Summary
Résumé
Introduction
Materials and methods
Results and discussion
References
I.F. Adu, B.A. Fajemisin and A. M. Adamu
National Animal Production Research Institute
Ahmadu Bello University, Shika-Zaria, Nigeria
The effect of Urea and graded levels of Lablab purpureus cv Rongai on the voluntary intake and utilisation of sorghum stover was determined with 30 Yankasa sheep. The physical and chemical composition of the sorghum stover and lablab as well as their stem and leaf fractions were described.
The intake of sorghum stover was depressed when supplemented with Lablab but overall feed intake improved with increasing levels of Lablab supplementation.
The addition of urea increased stover intake and the digestibility of the dry matter, neutral detergent fibre (NDF) and nitrogen. Supplementing sorghum stover with either Lablab or urea generally improved liveweight gains of the sheep. It is concluded that supplementing sorghum stover with Lablab improved its intake and utilisation. However at high levels of supplementation, Lablab tends to have a substituttion effect on sorghum intake.
L'effet de l'urée et de niveaux croissants de dolique (Lablab purpureus) cv. Rongai (blanc) sur ['ingestion volontaire et l'utilisation de la paille de sorgho a été étudié chez 30 moutons Yankassa. La composition physique (proportion de tiges, de feuilles) et chimique de la paille et du dolique est présentée.
La complémentation de dolique a déprimé l'ingestion de la paille de sorgho: (de 9 et 7% pour 90 et 180 g de dolique). Cette baisse est devenue significative (P<0.05) avec une complémentation de 270 9.
L'addition d'urée a augmenté l'ingestion de paille et la digestibilité de la matière sèche et des parois cellulaires, respectivement de 6,5, 14,6 et 11,8% et a entraîné un accroissement significatif (P <0,05) de la digestibilité de l'azote. La complémentation s'est globalement traduit par une amélioration du gain de poids des moutons. Au vu de ces résultats, il apparaît que la complémentation de la paille de sorgho par le dolique en améliore la consommation et l'utilisation. Toutefois, à niveau élevé (au-delà de 20%), le dolique tend à avoir un effet de substitution.
Quantitatively, sorghum is the most important cereal crop grown in Nigeria (Table 1). About 46% of the estimated 21795000 hectares of land under cultivation is devoted to sorghum production with an annuel total grain yield of about 5.53 million tonnes (Central Bank of Nigeria, 1988). Alongside this grain production is an estimated 22.14 million tonnes of stover which is available for ruminant livestock feeding. And since cereal crop growing areas are also the home of most of Nigeria's livestock population, cereal crop residues constitute an important feed resource during the dry season. Also, because Nigeria cannot as yet develop intensive livestock feeding systems based on expensive and scarce feed resources like grains, oilseed cakes, high-quality pastures, crop residues will continue to be important in Nigeria's livestock feed resources.
However, crop residues are known to have low content of available protein, energy and minerais. It is recognised that rumen fermentation is impaired and animal performance lowered when the nitrogen content of the diet is less than 1.2% (Conrad and Hibbs, 1968). The feeding of energy and protein supplements is known to enhance the utilisation of poor-quality feeds like crop residues by maximising roughage degradation and optimising rumen microbial protein synthesis (Anderson, 1978; O'Donovan, 1983). Because of high cost, scarcity and other logistic problems , the use of concentrates and non - protein nitrogen as supplements is not justified.
The current interest in a more intensive use of crop residues in Nigeria justifies the search for cheaper and readily available supplements. Lablab purpureus is a dualpurpose legume crop that is rapidly gaining acceptance by agropastoral farmers in northern Nigeria (Tanko et al, 1990). Lablab has high seed and forage yield as well as good hay-curing ability compared with other commonly grown legume crops in Nigeria.
The objective of this study was to compare the effect of urea and three levels of Lablab supplementation on the utilisation of a basal diet of sorghum stover by Yankasa sheep.
Table 1. Annual grain, stover/haulm yield and nutritive value of some common crops in Nigeria ('000 tonnes).
|
Crop |
Seed or grain¹ |
Stover or haulm/vines2 |
Crude protein content of stover/ haulm(%) |
|
Sorghum |
5534 |
22136 |
1.6-7.5 |
|
Maize |
1370 |
5480 |
2.6-4.9 |
|
Millet |
4170 |
25020 |
4.0-5.4 |
|
Rice |
307 |
2456 |
3.0-4,6 |
|
Cowpea |
698 |
3490 |
5.9-10.4 |
|
Groundnut |
709 |
2188 |
11.4-16.7 |
|
Benniseed |
36 |
324 |
2.0-5.1 |
|
Soyabean |
121 |
363 |
4.3-6.8 |
1. Central Bank of Nigeria (1988).
2. The extraction rates (seed:stover/haulm) developed by Alhassan and Kallah (1984) in NAPRI (unpublished) were used.
Sorghum (SK-5912) was planted at a seed rate of 10 kg ha-1. At planting, fertiliser was applied at the rate of 37.5 kg N ha-1 followed at 6 weeks by a side-dressing of 22 kg N ha-1 The sorghum was harvested for grains 123 days after sowing. After grain harvest, the whole plant was removed at ground-level and packed. Thereafter, a random sample was taken, weighed and subdivided into leaf and stalk portions. This paper reports the trials with ground sorghum stover (3-4 cm).
Lablab purpureus cv. Rongai (white) was planted from seed at the rate of 15 kg ha''. At 90 days the forage was cut and field- dried. A random sample was taken, weighed and separated into leaf and stem fractions. The Lablab was chopped into 1-2 cm pieces and used as the supplement in a series of experiments.
Samples of the whole sorghum and Lablab as well as their leaf and stem fractions were analysed for dry matter, nitrogen, NDF, lignin and ash (AOAC, 1975; Goering and Van Soest, 1970).
The nylon bag method (Orskov et al, 1980) was used to estimate ruminal degradation of the whole stover, Lablab and their respective leaf and stem fractions. About 3 g of each sample was placed in nylon bags (size 100 x 170 mm with 12 mm pore size) and were incubated in the rumen of 2 Bunaji cows in replicates. The bags were anchored by a 50-cm nylon string to the cap of the rumen cannulae and withdrawn at 12, 18, 24, 48 and 72 hours. They were then washed and dried at 60°C for 48 hours (Mehrez and Orskov, 1977) for the estimation of dry-matter and nitrogen disappearance. Thirty yearling Yankasa sheep with an average weight of 22.8+0.7 kg were treated for endo- and ectoparasites and used for the 78-day feeding trial. The treatments were:
A - Sorghum stover ad libitum
B - Sorghum stover + 90 g Lablab
C - Sorghum stover + 180g Lablab
D - Sorghum stover + 270g Lablab
E - Sorghum stover + 9 g urea + sulphur to achieve N:S ratio of 10:1
The Lablab supplements were intended to provide 10,20 and 30% of total intake while the urea represented 1.5% total intake. The urea was dissolved in about 5 cc of water and mixed with the sulphur. The resulting solution was mixed with a grabsample of the stover and fed to the animals first before offering the basal diets. This was to ensure a complete consumption of the urea. The stover was fed ad lib. Animals were weighed fortnightly. A 7-day total faecal collection was done at the end of the feeding trial.
All data were subjected to analysis of variance and differences among treatment means were determined (Snedecor and Cochran, 1980).
The sorghum stover is made up of 17.3% leaf, 26% upper softer stem and 56.7% lower woody stem while the corresponding figures for the Lablab are 38.7,13.5 and 47.7%, respectively. In terms of physical composition the leaf and upper softer stem, which generally contain a higher concentration of most nutrients, constituted approximately 43 and 53% of the stover and Lablab, respectively.
The apparently higher ash content (Table 2) of the leaf fraction may be partly due to soil contamination while being dried in the field. As expected, the NDF and lignin in the stem fractions were generally higher than in the leaf fractions. The grinding of the stover reduced selection of leaf fraction which are generally more nutritious and more relished by animals (Martin and Wedin, 1974; Powell, 1985) and enhanced a better utilisation of the whole plant.
Table 2. Chemical composition of whole, leaf and stem fractions of sorghum stover and Lablab.
|
|
Sorghum stover |
Lablab |
Sorghum stover+ urea |
||||
|
Whole |
Leaf |
Stem |
Whole |
Leaf |
Stem |
||
|
Dry matter |
96.6 |
95.9 |
96.5 |
94.6 |
93.1 |
95.1 |
94.8 |
|
Nitrogen |
0.84 |
1.1 |
0.74 |
1.6 |
2.1 |
1.2 |
2.2 |
|
NDF |
76.0 |
78.6 |
89.4 |
38.9 |
39.7 |
62.4 |
69.3 |
|
Lignin |
11.8 |
10.7 |
13.6 |
4.2 |
6.8 |
10.9 |
14.3 |
|
Cellulose |
43.0 |
21.9 |
47.3 |
10.5 |
21.9 |
40.4 |
39.3 |
|
Ash |
7.8 |
7.7 |
3.6 |
7.4 |
11.1 |
6.5 |
8.6 |
The 48-hour dry-matter disappearance rate (Table 3) increased with incubation time. Lablab was degraded more rapidly than stover. In both cases, the leaf fractions was degraded more rapidly than the stem fractions. Supplementation of sorghum stover with either Lablab or urea improved its degradability (Table 3) and digestibility (Table 4).
Table 3. Dry-matter disappearance (g/100 g) of whole leaf and stem fractions from nylon bag incubated in the rumen of Bunaji cows.
|
Hours of incubation |
Sorghum stover |
Lablab |
Sorghum stover + Lablab (4:1) |
Sorghum stover + urea |
||||
|
Whole |
Leaf |
Stem |
Whole |
Leaf |
Stem |
|||
|
12 |
8.9 |
13.8 |
7.6 |
10.9 |
14.7 |
9.7 |
12.7 |
10.3 |
|
18 |
13.1 |
21.5 |
11.8 |
15.1 |
19.1 |
12.5 |
17.2 |
14.2 |
|
24 |
25.4 |
31.8 |
21.1 |
29.2 |
32.4 |
22.2 |
30.7 |
27.6 |
|
48 |
33.8 |
42.4 |
29.6 |
35.5 |
43.5 |
28.4 |
37.4 |
38.1 |
|
72 |
41.2 |
50.6 |
37.0 |
48.6 |
53.6 |
35.9 |
44.3 |
44.2 |
Table 4. Digestibility (g/kg) of the different feed combinations used.
|
|
Sorghum alone |
Stover+ 90g Lablab (10%) |
Stover +180g Lablab (20%) |
Stover +270 g Lablab (30%) |
Stover + urea |
|
Dry matter |
457 |
476 |
537 |
541 |
524 |
|
Organic matter |
475 |
507 |
526 |
572 |
502 |
|
Crude protein |
613a |
693b |
761b |
789b |
768b |
|
NDF |
551 |
559 |
577 |
596 |
616 |
Means with different superscripts within each row are significantly different (P < 0.05).
Total feed intake increased significantly (P<0.05) when the stover was supplemented with 180 9 Lablab. The 85,170 and 255 9 actual Lablab intake accounted for 18.8,31.4 and 53.3% of the total dry matter intake, respectively. Total feed intake and utilisation were generally better in sheep given stover plus either urea or Lablab, a confirmation that nitrogen is deficient in the stover (Table 5). stover intake was depressed by 9 and 7% at the 10 and 20% levels of Lablab supplementation, while the depression (44%) was significant (P <0.05) at the 30% level of supplementation. This result tends to support the contention that supplements have beneficial effects on the utilisation of fibrous feeds if the level of supplementation does not exceed 20% of the diet dry matter (Preston and Leng, 1984; Wegad and NDumbe, 1987). It would appear that Lablab had a substitution effect beyond the 20% level of supplementation.
Table 5. Performance of sheep fed sorghum stover supplemented with urea or Lablab.
|
|
Stover alone |
Stover 90g Lablab (10%) |
Stover + 180 g Lablab (20%) |
Stover +270 g Lablab (30%) |
Stover + urea |
|
Stover intake |
401.3a |
367.1a |
372.3a |
223.5b |
427a |
|
Total DM intake |
401.3a |
452.2a |
542.2b |
478.8a |
427a |
|
Total DM intake (g/kgW0.75/day) |
41.3 |
45.4 |
57.2 |
47.7 |
43.6 |
|
Liveweight gain (g/day) |
-20.9 |
15.9a |
36.1b |
47.7b |
9.3a |
|
Feed efficiency |
|
28.4 |
15.0 |
10.0 |
45.9 |
Means with different superscripts within each row are significantly different (P < 0.05).
Though not significant (P>0.05) the digestion of dry matter, organic matter and NDF generally increased with increasing levels of Lablab supplementation.
Crude-protein digestibility was, however, significantly (P<0.05) improved by the supplements. The supplements generally improved rumen fermentation of the test diets and the range of improvement falls within that reported by Sharma et al (1972).
The improved liveweight gains of sheep fed Lablab supplement justify its use in preventing liveweight loss during the critical dry season period.
It is concluded that the use of sorghum stover as a feed resource is greatly enhanced by supplementing with Lablab. The planting of Lablab with sorghum or maize has been accepted as a cropping practice by farmers in the subhumid zone of Nigeria. The settled farmers who feed crop residues to animals in their rugas can be encouraged to further reduce particle size (or grind) to enhance better utilisation. Already some well-to-do farmers have installed grinders on their farms.
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