Abstract: Twenty Multi-Purpose Trees and Shrubs (MPTS) were ranked for their fodder potential based on degradation studies with rumen fistulated N’dama steers. Samples of oven-dried, one year re-growth leaf fractions of the 20 MPTS were milled to pass through a 2.5 mm screen in a laboratory mill. The oven-dried samples (5 g each) were put into nylon bags measuring 180x90 mm with a pore size of 41 μm. The bags were incubated in duplicates for 6, 12, 24, 48, 72 and 96 h in 3 rumen fistulated N’dama steers. The steers, aged about 3 years and weighing approximately 250 kg were grazed on a pasture of Panicum maximum supplemented with wheat bran at the rate of 2 kg/animal/day. At the end of each incubation period, the residues were dried to a constant weight at 60°C for 48 h in a forced air oven to compute Dry Matter (DM) disappearance. Results showed that E. cyclocarpum, S. spectabilis, B. monamdra and A. ferruginea were ranked in the high quality group, with Effective Degradability (ED) values >450 g kg^-1 DM; T. superba, L. leucocephala and A. noipoides were ranked in the medium quality group with ED range of 400-450 g kg^-1 DM, while P. bicolor, L. sericeus, P. santalinoides, X. xylocarpa and T. tetraptera belonged to the low quality group with ED values <400 g kg^-1 DM. The study showed that MPTS with high effective degradability qualitatively can be used to enhance better live weight gains in ruminant animals.

INTRODUCTION

Livestock are important components in the crop-based farming systems of the humid lowlands of West and Central Africa. The major constraints to livestock productivity in these regions is inadequate nutrition because the primary feed resources; natural pastures and crop residues, are bulky, high in fibre, low in nitrogen and of poor quality. The identification therefore, of Multi Purpose Trees and Shrubs (MPTS) species with potential for providing high quality fodder for livestock and maintaining soil fertility is a major focus of agro-forestry research in these regions (Larbi et al., 1997, 1998, 2000). Fodder trees and shrubs (browse) form part of the natural vegetation and are accessible to the majority of small holder farmers (Tedonkeng et al., 2006b). Besides being used as feed, they have additional benefits when integrated into farming systems. These benefits include fuel wood and timber, increased soil fertility (leguminous species) control of wind erosion, shade for man and livestock, folk medicine, etc. (Le Houerou, 1980). Tedonkeng et al. (2006a) observed that deficiencies in feed quality could be corrected by the addition of herbaceous legumes or multi-purpose trees to the basal diet.

The humid forest zone is endowed with a large variety of MPTS. Not all of these trees have potentials as forage for livestock, particularly small ruminants. Farmers in this region have long realized the utility of some particular species of trees for their livestock, for example, Microdesmis puberula-highly relished by sheep and goats but is now in danger of extinction. Small holder farmers, who practice cut-and-carry system, obtain these trees from the wild since there is hardly any attempt to preserve these highly valued species through deliberate planting or incorporation in farming systems.

So far, several indigenous and exotic MPTS have been evaluated for the development of integrated crop-livestock agro-forestry technology such as alley farming in the humid lowlands of West and Central Africa (AFNETA, 1991; Duguma et al., 1994). A considerable number of these species have potentials as forage (Onwuka, 1992).

There is however, a paucity of information on the nutritive value attributes of MPTS based on data obtained from previous studies.

Since, ruminant animals are an integral part of the farming system in the humid lowlands of West and Central Africa, this study was conducted to rank the fodder potential of 20 MPTS through Dry Matter (DM) degradation studies, with rumen fistulated N’dama steers.

MATERIALS AND METHODS

Site: The in sacco rumen degradation studies were carried out at the International Livestock Research Institute (ILRI), Onne (4°52'N; 6°57'E).

In sacco DM degradation: Leaf fraction samples of 20 species of MPTS were oven dried at 60°C and milled to pass through a 2.5 mm screen in a Christy Hunt laboratory mill. The oven-dried samples were weighed in an analytical balance and put into nylon bags measuring 180x90 mm with a pore size of 41 μm. The bags were incubated in duplicates for 6, 12, 24, 48, 72 and 96 h in three rumen fistulated N’dama steers. The steers, aged about 3 years with an average weight of 250 kg were grazed on a pasture of Panicum maximum supplemented with wheat bran at the rate of 2 kg/animal/day. At the end of each incubation period; bags were withdrawn from the rumen, put in a bucket of water at about 30°C and washed immediately under running tap water for about 25 min until the filtrate became clear. Residues were dried to a constant weight at 60°C for 48 h in a forced air oven to compute DM disappearance.

Statistical analysis: The degradation constants were estimated by fitting data to the exponential model of Orskov and McDonald (1979):

The effective degradability will be estimated from the model:

Assuming an outflow rate k of 3% h^-1. The estimated parameters were subjected to analysis of variance procedures using the ANOVA command of the statistical analysis systems (SAS, 1999).

RESULTS AND DISCUSSION

There were significant variations in DM degradation characteristics as shown in Table 1. The soluble fraction a, ranged from 139 g kg^-1 DM in L. sericeus to 333 g kg^-1 DM in A. ferruginea while, the degradable fraction b, ranged from 329 g kg^-1 in P. santalinoides to 680 g kg^-1 DM in L. sericeus. The rate of degradation c was as low as 0.11 h^-1 in M. griffoniana and T. africana to as high as 0.037 h^-1 in S. spectabilis. Calculated values for PD showed a range of 545 g kg^-1 DM for P. santalinoides to 883 g kg^-1 DM in M. griffoniana while, the ED showed a range of 330 g kg^-1 DM for T. tetraptera to 560 g kg^-1 DM in E. cyclocarpum.

The difference among the MPTS in degradation characteristics may be partly related to variations in chemical composition (Nashlai et al., 1994) and configuration of cell wall polysaccharides and their effect on rumen microbial attachment and colonization of digesta particles (Cheng et al., 1984). This could result in differential intakes and rates of synthesis of microbial nitrogen per unit intake of the species, when given as sole diets. The high ED recorded for E. cyclocarpum may relate to complete absence of tannins and other phenolic compounds as reported by Norton (1994). This confirmed earlier reports that in situ nylon bag method could be used to rank MPTS for quality in initial screening studies. Based on ED values in this study, MPTS could be ranked as high (> 450 g kg^-1 DM), medium (400-450 g kg^-1 DM) and low (<400 g kg^-1 DM) quality groups. E. cyclocarpum, S. spectabilis, B. monandra and A. ferruginea were among the high quality group; T. superba, L. leucocephala and A. noipoides were in the medium quality group, while P. bicolor, L. sericeus, P. santalinoides, X. xylocarpa and T. tetraptera belonged to the low quality group. Depending on the desired objectives, these groups could be targeted for further nutritional and soil improvement studies. It is important to point out that ranking of these species based on degradation data has to be interpreted with caution for the following reasons; firstly, the in sacco nylon bag method could over estimate in vivo digestibility (Larbi et al., 2000), secondly, there is not much documentation on the utilization by livestock of some species such as S. spectabilis and I. edulis, which are ranked high based on sacco studies and thirdly, some species could differ in animal preference and palatability. Since, animal output is a better determinant of forage quality (Moore et al., 1990), it remains to be seen whether these results could be transformed into better live weight gains in ruminants. Hence, further research is warranted to determine their performance in intake and digestibility studies.

Table 1:	Dry matter degradation characteristics1 of 1-year re-growth of 20 multi-purpose trees and shrubs
1Dry matter degradation constants from the non-linear model: PD = a + b (1-e-ct) suggested by Orskov and McDonald (1979), where: a = Zero time intercept, b = Insoluble but degradable fraction in time t, c = Degradation rate constant of the b fraction PD = Potential Degradability (a + b) and ED = Effective Degradability (ED) = a + b*c/(c+0.03)

CONCLUSION

Based on DM degradation values, E. cyclocarpum, S. spectabilis, B. monandra and A. ferruginea were ranked among the high quality group with ED values higher than 450 g kg^-1 DM; T. superba, L. leucocephala and Albizia noipoides were in the medium quality group with ED range of 400-450 g kg^-1 DM; while P. bicolor, L. sericeus, P. santalinoides, X. xylocarpa and T. tetraptera belonged to the low quality group with ED values <400 g kg^-1 DM. The study showed that MPTS, with high effective degradability, qualitatively can be used to enhance better live weight gains in ruminant animals.