BIOAVAILABILITY OF MINERALS IN THE POULTRY FEEDS
The term “bioavailability” has been defined as the degree to which an ingested nutrient in a particular source is absorbed in a form that the nutrient is “available” at the tissue level rather than just at the dietary level. Bioavailability should not be considered as an inherent property or characteristic of the material being assayed, but, rather, an experimentally determined estimate which reflects the absorption and utilization under conditions of the test.
The word bioavailable means how usable a particular mineral or substance is. Usable means that it must be digested, absorbed, and find its way into the correct body cells. Within the cells, it must be further altered or converted into other chemicals, usually, to be useful in some way for the body. Then, when its function is over, it must be able to be easily eliminated from the body so that it does not accumulate as a toxin and clog up the body. Bioavailability is often for a specific purpose, at a specific time and with specific conditions of the body. In other words, a specific form, valence or spin of a mineral can be well-suited or bioavailable for one location or enzyme system in the body, but not suitable in another location or enzyme binding site. The bioavailability of a mineral or trace element is defined as the fraction of the ingested nutrient that is absorbed and subsequently utilized for normal physiological functions. For some of the elements this is the incorporation into various metalloproteins, such as Fe in haemoglobin. In addition, some elements, such as Ca and Mg, have a structural role in bones and teeth. Most elements are an integral part of a wide range of enzyme systems, for example Se in glutathione peroxidase. Physiological requirements for different inorganic nutrients vary widely, depending upon age, sex, stage of growth, pregnancy, and lactation. Dietary requirements are calculated from physiological requirements and efficiency of absorption from the diet, which ranges from less than 1 to almost 100%. The variation depends on dietary and host-related factors, including the amount of the element consumed. Dietary components greatly influence the absorption of most of the nutritionally important trace elements and minerals, with the exception perhaps of Se and I. The utilization of I by the thyroid, however, can be impeded by goitrogenic substances such as thiocyanate. Minor plant constituents, such as phytic acid and phenolics, can have a strongly inhibitory effect on absorption, peptide digestion products from dietary proteins can enhance or inhibit absorption depending on their nature, and there are several mineral-mineral interactions. Dietary components appear to have the great effect on bioavailability.
• Before absorption by the absorbing enterocytes from the gastrointestinal tract can take place, the minerals must become available in ionic form (as cations and anions), which is suitable for uptake and transport.
• In principal, the trans-epithelial transport consists of both, an active trans- cellular component which can be regulated and/or a passive para-cellular component which depends on chemical and electrical gradients existing across the intestinal wall .
• Passive transport through the gut wall, mediated by hormonal control that is primarily based on their concentration in the extra cellular fluid.
• Before absorption by the absorbing enterocytes from the gastrointestinal tract, the minerals must become available in ionic form (as cations and anions), which is suitable for uptake and transport.
• Several interactions among various minerals (e.g. calcium and phosphorus; calcium and zinc; copper and zinc; copper, molybdenum and sulphur)
BIOAVAILABILITY
• The percentage of mineral absorbed as related to the amount fed to animal
• No nutrient is absorbed and utilized to the full extent that it is fed
• When 2.5 lbs. of protein fed per day. Digestibility is only 65 percent, actually received is about 1.625 lbs. The same is true with minerals.
• As the genetic progress of the herd improves forage mineral bioavailability mineral interactions stage of production breed
• Bioavailability of one mineral is influenced by the concentration of other minerals in the diet
• Ex: high levels of sulphur or molybdenum interfere with copper absorption
• Practical determination of animal’s mineral status is often very difficult.
• Blood analysis is a poor indication of mineral status for many of the minerals
. • Liver biopsy may be required to determine the mineral status of animal
COMPONENTS OF BIOAVAILABILITY
• Digestion
• Absorption
• Liver surveillance
• Transport
• Trans membrane movement
• Intracellular movement
• Absorptive Phase
• Assimilation Phase
• Target binding
. DIETARY FACTORS INFLUENCING BIOAVAILABILITY
A. OXALATES
Oxalates, tannins and phytate possess anti-nutritional properties, specifically in the binding of minerals, thereby impairing mineral absorption into the body. high-oxalate (primarily spinach) diet was fed, mean apparent balances of Ca, Mg and zinc were negative, indicating that this type of diet impaired mineral absorption. The mechanism could be a binding of both oxalic acid and dietary fibre to minerals in a dietary fibre-mineral-oxalate complex.
B. TANNINS
Tannins are also organic compounds that can inhibit mineral absorption. Tannins, also known as polyphenols, are responsible for the astringent quality found in certain grains such as sorghum. Most tannin research relates to impaired haem-iron bioavailabilityforming insoluble iron tannates within the gastrointestinal tract.
C. . PHYTATE
Phytate, like oxalates and tannins, is an organic compound (myo-inositol hexaphosphate) which occurs in all plants and serves as the storage form of P in the living plant. Phytate is a potent chelator of minerals and, thus, its presence in a food will strongly dictate the outcome of minerals associated with this molecule. Phytase is the enzyme which hydrolyses phytate, thereby releasing the bound mineral or minerals. Phytic acid (myoinositol hexaphosphate) is found in cereal grains and legume seeds and is a major determinant of the low Fe,Ca and P bioavailability in these feeds. It is thought to form an insoluble complex with Fe, other minerals and peptide degradation products in the intestinal lumen, from which the Fe cannot be absorbed . The degradation of phytic acid in wheat bran almost completely removes the inhibitory effect of wheat bran on Fe absorption and adding phytic acid to wheat rolls inhibits iron absorption dose dependently. Phytic acid is a major inhibitory factor in isolated soya protein. Fe absorption increased significantly when phytic acid free soya protein isolates were fed. Some traditional food processes such as fermentation, germination or soaking can activate native phytases in cereal grains which then degrade phytic acid and improve Fe absorption. The results from human studies with pure fibre fractions, such as cellulose and pectin, indicate that fibre per se does not influence Fe absorption . The inhibitory effect of bran can be attributed almost entirely to its high phytate level .
D. GOITROGENS
The most studied factors relating to I bioavailability are the goitrogens, but these only have a significant impact on I daily intake when the usual dietary intake of I is low. Goitrogens can reduce the levels of I uptake by the thyroid, or impair its metabolism. Thioglucosides are the most common goitrogens, as found in brassica vegetables, e.g. cabbage, cauliflower, broccoli, mustard and turnip. On hydrolysis thioglucosides yield thiocyanates and isothiocyanates which inhibit the selective concentration of I by the thyroid. Thiocyanates are also formed by hydrolysis in feeds such as nuts, cassava, maize and sweet potatoes.
E. POLYPHENOLS
The phenolic compounds present in plant include tannic acids, phenolic acids, flavonoids and polymerization products. They are particularly high in beverages such as tea, coffee, herb teas, cocoa, sal seed and sorghum. Hydrolysable tannins of have been shown to be a most potent inhibitor of iron absorption. Chlorogenic acid, the phenolic compound in certain feed, is also inhibitory and coffee also reduces Fe absorption . The monomeric and polymeric flavonoids also inhibit Fe absorption. Phenolics in vegetables can also strongly inhibit Fe absorption and there is a strong inverse relationship between their polyphenol content and Fe .
- BIOMARKERS
Another method for estimating bioavailability is to measure mineral responsive biomarkers, such as changesin gene expression, or the activity of a mineral-dependent enzyme. Biomarkers are particularly informative when measured in the small intestine. Metallothionein is one such biomarker, because its expression is regulated by zinc status; the magnitude of metallothionein messenger RNA (mRNA) and protein expression depends on the amount of zinc absorbed. Therefore, metallothionein mRNA or protein expression is often used as an indicator of the zinc status of humans and animals and to evaluate the bioavailability of different zinc sources.
. PRINCIPLES OF MINERAL BIOAVAILABILITY
The bioavailability of a mineral or other chemical element often depends upon such things as the valence, spin, mass, atomic number, isotopes, and other physical and chemical properties of the mineral.
- Atomic and sub-atomic factors.
These are the structure, size, weight and other properties of an atom or mineral.
A. Atomic of molecular spin. Spin is a primary physics property of all matter. The spin of any substance has a direction, a velocity and other qualities such as wobble. For example, in stoichemistry or stochiometry, the direction of spin an atom or a molecule is labeled as the D-form or the L-form of the molecule. D stands for dexto-rotary, which means spinning to the right. L stands for laevorotary or spinning to the left.
B. Valence. A second important factor in the bioavailability of a mineral and some other chemical substances is called its valence. Valence is the number of electrons in the outer shell of the atoms of the substance. For example, copper, iron and manganese usually have a valence of +2 or +3. If the valence is not correct, it will affect the availability of the mineral. For example, iron found in meat has a different valence, at times, than iron found in vegetables. Biologically active calcium usually has a +2 valence, as does magnesium. On occasion, however, it could change, or calcium could be bound to something that shifts this property and for this reason changes the biological value of the calcium or magnesium.
C. Atomic mass or weight of a mineral. Another physics property of a mineral is its atomic weight, mass or density. This depends mainly upon the number of neutrons and protons in its nucleus, according to atomic theory. For example, hydrogen and helium are the lightest elements because they have only one or two protons and electrons respectively. This is why blimps and balloons filled with helium or hydrogen are lighter than air and float up in the sky. Hydrogen and helium are also smaller atoms than all the others. In contrast, heavy metals such as cadmium and lead are literally more dense and heavy. Most are very poisonous for all life forms. They are not only heavier, but they are larger than the light elements. The correct minerals for health are in the middle between the lightest and heaviest elements. The body must have the right weight of minerals or it will not function properly. For example, the heavy metals are literally too big and do not “fit” as well into certain enzymes and other structures in our bodies. This is one of the main reasons they poison us. They are like nuts and bolts that are too big to fit where they are supposed to go. This is why so much attention in nutritional balancing is focused on getting rid of the heavy metals.
- Isotopes and the bioavailability of minerals Besides having a general size, and weight or mass, each mineral also comes in slightly different sizes and weights that are called isotopes. These are lighter or heavier versions or forms of the same atom. The heaviness or lightness of an isotope depends upon the number of neutrons in the nucleus of the atom, according to atomic theory.
A. Molecular factors.
These are the structure, shape, size or other properties of combinations of atoms, which are called in physics molecules or chemical compounds. The way that atoms are combined with, or bound to other atoms is a critical aspect of bioavailability. At times, the pure mineral is more effective and available. This is often called an ionized state of matter. In other cases, minerals form various types of compounds. These include colloids, which is a suspension of fine particles with an electrical charge. For example, in nutritional balancing science colloidal silver is used to kill germs very effectively and with much less toxicity than most antibiotics.
B. Chelated minerals- In other cases, a mineral is bound to a proteinaceous substance such as an amino acid. This is called a mineral chelate or a chelated mineral. This is a far more bioavailable form of a mineral than many others.
C. In other cases, a mineral is bound to oxygen, and called an oxide, and so forth. Hundreds of combinations are possible, especially in feed and water. This is tricky, because a mineral in one form may be very bioavailable in the liver, for example, but a different mineral compound may be needed in the brain.
D. The ability to transmute. This is a rather esoteric aspect of bioavailability, but an important one to know about. Biological transmutation of the chemical elements means their transformation into other elements and compounds that occurs at low temperature and pressures in living organisms.
- Interactions These are other factors or forces in our bodies such as its acidity, electrical balance, temperature and many others. Interactions with many factors and forces within the body. There are many such factors, but here are a few of the most important ones.
A. Intestinal absorption. This is the most important factor in the bioavailability of all minerals, vitamins, proteins and other nutrients. Impaired digestion results poor absorption of nutrients, so the nutrients just pass through the digestive tract and move out of the body in the faces. A lot of energy has been wasted chewing and attempting to digest the food, only to have it wasted.
Reasons for impaired digestion.
These include not chewing feed enough, eating too fast, eating when upset or anxious, low levels of salivary digestive enzymes, low levels of stomach acid or other digestive substances in the stomach such as intrinsic factor, low levels of bile salts, bile acids, or pancreatic enzyme deficiency, intestinal infections of many kinds, improper intestinal flora , toxic chemicals or toxic metals in the feed that irritates the intestines, eating too much at one meal, leaky gut syndrome for many reasons, an irritated intestine that moves the feed along too fast, parasitic infections in the intestines or colon that irritate the tissues, genetic malformations of the intestines or colon, and a few other rarer
reasons such as tumors or blockages of several kinds.
B. Binding, transport and releasing factors.
Minerals and other substances must usually be “unwrapped” and “rewrapped” or “repackaged” many times as they are absorbed and transported through the body. It is like moving cartons of merchandise around the world that must be carried in planes, trains, ships and other cargo containers. Some of the cargo (the minerals) is delicate, and some is hazardous or toxic, so the body has found ways to bind it and transport it safely when the body functions correctly. At the sites where the minerals and compounds are needed, they must be released properly as well, or they will not do their jobs correctly. Another common example is that to release some calcium and many other compounds requires a very low or acidic pH of the stomach. This causes calcium to be released so it can be made into usable chemicals in our bodies. Otherwise, calcium in the diet may be wasted. Keeping the stomach very acidic is critical for good digestion. Acid-blocking drugs make the stomach less acidic, which relieves heartburn but impairs calcium utilization and bioavailability Important transport or carrier molecules in the body include ferritin for iron, and metallothioneine and ceruloplasmin for copper and some other minerals. If these transporters are deficient for some reason – usually poor nutrition – then the minerals cannot be utilized well and become bio unavailable.
C.Conversion in the liver.
An important factor in this regard is how well the substance can be broken down in the liver. All of our feed goes to the liver after eating. The liver converts it to other substances in many cases, or stores it away, and throws away that which cannot be used. Some substances just do not fare well in the liver, and instead build up there or can even damage the liver. These include alcohol, most medical drugs, and hundreds of toxic chemicals such as pesticides. Even some vitamins such as high-dose niacin, and spirulina, chlorella and other green and blue-green algae are not able to be processed well by the liver in most cases.
D. The effects of blood circulation. In order to use most minerals and chemical compounds, the blood circulation must be excellent.
E. Hydration. This is another critical factor in making some substances biologically available to the body. Without enough of the right kind of water, the kidneys, the cell membranes and other structures do not function correctly. Drinking water should hydrate the body such as reverse osmosis water. Dehydration impairs or even stops the proper transformation of chemical substances in the body.
. CONCLUSION
The following four factors are the primary determinants of reduced mineral bioavailability.
- Shortened transit times, providing less time for mineral absorption to occur.
- Dilution of intestinal contents and faecal bulking.
- Chelation of minerals to dietary fibre matrices and their interactions.
- The property of dietary fibre and incriminating factors to influence active and passive transport of Uminerals
Compiled & Shared by- Team, LITD (Livestock Institute of Training & Development)
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Reference-On Request.
