Assessment of the nutritive value of the seeds of some tropical legumes as feeds for ruminants

S M Odeyinka, B L Hector*, E R Ørskov* and C J Newbold**

Department of Animal Science, Faculty of Agriculture,Obafemi Awolowo University, Ile-Ife, Nigeria
smodeyinka@yahoo.co.uk
*IFRU, The Macaulay Institute, Aberdeen, Scotland
**Rowett Research Institute, Greenburn Road, Bucksburn, Aberdeen AB21 9SB, Scotland

 

Abstract

 

Samples of eight tropical legume seeds (Macroptilium lathyroides (Phasey bean), Centrosema pubescens (centro), Pueraria phaseoloides (Puero), Calopogonium mucunoides (Calopo), Leucaena leucocephala (Leucaena), Stylosanthes guanensis (Stylo), Macroptillium atropurpureum (siratro) and Clitoria ternatea (Blue pea) from Tanzania were evaluated using percent nitrogen (protein) content, in vitro gas production, dry matter (DM) degradability and defaunating ability.

 

Clitoria ternatea seeds had the highest %N (7.07) while Centrosema pubescens had the lowest (3.52). The ranking of the seeds in terms of percent protein content was as follows: Clitoria ternatea>Pueraria phaseoloides> Calopogonium mucunoides>Stylosanthes guianensis> Macroptillium atropurpureum>Leucaena leucocephala> Macroptilium lathyroides> Centrosema pubescens. Species and PEG had significant effect on in vitro gas production.  Centrosema pubescens produced significantly highest volume of gas (55ml) while .Stylosanthes guianensis produced the lowest volume of gas. (29ml).The ranking of the seeds in terms of gas production was: Centrosema pubescens >Macroptillium atropurpureum> Macroptilium lathyroides > Leucaena leucocephala >Pueraria phaseoloides > Calopogonium mucunoides > Clitoria ternatea > Stylosanthes guianensis..  There was increase in gas production on addition of PEG only in Stylosanthes guianensis (P<0.05).  The seeds had high degradability. Leucaena leucocephala and Stylosanthes guanensis seeds were the least degraded while Centrosema pubescens was the most degraded. The ranking of the seeds based on nylon bag degradability was: Centrosema pubescens> Pueraria phaseoloides > Clitoria ternatea > Macroptilium lathyroides > Macroptillium atropurpureum> Calopogonium mucunoides > Leucaena leucocephala> Stylosanthes guianensis. There was a high positive correlation between in vitro gas production and nylon bag degradation (r=0.87). Only seeds of Calopogonium mucunoides and Clitoria ternatea.had defaunating activities.

 

It is concluded that the seeds of tropical legumes have potential as feed supplements for ruminants as they have high digestibility and are rich in nitrogen. Clitoria ternatea and Calopogonium mucunoides appear to have potential as defaunating agents.

Key words: Defaunation, in sacco degradability, in vitro gas production, seeds, tropical legumes.

Introduction

 

Ruminants play an important role in the livelihood of farmers in the developing world, providing sustenance as milk and meat, animal traction, manure for crop production and energy, cash income from sales of their products and a safety net of capital assets to face risks and misfortune in harsh environments (Ørskov and Viglizzo 1994). Projected increases in the human population throughout the developing world and the limited availability of land for increased food and forage production suggest that agricultural production needs to be intensified considerably to satisfy the escalating demand for food.

 

Lack of adequate nutrition all year round is one of the major causes of the low productivity of ruminants in sub-Saharan Africa (Osuji et al 1995). Ruminants have the ability to thrive on forages, which are abundant in the rainy season. However, tropical forages are nutritionally adequate only when the plants are very young. (Adegbola 1985). During this period, a lot of seeds are produced which are usually wasted. Some of these seeds are eaten in the field by grazing animals. It is therefore necessary to determine the composition of the seeds and determine which ones could be used as protein supplements especially during the dry season. It is also possible for some of the seeds to have defaunating activities. The seeds with high protein content combined with defaunating activities could result in greater microbial protein flow into the small intestine thus providing the host animal with more protein.

 

The objectives of the study were therefore:

1. To determine the protein content of the seeds of some tropical forages.
   
   
2. To determine their degradability and content of antinutritive factors using in sacco and in vitro methods.
   
   
3. To evaluate their potential as defaunating agents.

Materials and Methods

 

Description of the seeds

 

Below are listed the seeds of the tropical legumes used in the study as described by Partridge (1998):

 

Macroptilium lathyroides(DC) Urb. (phasey bean)

This is a self regenerating annual or biennial. It is tolerant of water-logging and it has flowering and fruiting branches.

 

Centrosema pubescens Benth, (centro)

It is a climbing, twining perennial that is the foundation of fattening and dairying pastures in the wet tropics. Centro combines well with tall grasses such as guinea grass, but has also done satisfactorily with pangola and para grass. While moderately palatable, centro can withstand heavy grazing. Centro has a good rooting system and can withstand a long dry season.

 

Pueraria phaseoloides (Roxb.) Benth (Puero)

Puero has been used as a pioneer crop, green manure and a good ground cover under plantation crops in the humid tropics. It establishes and grows vigorously in pastures, forming a dense, smothering mat under lightly grazed condition. As it does not persist under heavy grazing, puero should be sown with more persistent species such as centro.

 

Calopogonium mucunoides Desv.(calopo)

Calopo is a short-lived, vigorous trailing perennial which will climb over any vegetation to form a dense mat of foliage. It seeds freely and regenerates naturally from seed.

 

Leucaena leucocephala (Lam.) de Wit.(Leucaena)

It is drought resistant which makes it an invaluable dry season feed. Leaves and seeds of leucaena contain mimosine, a toxic amino acid which can produce ill effects in ruminants which do not have the necessary micro-organisms in their rumen to detoxify it.

 

Stylosanthes guanensis (Aubl.) Sw. (Stylo)

Stylo is a perrennial legume for warm humid tropics.It is fairly drought tolerant and also very tolerant of low fertility and acid soils. Seed should be surface sown or planted no deeper than 10mm without needing inoculation as seedlings nodulate with natural rhizobium strains. It is susceptible to anthracnose soils.

 

Macroptillium atropurpureum (DC) Urb.(Siratro)

Siratro is a perrennial twining legume for a wide range of reasonable soils. It combines with tall grasses but it is not tolerant of constant heavy grazing. It is a highly productive specie that is able to fix large amount of nitrogen and pass this quickly to the companion grasses.

 

Clitoria ternatea (L.) (Blue pea)

Tender perennial legume. Needs an abundance of water and good drainage

 

Treatments

Each of the seeds was subjected to a series of analyses, as described below:

 

Nitrogen analysis

The total nitrogen (N) content of the seeds was determined by an automated Dumas combustion procedure (Pella and Colombo 1973) using a Carlo Erba NA 1500 Elemental Analyser (Carlo Erba Instruments, Milan, Italy). The crude protein content was calculated by multiplying the total nitrogen value by 6.25.

 

In vitro gas production

The procedure used was that described by Menke et al (1979). The seed samples were oven dried at 70°C for 24 hours and milled using a 1-mm screen. In vitro gas production was measured using the method described by Blummel and Ørskov (1993) by incubating the samples with buffer and rumen fluid and recording the volume of gas produced over time. Measurements were made after 3, 6, 12, 24, 48, 72 and 96 hours of incubation. Analysis was carried out in triplicate in the presence and absence of 200mg PEG, molecular weight 4000 (Sigma-Aldrich Company Ltd, Poole, Dorset, UK). The gas syringes were incubated by suspension from a rack fitted above a water bath. The rumen fluid was obtained from two sheep, fitted with permanent rumen cannulae, receiving a diet of dried grass pellets and hay.

 

In sacco DM degradability

Estimations of rumen degradability were made using the nylon bag technique described by Ørskov et al (1980). The nylon bags used were 8cm x 14cm, 40 to 60-micron pore size (IFRU, The Macaulay Institute, Aberdeen, UK). Duplicate samples were incubated in 2 different sheep receiving the same diet as above. The following incubation times were used: 4, 8, 16, 24, 48, 72 and 96 hours.

 

The results of the experiments were analysed using the "Fitcurve" macro (Chen 1995, IFRU, The Macaulay Institute, Aberdeen, UK, Unpublished) for Microsoft Excel. The program is a utility for processing data of feed degradability or in vitro gas production; it fits the data to the exponential equation p=a+b(1-e^-ct) developed by Ørskov and McDonald (1979). For degradability characteristics, p is the percentage degraded at time t, a is the intercept of the line at time zero (or the soluble fraction), b is the insoluble but degradable fraction, therefore a+b is the potential degradability and c is the rate of degradation. Another method is to use A as the solubility, B as the insoluble but fermentable fraction (B=(a+b)-A). For in vitro gas production, the data is fitted to the same equation, p is the volume of gas produced at time t, a is the intercept of the line at time zero, b is the potential gas production and c is the rate constant (Ørskov and Ryle 1990).

 

Screening of seeds for antiprotozoal activity

Protozoal activity was measured by the breakdown of [¹⁴C]leucine-labelled Selenomonas ruminantium in vitro as described by Wallace and McPherson (1987). Rumen fluid was obtained 2 h after feeding from three mature rumen cannulated Dorset-cross sheep receiving 1 kg/d of a mixed diet of grass hay, barley, molasses, white fish meal and a mineral and vitamin mixture (500, 300, 100, 95 and 5 g/kg fresh weight). Rumen fluid was strained through two layers of muslin and pre-incubated at 39^oC with the seeds at 0.5, 1 or 5 g/litre for 1 h before adding Selenomonas ruminantium. Unlabelled L-leucine was included in all incubations at a final concentration of 5 mmol/litre to prevent re-incorporation of released [¹⁴C]leucine. When screening seeds for antiprotozoal activity, it was not possible to test all seeds with the same batch of rumen fluid from each sheep in a single day. Thus different seeds were tested on different days using rumen fluid with slightly different protozoa populations and hence different control activities.

 

Statistical Analysis

The results were subjected to statistical analysis using GENSTAT 5 Release 4.1 software package. Analysis of variance was done to detect differences between treatments. Variations in each dependent variable were partitioned into 2 components: variations attributable to known (experimental factors and their interactions) and unknown (random error) components. Differences between treatments were analysed using means across replications. Least significant difference (LSD) test was used to compare treatment means.

 

Results and Discussion

 

 Clitoria ternatea seeds had the highest %N and thus highest %CP (42.2) while Centrosema pubescens had the lowest (22%)  (Table 1 and Figure 1).

Centrosema pubescens produced a significantly higher volume of gas while Stylosanthes guianensis produced the lowest volume of gas (Table 2 and Figure 2). Only Stylosanthes guianensis showed significant increase on addition of PEG. There was a negative relationship between N content and gas production (r= -0.71).
 

 

 

Figure 2: Range of values for gas production in seeds of leguminous plants from Tanzania

 

 

Table 3 and Figure 2 shows the degradation characteristics of the seeds.

 

All the seeds had high DM degradability with Centrosema pubescens having 99% degradation. at 72 hour of incubation. Stylosanthes guianensis and Leucaena leucocephala seeds were the least degraded. (Table 4 and Figure 3).