Halophytic Plants for Animal Feed: Associated Botanical and Nutritional Characteristics

Halophytes are plants that initiate their growth, accomplish their life course, and outlive others in a salty environment. The word halophytes has two syllables (halo = salt, phyte = plant). However, halophytes vary greatly with respect to salt tolerance. This chapter discusses the soils in which halophytes grow and the climate as well as their effects. The halophyte biodiversity in different regions of the world is reviewed.

 Halophytes are a small group of higher plants. They represent about 1% of the world’s flora. There is no unanimous consensus on a distinct definition of halophytes. This is because of the taxonomic and ecological complexities of halophytes as well as their heterogeneity. Some authors consider the salt content of the native habitats to be the basis for the classification of halophytes. Others concentrated on the response of plants to salinity. However, different basal halophyte classifications are discussed in this chapter. 

Salinity and drought are abiotic stresses that most affect the growth and productivity of plant species all over the world. Salt-tolerant plants have a range of adaptive characteristics not only in morphological or structural features but also in metabolic and physiological processes that enable them to survive in extreme saline environments. Morphological and anatomical features of halophytes are commonly correlated with the prevailing environmental conditions under which the plants grow. There is a pertinent correlation between the histo-anatomical features of halophytes and the ecological environment in which they breed. Therefore, metabolic pathways and reactions are dramatically affected by such ecological factors. Moisture contents, dry matter contents, lignification, fiber, and starch contents, salt contents, proteins, and amino acids contents, lipids and free fatty acids contents, reactive oxygen species, plant secondary metabolites contents of halophytes are deeply discussed in relation to the histo-chemical characteristics of these unique plants.

In climatically unfavorable regions, the animals often consume the only available feed resource, i.e., halophytic plants. It was noticed that whenever halophytes are solely fed to animals, they need energy supplementation. Halophytic plant species vary greatly with respect to their chemical composition and nutritive value. Halophytes are characterized by great salt concentrations and high contents of acid detergent fiber and neutral detergent fiber. Halophytes are low-quality forages having fewer available nutrients and thus, requiring larger amounts of supplements to be added. They require energy supplementation more than any other kind of supplementation. Supplemental feeds are usually cereal grains. This chapter discusses in-depth and in detail the issue of halophytic energy when provided as animal feed (i.e., carbohydrates in halophytes, the effect of salinity on the carbohydrate content of halophytes, the effect of season on the carbohydrate content of halophytes, and the discrepancy in energy determination).

 Proteins are an important nutrient for all animal species as they are a primary component of all body tissues as well as fluids and vital organs. In evaluating proteins present in halophytes as dietary nutrients, one should take several issues into consideration (ie. the high percentage of nonprotein nitrogen fraction, the large percent of solubility of halophytic proteins, the high degradability of soluble proteins in the rumen by the microorganisms, and the lack of readily available carbohydrates in halophytes that increases nitrogen waste). The protein contents of halophytes, amino acids in halophytes, effects of salinity on protein and amino acid contents of halophytes, effects of season on protein and amino acid contents of halophytes, animal utilization of halophytic proteins, and factors affecting microbial protein synthesis from halophytic sources are all covered in this chapter.

Some halophytes are good sources of oil production for human consumption. However, lipids in halophytes have vital functions with respect to their adaptation to conditions of high salinity. They play an active role in cell membrane selective permeability to toxic ions. During the process of plant adaptation, the fatty acid compositions of halophytic lipids change to play a unique role. Fatty acid composition, as well as makeup, varies considerably from one organ to another in halophytes. This chapter discusses the lipid and fatty acid contents of halophytes, the effect of salinity on lipid contents and compositions of halophytes, the utilization of halophytic lipids by animals, and the interrelations between dietary fat and animal metabolism.

Since the halophytes complete their life cycle in a salty environment, they, consequently, have a high content of minerals in their components. The high content of ash is a typical characteristic of halophytes. However, the ash content of halophytes differs greatly according to several factors. This chapter discusses how halophytes vary in ash and ion content, the effects of halophyte species on mineral compositions, and geographic variations in the mineral contents of halophytes. 

Plant secondary metabolites (PSMs) are the intermediate or end products of the primary metabolism of higher plants and are not involved in metabolic activities. Primary metabolites are the compounds that are indispensable in the processes of photosynthesis, respiration, and growth and development. To a certain degree, these compounds are found in all plants, yet they are common in tropical forages. In spite of the high cost of energy for the biosynthesis of PSMs, they are produced for protective purposes. Most halophytic plant species produce secondary metabolites with wide biological activity, such as tannins, organic acids, carotene, ascorbic acid, glycosides, absinthin, and essential oils. This chapter discusses the occurrence of PSM's in halophytes, the origin and divisions of plant secondary metabolites, and the distribution of PSM's in plant species and organs. 

During the prolonged dry periods in arid and semi-arid areas, the average annual production of ruminant animals would decrease dramatically due to several reasons, which are the scarcity and insufficiency of feeds. It was reported that the improvement of the nutritional status of desert grazing livestock (sheep, camels, and goats) would lead to the amelioration of their productivity. This dictates the necessity of utilizing marginal resources like halophytes. Some halophytes, on the other hand, have been reported to have nutritional value to ruminants and are therefore worth feeding to some extent. This chapter discusses the abundance of halophyte production, the quality of halophytes as an animal feed with special reference to palatability and animal preference for halophytes, halophytic nutrient supply, and utilization by animals, ash, and mineral contents of halophytes, including factors affecting their contents in halophytes, protein and amino acid contents of halophytes (feeding and nutritive value of halophytic proteins), feeding and nutritive value of halophytic energy, and overall feeding value of halophytes to animals.

The greater demand for feed in most developing countries imposes certain pressures. Therefore, the use of non conventional feed resources is gaining a rising significance. Halophytes can, then, play an important role in the well being of different peoples. This chapter discusses the constraints of feeding halophytes, consequences of feeding halophytes to animals, methods and strategies to maximize utilization of halophytes (breeding halophytes, overcoming the effects of plant secondary metabolites, overcoming the effects of high salt contents, treatment of halophytes prior to feeding (mechanical treatments, drying, haylage, ensiling, pelleting and feed cubes or blocks, biological treatments, feed additives and supplements)).