Feeding value is the function of voluntary feed intake and the nutritive value of biomass which impacts meat, milk, and wool production. To meet nutritional requirements in the grazing system, it is important to deliberate the availability of halophytes and non-halophytes to provide complementary forages [11]. Supplements implicate the economic, labor, and transport costs. Therefore, to maximize the dependence on additional feed, we should maximize the feeding value of halophytes. Nutritive value is the function of digestibility of the nutrients and the efficiency of the nutrients used for animal production. Crude protein, minerals, and metabolites are the major contributors to nutritive value [12].

The function of the digestible organic matter in dry matter (DM) is known as metabolizable energy. This is generally lower in halophytes than in non-halophytes because of the presence of less organic matter [13]. D. spicata and S. virginicus provide a diet to animals with supplementary energy concentration. Researchers have studied the relationship between salinity and fiber value. In C. dactylon, neutral detergent fiber increased by 5%, while in T. ponticum it decreased by 3% [14]. Attia-Ismail [15] found no relationship between salinity and fiber content among five different halophytic species, A. lagopoides, S. tremulus, P. paspaloides, P. geminatum, A. nummularia, and S. tragus, which have 2.30, 2.38, 2.53, 2.33, 2.82, and 2.56 M cal kg⁻¹ energy, respectively.

Ruminants require the minutest protein for their growth. Adult ruminants require approximately 7–9% protein, while growing or lactating ruminants required 14–18%. Protein is degraded by the rumen microbe, but some of the degraded protein is converted back into microbial protein by the rumen microbe and passes down the gastrointestinal tract for amino acid absorption [16]. Undegraded dietary protein resists the rumen microbe and is absorbed in the lower gastrointestinal tract. Halophytes with protein content are listed in Table 1. Low protein content in halophytes could be enhanced by agronomic practices, for example, by harvesting halophytic grasses in the presence of nitrogen (N), fertilizer, and seawater [15]. In S. virginicus, protein content increased from 6.8–9.0% when irrigated with 12.5–50% seawater [17]. The relationship between protein content and soil salinity is not consistent, for example, protein content was 12% in C. gayana and 16% in C. dactylon, irrespective of salinity [18]. M. alba achieved 13% protein from using Rhizobia in root nodules to fix N [19].

In ruminants, the N compounds glycinebetaine (GB) and proline (Pro) have both positive and negative effects. GB acts as a methyl doner in protein for the recycling of amino acids and energy metabolism which is important in ruminants’ muscle growth. GB also assists in choline production, improves lean and fat ratio in meat, and also improves carcass composition [20]. In ruminants’ diets, more than 50% GB is degraded by rumen microbes. Pro as hydroxy proline is associated with collagen, which can be absorbed directly into the small intestine. Ruminants have the ability to synthesize adequate Pro to meet their necessities as it is important for their growth and production [21].

Plants have sulfur (S) concentrations mainly ranging from 0.05–0.5% DM. Sulfur is the main component of several vitamins, insulin, coenzyme A, and three amino acids (cystine, cysteine, and methionine). These amino acids are essential for protein synthesis. 0.2% DM S is recommended in the diet of sheep and 0.15% DM in the diet of cattle [25]. Sulfur is used with N. The optimal ratio of N:S is 12.5:1 which is considered best for sheep. Sulfur causes toxicity when converted into sulfide in the rumens of animals instead of ruminal protein. Sulfides reduce the reduced copper (Cu) absorption, which induces Cu deficiency. Sulfides reduce rumen motility and decrease voluntary feed intake [27].

Halophytes are different from other plants due to their ability to make osmotic adjustments, which in C. quinoa affects the mineral contents of the edible plants. Salinity tolerance is achieved by sodium (Na) and chloride ion exclusion from the root surface and ion secretion from the leaves. The total ash from halophytic C. quinoa contains 63–81% Na, potassium (K), and chloride ions, whereas legume chenopods contain only 40% [28]. Under salt stress, halophytes have the ability to modify their salt glands to excrete excess ions from inside the plant body, which also impacts the salt concentration in halophytic feed consumed by ruminants [22]. Many halophytes thicken their leaves in salt stress which increases tissue hydration. A. lentiformis had 2.4 g g⁻¹ OM water content and 15.9% DM ash concentration, while S. europaea had 23.7 g g⁻¹ OM water content and 51.4% DM ash content [29]. Consumption of salt accumulating shrubs, such as Atriplex species, can cause toxicities in grazing ruminants by the accumulation of S and selenium [30]. Sheep were allowed to adapt to feed for three weeks, but over a consequent week, the sheep had net losses of magnesium 0.8, calcium (Ca) 0.6, and K 0.4 g per day⁻¹. These facts show that Atriplex sp. as a solitary feed are inappropriate for ruminants. Hence, an advanced study is a prerequisite to evaluating the mineral stability in animals [30].

For osmotic adjustment, halophytes use organic acids such as divalent anion oxalate, malate, and trivalent citrate, as well as anions, to achieve cation–anion balance. Centofanti and Bañuelos [24] studied twenty-one halophytes and concluded that five species from Chenopodiaceae and one from Caryophyllaceae had oxalate of more than 50 mM, 26–62% of the total anionic charge, and 5% DM. One specie from Brassicaceae had more than 70 mM citrate with 21% of the total anionic charge and about 15% DM [16]. Leaves of Atriplex sp. can produce 3.6–6.6% DM and about 40% total between cation and anions. In A. spongiosa, 76% of extra cations were stable by oxalate. Oxalic acid forms insoluble calcium oxalate, which reduces Ca concentrations in the blood of animals causing milk fever and problems in bone development [31]. Moreover, the sleet of calcium oxalate in the kidneys leads to kidney destruction. Oxalate has the ability to bind to other minerals such as iron (Fe), manganese (Mn), zinc (Zn), and Cu [32]. In the leaves of A. spongiosa, oxalate binds to all present Ca²⁺. Therefore, oxalate is the cause of the loss of Ca in sheep grazing. Feed containing Ca supplement for animals is a significant tool to improve the utilization of halophytes [33].

In the ruminant diet, tocopherol, or vitamin E is a very prevailing antioxidant. Tocopherol is present in the thylakoid membranes of chloroplasts which defend lipids from oxidation by ROS [34]. The concentration of α-tocopherol varies according to different ecological stresses as well as during different growth stages of plants. A deficiency of tocopherol can be the reason for nutritional myopathy and animal death. Atriplex sp. contains 116–139 mg kg⁻¹ DM α-tocopherol [30]. Vitamin E present in Atriplex sp. suspension influences the oxidative transformation of oxymyoglobin to brown metmyoglobin by oxidation of lipids in meat, which improves the flavor as well as the shelf-life of meat. Vitamin A is another antioxidant present in halophytic shrubs [35]. A. nummularia contains 41 mg kg⁻¹ dry mater vitamin A. In ruminants, vitamin A improves visualization, immunity, bone development, and heart disorders. During droughts, the threat of vitamin insufficiency in ruminants is relatively high due to the lack of access to green feed [36].