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Chemical composition and in vitro digestibility of some range forage species of Iran

M.B. GHADAKI*, P.J. VAN SOEST**, R.E. MCDOWELL** and B. MALEKPOUR***

(*) M.B. Ghadaki: Animal Husbandry Research Institute, Heydarabad, Iran.
(**) P.J. Van Soest and R.E. McDowell: Cornell University, New York, U.S.A.
(***) B. Malekpour: Research Institute of Forests and Rangelands, Tehran, Iran.


Introduction
Area locations and characteristics
Study methods and materials
Results
Crude protein
Crude fibre
Cell wall constituents (CWC) (neutral detergent fibre)
Acid detergent fibre (ADF)
Lignin
Cellulose
In-vitro true digestibility of organic matter (IVTDOM)
Ash and minerals
Discussion
Bibliography


SUMMARY

The nutritive value of 33 species of introduced and native Iranian range plants grown under arid-zone conditions was assessed from collections made in 3 locations in Iran. These species include various grasses, legumes, fortes, and shrubs.

Chemical composition and in vitro true digestibility of organic matter (IVTDOM) for these species were determined at 4 stages of growth, using standard techniques. With the exception of shrubs, the young plant material had higher crude protein than comparable values reported for both temperate and sub-tropical species. Except for grasses and fortes, the young plant material had higher IVTDOM than values reported for both temperate and sub-tropical species.

Stage of growth had a significant influence on nutritive content in all species groups. Crude protein and IVTDOM decreased with the increasing age of plants, while cell wall constituents increased. The decline in crude protein with increased plant age was more pronounced for grasses than for legumes, fortes or shrubs.

In the early stage of growth, the quality of arid-zone forage species is adequate for livestock production. During that stage, the greatest problem is quantity and availability. As the plants mature, the quality decreases so that the forage, even if adequate in quantity and availability, cannot meet the livestock's nutritive demands.

The adequacy of quality and quantity is very important for breeding ewes. The range forage plant supply and its quality are adequate for only a limited time in the late spring and early summer each year. Following an autumn mating, the lambs are born in late winter or early spring. Under this regime, it is not possible to have more than one lamb crop per year. In addition, because the range forage for the ewes does not meet their requirements, the percentage of lambing is low and lamb mortality is high.

As is clear from the results presented here, for better success in lamb and mutton production, it is necessary to provide supplemental rations during early spring and late fall and winter.

Introduction

Research on Iranian rangelands and pastures did not get under way until about 20 years ago. Overgrazing and poor range management have resulted in serious resource deterioration in Iran. Much information is needed about the range flora and the capacity of the rangelands, as a basis for solving such problems.

The climate of Iran is another factor contributing to the low productivity of the rangelands. Hot, dry summers (except in the Caspian Sea area) and cold winters make range improvement very difficult. The precipitation generally is low and variable.

Some work has been undertaken in Iran on range management and ecology. Such aspects of a number of species which are native to Iran or predominant in some other specific arid or semi-arid regions have been rather thoroughly studied (Raleigh, 1969; Nelson, Herbel, and Jackson, 1970; Smith, 1970; Rittenhous, Clanton, and Streeter, 1970; Chatterton et al., 1971; and Wilson, Weir, and Torrell, 1971). There has also been considerable study of North American species (Cook, Stoddart, and Harris, 1952-3; and Cook, Kothmann and Harris, 1965).

No work has been reported in Iran on the chemical composition and in vitro true digestibility of organic matter (IVTDOM) of range plants. This new area merits investigation because the amount of forage available, as determined in dry matter per hectare, by itself is not a sufficient measure of forage adequacy for animal use.

In order to study the nutritive values of introduced and native range plants grown under natural conditions in Iran, samples of 33 species of range plants from three different arid-zone areas of the Central Province were collected and analyzed. This report is concerned with the chemical composition and IVTDOM of these plants.

Area locations and characteristics

Some basic data for the areas where the samples were collected are as follows:

1. Homand Experiment Station

Location: intermountain valley in foothills of Alborz Mountains, about 70 kilometres east of Tehran, Iran.
Elevation: 1,960 metres.
Precipitation: about 325 millimetres per year (average).

2. Kamalabad Exclosure

Location: about 160 kilometres northwest of Tehran, Iran.
Elevation: 1,200 metres.
Precipitation: about 200 millimetres per year (average).

3. Rudshur Exclosure

Location: about 55 kilometres southwest of Tehran, Iran.
Elevation: 1,050 metres.
Precipitation: less than 800 millimetres per year (average), primarily in autumn and spring.

Study methods and materials

Samples of each species were cut at four stages of growth: initial growth (IG); vegetative growth (VG); ripe seed (SR); and fall regrowth (FR). The samples were analyzed at the Animal Husbandry Research Institute, Heydarabad. They were weighed when cut, then oven-dried at 70°C, after which the percentages of dry matter were calculated. The samples were ground after drying and analyzed for crude protein by the Kjeldahl method and for fibre by the official methods of the Association of Official Analytical Chemists.

Procedures described by Goerin and Van Soest, 1972, were used for analysis of: neutral detergent fibre (cell wall constituents) and ash; acid detergent fibre, lignin, cellulose and ash; insoluble silica; and total ash. In vitro digestibility (IVTDOM) and in vitro ash contents were also determined. The amounts of aluminium, calcium, copper, iron, magnesium, manganese, phosphorus, potassium, sodium, and zinc in some samples were found by the spectrographic method. To eliminate the effect of silica on mineral determination after ashing, 0.5 grams of each sample was treated in a platinum crucible by about 1 to 2 millimetres of hydrofluoric acid, evaporated to dryness, and treated by the same amount of 6N hydrochloric acid, evaporated to dryness. The ash residue was dissolved by 5 millimetres of a solution of dilute nitric acid with a lithium internal standard.

Due to the dry climate of the areas of the study, some samples were contaminated by dust and soil. The soil contamination was studied by the determination of insoluble silica in 40 % ethylenediamine.

The resulting percentage of plant silica was reported as the silica soluble in ethylenediamine.

Results

Results of chemical analysis and in vitro digestibility (IVTDOM) tests are reported in Table I. The results are grouped as for grasses, legumes, fortes, and shrubs.

In general, crude protein IVTDOM decreased with the increasing age of the plants, while the amount of cell wall constituents increased. The amplitude of variation is different among legumes, grasses, shrubs and fortes, as well as among different species in the same forage group (Table I). The variations for different components of the plants and plant groups will be presented separately.

Crude protein

During the IG stage, crude protein content was high for legumes and grasses, moderate for fortes and low for shrubs. The IG mean values are 27.4, 23.9, 21.1 and 15.8 %, respectively. The decline in crude protein with increasing plant age is much more pronounced for grasses than for legumes, fortes or shrubs. The mean values of crude protein for mature plants were 8.7, 4.4, 5.6 and 6.3 % for legumes, grasses, fortes and shrubs, respectively.

In the IG stage, the percentage of crude protein varied between 25 % and 28 % for legumes; between 18.8 % and 29.5 % for grasses, with the exception of Aeluropus littoralis (11.0%) and Hordeum bulbosum (]6.5 %); between 20.1 % and 22.2 % for fortes; and between 10.4 % and 22.4 % for shrubs.

There was a high degree of variability in crude protein content, both between plant groups and within groups, at comparable stages of growth.

Crude fibre

In the IG stage, the average crude fibre contents were 22.1, 17.2, 17.0, and 22.2 % for grasses, legumes, fortes, and shrubs, respectively. The variation in crude fibre during all growth stages was higher for grasses and shrubs than for legumes and fortes. The crude fibre percentage for mature plants was 35.9 % for grasses, 39.2 % for shrubs, 33.6 % for legumes, and 29.5 % for fortes. The differences in crude fibre content for the various species in each plant group were as great as the differences between the 4 groups.

As the plants became older, the crude fibre tended to increase for all plants, but for some plants more than others. Taraxacum had the least increase and Kochia prostrata, Camphorosma perenne, Noaea mucronata and Lactuca orientalis showed the greatest increase.

Cell wall constituents (CWC) (neutral detergent fibre)

In the IG stage, the CWC of the grasses was slightly higher than that of the shrubs but much higher than that of the fortes and legumes. The IG mean values of CWC for the 4 groups were 43.8, 41.4, 26.4 and 30.9 %, respectively. There was little CWC variation for Taraxacum in the various growth stages.

Acid detergent fibre (ADF)

During the IG stage, the ADF content of the shrubs was slightly higher than that of the legumes, grasses and fortes. The IG mean values were 28.3, 26.1, 25.9 and 28.5 %, respectively. Regardless of plant age, the ADF content of Taraxacum showed little variation. The variation in ADF during all stages of growth was higher for the grasses than for the fortes, legumes and shrubs. However, the amplitude of variation was different for the various species within each plant group. The highest variations were for Lactuca orientalis, Camphorosma perenne, and Kochia prostrata.

Lignin

The lignin content of grasses was lower than that of shrubs, fortes and legumes. In the IG stage, the mean values were 4.4, 7.8, 7.6 and 6.8 %, respectively. Among the grasses, Agropyron intermedium, Ag. tauri, Ag. aucheri, Hordeum bulbosum and Elymus junceus had the highest values. The differences for the various species within the plant groups were greatest for the IG stage of shrubs, ranging from 4.2 % for Kochia prostrata to 13.5 % for Artemisia herba alba.

The lignin content increased with increasing age for all species except Taraxacum. For the other species, the amplitude of variations was not the same. In some cases, between the SR and FR stages, the lignin content decreased. This could be explained as being due to plant regrowth.

Cellulose

The cellulose content of grasses was higher than that of shrubs, fortes, and especially legumes. Mean IG values were 18.4, 15.3, 11.6 and 7.4 %, respectively. The cellulose content differed for the various species of the same group. In general, the cellulose content increased until the end of the SR stage of growth. For the FR stage, the cellulose content of some species increased while that of others decreased.

In-vitro true digestibility of organic matter (IVTDOM)

Apparent digestibility is estimated by subtraction of a mean value of 12.9 from the various values of IVTDOM.

During the IG stage, the IVTDOM was higher for grasses (93.1 %) and for fortes (92.4 %) than for legumes (83.6 %) and especially for shrubs (71.8 %). During all other stages of growth, the IVTDOM remained higher for grasses and fortes than for legumes and especially for shrubs. For mature plants in the SR stage the IVTDOM mean for grasses (excluding Ae. littoralis) was 72.2 %; for fortes, 71.9 %; for legumes, 65.8 %; for shrubs, 42.6 %.

Within the grass group, the IVTDOM for the various species was approximately the same. The differences between species were not large for grasses of the same age, especially for the IG stage (Fig. 1). The differences for the various grass species at later stages were more pronounced than in the IG stage.

The greatest variation in IVTDOM values occurred among shrubs. In the IG stage, the maximum shrub IVTDOM was 89.8 % and the minimum was 42.6 %. The differences were in about the same order of magnitude for the other stages (Fig. 4).

The IVTDOM of Taraxacum increased between the IG and VG stages, then decreased slightly. The IVTDOM of Ar. herba alba increased with the increasing age of plants, from 55.2 % in the IG stage to 83.7 % in the VG stage.

Ash and minerals

For all stages of growth, the total ash contents of shrubs were higher than those of the. grasses, fortes and legumes. The mean values at the IG stage were 19.2, 18.9, 12.6 and 11.5 % for shrubs, fortes, legumes, and grasses, respectively. The total ash contents were different for various species of the same plant group.

The silica contents of the legumes were less than those of the shrubs, grasses and fortes. At the IG stage, the mean values were 1.8, 3.9, 4.0 and 5.1 % for legumes, fortes, grasses and shrubs, respectively. The variations in silica contents during all stages of growth were not the same for all plant groups. Variations were essentially- the same with increasing age for grasses, but decreased considerably for legumes, fortes, and shrubs. The highest value for silica was 18.8 % for Camphorosma perenne at the IG stage.

The phosphorus contents of the grasses were similar to those of the fortes, legumes, and shrubs. The calcium contents of the grasses were lower than those of the shrubs and especially those of the legumes. The magnesium contents of the grasses were lower than those of the legumes and shrubs. For iron and aluminium, the values varied for the different species and plant groups.

Many of these samples contained a significant amount of soil and dust contamination, which affected the apparent plant content of silica, iron, aluminium and perhaps other elements. This contamination was more serious for the leafier and young plants than for the woody and mature plants.

Discussion

For the plants in the IG stage, especially the legumes, grasses and fortes, the crude protein contents are very high, compared with those of the shrubs. The Iranian grasses and legumes at a very early (IG) stage of growth (20-45 days old), without fertilization, have higher percentages of crude protein than at later stages. (Deinum, Van Es and Van Soest 1968; Tessema, 1972.)

The work of Deinum et al., 1968, has shown that temperature, as well as maturity, has great influence on the nutritive value of grasses; the digestibility of the whole plant is affected by temperature (Fox, 1972).

The IVTDOM of grasses at the IG stage is about 95 %. Considering the age of the plants and the temperatures during the season of growth, the digestibility of arid-zone Iranian grasses is higher than that of temperate-zone grasses (Deinum et al., 1968). The differences in digestibility of arid-zone grasses and temperate-zone grasses can be explained by the differences in the amounts of precipitation in these zones. However, Snaydon, 1972, found a negative correlation between the amount of water and the digestibility of alfalfa.

The IVTDOM of the grasses and fortes at the IG stage of growth is higher than that of the legumes and especially the shrubs. The differences in IVTDOM in the various shrub species are considerable (Fig. 4). In range improvement activities and when introducing new varieties, the yield of digestible organic matter per hectare must be taken into consideration. The amount of dry matter produced is not a good criterion of the nutritive value of plants. For example, for the same amount of dry matter per hectare, the digestible organic content of Camphorosma perenne would be about 1/2 that of Taraxacum.

The changes in the IVTDOM and especially in the crude protein content of the Iranian forage plants during the season of vegetative growth are completely different from such changes for forage plants grown in a temperate zone. The crude protein and IVTDOM of the Iranian plants decrease very rapidly and the CWC, ADF, crude fibre and cellulose increase.

The change in chemical composition in relation to increasing age of Iranian forage grown in the arid zone is more pronounced than the change for forage from temperate zones, but it is less than that for the forage from tropical zones (Tessema, 1972).

The chemical composition of the grasses is completely different from that of the legumes. Grasses have higher percentages of CWC, ADF, cellulose, crude fibre and silica, and lower percentages of lignin, than do legumes. Because of these differences, the IVTDOM of the grasses is higher than that of the legumes. The IVTDOM of grasses 70 days old averages greater than 80 % but, for legumes, the IVTDOM exceeds 80 % only until 30 days of age (Figs. 1 to 4). This difference indicates that the correlation between the chemical composition of the plant material and the plants IVTDOM is due to the species of forage involved.

The chemical composition of fortes and shrubs is approximately the same as that of grasses, except that shrubs have higher percentages of lignin. The chemical composition and the IVTDOM are very different among the various species of shrubs. Fig. 4 shows the relationship between lignin content and IVTDOM of shrubs. For Camphorosma perenne and Atriplex verruciforum, for example, which have virtually the same percentage of lignin (8.9 % and 8.7 %) the IVTDOM ratings are much different (42.6 and 65.9 % respectively).

The pattern of variation between lignin content and IVTDOM is similar for grasses, fortes and legumes, but different for shrubs (Figs. 1 to 4). Also the chemical composition of different species of grasses, legumes, fortes, and shrubs is not the same. The amplitude of variation between different species in the same plant group is similar. So it seems that the lignification does not have the same effect for the different species of shrubs as it does for the grasses, fortes, and legumes.

In the IG stage of growth, the forage quality of the various tested Iranian species grown under arid-zone conditions is very good. The crude protein content and IVTDOM of grasses, legumes and fortes is very high, and the quality of this forage is adequate for livestock production.

At the IG stage, the greatest problem is the quantity and availability of the forage, which in most cases is not sufficient. As the plants mature, their forage quality decreases very rapidly. After plant maturity, even if the quantity is sufficient, the quality is so low that it is not possible to meet even the maintenance requirements of the livestock. That is an important reason why animals lose weight on Iranian summer and fall ranges. In late autumn and winter, only when fed supplemental rations will Iranian livestock gain weight before being sent to the slaughterhouse.

The adequacy of quality and quantity is very important for breeding ewes. The range forage plant supply and its quality are adequate only for a limited time in the late spring and early summer each year. Following an autumn mating, the lambs are born in late winter or early spring. Under this regime, it is not possible to have more than one lamb crop per year. In addition, because the range for the ewes does not meet their requirements, the percentage of lambing is low and lamb mortality is high.

Bibliography

1. Association of Official Analytical Chemist. - Official Methods of Analysis, 11th edition, 1970.

2. CHATTERTON, N.J. et al. - Monthly variation in the chemical composition of desert saltbush. J. Range Management, 1971, 24: 37-40.

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12. SMITH, D.F. - Hordeum species in grassland. Herbage Abstract, 1972.

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14. TESSEMA, S. - Nutritive value of some tropical grass species as compared to some temperate grass species. Ph. D. Thesis, Cornell University, U.S.A., 1972.

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17. WILSON, A.D., WEIR, W.C. and TORELL, D.T. - Evaluation of chemise and interior live oak as feed for sheep. Journal Ag. Sci., 1971.

Figure 1 - Relationship between IVTDOM and age of grasses from Iran - Rapport entre le DRIVMO et l'âge des graminées de l'Iran

Figure 2 - Relationship between IVTDOM and age of legumes from Iran - Rapport entre le DRIVMO et l'âge des légumineuses de l'Iran

Figure 3 - Relationship between IVTDOM and age of herbs from Iran - Rapport entre le DRIVMO et l'âge des graminées de l'Iran

Figure 4 - Relationship between IVTDOM and age of shrubs from Iran - Relation entre le DRIVMO et l'âge des arbustes de l'Iran


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