Chemical composition and degradation characteristics of foliage of some African multipurpose trees

Animal Feed Science and Technology 86 (2000) 27±37

Chemical composition and degradation characteristics of foliage of some African multipurpose trees S.M. El hassana,b,1, A. Lahlou Kassib, C.J. Newbolda, R.J. Wallacea,* a

Rowett Research Institute, Greenburn Road, Bucksburn, Aberdeen AB21 9SB, Scotland, UK b International Livestock Research Institute, Addis Ababa, Ethiopia

Received 24 September 1999; received in revised form 28 March 2000; accepted 17 May 2000

Abstract Samples of foliage from multipurpose leguminous trees (MPT) which had been selected as potential feed supplements for ruminants were examined for their chemical composition and in situ degradation characteristics, and were compared with alfalfa (Medicago sativa) hay and teff (Eragrostis abyssinica) straw. Organic matter (OM), acid detergent ®bre (ADF), neutral detergent ®bre (NDF), nitrogen, neutral detergent nitrogen, acid detergent lignin (ADL), soluble phenolics, NDF-bound proanthocyanidins and in vitro digestibility were determined in Acacia angustissima, Chamaecytisus palmensis (Tagasaste), Leucaena leucocephala, two cultivars of Sesbania sesban and Vernonia amygdalina (bitter leaf). The MPT all had a nutrient content, particularly in terms of N (up to 39.5 g available N per kg dry matter (DM)) similar to alfalfa hay, which would be suitable for supplementing teff straw, which had a high ®bre, but low N (4.0 g available N per kg DM) content. In situ nylon bag digestion and in vitro gas production analyses were carried out to assess microbial degradation characteristics. The MPT were highly degradable in situ, however gas production in vitro decreased as the MPT:teff straw ratio increased in A. angustissima, indicating that antimicrobial components were present in this species. None of the chemical estimations were correlated with antimicrobial properties. It is concluded that some of the MPT tested may prove to be useful dietary supplements for ruminants receiving poor quality forages like teff straw, as has been found in other studies. However, chemical analysis alone will be of limited value in predicting the nutritive value of a new MPT which contains antimicrobial components or material toxic to the animal itself. # 2000 Elsevier Science B.V. All rights reserved. Keywords: Ruminants; Foliage; Supplement *

Corresponding author. Tel.: ‡44-1224-716656; fax: ‡44-1224-716687. E-mail address: [email protected] (R.J. Wallace) 1 Present address: Faculty of Veterinary Medicine, Department of Physiology, University of Khartoum, Khartoum North, Sudan. 0377-8401/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 7 - 8 4 0 1 ( 0 0 ) 0 0 1 5 8 - 9

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1. Introduction Tropical graminaceous fodder and crop by-products in sub-Saharan Africa have a low nutritive value due to their low protein and fermentable energy content. Leguminous forages and the foliage of multipurpose trees (MPT) which are found throughout Africa and Asia (Devendra, 1990) are promising sources of protein if used as a supplement to ruminants receiving these low-quality forages. MPT have the added bene®ts that they provide fuel and shelter and help in preventing erosion in the rural environment. Many of the MPT are problematic as feed supplements because they often contain antinutritional compounds, such as tannins, saponins and non-protein amino acids, which are either toxic to rumen microbes or to the animal, or their metabolic products are toxic (D'Mello, 1992; Lowry et al., 1996). Chemical analysis, particularly in combination with in vitro digestibility and in situ degradability, can help in the preliminary evaluation of the likely nutritive value of previously uninvestigated MPT (Bamualim et al., 1980; Rittner and Reed, 1992). These analyses give no indication of antimicrobial activity, however, which may be signi®cant (El hassan et al., 1995; Nsahlai et al., 1995a). This study therefore investigated the chemical composition, in vitro enzymatic digestibility, and in situ degradation characteristics of six cultivars of MPT of interest to the International Livestock Research Institute (ILRI), comparing their properties with those of alfalfa (Medicago sativa) hay and teff (Eragrostis abyssinica) straw. These data were then compared with in vitro gas production characteristics at different ratios of forage:MPT in order to detect antimicrobial properties of different MPT. 2. Materials and methods 2.1. MPT Acacia angustissima, Chamaecytisus palmensis (Tagasaste), Leucaena leucocephala, two cultivars of Sesbania sesban (10 865 and 15 036), and Vernonia amygdalina (bitter leaf) were examined for their chemical composition, in vitro dry matter (DM) digestibility, soluble phenolics content and neutral detergent ®bre (NDF)-bound proanthocyanidins. Alfalfa hay and teff straw were also evaluated. The samples of A. angustissima, L. leucocephala and S. sesban were leaves with small twigs. The sample of C. palmensis and V. amygdalina were leaves only. The alfalfa hay sample was the whole plant, while teff straw was the straw of the staple crop of the Ethiopian highlands. The plant samples were shade-dried except teff straw. 2.2. Chemical analysis Samples were ground to pass a 1 mm screen and analysed for DM, ash and organic matter (OM) by the methods of the Association of Analytical Chemists (1975). The nitrogen (N) content of the whole plant and NDF fraction (NDF-N) were determined by Kjeldahl digestion using Na2SO4 and CuSO4 as catalysts. Digests were made alkaline and

S.M. El hassan et al. / Animal Feed Science and Technology 86 (2000) 27±37

29

ammonia was determined by steam distillation, trapping in boric acid and titrating with 0.1N HCl. The available N was estimated by subtracting NDF-N from the total N content of the sample. Acid detergent ®bre (ADF), acid detergent lignin (ADL), and NDF were determined by the methods of Van Soest and Robertson (1985). NDF was determined with amylase and sodium sulphite and is expressed as ash-free NDF. The in vitro digestibility was determined by the method of Tilley and Terry (1963) as modi®ed by Van Soest and Robertson (1985) by substituting the second stage (pepsin digestion) with neutral detergent extraction). This treatment removes all indigestible microbial matter and leaves a residue of undigested plant cell walls. Values are expressed as in vitro DM digestibility percentage (IVDMD%). The soluble phenolics and insoluble NDF-bound proanthocyanidins were extracted from the sample which was air-dried at 258C and analysed as described by Reed et al. (1985) and Reed et al. (1982), respectively. 2.3. In situ degradability The disappearance of DM, OM and N from nylon bags was determined as described by érskov et al. (1980). Samples were ground through a 2.5 mm mesh screen using a hammer mill. Nylon bags with a pore size of about 41 mm2 and 5 cm8 cm size were used. Three grams of samples were placed in the nylon bag and incubated in the rumen of three cannulated (ZebuFriesian) bulls. As the variation between nylon bags (3.3%) was lower than variation between days (4.9%; Mehrez and érskov, 1977), it was decided to compare all the plants at the same time, thus one bag from each plant for each incubation time was incubated in the rumen of each of the three bulls. The bulls were fed 2 kg noug cake (Guizotia abyssinica, an oil seed grown in the Ethiopian highlands) per day, and grass hay ad libitum. Salt block and water were available at all times. Bags were removed after 0, 6, 12, 24, 48, 72 and 96 h of incubation. The bags were then washed in a washing machine for about 30 min in cold water, spun and allowed to dry to constant weight at 608C in a forced air oven for 48 h. The initial washing losses were estimated from bags in the washing machine for 30 min. The dried bags were weighed at room temperature after cooling in a desiccator. The disappearance of DM, OM and N were expressed as percentages and were determined for each bag. The percentages of DM, OM and N disappearance were used to derive the potential extent (asymptote) and rate of sample degradation using the model described by érskov and McDonald (1979). 2.4. In vitro gas production The technique described by Menke et al. (1979) and Menke and Steingass (1988) was followed. DM (300 mg) was weighed in triplicate into 100 ml calibrated glass syringes. Arti®cial saliva, comprising macro elements, buffer, micro elements and reducing solution, was prepared as described by Menke et al. (1979) and Menke and Steingass (1988). Rumen ¯uid from the same bulls used in in situ incubations was strained through muslin and mixed with arti®cial saliva (1:2). The inoculum (30 ml) was injected into each syringe. The volume of the syringe barrel was then recorded and the syringe was incubated at 398C in a water bath covered with a perspex lid ®tted with holes to hold the

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S.M. El hassan et al. / Animal Feed Science and Technology 86 (2000) 27±37

syringes upright. The volume of the gas produced was recorded at 0, 3, 6, 9, 12, 24, 72 and 96 h. Three syringes containing rumen ¯uid inoculum were incubated as controls. These controls were used to compensate for gas production in the absence of substrate. The syringes were inverted by hand frequently. 2.5. Statistical analysis Unless indicated otherwise, data are the result of duplicate analysis. In situ degradability and in vitro gas production from the various plants were compared using a General Linear Model Procedure (SAS, 1989). 3. Results All the samples of MPT had a similar DM and OM content, and none had a particularly high ash content (Table 1); V. amygdalina was highest, at 13.4%. Their N content was highly variable, however, ranging from 25 g/kg DM (V. amygdalina) to 41.4 g/kg DM (S. sesban 10 865), compared with 34.7 g/kg DM for alfalfa hay and 6.7 g/kg DM for teff straw (Table 1). Substantial quantities of N were associated with NDF in L. leucocephala, C. palmensis, V. amygdalina and A. angustissima, decreasing available N signi®cantly. The highest contents of NDF and ADF were present in teff straw, yet its ADL and phenolics contents were low (Table 2). The other materials had much lower NDF values, with S. sesban being particularly low in both samples investigated (Table 2). In vitro digestibilities were variable within the MPT examined, ranging from 58.6% (A. angustissima) to 76.7% (S. sesban 10 865), while the digestibility of teff straw was only 39.3%. The soluble phenolics of MPT ranged from 308 g/kg DM (A. angustissima) to 126 g/kg DM (V. amygdalina). The NDF-bound proanthocyanidin content varied between 47.3 AU/g (L. leucocephala) and 3.8 AU/g (V. amygdalina), while alfalfa hay contained no NDF proanthocyanidins. Table 1 Dry matter (DM), organic matter (OM), nitrogen, neutral detergent ®bre (NDF)-bound nitrogen and available nitrogen in alfalfa hay, teff straw and various multipurpose trees (MPT)

Teff (E. abyssinica) straw Alfalfa (M. sativa) hay MPT A. angustissima C. palmensis L. leucocephala S. sesban (10 865) S. sesban (15 036) V. amygdalina

DM (g/kg)

OM (g/kg DM)

Nitrogen (g/kg DM)

NDF-bound nitrogen (g/kg DM)

Available nitrogen (g/kg DM)

932 918

908 898

6.7 34.7

2.7 3.0

4.0 31.7

908 920 908 918 904 890

909 941 897 903 882 866

40.8 33.3 31.5 41.4 36.3 25.0

14.5 11.0 13.4 1.9 5.5 12.0

26.3 22.3 18.1 39.5 30.8 13.0

S.M. El hassan et al. / Animal Feed Science and Technology 86 (2000) 27±37

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Table 2 Fibre content, in vitro digestibility, soluble polyphenolics and NDF-bound proanthocyanidin content of alfalfa hay, teff straw and various MPT

Teff (E. abyssinica) straw Alfalfa (M. sativa) hay MPT A. angustissima C. palmensis L. leucocephala S. sesban (10 865) S. sesban (15 036) V. amygdalina

NDF (g/kg DM)

Acid detergent fibre (g/kg DM)

Acid detergent lignin (g/kg DM)

In vitro Soluble NDF-bound DM phenolics proanthocyanidin digestibility (g/kg DM) (AU/g)a (%)

808 415

446 325

51 63

39.3 62.3

77 140

2.1 0.0

364 388 346 170 242 395

179 217 192 117 160 314

82 76 94 32 54 87

58.6 67.8 66.5 76.7 67.8 63.6

308 176 251 196 246 126

10.2 3.3 47.3 36.4 45.9 3.8

a NDF-bound proanthocyanidin is expressed as A550 absorbance units (1 cm pathlength) per gram of NDF as described by Reed et al. (1982).

The in situ degradability of the plants (Table 3) was calculated from their degradation characteristics. The mean effective degradability (P) of DM, OM and N degradabilities was calculated using the equation Pˆa‡(bc/(c‡k)) (érskov, 1982) where k is the out¯ow rate. In the present study, the out¯ow rate was assumed to be 5%/h, which is generally accepted to be a typical ruminal out¯ow rate in sheep receiving similar low-quality forages. The rumen degradable N (RDN) and RDN per kg rumen degradable OM (RDN/ kg DOMR) were estimated from the P value of N and OM, respectively. DM degradability varied between the plants, in S. sesban 10 865 having the highest effective degradability (Table 3). Soluble N losses were particularly high for alfalfa hay (Table 3). The RDN and RDN/kg DOMR values were highest for S. sesban 10 865 (29.8 and 50.3%, respectively) and lowest for teff straw where N associated with particulate material increased, presumably due to microbial colonisation (Table 3). Unfortunately, it was not possible technically to evaluate the effect of all the MPT on gas production on the same day. Thus, the value for 0% inclusion (teff straw only) is higher for C. palmensis, L. leucocephala, alfalfa hay and S. sesban 10 865 than A. angustissima, S. sesban or V. amygdalina, presumably re¯ecting differences in the inoculum recovered from the bulls on the two days of incubations (Table 4). A standard material incubated on both days may have avoided this dif®culty, and incubation of such a standard is now common in many laboratories. The rate of gas production (c) increased progressively with the inclusion of MPT or alfalfa hay. Potential gas production (b) decreased with inclusion of A. angustissima, V. amygdalina, C. palmensis, L. leucocephala and S. sesban. Alfalfa hay decreased b progressively as its inclusion rate increased. The ®nal gas production after 96 h incubation (GP 96) decreased when A. angustissima and V. amygdalina were added to teff straw. The GP 96 was neither affected by L. leucocephala nor by S. sesban except at the 15% level. The GP 96 was increased by C. palmensis at the 30 and 60% levels and alfalfa hay at 15% inclusion.

32

Plant

Teff (E. abyssinica) straw Alfalfa (M. sativa) hay MPT A. angustissima C. palmensis L. leucocephala S. sesban (10 865) S. sesban (15 036) V. amygdalina SED

DM

OM ÿ1

Nitrogen ÿ1

ÿ1

RDN (g/kg DM)

RDN/kg DOMR

a

b

c (h )

P

a

b

c (h )

P

a

b

c (h )

P

19.6 42.0

57.5 35.7

0.017 0.105

34.0 66.2

17.4 39.7

59.9 38.0

0.018 0.095

33.2 64.5

21.6 58.9

42.8 34.7

ÿ0.023 0.099

ÿ16.4 81.5

ÿ1.1 28.3

ÿ3.6 37.0

36.8 56.9 43.5 38.2 45.1 34.5 3.46*

37.8 36.8 42.5 55.2 46.4 50.3 2.74*

0.032 0.037 0.036 0.110 0.060 0.044 0.006*

51.5 72.5 61.3 76.1 70.4 58.0

37.1 56.0 40.7 35.0 42.6 31.6 3.52*

40.0 37.7 46.2 59.0 50.4 53.6 2.88*

0.029 0.036 0.036 0.110 0.059 0.044 0.055*

52.0 71.9 59.9 65.5 69.9 56.6

26.9 45.7 24.6 34.4 25.5 19.1 3.88*

52.9 53.8 68.0 63.7 70.9 68.5 8.70

42.0 68.4 47.9 71.9 62.6 48.9

17.2 22.8 15.1 29.8 22.7 12.2

26.3 33.7 28.1 50.3 37.0 24.9

0.020 0.036 0.026 0.071 0.055 0.038 0.007*

nˆ3; a, b and c are described by the equation dˆa‡b (lÿeÿct), where d is the percentage degraded at time t; a the zero time intercept; a‡b the total degradability; c the rate of degradation (hÿ1). P is the effective degradability calculated using the equation Pˆa‡(bc/(c‡k)), where k is out¯ow rate from the rumen, assumed to be 5%/h. * p<0.001. a

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Table 3 In situ degradation of DM, OM and nitrogen together with the calculated rumen degradable nitrogen (RDN) and the RDN as fraction of the degradable organic matter in the rumen (DOMR) from alfalfa hay, teff straw and various MPTa

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Table 4 In¯uence of inclusion of alfalfa hay and the foliage from MPT on gas production by mixed rumen microorganisms incubated with teff strawa Plant

Inclusion level (%)

a

b

c

GP 96

Alfalfa (M. sativa) hay

0 15 30 60

ÿ2.1 3.6 6.6 5.1 0.78**

71.5 68.0 58.2 52.2 1.30**

0.021 0.030 0.033 0.045 0.002*

59.6 67.8 62.5 58.7 2.27***

0 15 30 60

ÿ0.8 1.2 0.9 1.3 0.22

67.9 48.5 20.9 11.8 1.17*

0.018 0.014 0.026 0.043 0.002*

55.4 36.2 20.2 12.6 0.25*

0 15 30 60

ÿ2.1 3.2 6.4 11.6 0.60*

71.5 64.2 60.8 56.9 0.57*

0.021 0.027 0.031 0.047 0.001*

59.6 62.9 64.5 68.8 1.23*

0 15 30 60

ÿ2.1 3.4 4.6 7.5 0.39*

71.5 64.5 61.0 57.2 1.02**

0.021 0.029 0.030 0.041 0.001*

59.6 63.9 62.8 64.4 2.03

0 15 30 60

ÿ2.1 2.9 5.0 6.3 0.65**

71.5 65.7 54.5 45.5 2.11**

0.021 0.026 0.029 0.039 0.001*

59.6 63.3 55.4 52.3 2.69

0 15 30 60

ÿ0.8 3.1 5.0 8.0 0.29*

67.9 53.2 56.1 45.9 2.81*

0.018 0.027 0.025 0.083 0.027

55.4 52.7 55.9 56.9 0.79**

0 15 30 60

ÿ0.8 1.9 4.1 6.8 1.19***

67.9 53.1 47.0 33.8 3.21**

0.018 0.024 0.022 0.038 0.002**

55.4 49.5 46.1 44.1 0.25*

SED A. angustissima

SED C. palmensis

SED L. leucocephala

SED S. sesban (10 865)

SED S. sesban (15 036)

SED V. amygdalina

SED

a nˆ3; a, b and c are described by the equation dˆa‡b(lÿeÿct) where d is the volume of gas after time t; a the intercept of gas volume curve at tˆ0; b the volume of gas produced at asymptote; c the rate constant of gas production (hÿ1). GP 96 is the gas produced at 96 h. * p<0.001; ** p<0.01; *** p<0.05.

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4. Discussion All of the MPT used in the present experiments have been investigated in previous studies: L. leucocephala (Girdhar et al., 1991; Bonsi et al., 1994, 1995a; Goodchild and McMeniman, 1994; Garcia et al., 1996; Kaitho et al., 1996) and S. sesban (Bonsi et al., 1994, 1995a; Nsahlai et al., 1994, 1995a,b; Dzowela et al., 1995a; Wiegand et al., 1995; Woodward and Reed, 1995; Kaitho et al., 1996; Nsahlai and Umunna, 1996; Umunna et al., 1997) are particularly well analysed and understood, but much information is also available about A. angustissima (Dzowela et al., 1995a,b; Odenyo et al., 1997), C. palmensis (Bonsi et al., 1995a; Kaitho et al., 1996) and V. amygdalina (Bonsi et al., 1995a,b; Igile et al., 1995). The ILRI maintains germplasm from thousands of plant materials, any of which might prove to be an excellent feed additive as part of a subsistence farming regime in ILRI's mandate areas. Since such materials are often scarce, it would be advantageous to evaluate plants at as early a stage of development as possible using as small quantities as possible. Then, at least some unsuitable species might be rejected for inadequate nutrient content. It would be additionally advantageous, because so many of these plants contain factors toxic either to the rumen microbes or the animal (D'Mello, 1992), to eliminate some species at a similar stage on the grounds of toxicity. The present study aimed to compare a comprehensive chemical evaluation of some MPT with their effects on rumen fermentation properties in vitro. None of the chemical estimations of N or ®bre differed greatly from published values. N and RDN in particular are very important indices of nutritional quality, since these MPT are intended to be used as protein supplements for low-quality tropical fodders and crop by-products which are low in protein. While the N content of the MPT was variable, all compared favourably with teff straw, and several exceeded alfalfa hay in N content. In principle, therefore, A. angustissima, C. palmensis, L. leucocephala, S. sesban and V. amygdalina would be good protein supplements, if they were degraded adequately and were non-toxic. All of the MPT contained signi®cant ADF and NDF, but in vitro digestion indicated that the ®bre was as digestible as that of alfalfa hay, and much more so than that of teff straw. In situ nylon bag degradation characteristics con®rmed this ®nding, with S. sesban and C. palmensis being most extensively degraded. Thus, digestibility would not appear to be a problem. The production of gas by rumen ¯uid incubated with feedstuff materials in vitro has received much attention as a means of evaluating the nutritional quality of feedstuffs. In the present study, its main value was to detect antimicrobial components in MPT by comparison of the gas produced from increasing proportions of MPT:teff straw in the incubations. Table 5 was drawn up to bring together the most pertinent data from other tables in assessing whether an antimicrobial activity may be present in the MPT foliage. In situ degradation might be affected by antimicrobial factors, but inhibition would only be transient because of washout of soluble materials from the nylon bag. This method would give only an indication of the maximum potential digestion of the MPT. Since all of the MPT had higher in situ digestibility than teff straw, gas production should increase as the proportion of MPT:teff straw increases, unless an antimicrobial effect occurs. A. angustissima stands out as being particularly antimicrobial according to these criteria.

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Table 5 Direct comparison of in vitro and in situ analysis to assess potential antimicrobial effects of MPT In vitro digestibility (%) (Table 2)

A. angustissima C. palmensis L. leucocephala S. sesban (10 865) S. sesban (15 036) V. amygdalina

58.6 67.8 66.5 76.7 67.8 63.6

In situ OM degradation P (%) (Table 3)

52.0 71.9 59.9 65.5 69.9 56.6

Gas production at 96 h (ml/200 mg) (Table 4), Inclusion rate of MPT (%) 0

15

30

60

55.4 59.6 59.6 59.6 55.4 55.4

36.2 62.9 62.9 63.3 52.7 68.7

20.2 64.5 64.5 55.4 55.9 46.1

12.6 68.8 68.8 52.3 56.9 44.1

Soluble phenolics (g/kg DM) (Table 2)

NDF-bound proanthocyanidin (AU/g) (Table 2)

308 176 251 196 246 126

10.2 3.3 47.3 35.4 45.9 3.8

Dzowela et al. (1995a) found a high tannins content in A. angustissima. Tannins at high concentration affect the enzyme activities of rumen bacteria (Makkar et al., 1988). Methods are available for detoxi®cation by complexing the tannins with polyethylene glycol (PEG; Pritchard et al., 1992), and microbiological solutions are being sought (Miller et al., 1995, 1996, 1997). Odenyo et al. (1997) found that gradual introduction of A. angustissima avoided the toxicity and morbidity associated with more rapid introduction, suggesting that the toxic principle was destroyed by rumen microorganisms. V. amygdalina also depressed gas production at higher inclusion rates. V. amygdalina has a high saponins content which is known to cause toxicity in mice (Igile et al., 1995) and intake problems in sheep (Bonsi et al., 1995b). Previous studies had indicated a mild toxicity to rumen ciliate protozoa and bacteria (El hassan et al., 1995). In conclusion, although chemical analysis is essential for understanding the nutritional potential of a new plant species, it is not suf®cient. In situ digestion can help, but cannot predict the potency of antimicrobial or other antinutritional factors. The analysis of speci®c soluble and ®bre-bound phenolics is valuable in predicting potential problems, but its main value is in selecting between different, but related, cultivars to select the least likely to be toxic. The gas production measurement gives an indication of antimicrobial activity, neither it can simulate adaptation nor it is sensitive to factors that might affect the host animal, either directly or as a result of microbial fermentation. For example, the effects of mimosine in L. leucocephala are now well understood (Jones and Lowry, 1984; Jones and Megarrity, 1986), but they could not have been predicted in vitro by the present, or indeed any other method. Furthermore, if the secondary compound has antiprotozoal activity, such as the saponins of S. sesban, the forage may in fact have greater nutritional merit than its nutrient content would imply (Newbold et al., 1997). Finally, it is hard to imagine how any in vitro analysis would predict palatability. Even testing in rats and mice might not prove accurate, if metabolic transformations in the rumen cause decreased, or in some cases increased, toxicity to the animal (Kadiri et al., 1996). We conclude that although all of the methods mentioned and used here have some merit, none replaces, or is likely to replace, the practical feeding experiment with the target ruminant species.

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Acknowledgements This work was funded by the Scottish Executive Rural Affairs Department and the International Livestock Research Institute. We thank J. Hanson, P.O. Osuji and A.N. Said for their advice and help during the work. References Association of Analytical Chemists, 1975. Of®cial Methods of Analysis. Association of Analytical Chemists, Washington, DC. Bamualim, A., Jones, R.J., Murray, R.M., 1980. Nutritive value of tropical browse legumes in the dry season. Proc. Aust. Soc. Anim. Prod. 13, 229±232. Bonsi, M.L.K., Osuji, P.O., Nsahlai, I.V., Tuah, A.K., 1994. Graded levels of Sesbania sesban and Leucaena leucocephala as supplements to teff straw given to Ethiopian menz sheep. Agrofor. Syst. 59, 235±244. Bonsi, M.L.K., Osuji, P.O., Tuah, A.K., 1995a. Effect of supplementing teff straw with different levels of leucaena or sesbania leaves on the degradabilities of teff straw, sesbania, tagasaste and vernonia and on certain rumen and blood metabolites in Ethiopian menz sheep. Anim. Feed Sci. Technol. 52, 101± 129. Bonsi, M.L.K., Osuji, P.O., Tuah, A.K., Umanna, N.N., 1995b. Vernonia amygdalina as a supplement to teff straw (Eragrostis tef) fed to Ethiopian menz sheep. Agrofor. Syst. 31, 229±241. Devendra, C., 1990. The use of shrubs and tree fodders by ruminants. In: Devendra, C. (Ed.), Shrubs and Tree Fodders for Farm Animals. International Development Research Center, Ottawa, Canada, pp. 42±60. D'Mello, J.P.F., 1992. Chemical constraints to the use of tropical legumes in animal nutrition. Anim. Feed Sci. Technol. 38, 237±261. Dzowela, B.H., Hove, L., Topps, J.H., Mafongoya, P.I., 1995a. Nutritional and anti-nutritional characters and rumen degradability of dry matter and nitrogen for some multipurpose tree species with potential for agroforestry in Zimbabwe. Anim. Feed Sci. Technol. 55, 207±214. Dzowela, B.H., Hove, L., Mafongoya, P.I., 1995b. Effect of drying method on chemical composition in vitro digestibility of multipurpose tree and shrub fodders. Trop. Grassl. 29, 263±269. El hassan, S.M., Lahlou-Kassi, A., Newbold, C.J., Wallace, R.J., 1995. Antimicrobial factors in African multipurpose trees. In: Wallace, R.J., Lahlou-Kassi, A. (Eds.), Rumen Ecology Research Planning. International Livestock Research Institute, Addis Ababa, Ethiopia, pp. 43±54. Garcia, G.W., Ferguson, T.U., Neckles, F.A., Archibald, K.A.E., 1996. The nutritive value and forage productivity of Leucaena leucocephala. Anim. Feed Sci. Technol. 60, 29±41. Girdhar, N., Lall, D., Pathak, N.N., 1991. Effect of feeding Leucaena leucocephala as the sole ration on nutrient utilization and body weight in goats. J. Agric. Sci. 116, 303±307. Goodchild, A.V., McMeniman, N.P., 1994. Intake and digestibility of low-quality roughages when supplemented with leguminous browse. J. Agric. Sci. 122, 151±160. Igile, G.O., Oleszek, W., Burda, S., Jurzysta, M., 1995. Nutritional assessment of Vernonia amygdalina leaves in growing mice. J. Agric. Food Chem. 43, 2162±2166. Jones, R.J., Lowry, J.B., 1984. Australian goats detoxify the goitrogen 3-hydroxy-4(1H) pyridone (DHP) after rumen infusion from an Indonesian goat. Experientia 40, 1435±1436. Jones, R.J., Megarrity, R.G., 1986. Successful transfer of DHP-degrading bacteria from Hawaiian goats to Australian ruminants to overcome the toxicity of leucaena. Aust. Vet. J. 63, 259±262. Kadiri, M., Bedri, B.A., Ajao, S.S., 1996. Toxicological screening of some Nigerian wild legumes. Rev. Biol. Trop. 44, 269±274. Kaitho, R.J., Umunna, N.N., Nsahlai, I.V., Tamminga, S., Van Bruchem, J., Hanson, J., Van de Wouw, M., 1996. Palatability of multipurpose tree species Ð effect of species and length of study on intake and relative palatability by sheep. Agrofor. Syst. 33, 249±261. Lowry, J.B., McSweeney, C.S., Palmer, B., 1996. Changing perceptions of the effect of plant phenolics on nutrient supply in the ruminant. Aust. J. Agric. Res. 47, 829±842.

S.M. El hassan et al. / Animal Feed Science and Technology 86 (2000) 27±37

37

Makkar, H.P.S., Dawra, D.K., Singh, B., 1988. Changes in tannin content, polymerisation and protein precipitation capacity in oak (Quercus incana) leaves with maturity. J. Sci. Food Agric. 44, 301±307. Mehrez, A.Z., érskov, E.R., 1977. A study of the arti®cial ®bre bag technique for determining the digestibility of feeds in the rumen. J. Agric. Sci., Camb. 88, 645±650. Menke, K.H., Steingass, H., 1988. Estimation of the energetic feed value obtained from chemical analysis and in vitro gas production using rumen ¯uid. Anim. Res. Dev. 28, 8±55. Menke, K.H., Raab, L., Salewski, A., Steingass, H., Fritz, D., Schneider, W., 1979. The estimation of the digestibility and metabolizable energy content of ruminant feedstuffs from the gas production when they are incubated with rumen liquor. J. Agric. Sci., Camb. 93, 217±222. Miller, S.M., Brooker, J.D., Blackall, L.I., 1995. A feral goat rumen ¯uid inoculum improves nitrogen retention in sheep consuming a mulga (Acacia aneura) diet. Aust. J. Agric. Res. 46, 1545±1553. Miller, S.M., Brooker, J.D., Phillips, A., Blackall, L.I., 1996. Streptococcus caprinus is ineffective as a rumen inoculum to improve digestion of mulga (Acacia aneura) by sheep. Aust. J. Agric. Res. 47, 1323±1331. Miller, S.M., Klieve, A.V., Plumb, J.J., Aisthorpe, R., Blackall, L.I., 1997. An in vitro cultured rumen inoculum improves nitrogen digestion in mulga-fed sheep. Aust. J. Agric. Res. 48, 403±409. Newbold, C.J., El hassan, S.M., Wang, J., Ortega, M.E., Wallace, R.J., 1997. In¯uence of foliage from African multipurpose trees on activity of rumen protozoa and bacteria. Br. J. Nutr. 78, 237±249. Nsahlai, I.V., Umunna, N.N., 1996. Sesbania and lablab supplementation of oat hay basal diet fed to sheep with or without maize grain. Anim. Feed Sci. Technol. 61, 275±289. Nsahlai, I.V., Siaw, D.E.K.A., Osuji, P.O., 1994. The relationships between gas production and chemical composition of 23 browses of the genus sesbania. J. Sci. Food Agric. 65, 13±20. Nsahlai, I.V., Umunna, N.N., Negassa, D., 1995a. The effect of multipurpose tree digesta on in vitro gas production from Napier grass or neutral-detergent ®ber. J. Sci. Food Agric. 69, 519±528. Nsahlai, I.V., Osuji, P.O., Umunna, N.N., 1995b. The degradability by sheep of fruits of acacias and leaves of Sesbania sesban and the effects of supplementation with mixtures of browses and oilseed cake on the utilization of teff (Eragrostis tef) straw. J. Anim. Sci. 61, 539±544. Odenyo, A.A., Osuji, P.O., Karan®l, O., Adinew, K., 1997. Microbiological evaluation of Acacia angustissima as a protein supplementation for sheep. Anim. Feed Sci. Technol. 65, 99±112. érskov, E.R., 1982. Protein Nutrition in Ruminants. Academic Press, London. érskov, E.R., McDonald, I., 1979. The estimation of protein degradability in the rumen from incubation measurements weighed according to rate of passage. J. Agric. Sci., Camb. 92, 499±503. érskov, E.R., Hovell, F.D.D., Mould, F., 1980. The use of the nylon bag technique for the evaluation of feedstuffs. Trop. Anim. Prod. 5, 195±213. Pritchard, D.A., Martin, P.R., O'Rourke, P.K., 1992. The role of condensed tannins in the nutritional value of mulga (Acacia aneura) for sheep. Aust. J. Agric. Res. 43, 1739±1746. Reed, J.D., McDowell, R.E., Van Soest, P.J., Horvath, P.J., 1982. Condensed tannins, a factor limiting the use of cassava forage. J. Sci. Food Agric. 33, 213±220. Reed, J.D., Horvath, P.J., Allen, M.S., Van Soest, P.J., 1985. Gravimetric determination of soluble phenolics including tannins from leaves by precipitation with trivalent ytterbium. J. Sci. Food Agric. 36, 255±261. Rittner, U., Reed, J.D., 1992. Phenolics and in vitro degradability of protein and ®bre in west African browse. J. Sci. Food Agric. 58, 21±28. SAS, 1989. User's Guide: Version 6, Vol. 1, 4th Edition. Statistical Analysis System Institute Inc., Cary, NC. Tilley, J.M.A., Terry, R.A., 1963. A two-stage technique for the in vitro digestion of forage crops. J. Br. Grassl. Soc. 18, 108±112. Umunna, N.N., Osuji, P.O., Nsahlai, I.V., 1997. Strategic supplementation of crossbred steers fed forages from cereal±legume cropping systems with cowpea hay. J. Appl. Anim. Res. 11, 169±182. Van Soest, P.J., Robertson, J.B., 1985. Analysis of forages and ®brous foods. Laboratory Manual for Animal Science. Cornell University, Ithaca, NY. Wiegand, R.O., Reed, J.D., Said, A.N., Ummuna, V.N., 1995. Proanthocyanidins (condensed tannins) and the use of leaves from Sesbania sesban and Sesbania goetzei as protein supplements. Anim. Feed Sci. Technol. 54, 175±192. Woodward, A., Reed, J.D., 1995. Intake and digestibility of sheep and goats consuming supplementary Acacia brevispica and Sesbania sesban. J. Anim. Sci. 56, 207±216.