Title
Factors affecting the nutritive value of sorghum and millet crop residues
Author
Jess D. Reed1, Yilma Kebede2 and Les K. Fussell3
1. ILCA, P.O. Box 5689, Addis Ababa, Ethiopia
2. Institute of Agricultural Research, Nazareth, Ethiopia.
3. International Crops Research Institute for the Semi-Arid Tropics, Sahelian Center, B.P. 12404, Niamey, Niger
Sorghum and millet crop residues are an important potential feed resource. In 1981, 55.2 and 51.4 million tonnes of crop residue were produced from sorghum and millet respectively (Kossila, 1985). Assuming a digestibility of 45% and 20% wastage, the annual maintenance requirements of 39 million tropical livestock units (250 kg liveweight) could be met by sorghum and millet crop residues supplemented with low-levels of protein or non-protein nitrogen. However, to raise productivity above maintenance, digestibility and protein supplementation would need to be increased.
Livestock are an important component of agricultural systems in the semi-arid regions of Africa. They are an important source of income and a means of saving capital for use in times of need. Under conditions of improved productivity, livestock may serve as a catalyst to increase overall farm productivity. Ruminant livestock can complement crop production by increasing soil fertility through manure, by providing traction for cultivation, by grazing areas that can not be cultivated and by using crop residues for feed. However, poor nutrition is a major constraint to increased livestock productivity. Feed is often in short supply and nutritive value low. Grazing and crop residues are low in protein and energy and may also be deficient in important mineral nutrients.
Improved livestock feeding systems need to be developed for the smallholder farmer of Africa who depends on millet and sorghum for subsistence. Although these cereals are a staple food crop, they have low economic value during years of average and above average rainfall. The stability and overall productivity of farming systems could be improved by the introduction of livestock rearing activities that combine efficient use of crop residues with forage legumes and multipurpose trees.
Although much research has been devoted to upgrading straw by chemical treatment (Jackson, 1978), little attention has been given to variation in the nutritive value of untreated crop residues as influenced by variety and environment. Quantity and quality of cereal crop residues are important criteria in a farmer's decision to grow a particular variety. Varietal and environmental effects on the nutritive value of cereal crop residues are also important. The nutritive value of residues from a given variety varies widely due to differences in growing conditions (season, elevation or latitude). High temperature during growth increases cell wall and lignin contents and decreases digestibility (Deinum, 1976). High humidity and rain during and after grain harvest reduce nutritive value. Loss of leaves through wind or trampling of cereal crop residues left in the field also causes deterioration. These losses can be reduced by improved conservation practices.
It is well known that cereal crop residues are deficient in protein. However, supplementation with non-protein nitrogen or protein does not always increase intake and digestibility because other factors limit nutritive value. These factors need to be determined because, within the range of energy intake of cereal crop residues, large increases in animal productivity can be achieved by relatively small increases in digestibility and intake.
Cell wall, as estimated by neutral-detergent fibre, accounts for as much as 80% of the dry matter in cereal crop residues and represents a large source of energy for ruminants. However, the ability of rumen micro-organisms to digest cell wall polysaccharides (cellulose and hemicellulose) is limited by the presence of phenolic and other aromatic compounds which are generally referred to as lignin. The phenolic constituents of sorghum and millet have been subject to little investigation. However, the digestibility of the crop residues will be correlated with the nature and amount of phenolics associated with their cell walls and the influence of environment on phenolics (Hartley, 1981).
BR and NBR varieties do not differ in their N or neutral-detergent fibre (NDF) contents and leaves contain twice as much N as stems (Reed et al, 1987). The total cell wall as estimated by NDF is greater than 70% of the organic matter in sorghum leaves. Silica is also a cell wall component (Jones and Handreck, 1967), but is not completely recovered in the NDF. Silica content of sorghum leaves (9 to 15% of the dry matter) is much higher than that found in temperate forages and most other cereal crop residues (Reed et al, 1987).
Most of the energy obtained by ruminants fed sorghum crop residues comes from rumen fermentation of cell wall carbohydrates. Factors that limit the digestibility of these carbohydrates would have the greatest influence on differences in nutritive value between varieties after N deficiencies are corrected. Leaf blades and leaf sheaths from BR varieties have higher levels of insoluble proanthocyanidins and soluble red pigments than those of NBR varieties (Table 1). Leaf sheaths from BR varieties are higher in lignin than those from NBR varieties.
In leaves and stems, linear correlation coefficients among insoluble proanthocyanidins, soluble red pigments and soluble phenolics as measured by absorbance are positive and significant (Table 2).
Leaves and stems from BR varieties contain red pigments that are extracted by polar organic solvents. However, NDF from BR varieties, prepared by sequential extraction with aqueous acetone and neutral-detergent, is also red. Red pigmentation, as measured by absorbance of insoluble proanthocyanidins at 550 nm, is associated with larger amounts of lignin in BR varieties (Figure 1).
In leaves, lignin, insoluble proanthocyanidins and soluble red pigments contents are negatively correlated with extent of NDF digestion and digestibility of NDF at 48 hours, and positively correlated with indigestible NDF (Table 3). Insoluble proanthocyanidins and soluble red pigments contents are negatively correlated with rate of NDF digestion.
Phenolics are a major factor limiting digestibility of NDF in leaves. BR varieties are higher in phenolics than NBR varieties. Digestibility of NDF at 48 hours is an important parameter because it is used to estimate in vivo digestibility (Goering and Van Soest, 1970). Phenolics (lignin and insoluble proanthocyanidins) accounted for most of the variation in digestibility of NDF at 48 hours in leaves (Figure 2).
Table 1. The effect of site and bird resistance on content of neutral detergent fibre (NDF), digestibility of NDF (DNDF), content of lignin, soluble red pigments (A550 sol.) and insoluble proanthocyanidins (A550 insol.) in leaf blades, leaf sheaths and stems from the crop residue of bird resistant (BR, n=6) and non-bird-resistant (NBR, n=8) sorghum varieties.
Table 2. Linear correlation coefficients among lignin, insoluble proanthocyanidins, soluble red pigments and soluble phenolics as measured by absorbance at 280 nm (A280) in leaves and stems from 24 sorghum varieties.
Table 3. Linear correlation coefficients between parameters of digestibility of neutral-detergent fibre (NDF) and lignin, insoluble proanthocyanidins, soluble red pigments and soluble phenolics as measured by absorbance at 280 nm in leaves and stems from 24 sorghum varieties.
In stems, there is a significant correlation between lignin content and indigestible NDF but no correlation between lignin content and digestibility of NDF at 48 hours (Table 3). Lignin may be more unevenly distributed in stems than in leaf blade and sheaths. The amount of lignified tissue may determine the amount of indigestible NDF in relation to different proportions of rind and pith. Soluble red pigments and insoluble proanthocyanidins contents are lower in stem than in leaves, suggesting that these phenolics are less important in the digestion of NDF in stems (Reed et al, 1987).
The range in NDF digestibility in leaves and stems from sorghum crop residue is large. The amount of phenolics in leaves accounts for most of the variation in digestibility. Leaves are more important than stems in determining nutritive value because of their greater N content and greater consumption by livestock (Powell, 1984). BR varieties have a higher phenolics content than NBR varieties. These relationships indicate that breeding for bird resistance in sorghum lower the nutritive value of the crop residue. However, some varieties may have bird-resistant grain and low phenolic content in the crop residue. Such varieties may be useful in farming systems in semi-arid areas of Africa where birds are an important pest and the crop residue is an important feed.
Five sorghum varieties, selected on yield criteria, were used to determine the effect of variety on intake and digestibility of the crop residue in mature highland zebu oxen. After grain harvest, the crop residue from each variety was coarsely chopped and fed to five oxen in a latin square design. Oxen were offered 12 kg of crop residue dry matter per day. This diet was supplemented with 60 g of urea added to the drinking water.
Daily dry-matter intake varied by more than 1 kg among varieties (Table 4). The variety with the lowest intake (MW5020) is a dwarf, bird-resistant variety which gives high grain yield but little residue. MW5020 had the highest proportion of leaves in the crop residue but its leaves were strongly pigmented. It was the only variety with a measurable amount of leaf in the feed refusals. The intake of digestible energy from MW5020 would be adequate for maintenance requirements only, whereas the intake from Melkamash and 5DX 160 would allow weight gains of over 200 g per day.
Table 4. The effect of sorghum variety on intake of crop residue by highland zebu oxen.
Table 5. The effect of variety on content of neutral-detergent fibre (NDF), digestibility of NDF (DNDF) and content of lignin in leaf blades, leaf sheaths and stems from the crop residue of 12 millet varieties.
The digestibility of NDF in the leaf sheath and stem fractions of the 12 millet varieties was low. Varieties with higher digestibility and adaptation to the Sahel need to be sought.
Similar ruminant production systems exist around urban areas in Africa. More efficient utilisation of sorghum and millet crop residues could contribute to increased productivity and income for both livestock producers and smallholder farmers. Crop improvement programmes could improve these systems by developing crop varieties that are suitable for dual purpose production of both grain and fodder.
Cummins D G. 1971. Relationships between tannin content and forage digestibility in sorghum. Agronomy Journal 63:501-502.
Deinum B. 1976. Effect of age, leaf number and temperature on cell wall and digestibility of maize. In: Carbohydrate research in plants and animals. Miscellaneous Papers, Agricultural University, Wageningen, No. 12:29-41.
Goering H K and Van Soest P J. 1970. Forage fibre analysis. Agriculture Handbook No. 379. Agricultural Research Service, United States Department of Agriculture, Washington DC, USA.
Gourlay L M. 1979. Nutritional quality of sorghum leaves. In: Eleventh biennial grain sorghum research and utilisation conference, Lubbock, Texas, USA.
Gupta R K and Haslam E. 1980. Vegetable tannins structure and biosynthesis. In: J H Hulse (ed.), Polyphenols in cereals and legumes. IDRC, Ottawa, Canada.
Hartley R D. 1981. Chemical composition, properties and processing of lignocellulosic wastes in relation to nutritional quality for animals. Agriculture and Environment 6:91-113.
Hulse J H. Laing E M and Pearson O E. 1980. Sorghum and millets: Their composition and nutritive value. Academic Press, London, UK.
Jackson M G. 1978. Treating straw for animal feeding. FAO Animal Production and Health Paper 10. Food and Agricultural Organization of the United Nations, Rome, Italy.
Jones L H P and Handreck K A. 1967. Silica in soils, plants and animals. Advances in Agronomy 19:107-149.
Kossila V S. 1985. Global review of the potential use of crop residues as animal feed. In: T R Preston, V L Kossila, J Goodwin and S B Reed (eds), FAO Animal Production and Health Paper 50. Food and Agricultural Organization of the United Nations, Rome, Italy.
Parthasarathy Rao P. 1985. Marketing of fodder in rural and urban areas of India. In: Agricultural markets in the semi-arid tropics. Proceedings of the International Workshop, 24-28 October 1983, ICRISAT Center, Patancheru, India. International Crops Research Institute for the Semi-Arid Tropics, India.
Powell J M. 1984. Sorghum and millet yields and consumption by livestock in the subhumid zone of Nigeria. Tropical Agriculture (Trinidad) 62:77-81.
Reed J D, Tedla A and Kebede Y. 1987. Phenolics, fibre and fibre digestibility in the crop residue from bird resistant and non-bird resistant sorghum varieties. Journal of the Science of Food and Agriculture 39:113-121.
Saini M L, Paroda R S and Goyal K C. 1977. Path analysis for quality characters in forage sorghum. Forage Research 3:131-136.
Walker T S. 1987. Economic prospects for agroforestry interventions in India's SAT: Implications for research resource allocation at ICRISAT. Resource Management Program, Economics Group, Progress Report-79. International Crops Research Institute for the Semi-Arid Tropics, Patancheru, India.
Reed: We need to look for low pigmented, bird-resistant cultivars. Pigmentation varies considerably among bird-resistant cultivars but this is also heavily influenced by environment, which could lead to genotype by environment interactions. We could score blade pigmentation at various sites; this could easily be incorporated into bird-resistance trials.
Berhane: You singled out one variety which was bird resistant and was high in tannin and high in digestibility. Was that variety incorporated in animal feeding trials?
Reed: I cannot recall if we used this variety in our feeding trials. The variety that had the highest intake in the oxen trial was selected because of the high digestibility of its stems, which indicates that stem digestibility may be a major factor determining the nutritive value of sorghum. This variety was also bird resistant.
Ørskov: What is the correlation between stem, blade and sheath digestibility?
Reed: The correlation was very poor in our data on sorghum.
Pearce: In ryegrass the correlation is quite good: if stem is highly digestible, the sheath and blade will also be highly digestible.
Capper: We looked at botanical fractions in sorghum at ICRISAT. When you plot these against height, over the range of 150 to 300 cm there is little change in the proportion of botanical fractions, but below 150 em the amount of leaf sheath, which is the least digestible fraction and in which there was the most variation in digestibility, starts to increase quite rapidly. If plant breeders breed for shorter varieties, the amount of less-digestible leaf sheath could become very significant. We found that leaf blade and stem have virtually the same digestibility. As suggested, the proportion of leaf sheath has the greatest effect on the nutritive value of sorghum.
Reed: The proportions of plant parts means nothing to a farmer who will feed coarse stovers. The amount of crop residue and the amount of a fraction that can be fed are more important. As such, we should also express our results in yield of the different components per hectare, which may give different relationships. For example, in our trials, medium-height varieties gave a much higher yield of leaf than dwarf varieties, despite having a smaller proportion of leaf in the straw. If you are feeding animals you may want the quantity, not the proportion, except if you were to grind the entire residue and feed it. But when grazed in the field, the leaf fractions are preferred and are of higher nutritive value.
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Factors affecting the nutritive value of sorghum and millet crop residues
Author
Jess D. Reed1, Yilma Kebede2 and Les K. Fussell3
1. ILCA, P.O. Box 5689, Addis Ababa, Ethiopia
2. Institute of Agricultural Research, Nazareth, Ethiopia.
3. International Crops Research Institute for the Semi-Arid Tropics, Sahelian Center, B.P. 12404, Niamey, Niger
Introduction
Sorghum (Sorghum bicolor) and pearl millet (Pennisetum typhoides) are the most important food crops in the semi-arid, drought-prone areas of Africa. Over 10 million tonnes of grain from each cereal are produced annually, 95% of which is used for human food (Hulse et al, 1980).Sorghum and millet crop residues are an important potential feed resource. In 1981, 55.2 and 51.4 million tonnes of crop residue were produced from sorghum and millet respectively (Kossila, 1985). Assuming a digestibility of 45% and 20% wastage, the annual maintenance requirements of 39 million tropical livestock units (250 kg liveweight) could be met by sorghum and millet crop residues supplemented with low-levels of protein or non-protein nitrogen. However, to raise productivity above maintenance, digestibility and protein supplementation would need to be increased.
Livestock are an important component of agricultural systems in the semi-arid regions of Africa. They are an important source of income and a means of saving capital for use in times of need. Under conditions of improved productivity, livestock may serve as a catalyst to increase overall farm productivity. Ruminant livestock can complement crop production by increasing soil fertility through manure, by providing traction for cultivation, by grazing areas that can not be cultivated and by using crop residues for feed. However, poor nutrition is a major constraint to increased livestock productivity. Feed is often in short supply and nutritive value low. Grazing and crop residues are low in protein and energy and may also be deficient in important mineral nutrients.
Improved livestock feeding systems need to be developed for the smallholder farmer of Africa who depends on millet and sorghum for subsistence. Although these cereals are a staple food crop, they have low economic value during years of average and above average rainfall. The stability and overall productivity of farming systems could be improved by the introduction of livestock rearing activities that combine efficient use of crop residues with forage legumes and multipurpose trees.
Although much research has been devoted to upgrading straw by chemical treatment (Jackson, 1978), little attention has been given to variation in the nutritive value of untreated crop residues as influenced by variety and environment. Quantity and quality of cereal crop residues are important criteria in a farmer's decision to grow a particular variety. Varietal and environmental effects on the nutritive value of cereal crop residues are also important. The nutritive value of residues from a given variety varies widely due to differences in growing conditions (season, elevation or latitude). High temperature during growth increases cell wall and lignin contents and decreases digestibility (Deinum, 1976). High humidity and rain during and after grain harvest reduce nutritive value. Loss of leaves through wind or trampling of cereal crop residues left in the field also causes deterioration. These losses can be reduced by improved conservation practices.
It is well known that cereal crop residues are deficient in protein. However, supplementation with non-protein nitrogen or protein does not always increase intake and digestibility because other factors limit nutritive value. These factors need to be determined because, within the range of energy intake of cereal crop residues, large increases in animal productivity can be achieved by relatively small increases in digestibility and intake.
Cell wall, as estimated by neutral-detergent fibre, accounts for as much as 80% of the dry matter in cereal crop residues and represents a large source of energy for ruminants. However, the ability of rumen micro-organisms to digest cell wall polysaccharides (cellulose and hemicellulose) is limited by the presence of phenolic and other aromatic compounds which are generally referred to as lignin. The phenolic constituents of sorghum and millet have been subject to little investigation. However, the digestibility of the crop residues will be correlated with the nature and amount of phenolics associated with their cell walls and the influence of environment on phenolics (Hartley, 1981).
Sorghum
In Africa, birds are a major crop pest and limit grain production from sorghum (Bullard and Elias, 1980). Bird resistance is related to the amount of proanthocyanidins (condensed tannins) in the grain (Gupta and Haslam, 1980). Sorghum improvement programmes in Africa are breeding for bird resistance in varieties for semi-arid zones. The phenolic content of the vegetative components of bird resistant (BR) and forage varieties is negatively associated with digestibility (Saint et al, 1977; Cummins, 1971). Weanling rats fed a diet containing leaves from BR varieties had lower feed efficiency and N retention than those fed a diet containing leaves from non-bird-resistant (NBR) varieties (Gourlay, 1979). In this section the differences between BR and NBR varieties in content of phenolics and their relationship to digestibility of fibre in the crop residue are discussed.BR and NBR varieties do not differ in their N or neutral-detergent fibre (NDF) contents and leaves contain twice as much N as stems (Reed et al, 1987). The total cell wall as estimated by NDF is greater than 70% of the organic matter in sorghum leaves. Silica is also a cell wall component (Jones and Handreck, 1967), but is not completely recovered in the NDF. Silica content of sorghum leaves (9 to 15% of the dry matter) is much higher than that found in temperate forages and most other cereal crop residues (Reed et al, 1987).
Most of the energy obtained by ruminants fed sorghum crop residues comes from rumen fermentation of cell wall carbohydrates. Factors that limit the digestibility of these carbohydrates would have the greatest influence on differences in nutritive value between varieties after N deficiencies are corrected. Leaf blades and leaf sheaths from BR varieties have higher levels of insoluble proanthocyanidins and soluble red pigments than those of NBR varieties (Table 1). Leaf sheaths from BR varieties are higher in lignin than those from NBR varieties.
In leaves and stems, linear correlation coefficients among insoluble proanthocyanidins, soluble red pigments and soluble phenolics as measured by absorbance are positive and significant (Table 2).
Leaves and stems from BR varieties contain red pigments that are extracted by polar organic solvents. However, NDF from BR varieties, prepared by sequential extraction with aqueous acetone and neutral-detergent, is also red. Red pigmentation, as measured by absorbance of insoluble proanthocyanidins at 550 nm, is associated with larger amounts of lignin in BR varieties (Figure 1).
In leaves, lignin, insoluble proanthocyanidins and soluble red pigments contents are negatively correlated with extent of NDF digestion and digestibility of NDF at 48 hours, and positively correlated with indigestible NDF (Table 3). Insoluble proanthocyanidins and soluble red pigments contents are negatively correlated with rate of NDF digestion.
Phenolics are a major factor limiting digestibility of NDF in leaves. BR varieties are higher in phenolics than NBR varieties. Digestibility of NDF at 48 hours is an important parameter because it is used to estimate in vivo digestibility (Goering and Van Soest, 1970). Phenolics (lignin and insoluble proanthocyanidins) accounted for most of the variation in digestibility of NDF at 48 hours in leaves (Figure 2).
Table 1. The effect of site and bird resistance on content of neutral detergent fibre (NDF), digestibility of NDF (DNDF), content of lignin, soluble red pigments (A550 sol.) and insoluble proanthocyanidins (A550 insol.) in leaf blades, leaf sheaths and stems from the crop residue of bird resistant (BR, n=6) and non-bird-resistant (NBR, n=8) sorghum varieties.
Table 2. Linear correlation coefficients among lignin, insoluble proanthocyanidins, soluble red pigments and soluble phenolics as measured by absorbance at 280 nm (A280) in leaves and stems from 24 sorghum varieties.
Lignin
|
Insoluble proantho-cyanidins
|
Soluble red pigments
| |
Leaves
| |||
| Insoluble proanthocyanidins |
0.733**
| ||
| Soluble red pigments |
0.762**
|
0.917**
| |
| Soluble phenolics |
0.446*
|
0.457*
|
0.599**
|
Stems
| |||
| Insoluble proanthocyanidins |
0.286
| ||
| Soluble red pigments |
0.390
|
0.826**
| |
| Soluble phenolics |
0.401
|
0.726*
|
0.909**
|
Source: Reed et al (1987).Environmental factors have a large effect on pigmentation in sorghum leaf blades and sheaths. BR varieties grown at Melkasa (elevation 1500 m) in the Ethiopian Rift Valley had greater pigmentation in blades and sheaths than the same varieties grown at Debre Zeit at higher elevation (1800 m). The effects of these phenolic pigments on NDF digestibility was greatest in leaf sheaths from BR varieties grown at Melkasa (Table 1). Average maximum temperatures during the growing season at Melkasa were 2 to 3° C higher, and average minimum temperatures 5 to 7°C higher, than at Debre Zeit. Total rainfall during the growing season was 645 mm at Melkasa and 693 mm at Debre Zeit. The mean digestibility of leaf sheaths from BR varieties grown at Melkasa was 8.4 percentage units lower than that of the same varieties grown at Debre Zeit and over 12 units lower than that of NBR varieties grown at either site (Table 1). These results suggest that phenolic pigments have their greatest effect on leaf sheath digestibility and that environmental effects may also be greatest on this plant fraction.
* P<0.05.
** P<0.01.
Figure 1. Relationship between lignin and insoluble proanthocyanidins contents of leaves from the crop residue of bird-resistant and non-bird-resistant sorghum.
Potentially digestible NDF
|
Rate of NDF digestion NDF
|
Indigestible at 48 h
|
NDF digestion
| |
Leaves
| ||||
| Lignin | -0.784** | -0.248 | 0.808** | -0.884** |
| Insoluble proanthocyanidins | -0.525** | -0.518* | 0.520* | -0.797** |
| Soluble red pigments | -0.553** | -0.493* | 0.623** | - 0.846** |
| Soluble phenolics | -0.542** | -0.195 | 0.491* | - 0.603** |
Stems
| ||||
| Lignin | 0.270 | -0.099 | 0.759** | -0.364 |
| Insoluble proanthocyanidins | 0.390 | 0.222 | 0.067 | 0.361 |
| Soluble red pigments | 0.410 | 0.295 | 0.214 | 0.366 |
| Soluble phenolics | 0.362 | 0.247 | 0.270 | 0.249 |
* p<0.05.Figure 2. Relationship between digestibility of neutral-detergent fibre (DNDF) and lignin and insoluble proanthocyanidins in leaves from the crop residue of bird-resistant and non-bird-resistant varieties of sorghum.
** p<0.01.
Figure a
Figure b
The range in NDF digestibility in leaves and stems from sorghum crop residue is large. The amount of phenolics in leaves accounts for most of the variation in digestibility. Leaves are more important than stems in determining nutritive value because of their greater N content and greater consumption by livestock (Powell, 1984). BR varieties have a higher phenolics content than NBR varieties. These relationships indicate that breeding for bird resistance in sorghum lower the nutritive value of the crop residue. However, some varieties may have bird-resistant grain and low phenolic content in the crop residue. Such varieties may be useful in farming systems in semi-arid areas of Africa where birds are an important pest and the crop residue is an important feed.
Five sorghum varieties, selected on yield criteria, were used to determine the effect of variety on intake and digestibility of the crop residue in mature highland zebu oxen. After grain harvest, the crop residue from each variety was coarsely chopped and fed to five oxen in a latin square design. Oxen were offered 12 kg of crop residue dry matter per day. This diet was supplemented with 60 g of urea added to the drinking water.
Daily dry-matter intake varied by more than 1 kg among varieties (Table 4). The variety with the lowest intake (MW5020) is a dwarf, bird-resistant variety which gives high grain yield but little residue. MW5020 had the highest proportion of leaves in the crop residue but its leaves were strongly pigmented. It was the only variety with a measurable amount of leaf in the feed refusals. The intake of digestible energy from MW5020 would be adequate for maintenance requirements only, whereas the intake from Melkamash and 5DX 160 would allow weight gains of over 200 g per day.
Table 4. The effect of sorghum variety on intake of crop residue by highland zebu oxen.
Variety
|
Percent leaves
|
Mean intake (kg day-1) (n=5)
|
| MW5020 |
43.7
|
4.11a
|
| Buraihi |
23.2
|
4.43a
|
| 2KX17 |
37.9
|
4.90b
|
| Melkamash |
39.3
|
4.96b
|
| 5DX-160 |
35.3
|
5.18b
|
Means with different superscripts are significantly different (p < 0.05).
Millet
Variety had a significant effect on NDF content and NDF digestibility in blades, sheaths and stems from 12 millet varieties (Table 5), and on lignin content in blades and stems. The millet varieties were sampled from an advanced agronomic trial at the ICRISAT (International Crops Research Institute for the Semi-Arid Tropics) Sahelian Center, Sodore, Niger.Table 5. The effect of variety on content of neutral-detergent fibre (NDF), digestibility of NDF (DNDF) and content of lignin in leaf blades, leaf sheaths and stems from the crop residue of 12 millet varieties.
Mean
|
Range
|
Varietal effect
| ||
| Leaf blade | ||||
| NDF (% OM) |
59.9
|
57.7-63.0
|
**
| |
| DNDF (%) |
60.1
|
55.7-62.2
|
***
| |
| Lignin (% OM) |
3.9
|
3.5-4.5
|
**
| |
| Leaf sheath | ||||
| NDF (% OM) |
69.2
|
65.5-70.8
|
**
| |
| DNDF (%) |
42.4
|
38.1-44.9
|
***
| |
| Lignin (% OM) |
5.1
|
4.8-5.9
|
NS
| |
| Stem | ||||
| NDF (% OM) |
76.2
|
72.5-79.6
|
**
| |
| DNDF (%) |
30.7
|
27.6-35.2
|
*
| |
| Lignin (% OM) |
8.7
|
7.6-9.7
|
***
| |
Varietal effect significant at: * P<0.05; ** P<0.01;Although varietal effects were significant, the range in parameters of nutritive value among varieties is lower than among sorghum varieties. The range in NDF digestibility within sorghum plant parts is greater than 15 percentage units (Figure 2), whereas in the 12 millet varieties tested the range was less than 8 percentage units (Table 5). Millet lacks the phenolic pigments that have a large effect on NDF digestibility in BR sorghum varieties.
*** P<0.001; NS not significant.
The digestibility of NDF in the leaf sheath and stem fractions of the 12 millet varieties was low. Varieties with higher digestibility and adaptation to the Sahel need to be sought.
Conclusions
Crop residues will continue to be important feed resources in developing countries and increased ruminant production can be accomplished through improved utilisation of the crop residues from sorghum and millet. Dairy producers in many urban areas of India depend on these crop residues as the major source of roughage. They are supplied by smallholder farmers at organised fodder markets and sale of crop residue can account for more than 50% of total income from crops (Parthasarathy Rao, 1985). These dairy enterprises are meeting the increased demand for milk and milk products in urban areas of India (Walker, 1987).Similar ruminant production systems exist around urban areas in Africa. More efficient utilisation of sorghum and millet crop residues could contribute to increased productivity and income for both livestock producers and smallholder farmers. Crop improvement programmes could improve these systems by developing crop varieties that are suitable for dual purpose production of both grain and fodder.
References
Bullard R W and Elias D J. 1980. Sorghum polyphenolics and bird resistance. In: J H Hulse (ed.), Polyphenols in cereals and legumes. IDRC, Ottawa, Canada.Cummins D G. 1971. Relationships between tannin content and forage digestibility in sorghum. Agronomy Journal 63:501-502.
Deinum B. 1976. Effect of age, leaf number and temperature on cell wall and digestibility of maize. In: Carbohydrate research in plants and animals. Miscellaneous Papers, Agricultural University, Wageningen, No. 12:29-41.
Goering H K and Van Soest P J. 1970. Forage fibre analysis. Agriculture Handbook No. 379. Agricultural Research Service, United States Department of Agriculture, Washington DC, USA.
Gourlay L M. 1979. Nutritional quality of sorghum leaves. In: Eleventh biennial grain sorghum research and utilisation conference, Lubbock, Texas, USA.
Gupta R K and Haslam E. 1980. Vegetable tannins structure and biosynthesis. In: J H Hulse (ed.), Polyphenols in cereals and legumes. IDRC, Ottawa, Canada.
Hartley R D. 1981. Chemical composition, properties and processing of lignocellulosic wastes in relation to nutritional quality for animals. Agriculture and Environment 6:91-113.
Hulse J H. Laing E M and Pearson O E. 1980. Sorghum and millets: Their composition and nutritive value. Academic Press, London, UK.
Jackson M G. 1978. Treating straw for animal feeding. FAO Animal Production and Health Paper 10. Food and Agricultural Organization of the United Nations, Rome, Italy.
Jones L H P and Handreck K A. 1967. Silica in soils, plants and animals. Advances in Agronomy 19:107-149.
Kossila V S. 1985. Global review of the potential use of crop residues as animal feed. In: T R Preston, V L Kossila, J Goodwin and S B Reed (eds), FAO Animal Production and Health Paper 50. Food and Agricultural Organization of the United Nations, Rome, Italy.
Parthasarathy Rao P. 1985. Marketing of fodder in rural and urban areas of India. In: Agricultural markets in the semi-arid tropics. Proceedings of the International Workshop, 24-28 October 1983, ICRISAT Center, Patancheru, India. International Crops Research Institute for the Semi-Arid Tropics, India.
Powell J M. 1984. Sorghum and millet yields and consumption by livestock in the subhumid zone of Nigeria. Tropical Agriculture (Trinidad) 62:77-81.
Reed J D, Tedla A and Kebede Y. 1987. Phenolics, fibre and fibre digestibility in the crop residue from bird resistant and non-bird resistant sorghum varieties. Journal of the Science of Food and Agriculture 39:113-121.
Saini M L, Paroda R S and Goyal K C. 1977. Path analysis for quality characters in forage sorghum. Forage Research 3:131-136.
Walker T S. 1987. Economic prospects for agroforestry interventions in India's SAT: Implications for research resource allocation at ICRISAT. Resource Management Program, Economics Group, Progress Report-79. International Crops Research Institute for the Semi-Arid Tropics, Patancheru, India.
Discussion
Berhane: What are the implications for a plant breeding programme when temperature has such a large effect on pigmentation and digestibility?Reed: We need to look for low pigmented, bird-resistant cultivars. Pigmentation varies considerably among bird-resistant cultivars but this is also heavily influenced by environment, which could lead to genotype by environment interactions. We could score blade pigmentation at various sites; this could easily be incorporated into bird-resistance trials.
Berhane: You singled out one variety which was bird resistant and was high in tannin and high in digestibility. Was that variety incorporated in animal feeding trials?
Reed: I cannot recall if we used this variety in our feeding trials. The variety that had the highest intake in the oxen trial was selected because of the high digestibility of its stems, which indicates that stem digestibility may be a major factor determining the nutritive value of sorghum. This variety was also bird resistant.
Ørskov: What is the correlation between stem, blade and sheath digestibility?
Reed: The correlation was very poor in our data on sorghum.
Pearce: In ryegrass the correlation is quite good: if stem is highly digestible, the sheath and blade will also be highly digestible.
Capper: We looked at botanical fractions in sorghum at ICRISAT. When you plot these against height, over the range of 150 to 300 cm there is little change in the proportion of botanical fractions, but below 150 em the amount of leaf sheath, which is the least digestible fraction and in which there was the most variation in digestibility, starts to increase quite rapidly. If plant breeders breed for shorter varieties, the amount of less-digestible leaf sheath could become very significant. We found that leaf blade and stem have virtually the same digestibility. As suggested, the proportion of leaf sheath has the greatest effect on the nutritive value of sorghum.
Reed: The proportions of plant parts means nothing to a farmer who will feed coarse stovers. The amount of crop residue and the amount of a fraction that can be fed are more important. As such, we should also express our results in yield of the different components per hectare, which may give different relationships. For example, in our trials, medium-height varieties gave a much higher yield of leaf than dwarf varieties, despite having a smaller proportion of leaf in the straw. If you are feeding animals you may want the quantity, not the proportion, except if you were to grind the entire residue and feed it. But when grazed in the field, the leaf fractions are preferred and are of higher nutritive value.
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