Halophytes as animal feeds: potentiality, constraints, and prospects
El-Shaer, H.M. and Attia-Ismail, S.A.
Department of Animal and Poultry Nutrition
Desert Research Center
Matareya, Cairo, Egypt
Abstract
The future prosperity of feed resources in the countries located in the arid and semi-arid regions rely on the economic feasible use of marginal and long-neglected resources. Halophytic plants are one of such resources. Halophytes have many uses; they can be used as animal feeds, as vegetables, in drugs, sand dune fixation, wind shelter, soil cover, cultivation of swampy saline lands, laundry detergents, paper production and many other uses. Halophytes can, then, play an important role in the welfare of people in such regions. However, the concentration of this paper will be on the use of halophytes as animal feeds.
As an animal feed component, halophytes are promising as they have the potentiality of being good feed resources. Yet this potentiality does not go far as several constraints are limiting. The high content of ash is a typical characteristic of halophyte plants. Nitrate and nitrite complexes may be present in some of them. Others have anti-nutritional factors such as tannins, glycosides, phenolic compounds, saponines, oxalates, alkaloids, etc. The presence of such anti-nutritional factors makes halophytes less or unpalatable feeds for animals. Low feed intake, low nutrient utilization, hence the negative impacts on animal performance are major constraints for the use of halophytes as animal feed component.
Several treatments, however, have been applied on both nutritional and agronomic scales. Drying (particularly sundry), chopping, ensiling, use of additives, use of appetizers are common practices in this nutritional manner. Botanical management such as method of irrigation, interplantation, fertilization, etc are also potential improvement ways for the quality of halophytes as animal feed.
Keywords: salt marsh plants, feeds, anti-nutritional factors, animal performance, treatments, deserts
6
Introduction
Natural resources have been diminishing because of increased demands. This sort of pressure resulted from the ever-increasing population of the world. Inevitably, marginal and long-neglected natural resources have to be re-assessed in preparation for utilization. It is estimated that 7-10% of the world land area is salt affected (Dudal and Purnell, 1986). Table (1) shows the distribution of salt-affected soils in the world. Clearly, not a single continent is free of that kind of soils (Kovda and Szabolcs, 1979). Halophytes grow in many arid and semi-arid regions around the world and are distributed from coastal areas to mountains and deserts. Halophytes (salt plants, Squires, 1994) belong to several taxonomic groups. The word halophyte, then, does not imply any reference to being a particular taxon or any specific geographic or physiogeographic area.
Table 1. Areas of salt–affected soils in different regions of the world
Region
/Area (ha x 103)
N America
/15,755
Mexico & Central America
/1,965
S. America
/129,163
Africa
/80,538
S. Asia
/87,608
North and Central Asia
/211,686
South-East Asia
/19,983
Australia
/357,330
Europe
/50,804
Adapted from Kovda and Szabolcs, (1979)
Nature and ecology of halophytes
Le Houerou, (1994) concluded that nature and ecology of halophytes are very complex. They do not necessarily need salinity to grow. Halophytes constitute around 6,000 species in the world. In a previous study, Le Houerou, (1993) interestingly divided halophytes into “optional or fluctuative halophytes” implying those that do not necessarily need salinity to grow and “obligate or true halophytes” to refer to those need saline conditions for their growth. Of the former he mentioned Atriplex spp, Maireana spp, Tamarix spp, Salsola spp, Limonium spp, Puccinellia spp, and of the latter Halocnemum spp, Arthrocnemum spp, Salicornia spp, Sueda spp, etc. A third class was the “preferential halophytes”; examples of them are some Atriplex spp, some Maireana spp and some Tamarix spp. There are no clear limits, however, between these different classes (Le Houerou, 1994). Aronson, (1989) estimated that about one-third of the approximately 350 families of flowering plants contain halophytes and about 50% of the genera belong to 20 of these families (Flowers et al, 1986). Therefore, it appears that halophytes are widely distributed among several families of flowering plants. Based on these studies and those by Chapman, (1975) and Flowers et al (1977), it is clear that no family in which more than half of the species is halophytes. The fact that the limited number of halophytic species is spread among so many different families indicates that halophytism, even though a trait controlled by several genes, is not such a complex characteristic that only arose once during evolution. This polyphyletic origin of halophytism (Flowers et al, 1986) suggests that it is characteristic that could be introduced into species not yet possessing it, particularly species in the same families that already contain halophytic species. Both climate and soil characteristics have influence on the distribution of halophytes (Szabolcs, 1994). He mentioned that salt affected soils are distributed not only in the deserts and semi-deserts, but also in fertile alluvial plains, river valleys and coastal areas, close to highly populated areas and irrigation systems. Salt affected soils are most appropriate for the growth of halophytes; although they occur in completely different soils. A wide range of plant genera inhabits salt-affected soils and referred to as halophytes. Not all of the halophyte plants are able to germinate in their native saline habitats without early leaching of the soil (Batanouny, 1993). He concluded that the correlation between salt tolerance of a plant and its tolerance at other stages is not obligatory. This has been noted in certain halophytes (Waisel, 1975). The water relations of their habitats therefore, affect germination of halophytes. Water content (= water budget) is a critical factor for the growth of halophytes. Therefore, Le Houerou, (1994) classified saline soils with respect to water budget into permanently wet, quasi-permanently dry and permanent or a temporary table or not. The soil chloride content affects the germination of halophytes. This is called ionic budget. However, vegetative reproduction is a major means of reproduction in many halophytic species (e.g. Limonium vulgare, L. humile, and Tamarix aphylla).
Halophytes in the Mediterranean basin and Arab region
The Mediterranean area in its broad meaning refers to the area from the Aral Sea to the Atlantic Ocean. The halophyte forage species in the Mediterranean Basin are very diverse in terms of plant systematic, biology and ecology. They constitute around 700 species. As is the case with halophytes in any other area, they include both perennial and annual species. They are also divided into shrubs and trees. Table (2) shows different proportions of different halophytes in the Mediterranean Basin. Chenopodiaceae dominates the plant communities either alone or mixed with other types of plants. Halocnemum strobilaceum, Arthrocnemum indicum, Salicornia, Salsola, Sueda, and Atriplex are examples of that dominance.
Table 2. Proportions of different halophytes in the Mediterranean Basin.
Family / PercentageChenopodiaceae / 27.5
Graminaceae / 15
Compositeae / 6
Caryophyllaceae / 5
Leguminoseae / 5
Zygophyllaceae / 5
Aizoaceae / 3
Frankeniaceae / 3
Tamaricaeae / 3
Cyperaceae / 3
Plantaginaceae / 2
Ombellifereae / 2
Crucifereae / 2
Boraginaceae / 0.5
Convolvulaceae / 0.5
Gentianaceae / 0.5
Juncaginacea / 0.5
Other families / 6
Adapted from (Le Houerou, 1969a, 1986, 1993a, and Le Houerou et al, 1975)
Batanouny, (1994) reviewed halophytic plant communities in the Arab region. The area partially includes a large proportion of the Mediterranean Basin, part of west Asia, and part of east and west Africa. Therefore, it has a wide variety of halophytes. The halophytes in the Arab area represent less than 5% of the flora of the area. However, the floras comprise some 150 halophytic species in about 55 genera and about 22 families. The salinity of the soils in both the Mediterranean Basin and the Arab world varies from place to place with different types of salt distribution in the profile. A few annual species, which are usually succulent, are recorded, e.g. Salsola europaea, Binertia cyclopetra, Sueda aegyptiaca, Sueda salsa, and Halopeplis amplexicaulis. The main halophyte families are Chenopodiaceae, Gramineae, Aizoaceae, Avicenniaceae, Caryophyllaceae. Compositae, Convolvulaceae, Cynomoriaceae, Cyperaceae, Frankeniaceae, Juncaeae, Leguminosae, Nitrariaceae, Plantaginaceae, Plumbaginaceae, Rhizophoraceae, Salvadoraceae, Tamaricaceae, Typhaceae, and Zygophyllaceae.
Potential uses of halophytes
A number of halophytes have been used for different purposes. Aronson, (1989) enumerated 1560 halophyte species which are already in use. There are, however, several broad situations in which halophytes are used by livestock. Halophytes are being trailed under irrigation, mainly in developing countries (Squires, 1994). Other uses of halophytes are: land rehabilitation, utilization of desert and saline water in irrigation, feedstuff component, medicinal materials, fuel wood, shade and shelter, sequestration of carbon dioxide, etc. Some halophytes are used as building materials (eg. Avicennia marina, Prosopis tamarugo), others as wood for furniture, timber, charcoal, fire wood (e.g. Tamarix spp). Many halophytes are used in medical purposes as drugs; these include Annona glabra, Gomphrena globosa, Juncus acutus, Salsola kali. Moreover, halophytes have been reported to be used as fertilizers (e.g. Sesbania speciosa and Zostera marina). Many of them are edible and utilized as vegetables such as Aster tripolium, Sueda glauca, and Salicornia fruticosa, which are used for oil production. Other uses of halophytes include the utilization in reclamation of saline lands, laundry detergent, paper production, herbal tea, sea floor fixation, as a green cover, as ornamental plants and as hedges.
Prospects of halophytes as animal fodder
Halophytes can play a significant role in the well being of different peoples. The way in which halophytes are assessed will very much depend on which system dominates. Any evaluation must depend on viewing performance in the context (biological/ economic) in which it occurs.
Value of halophytes as feed component for livestock
The shortage of animal feeds is the main constraint to increase indigenous animal production. Animal husbandry, as the main income resource for nomads, is based mostly on the natural vegetation for rearing sheep, goats and other herbivores. However, unpalatable halophytes are widely distributed throughout the world. Halophytic plants such as Atriplex spp, Nitraria retusa, Salsola spp, are generally considered extremely valuable as a fodder reserve during drought. The chemical analysis of some halophytic plants (Table 3) reveals that halophytic species have the potentiality as an animal fodder (Gihad and El-Shaer, 1994). However, the highest forage values are found during the wet season of the year when plants are green and actively growing (Chatteron et al, 1971 and Kandil and El-Shaer, 1990). In comparison with other shrub species, all chenopod shrubs contain high concentrations of digestible crude protein, and Na, K, and Cl- ions. The acceptability of most chenopod shrubs to domestic animals is moderate to low when grasses and herbs are available but it increases, as these components become scarce (Wilson, 1984). Suaeda species is considered one of the most palatable chenopod shrubs (El-Shaer, 1986). Factors influencing grazing and nutritive values of halophytes are the plant species, ecotypes (Rizk, 1986), stage of growth (El-Shaer, 1981), season of use (wet season versus dry season), environmental factors (Gihad, 1993), and location (Gihad and El-Shaer, 1994). Halophytic plants differ in their nutritive value as from one species to another. Chemical composition of saltbush species differ widely. Even more, the differences exist within the same species. More exiting is that the chemical composition of the same salt plant species differs seasonally and even within the same season according to the stage of growth. Table (3) shows some of the differences that exist between some halophytic species in different seasons. Examples are many that show the differences in chemical composition and, hence, nutritive values within the same species. Ramirez and Torres, (1997) found that Acacia rigidula and Acacia farnesiana were different in their nutritive values. Degen et al, (1997) reported the same results when fed Acacia saligna and Acacia salicina to goats and sheep.
Table (3). Average values of chemical composition of common range plants in southern Sinai
Plant species / CP / CF / EE / Ash / NFEDM / DM basis, %
Halocnemum strobilaceum
Wet season / 28.6 / 6.78 / 14.6 / 2.46 / 35.7 / 40.46
Dry season / 37.8 / 4.22 / 19.6 / 2.16 / 42.5 / 31.52
Zygophyllum album
Wet season / 30.4 / 7.12 / 14.6 / 2.25 / 26.5 / 49.42
Dry season / 39.3 / 6.30 / 16.2 / 1.63 / 28.5 / 47.31
Tamarix mannifera
Wet season / 57.4 / 7.64 / 16.1 / 2.21 / 26.0 / 47.97
Dry season / 63.1 / 6.26 / 17.5 / 1.78 / 30.9 / 43.47
Salsola tetrandra
Wet season / 45.0 / 9.73 / 12.4 / 2.61 / 30.1 / 45.1
Dry season / 49.9 / 8.38 / 14.4 / 1.67 / 35.8 / 39.68
Nitraria retusa
Wet season / 14.6 / 9.10 / 12.8 / 3.01 / 16.2 / 58.87
Dry season / 20.1 / 7.20 / 18.2 / 2.28 / 19.7 / 52.62
Atriplex halimus
Wet season / 42.1 / 9.21 / 18.7 / 3.2 / 31.4 / 37.49
Dry season / 58.4 / 6.32 / 22.6 / 3.10 / 36.7 / 31.28
Saueda fruticosa
Wet season / 30.9 / 11.1 / 10.9 / 3.9 / 25.4 / 48.66
Dry season / 48.3 / 8.4 / 13.7 / 3.0 / 30.3 / 44.6
Utilization of fresh and dried halophytic fodders
Intake and nutrient utilization
Voluntary feed intake (VFI) (Table 4) and digestibility are considered the two major components reflecting upon forage quality of grazing ruminants. The process of aging and maturation of the ranges was found to be associated with a decline in digestibility, and CP content, consequently the nutritive value (El-Shaer,1981and El-Bassosy, 1983 ). The DMI and DM digestibility of halophytic forages were higher in grazing season than in drought season with both sheep and goats. Rams consumed less DMI of forages than bucks in drought season ( 34.4 vs. 44.1 g/kg075) as reported by El Shaer, (1981). Warren et al. (1990) recorded dry matter intakes of 400-800 g/day for 4 species (A. undulata, A. Ientiformis, A. ammicolla and A. cinerea) fed to sheep that had dry matter digestibilities of 53-62%. Le Houérou, (1993) reported that sheep became adapted to saltbush and increased their intake of forage over a 3-5 month period. Therefore, it seems that feeding halophytes need more time than other feeds for animals to be adapted on such feeding particularly the less palatable forages.