Session 2 Uses

Session Papers

Nutritive Value of Leaves and Fruits of Faidherbia albida and their Use for Feeding Ruminants

J.D. Reed¹, U. Rittner², J.Tanner³, and O. Wiegand¹

Abstract

Grasses available on nonarable land and cereal crop residues are the most important feed resources available to-farmers in the semi-arid zone of West Africa. Cell-wall carbohydrates (cellulose and hemicellulose) account for more than 70% of the dry matter in these feeds but their use is limited, because they are deficient in protein.

Research was conducted at the International Livestock Centre for Africa (ILCA) to determine the nutritive value of important trees, with emphasis on their use as sources of protein in diets for ruminants. The use of leaves and pods of Faidherbia albida for feeding ruminants was compared with other multipurpose trees, legume forages, and oilseed cakes.

The tannins and related phenolic compounds in F. albida did not lower performance of sheep fed F. albida leaves and pods in comparison with sheep fed oilseed meals or legume hay in diets based on cereal crop residues. More research is required on the use of pods because of potential toxicity. More research is also needed to determine the variability in nutritive value of leaves and pods that exist among provenances and races of F. albida in order to find germplasm with superior characteristics.

Introduction

Vegetation available on nonarable land and crop residues from cereals and grain legumes are the most important feed resources available to farmers in the semi-arid zone of West Africa. Feed grains are not produced, and livestock receive grain only under exceptional situations. Farmers seldom cultivate forages. Grazing on nonarable land is seasonal and corisists of unimproved species. Herbaceous legumes and other dicotyledons are important during the growing season but grasses are usually dominant. During the dry season, only senescent grasses and crop residues, both low in protein, energy, and minerals, remain in the herb layer. In many areas they are completely grazed before the beginning of the next growing season. Browses from woody legumes are important livestock subsistence components of the vegetation.

Agroforestry with multipurpose trees (MPTS) that provide fodder could be integrated with the farming system as a way to improve livestock productivity (Torres 1983). Faidberbia albida and other native trees are important in the agrosilvipastoral farming systems of semi-arid West Africa. These trees produce both leaves and fruits in the dry season which are used as feed for sheep, goats, cattle, and camels.

Intake and digestibility of energy and protein are the most important parameters which determine the nutritive value of feeds. Cell-wall carbohydrates (cellulose and hemicellulose) account for more than 70% of the dry matter in cereal crop residues and represent a large source of energy for ruminant feeding. However, the ability of rumen microorganisms to digest these carbohydrates is limited, because cereal crop residues are deficient in protein. This deficiency is also responsible for their low intake. Forage from leguminous trees is usually high in protein and can be an important protein supplement to the normal ruminant diet of grasses and cereal crop residues-which are otherwise deficient in protein-improving their intake and digestibility.

Nutritive Value of Leaves from F. albida

Twenty F. albida leaf samples were collected at the ICRISAT Sahelian Center, Niamey, Niger, from individual 7-month old plants. Four half-sib progeny grown from each of five different mother trees were sampled to determine the effect of parent tree on content of phenolic compounds and nutritive value. Samples of leaves of 20 other important browse species from the region were also collected. Four introduced acacia species from Australia (Acacia cawleana, A. holosericea, A. laccata, and A. tumida) were collected at Dosso, Niger.

There was a large range in parameters of nutritive value among the samples of leaves from these tree species (Rittner and Reed, in press). F. albida had values that were similar to the mean of the other African species sampled but had a higher content of crude protein (CP, nitrogen x 6.25) and a lower content of lignin and soluble phenolics than the Australian species (Table 1).

Parent tree did not have a significant effect on chemical composition, content of phenolic compounds, or degradability of protein in their young progeny (1-1.5 m height). However, because the parent trees were from only one population (Sadoré, Niger), these results may not represent the genetic variation in content of phenolic compounds in F. albida, which has a very large geographical distribution.

Microbial degradation of protein decreases as concentrations of phenolic compounds increase, because tannins and related phenolic compounds form indigestible complexes with protein and inhibit enzymes (Reed 1986; Reed et al. 1985). Protein degradability of leaves from F. albida was lower than that of other types of feeds, e.g., oilseed meals and common forage legumes, which have more than 50% protein degradability. This may be related to the content of phenolic compounds. The Australian species contained high levels of all phenolic fractions, and the protein was nondegradable in the in-vitro system used (Table 1).

Table 1. Content (% DM) of nitrogen (N), neutral detergent fiber (NDF), lignin (L), soluble phenolics (SP), proanthocyanidins (PAC) and protein degradability (PD) of Faidherbia albida, other western African acacia species, and 5 Australian acacia species, International Livestock Centre for Africa, 1989.

Table 2 shows the composition of leaves from multipurpose trees, alfalfa hay (Medicago sativa), oil-seed meals, and cereal crop residues used in the feeding trials described below. These feeds vary widely in their content of crude protein, fiber, and phenolic compounds (lignin, soluble phenolics, and insoluble proanthocyanidins). Tree leaves in general tend to have higher phenolic compounds than forage legumes or oilseed cakes; in crude protein, they are lower than oilseed cakes but comparable to forage legumes. Of the MPTS we tested, Leucaena leucocephala and Sesbania sesban—with the highest content of crude protein and low levels of fiber and phenolic compounds-are the best sources of protein for diets based on cereal crop residues. Carissa edulis and Dichrostachys cinera—low crude protein and high phenolics—were the least useful as protein sources.

Although F. albida can contain high levels of crude protein, it also contains phenolic compounds that may reduce protein digestibility. Cereal crop residues contain low levels of CP (Table 2), which are below the maintenance requirements (>7% CP) for adult ruminants. Cereal crop residues contain much higher amounts of cell-wall carbohydrates than leaves from multipurpose trees but much lower amounts of lignin and other phenolic compounds. Lignin is covalently bound to cell-wall carbohydrates and limits digestibility. The potential digestibility of the cell-wall in many cereal crop residues is high when adequate protein is supplied in the diet.

Dried leaves of F. albida, A. seyal, and Balanites aegyptiaca and cottonseed meal were fed to 48 year-ling male sheep in a 70-day growth trial (Rittner and Reed 1989). Sorghum stover was fed to all sheep at 50 g kg^-1 of body weight, and the amount offered was adjusted weekly. Leaves and cottonseed cake were fed to supply 30 and 45 g of CP day^-1.

Differences in growth rate were not large (Table 3). Intake of sorghum stover was highest on the cottonseed meal diet. Less cottonseed meal was fed in order to obtain the required CP level. Substitution of supplement intake for stover intake was least on the diet containing cottonseed meal. Sheep fed F. albida, A. seyal, and B. aegyptiaca had similar levels of stover intake at both levels of protein. Browse did not have a significant effect on total intake. These results indicate that the leaves of these three multipurpose trees can substitute for cottonseed meal as sources of protein for feeding in combination with sorghum stover. However, stover intake will decrease, because more leaf material than cottonseed meal is required to obtain the equivalent intake of protein.

Table 2. Content of crude protein (CP), neutral-detergent fiber (NDF), acid-detergent lignin (ADL), soluble phenolics (SP) and insoluble proanthocyanidins (IPAC) in leaves from multipurpose trees, forage legumes, oilseed meals, and cereal crop residues used in feeding trials, International Livestock Centre for Africa, 1989.

Table 3. Growth rate and feed intake of sheep fed leaves from Faidherbia albida, Acacia seyal, and Balanites aegyptiaca in comparison with cottonseed meal as sources of two levels of protein (CP, crude protein) in diets of sorghum stover, International Livestock Centre for Africa, 1989.

Table 4. Growth rate and feed intake of sheep fed leaves from Faidherbia albida, Sesbania sesban, Leucaena leucocephala, Dichrostachys cinera, or Carissa edulis in comparison with hay from Medicago sativa as sources of protein in diets of teff straw with or without 100 g day^-1 of maize grain, International Livestock Centre for Africa, 1989.

In another trial, leaves from F. albida and four other MPTS were compared with alfalfa (M. sativa) as sources of protein in diets based on teff (Eragrostis abyssinica) straw (Wiegand et al. 1991). Forty-eight rams were randomly assigned to six sources of protein (leaves from F. albida, L. leucocephala, S. sesban, C. edulis, and D. cinera, and alfalfa hay) and two levels of energy (no maize grain and maize grain fed at 100 g day^-1).

Rams fed F. albida grew at rates similar to rams fed L. leucocephala, S. sesban, and alfalfa hay (Table 4). Rams fed C. edulis and D. cinera with no maize grain lost weight throughout the trial and rams fed these leaves with maize grain only maintained their bodyweight. Teff straw intake was highest for rams fed L. leucocephala and S. sesban. Teff straw intake for rams fed F. albida was similar to alfalfa hay. F. albida and alfalfa hay had similar levels of crude protein. Teff straw intake was the lowest for the rams fed C. edulis and D. cinera because they consumed less than 30% of the leaves offered.

Nutritive Value of F. albida Pods

Acacia pods are fed to animals in the dry season when they are ripe. In many areas, pods are collected and brought back to the village to feed cattle, sheep, and goats or sold in organized fodder markets. In other regions, animals are taken to the trees and pods are consumed as they fall naturally or are knocked down by herders. Thus, circumstantial evidence indicates that acacia pods are of high nutritive value; however, few studies have been conducted to quantify the animal response to diets containing them.

An experiment was designed to examine the nutritive value of pods from F. albida, A. nilotica, A. sieberiana, and A. tortilis (Tanner and Reed 1990). The fruits of these four species were compared with the meal produced by industrial extraction of oil from noug (Guizotia abyssinica). These feeds were compared as sources of protein when fed in combination with maize stover (Zea mays).

Forty yearling rams of the Menz breed (common to the Ethiopian Highlands) were blocked according to their initial bodyweights (20-22 kg) and randomly assigned from the blocks to five treatments (8 sheep per treatment). Each treatment received maize stover (1 kg fresh mass for each sheep), fed in combination with pods of F. albida, A. nilotica, A. sieberiana, A. tortilis, and noug meal.

The diets were formulated to provide approximately 8 g N day^-1 to each animal. A daily intake of all the pod or noug meal offered and half the maize stover offered would supply 6 g N day^-1, which is sufficient for an average daily gain of 50 g day^-1 in male sheep of around 20 kg live weight.

Whole pods of A. nilotica had the highest content of insoluble proanthocyanidins, which were primarily located in the pod (Table 5); whole pods of A. sieberiana had the next highest content, evenly distributed between the pod and seed. Pods of F. albida and A. tortilis had a lower content of soluble phenolics and insoluble proanthocyanidins than A. nilotica and A. sieberiana.

The sheep consumed all of the pods and noug meal offered throughout the growth trial (Table 6) The variation in N intake between treatments was caused by differences in the quantity of maize stover ingested.

Sheep fed noug meal and A. tortilis had the highest growth rates but were not significantly different from those fed F. albida (Table 6). Sheep fed A. nilotica grew at a lower rate but were not significantly different from those fed F. albida. Sheep ted A. sieberiana had the lowest growth rate.

Table 5. Content of nitrogen (N), neutral-detergent fiber (NDF), acid-detergent lignin (ADC), soluble phenolics (SP) and insoluble proanthocyanidins (IPAC) in fruits from Faidherbia albida, Acacia nilotica, A. sieberiana, and A. tortilis, International Livestock Centre for Africa, 1989.

Table 6. Growth rate and feed intake of sheep fed acacia pods and noug meal in combination with maize stover, International Livestock Centre for Africa, 1989.

Table 7. Growth rate and feed intake of sheep fed pods from Faidherbia albida and Acacia tortilis in comparison with cottonseed meal as sources of two levels of crude protein (CP) in diets of teff straw and vetch hay, International Livestock Centre for Africa, 1989.

Intake of maize stover was high for sheep fed noug meal, A. tortilis, and F. albida and low for sheep fed A. sieberiana and A. nilotica. The differences between diets in intake of N and energy were not large during the growth trial and yet significant differences were observed in growth rate. Browse species, including acacias, often contain tannins and related poly-phenolic compounds. The results indicate that the phenolic compounds present in acacia pods have an effect on the N balance.

The growth rates of sheep fed F. albida and A. tortilis were not significantly different from sheep fed noug meal, indicating that these pods could replace noug meal in ruminant diets. Most oilseed meals are produced in centralized oil extraction plants and are not easily available to smallholders, who either cannot afford to purchase them or are farming in remote areas to which transport of animal feeds is not possible. The pods from A. tortilis and F. albida could constitute a low-cost, widely occurring alternative to oilseed meals.

The growth rate of rams fed F. albida and A. tortilis pods was similar to that of rams fed cottonseed cake when these feeds were used as sources of protein in diets based on a combination of vetch hay and teff straw (Table 7). Feeding acacia pods at over 50% of total intake produced no adverse effects; however, when F. albida pods were fed to sheep and goats as the sole ration, there appeared to be some toxicity problem. Goats had higher intake and lost less weight than sheep when fed on F. albida pods (Fig. 1). All animals were slaughtered after 84 days of feed, and analyses were conducted on digestive tract content and histology. All animals receiving F. albida pods had ulcerations in the ventral sack of the rumen. However, in goats, papillae were normal and dense, whereas in sheep, they were eroded in patches in the ventral sack and the remaining ones were abnormal. F. albida pods probably contain a digestive tract toxin, the nature of which is presently unknown. There appears to be a large difference between sheep and goats in their ability to adapt to this toxin.

Figure 1. Intake by sheep and goats fed solely on Faidherbia albida pods for 84 days.

Conclusion

The leaves and pods of F. albida appear to be good sources of protein in diets for ruminants. Our research on F. albida indicates that the tannins and related phenolic compounds in leaves and pods have an effect on protein metabolism, but these effects do not lower performance of sheep fed leaves and pods in comparison with sheep fed oilseed meals or legume hay in diets based on cereal crop residues. More research is required on the use of the pods as the sole feed be-cause of the potential toxicity. However, the practice of feeding ruminants only pods is not likely to be common. The leaves and fruits used in the trials described in this paper were from two areas, the Debre Zeit region of Ethiopia (feeding trials) and trees established at the ICRISAT Sahelian Center, Niger. This is a very limited sample of a species that spans most of the continent, and more research is needed to determine the variability in nutritive value in order to find germplasm with superior characteristics.

References

Reed, J.D. 1986. Relationships among soluble phenolics, insoluble proanthocyanidins and fiber in East African browse species. Journal of Range Management 39:5-7.

Reed, J.D., Horvath, P.J., Allen, M.S., and Van Soest, P.J. 1985. Gravimetric determination of soluble phenolics including tannins from leaves by precipitation with trivalent ytterbium. Journal of the Science of Food and Agriculture 36: 255-261.

Rittner, U., and Reed, J.D. 1989. Nutritive value of leaves from Acacia albida, Acacia seyal, and Balanites aegyptiaca. Presented at the ICRISAT-University Hohenheim Workshop, 27-28 Nov 1989, ICRISAT Sahelian Center, Sadore, Niger. Niamey, Niger: ISC.

Rittner, U., and Reed, J.D. (In press.) Phenolics and in vitro degradability of protein and fibre in West African Browse. Journal of the Science of Food and Agriculture.

Tanner, J., and Reed, J.D. 1990. The nutritive value of fruits (pods with seeds) from four Acacia spp. compared with extracted noug. Animal Production 51:127-133.

Torres, F. 1983. Role of woody perennials in animal agroforestry. Agroforestry Systems 1:131-163.

Wiegand, R.O., Reed, J.D., and Combs, O.K. 1991. Multi-purpose trees in the diets of small ruminants. Presented at Midwestern Section, American Society of Animal Science Meeting, 25-27 Mar 1991, Des Moines, Iowa, USA. (Limited distribution.) .

Footnote__________

1 Department of Animal Sciences, University of Wisconsin, 1675 Observatory Drive, Madison, Wisconsin, USA.

2 Institut fur Tierernahrung, University of Hohenheim, Stuttgart, Germany.

3 Department of Agriculture, University of Reading, Reading, UK.

Reed, J.D., Rittner, U., Tanner, J, and Wiegand, 0.1992. Nutritive value of leaves and fruits of Faidherbia albida and their use for feeding ruminants. Pages 43-49 in Faidherbia albida in the West African semi-arid tropics: proceedings of a workshop, 22-26 Apr 1991, Niamey, Niger (Vandenbeldt, R.J., ed.). Patancheru, A.P. 502 324, India: International Crops Research Institute for the Semi-Arid Tropics; and Nairobi, Kenya: International Centre for Research in Agroforestry.