| Livestock Research for Rural Development 24 (10) 2012 | Guide for preparation of papers | LRRD Newsletter | Citation of this paper |
The potential nutritional value of four species of leguminous forage (Hedysarum coronarium L, Medicago truncatula L, Vicia sativa L, Pisum sativum L ) grown in Tunisia were harvested at 50 % of flowering stage and evaluated for their nutritive value by chemical composition and gas production technique.
The content of organic matter ranged from 846.7 to 946.5 g/kg dry matter (DM). The forage had high crude protein (195–216 g/kg DM) and variable neutral detergent fiber (NDF: 397- 432 g/kg DM) contents. All species contained satisfactory levels of phosphorus, calcium, potassium, sodium, magnesium and iron. The gas production after 48 h incubation ranged from 45.6 to 65 mL/200 mg DM. Metabolisable energy (ME) and short chain fatty acids (SCFA) were different among the species, with the highest value recorded for Hedysarum coronarium L and Vicia sativa L. The result indicates that such legumes have the potential to be used to feed ruminants.
Key words: gas production, in vitro digestibility, mineral composition
Mediterranean legume forages have a considerable role as protein source in animal diets. Feed legumes provide grazing in spring and early summer or silage, hay, straw, and seed for the periods of forage deficit, such as winter (Thomson and Bahhady 1992). They are rich in most nutrients, such as proteins and minerals, and tend to be more digestible than grass.
Medicago truncatula is recognized as a high quality dry-land pasture. It has high nutritive value, and the forage is highly acceptable to stock and so has high voluntary intake characteristics (Brand et al 1991). Sulla (Hedysarum coronarium L.) is a legume well grazed by animals and is resistant to grazing and trampling (Watson 1982). It was reported that fresh Sulla is forage with good nutritive value (Dentinho et al 2011).
Another legume with potential is Pisum sativum which has long been used in livestock feeds as a source of energy and protein (Teresa et al 1991). Common vetch (Vicia sativa L.) is annual leguminous commonly used forage in the Mediterranean basin and West Asia in rotation with winter cereal small grain (Hadjipanayiotou et al 1985).
In this study we used four legume plants (Hedysarum coronarium L , Medicago truncatula L, Vicia sativa L and Pisum sativum L.) well adapted to the Mediterranean conditions and considered of interest for feeding ruminants. The objective was to determine the potantial nutritive value using their chemical composition and in vitro fermentation pattern.
Four legume species Hedysarum coronarium L , Medicago truncatula L, Vicia sativa L and Pisum sativum L. were evaluated in the present study. All the species were grown on the National Institute for Research in Agronomy. This area is located in northern Tunisia at an altitude of 600 m above sea level with an average annual rainfall and temperature of 450 mm and 20–23°C, respectively. Forage legumes (stem and leaves) were cut 10 cm above the ground at 50 % of flowering stage in April, 2008.
The harvested samples were oven dried at 50°C for 48 h then ground to pass through a 2.0 mm sieve. The samples were then sub-sampled to obtain three samples for each legume species and used for laboratory analysis. The dry forage samples were further ground to pass through a 1.0 mm sieve for the in vitro gas production experiments and chemical analysis.
Forage samples were analysed for dry matter (DM), organic matter (OM) and crude protein (CP). The fiber fractions (neutral detergent fiber: NDF) and acid detergent fiber (ADF) were analysed according to Van Soest et al (1991). Phosphorus (P), Calcium (Ca), Potassium (K), Sodium (Na), Magnesium (Mg) and Iron (Fe) were determined on a VARIAN Atomic Absorption Spectrometer (Spectraa-5 Model). All chemical analyses were carried out in triplicate.
In vitro incubations of forage samples were carried out using the method of Menke & Steingass (1988). Samples (0,2 g) were incubated in triplicate with rumen fluid taken before the morning feed from a rumen-cannulae sheep fed oat hay (70%) and concentrate (30%). The inoculum was mixed with a buffer solution in a ratio of 1:2 (v/v). Three syringes containing 40 ml inoculum served as blanks. Gas production was recorded at 0, 2, 4, 6, 8, 12, 24, 36 and 48 hours. Calculation of potentially gas production (b) and the rate of fermentation (c) values were those outlined by France et al. (1993). The data obtained were fitted to the non-linear equation: V (ml/200mg DM) = b (1-e-ct) where:
V = potential gas production at time t,
b = the volume of gas that will evolve with time, and
c = the fractional rate of gas production.
The ME, organic matter (OM) digestibility (OMD, %) and SCFA produced in syringe were calculated as follows:
ME (MJ / Kg DM) = 2.20 + 0.136 Gp + 0.057 CP (Menke and Steingass 1988),
OMD=24.91+0.7222 GP+0.0815 CP n =185, R2=0.78
SCFA (mmol/syringe)= 0.0239.Gas -0.0601 (Getachew et al 2000)
Where ME is the metabolisable energy; SCFA: short chain fatty acids; CP, crude protein in % and Gp, the net gas production in ml from 200 mg dry sample after 24 h of incubation.
Apparent organic matter (OM) digestibility (OMD, %) of legumes was estimated from the volume of gas produced after 24 h of incubation (GP, ml/200 mg DM) and the proportion of crude protein (CP, g/kg DM)
One-way analysis of variance (ANOVA) was carried out to compare the chemical composition, gas production, OMD , ME and SCFA values using the General Linear Model (GLM) of Statistica for windows (1993). Significance between individual means was identified using the Tukey's multiple range tests.
The chemical composition of four forage samples are given in Table 1. Although there were significant differences among forage samples in terms of DM and organic matter contents, there were no significant differences among forage samples in terms of CP and cell wall contents (NDF and ADF).
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Table 1: Chemical composition ( % DM, except for DM which is on fresh basis) of forages |
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|
Species |
DM |
OM |
CP |
NDF |
ADF |
|
Medicago truncatula L |
21c (0.4) |
87.6b (0.9) |
19.6 (0.8) |
41.01 (1.07) |
28.7 (1.4) |
|
Pisum sativum L |
26.0d(2.05) |
88.6a (0.01) |
19.4 (0.01) |
43.2 (0.01) |
27.8 (0.01) |
|
Hedysarum coronarium L |
15.2b(1.2) |
88.7a (1.6) |
19.3 (1.3) |
40.2 (5.81) |
29.8 (1.4) |
|
Vicia sativa L |
13.5a (0.9) |
87.1b (0.4) |
21.6 (1.7) |
39.7 (3.06) |
28.2 (2.2) |
|
Pr>F |
0.001 |
0.001 |
0.1234 |
0.1835 |
0.4283 |
|
a, b, c and d: means in the same column with different superscripts are significantly different at p< 0.05. |
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In general, all species contained satisfactory levels of P, Ca, K, Na, Mg and Fe (Table 2). The highest potassium content was found in Vicia Sativa and the lowest was in Hedysarum coronarium L. A high amount of sodium was recorded in Hedysarum coronarium L. Magnesium content was higher in Vicia sativa L and Medicago truncatula L.
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Table 2: Mineral contents (% of dry matter) of forage legume (stem and leaves) at 50 % of flowering stage |
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|
Species |
P |
Ca |
K |
Na |
Mg |
Fe |
|
Medicago truncatula L |
0.18 |
2.7 |
1.52 |
0.28 |
0.37 |
0.03 |
|
Pisum sativum L |
0.11 |
2.4 |
0.83 |
0.10 |
0.27 |
0.02 |
|
Hedysarum coronarium L |
0.10 |
2.3 |
0.67 |
0.35 |
0.28 |
0.02 |
|
Vicia sativa L |
0.13 |
2.3 |
1.93 |
0.21 |
0.38 |
0.04 |
|
Probability |
NS |
NS |
0.021 |
0.035 |
0.010 |
NS |
| NS: value in the same column are not different (P>0.05) | ||||||
There were significant (p< 0.05) differences in gas production among the four species (Table 3). The highest value of parameter b was determined for Hedysarum coronarium L and the lowest for Medicago truncatula L . The highest volume of gas at 48 h was produced by Hedysarum coronarium L and Vicia sativa L and the lowest by Medicago truncatula L. These gas production results indicate that Hedysarum coronarium L is the highest fermentable legume species. Fast degrading forage is a desirable characteristic because it can result in increased feed intake by grazing ruminants. It has been speculated that the gas production technique may not be suitable for evaluating high-protein feeds because released ammonia may react with CO2 and precipitate, thus reducing gas volume (Menke and Steingass 1988), and an inverse relationship has been observed between protein content of the test food and gas volume. In our case, in vitro 48h incubation showed higher results for Hedysarum coronarium L and Vicia sativa L. indicating that, although an underestimation of OM fermentation could have occurred because of a higher ammoniacal nitrogen production (which cannot be verified in our results), differences between Hedysarum coronarium L, Vicia sativa L and the other species still remained.
As it is depicted in Table 3, all studied species were fermented at the same rate (p>0.05) but the volume of gas production (b) was significantly different among species and the highest values were found in Hedysarum coronarium L and Vicia sativa L.
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Table 3: Parameters of In vitro gas production |
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|
Species |
b (ml) |
c (h-1)) |
G48 (ml) |
SCFA (mmol/syringe)* |
ME (kcal/kg DM) ** |
OMD (%)*** |
|
Medicago truncatula L |
49.0 |
0.08 |
45.6c (1.15) |
0.85c |
2038b |
67.6c (0.18) |
|
Pisum sativum L |
54.8 |
0.08 |
49b (1) |
0.94b |
2155b |
70.5b (0.24) |
|
Hedysarum coronarium L |
65.7 |
0.06 |
65a (3) |
1.08a |
2349a |
74.6a (0.99) |
|
Vicia sativa L |
62.9 |
0.06 |
62.3a(1.15) |
1.13a |
2445a |
78.1a (1.36) |
|
Probability |
0.01 |
0.52 |
0.001 |
0.001 |
0.001 |
0.024 |
|
*SCFA: short chain fatty acids, **ME: Metabolizable energy, ***OMD: Organic Matter Digestibility. a, b, c : means in the same column with different superscripts are different at p< 0.05 |
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All calculated variables (SCFA, ME, OMD) were significantly affected by the species (Table 3). The ME, SCFA and OMD were highest (P<0.05) in Hedysarum coronarium L and Vicia sativa and lowest (P<0.05) in Medicago truncatula L.
Alfalfa leaves are protein-rich and low in cell wall concentration and, therefore, highly digestible (Jung et al 1997). In contrast to leaves, stems exhibit low digestibility as a result of high concentrations of cell wall polysaccharides and lignin (Buxton and Russell 1988). Selmi et al (2010) investigated the leaves of Medicago truncatula L , Pisum sativum L, Hedysarum coronarium L and Vicia sativa and observed greater CP and much lower fibre fraction (NDF and ADF) concentrations compared with whole plants utilized in this study. A good performance of the four studied legumes was observed also by the same authors in an in vitro study. This may be explained by the low potential feeding value of stem which represents 50 to 70% of biomass.
Plants of Medicago truncatula L , Pisum sativum L, Hedysarum coronarium L and Vicia sativa L are good sources of CP and metabolisable energy.
Adequate feed rations can be formulated by combining these leguminous with grasses and will help ameliorate the overall productive performance of ruminants with lower cost of feeding.
This research was financially supported by the Laboratory of Economie Agro-alimentaire and AECI (Agence Espagnole de Coopération Inter-universitaire).
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Received 2 September 2012; Accepted 22 September 2012; Published 1 October 2012