Penificial effects of natural clays in pollution reduction

Natural clays are crystalline alumino-silicates characterized by their ably to exchange cations without major changes in structure. Zeolite and bentonite are the most common natural clays wed in rabbi production. Natural clays can be used as feed binders hi feed manufacturing. Natural clays can adsorb toxic products of digestion and decrease the accumulation of toxic substance in rabbit tissues, thus decreasing the incidence of internal disorders. Natural clays may stimulate the lining of the intestinal tract, that increases the production of antibodies, which could then inhibit the onset of enteritis. Addition of natural clays in rabbit diets improves growth rate, feed conversion and increases return from body gain and final margin. Nutrient digestibility increases by natural clay supplementation in rabbi diets, due to ifs low rate of passage.

Keywords:       Natural clays, ion exchange, adsorption, productive performance, toxicity.

Numerous mineral materials are receiving greater attention in rabbit production. In this respect, the research and development efforts aimed to find out the possibility of employing of natural clay properties, such as ion exchange, adsorption and binding properties in enhancement of rabbi production. Earlier studies in the United States of America showed that as much as 40% clay coin be added to animal rations without adverse effects (Ousterhout, 1970). Addition of natural clays in animal diet as growth promoters was reported by many authors.

The present article will throw some lights on the importance and uses of natural clays in rabbit production. Classification and composition of common natural clays; are also included.

Clays are dominantly colloidal and crystalline i.e. have a definite, repeated arrangement of atoms of which they are composed and are hydrated from aluminum silicate (Fitzpatrick, 1983). Minerals of natural clays can be divided into non-silicates and silicates. The first group contains oxides, hydroxides, sulfates, chlorides, carbonates and phosphates. Such compounds have variable structures, but they are very wide in solubility and resistance to decomposition. The second group has a complex structure in which the fundamental unit is the silicon-oxygen tetrahedron. This unit is composed of central silicon ion (Si4+) surrounded by four equal-spaced oxygen ions (O^2-). The four positive charges of Si⁴⁺ are balanced by four negative charges from oxygen ions O^2-, one from each ion. Thus each discrete tetrahedron has four negative charges. The tetrahedral themselves are linked together in different ways. The type of inking determines the crystal structure, as well as, its resistance to weathering. A significant variation in the tetrahedral structure is the substitution of aluminum (Al) for Si, that produces as imbalance in the charges within the structure, which is satisfied by some cations such as sodium (Na⁺), potassium (K⁺), calcium (Ca⁺⁺), magnesium (Mg⁺⁺) and (NH₄⁺) ammonium (Fitzpatrick, 1983). Silicates are divided broadly kilo rings, chain, sheets and framework silicates.

Some silicates may have nutritional benefit (Jordan, 1953 and Erwin et al.,1957) and are used as feed additives in rabbit diets such as zeolite and bentonite, and some others may have no nutritional value and are considered as diluents in the diet (Moody, 1963, Ershoff and bajwa, 1965 and Jones and Handreck, 966).

Zeolites are crystalline, hydrated alumino-silicates of alkaline earth cations, that have infinite, three dimensional network structures. Such structures consist of three-dimensional frameworks of SiO₄^-4 tetrahedral. The arrangement of silicate tetrahedral reduces the overall Si : O ratio to 1 : 2, and if each tetrahedron in the framework contains silicon as the cation, the structures are electrically neutral, as in quartz (SiO₂). In zeolite structures, some of the quadrivalent silicon is replaced by trivalent aluminum giving rise to a deficiency of positive charge. This charge is balanced by the presence of mono and divalent cations, such as Na⁺, Ca⁺ and K⁺, elsewhere in the structure. The most common of the natural zeolites follow the structure: (Na, K)₂O - Al₂O₃ - 6SiO₂ - 6H₂O. Ions within the first set of parentheses in the unit-cell formula are known as exchangeable cations (Mercer and Olson, 1971, Breck, 1974 and Mumpton and Fishman, 1977). Natural zeolites are characterized by ability to loss and gain water reversibly and to exchange cations without major change of stricture (Mumpten and Fishman, 1977). The chemical composition of clinoptilolite, which is nature zeolites, is 70 - 97% silicon oxide (SiO₂), 13.1% aluminum oxide (Al₂O₃), 0.68% hematite (Fe₂O₃), 0.21% ferrous oxide (FeO), 0.15% titanium Oxide (TiO₂), 3.44% calcium oxide (CaO), 0.68% manganese oxide (MgO), 0.014% phosphorus oxide (P₂O₅), 2.64% potassium oxide (K₂O), 0.39% sodium oxide (Na₂O) and 4.56% water (H₂O). Each kg of dry matter soils also includes 4.47 mg copper, 483.7 mg manganese and 29.9 mg zinc (Grabovenskii and Kalachnyuk, 1984).

Bentonite, like other clays, is colloidal clay and is hydrated from aluminum silicate. Thechemical composition of bentonite clay was 53.14% SiO₂, 0.38% TiO₂, 17.74% Al₂O₃, 3.53% Fe₂O₃, 0.22% FeO, 4.64% MgO, 2.41% CaO, 1.32% Ne₂O, 0.64% K₂O and 0.70% SO₄ (Katsitadze and Epitov, 1983). In Egypt, the chemical composition of bentonite at Fayoum area was 51.1% SiO₂, 1.4% TiO₂, 19.8% Al₂O₃, 8.4% Fe₂O₃, 1.6% MgO, 0.3% CaO, 1.3% Ne₂O, 0.8% K₂O, 0.2% P₂O₅ and 0.02% MnO (Attia et al., 1985). Marai et al. (1996) found in Egypt at Inshas area (Sharkia Governorate) that the soluble cations and anions (Milliequivalent (meq)/100 g dry soil) of tafla (which is a type of natural clay that includes 80% bentonite) were 0.75 Ca⁺⁺, 0.25 Mg⁺⁺, 0.05 Na⁺, 0.10 K⁺, 0.55 Cl^-, 0.30 SO₄^-- and 0.75 HCO₃^-. Exchangeable cations was 2.65 meq/100 g dry soil and available nutrients (mg/100 g dry soil) were 5.0 P, 1.2 K, 2.4Mn, 0.74 Zn and 0.30 Cu, and Fe was 0.55 ppm. Bentonite, like other clays, is able to absorb much water and cations, appears to improve the physical nature of pelleted feeds (Martin et al., 1969) and may in some ways influence absorption from the gut (Mendel, 1971). Ions before the brackets of the unit-cell formula are known as exchangeable cations (Fitzpatrick, 1983).

Clay minerals have various locations that have negative charges from isomorphous substitution. Positive ions (cations) are adsorbed at the negative charged sits. These adsorbed cations resist removal by water leaching, but can be exchanged by other cations through mass action. The most numerous cations on exchange ekes In soil are Ca⁺⁺, Mg⁺⁺, H⁺, Na⁺, K⁺ and Al⁺⁺⁺, indicating that soil acts as a large cation exchanger. Any solution moving through the exchanger will loose many of Is soluble cations to the exchanger and pick up those cations that flaw been replaced from exchange sites. Cation exchange capacity is the amount of exchangeable cations per unit weight or dry soil (Donahue, 1983). Crystalline zeolites are some of the most effective cotion exchangers waft capacity of 3 to 4 milliequivalent per gram. Ion-exchange capacity is basically a function of the degree of substantiation of aluminum for silicon in the framework structures; the greater substantiation, the greater change deficiency and the greater the number of alkaline earth cations for electrical neutrality (Mumpton and Fishman, 1977). Ion-exchange capabilities of zeolite could possibly influence microbial and animal metabolism through the preferential trapping and release of cations (McCollum and Galyean, 1983).

Under normal conditions, the large cavities and entry channels of clay minerals are filled with water molecules forming hydration spheres around the exchangeable cations. If the water is removed by heating, molecules having effective cross sectional diameters smell enough the entry channels, are readily absorbed on the inner surfaces of the dehydrated cavities. The surface area available for absorption ranges up to several hundred square meters per gram. Some clay minerals are capable of absorbing up to about 30% of a gas, based on dry weight of the clay mineral. Carbon dioxide (CO₂) is preferentially adsorbed by certain zeolites over (CH₄) methane (Mumpton and Fishman, 1977). Natural clays can absorb toxic products of digestion and decrease accumulation of toxic substance in tissues, thus decreasing the Incidence or internal disorders.

Natural clays such as zeolite and bentonite are used at a 2% level in feed manufacturing as a pellet binder.

The physical and chemical properties of much natural clay make them act to a wide variety of applications in rabbi production.

Malodor and associated pollution are reduced with dietary supplementation of natural clays. T-2 toxin is a trichothecen mycotoxin produced by some strains of Fusarium and causes feed refusal and growth depression (Uneo, 1977). Supplementation of 2.5, 5.0, 7.5 or 10.0% bentonite in the diets decreased the toxicity effect of T-2 toxin. Residual of T-2 toxin in muscle is reduced, but that in the liver or kidney is not affected by dietary bentonite supplementation. Bentonite feeding reduces T-2 toxicity by reducing intestinal absorption and increasing faecal excretion of the toxin (Carson and Smith, 1983), i.e. natural clays adsorb the toxic material and excrete it in faeces. In rabbits natural clays are inexpensive natural minerals, which have a protective effect against diarrhea (Ayyat and Marai, 1997). Watanabe et al. (1971) reported that diarrhea was noticeably less prevalent in animals fed diets including zeolite. Grobner et al. (1982) added that inclusion of zeolite in rabbit rations might be beneficial in reducing incidence of enteritis as characterized by diarrhea. Ayyat et al. (2000) found that the supplemented of natural clay (bentonite) in rabbit diets contaminated with the pesticide decreased the mortality rate (3.3% vs. 16.7%).

Bentonite inclusion in the rabbit diets causes a marked decrease in transfer and accumulation of radionuclides in their meat, liver and kidneys. Transfer factors for supplemented and unsupplemented bentonite expressed in international units were 0.41 and 1.55 d/kg for ¹³⁷Cs, respectively, and 0.39 and 1.46 d/kg for ¹³⁴Cs, respectively. At the same time, bentonite significantly increases faecal excretion of radio nuclides and other radionuclides in the diets (¹⁰⁶Ru or ¹²⁵Sb) that are almost totally excreted it faeces (Piva et al., 1991). Pietri et al.(1993) clarified that total body radioactivity was reduced (P< 0.01) with the increase of zeolite in the diet and a maximum of 51% reduction of radioactivity was achieved with 6% zeolite added to a rat diet.

Dietary supplementation with natural clays showed no differences in growth performance of rabbis (Grobner et al., 1982 and Lambertini et al., 1987 and 1989). Marai et al. (1999) found that rabbit final body weight, body gain, return from body gain and final margin increased with 5.8, 8.16, 8.3 and 23.6%, when compared with those fed diet without clay supplementation.

Avallone et al. (1987) found that digestibility of nutrients was not affected by 3% Zeolite, while with 5% dietary zeolite, digestibility of dry matter, ash, fibre, nitrogen-detergent and acid-detergent fibre and cellulose decreased and nitrogen balance was not affected. Natural clays decrease liquid fractional rate of passage and liquid flow rate, while slightly decrease fractional rate of passage food particles in digestive tract (Ayyat and Marai, 1997).

Feed conversion is improved by dietary supplementation with the natural clays.

Marai et al. (1999) reported that 5% tafla (natural clay that includes 80% bentonite) supplementation in rabbit diets improved feed conversion with 18.2% than those fed diet without clay supplementation, while feed intake decreased with 11.6% and water intake decreased with 27.5%. Zeolites may act to stimulate the lining of the stomach and Intestinal tract, that increases the production of antibodies, which could then inhibit the onset of enteritis (Mumpton end Fishman, 1977).

Caecal contents of ash, water, magnesium, potassium and sodium were found to be higher and the caecal calcium content was lower when rabbis were given bentonite. Solubility of calcium or potassium in caecal contents was lower in bentonite-treated rabbits than in untreated rabbits (Lambertini et al., 1989). Caecum weight, ash content and pH were greater it bentonite treated rabbits (Lambertini et al., 1987).

Lambertini et al. (1989) reported that bentonite supplementation in rabbit diets increased chilling shrink and reduce perirneal fat. Marai et al. (1999) found that supplementation 5% tafla in rabbit diets increased weights of carcass (3.1%), fore part (4.2%), intermediate part (8.1%) and hind part (5.1%) and decreased empty gut weight (20.1%), liver weight (24.9%) and kidney fat weight (3.3%) when compared with those fed diets without supplementation.

Healthier environments for confined rabbits are created with dietary supplementation of natural clays. Marai et at. (1999) reported that tafla addition (5% of the diet) to heat-stressed rabbit diets increased final live body weight, body gain weight, feed conversion, return from body gain and final margin than these which reared under heat stress conditions without tafla clay supplementation. Improvement of body gain weight by addition of tafla clay may be due to its role in decreasing rate of food passage that increase each of ion exchange capacity, digestibility and absorption, in addition to Is reaction with dietary protein forming a complex which has positive effect on protein degradability and improvement of nitrogen utilization that are reflected in the increase in body gain weight.

Supplementation rabbit diets up to 5% with natural clays (zeolites or bentonite) enhance growth rate. This may be due to improvement in each feed conversion, digestibility, mineral retention, microbial protein supply and nitrogen retention in animal's body, in addition to reduction of toxicity and diarrhea. Ability of clays to diminish the harmful effects of radiation may have a role it this respect.

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