures de manioc (83 p.cent), d'igname (86 p.cent) et de patate douce (95 p.cent), la dégradabilité était bonne. Ces valeurs sont plus élevées que celles de 5 fourrages normalement utilisés en saison sèche et soulignent la valeur nutritive potentielle.
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 (Figure 1) 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, which are produced in large amounts during the dry season, 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 byproducts 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.
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 70°C 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 each Keteku cattle (150 kg initial weight), West African Dwarf sheep (18 kg) and 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 mo 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 spent grains ad libitum. A salt lick was permanently available.
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) | |
|
Forage |
|
|
| |
|
|
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 peals |
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 |
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 70°C and cooled in a desiccator. Samples were weighed into nylon filter cloth bags (195 mm x 105 mm, 40 m 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 was incubated at a time in cattle, and 6 in sheep and goats. Open ends of bags were fastened with nylon fishing line, leaving a 250 mm free length in sheep and goats and 500 mm in cattle.
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 70°C 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 was added, was filtered through 3 layers of cheese-cloth, centrifuged at 5000 rpm for 20 min at 10°C and the supernatant analysed for NH3-N (Preston and Leng, 1986).
Statistical analyses
Dry matter degradability was analysed 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.
Forages
The 3 ruminant species degraded the various forages to a similar (P > 0.05) extent (Table 2) with mean values of 55.1%, 54.9% and 56.6% (± 0.6% s.e.) 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).
Table 2. Mean squares from the analysis of variance for degradability of potential feeds in Nigeria.
|
Source of variation |
Feed type |
|||||
|
Forage |
Browse |
Crop-residue |
||||
|
d.f. |
m.s. |
d.f. |
m.s. |
d.f. |
m.s. |
|
|
Feed type (T) |
4 |
430.2* |
5 |
2971.5* |
12 |
2627.1* |
|
Animal species (S) |
2 |
13.2 |
2 |
32.0 |
24 |
8.6* |
|
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
Browse
Dry matter degradability of browse was affected only by type, neither of species or species by browse type effects being 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 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 |
In the same column, 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%).
Table 4. Nylon bag dry matter degradability of forages fed to ruminants in Nigeria.
|
Forage |
Ruminant species |
||
|
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 |
In the same column, and along rows, values without a suffix letter in common differ (P < 0.05).
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.
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.
Table 5. Nylon bag dry matter degradability 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 |
70.3e |
67.3e |
65.1c |
|
Mature corn stover |
56.7a |
55.2a |
56.7a |
|
Cowpea husk |
71.9e |
76.3e |
73.3e |
|
Foofoo residue |
75.4e |
76.0c |
83.7d |
|
Corn bran |
77.2e |
81.7c |
83.5c |
|
Yam peels |
90.3d |
81.7c |
83.9c |
|
Plantain peels |
74.4c |
72.0e |
74.6c |
|
Sweet potato peels |
94.1d |
93.1d |
96.7d |
|
Rice bran |
43.4b |
38.7b |
37.0b |
|
Cassava peels |
82.3e |
76.3c |
90.2d |
|
Brewers dried grains |
71.1c |
50.8a |
52.9a |
In the same column, and along rows, values without a suffix letter in common differ (P < 0.05).
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 cannulae 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, 1986).
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 synchronized 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 byproducts 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.
This study was jointly financed by the International Foundation for Science and the Obafemi Awolowo University, Nigeria.
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