FACTORS AFFECTING BIO AVAILABILITY OF MINERALS PRESENT IN FEEDS & FEED SUPPLEMENT
INTRODUCTION ————-
Bioavailability is the degree to which a nutrient is absorbed and utilized by the body. Mineral nutrition is vital to overall cow performance. Without an appropriate balance of minerals, cows may not perform as expected or could exhibit detrimental effects.
The term bioavailability is used in pharmacology and toxicology as well as in nutrition. Its pharmacologic definition is as follows: “Bioavailability is a measurement of the rate and extent of therapeutically active drug that reaches the systemic circulation and is available at the site of action (Shargel and Yu 1999). Extended to nutrients the definition can be formulated: Bioavailability is a measurement of the rate and extent of a nutrient that reaches the systemic circulation and is available at target tissue level. For minerals bioavailability depends strongly on absorption from the gastrointestinal tract into the systemic circulation. For most minerals this is the limiting step. Consequently true digestibility is often used to quantify mineral bioavailability. There are, however, situations where other factors than absorption from the gastrointestinal tract may be limiting bioavailability of minerals. For instance, in copper deficient animals iron cannot be used to build hemoglobin (Mertz 1986). The bioavailability of a mineral in an animal is a rather elusive entity which may be changing relatively quickly. Factors which affect bioavailability of minerals relating to the animal are species, life stage, health and nutritional status. Factors relating to the diet are level of intake (in relation to requirements), intake of other minerals, intake of substances which may enhance or impair the absorption of the mineral in question.
And finally there are factors related to the mineral compound used, such as water solubility and chelating qualities of the mineral
• Nutritional status of animals reflects the productive and reproductive functions
• Animals in the tropics suffer from mineral imbalances or deficiencies
• In India livestock are maintained on grazing with little or no supplementation of mineral mixture, except common salt
• Locally available feeds and fodder vary in mineral content and mineral deficiency is an area specific problem
• Bioavailability of Mineral supplements is essential
• Mineral content in green vegetation depends on physical and chemical properties of soil, soil erosion, cropping pattern, fertilizers and chemicals application, species and genetic differences among plants, stage of growth, presence of other minerals etc
• Availability of minerals also decreases with maturity of fodder
• Changing availability of feed and fodder resources and deterioration condition of grazing lands, evaluation of the mineral content of feeds and fodders is required for assessing the deficiency/ excess and development of suitable area specific supplementation.
•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
• 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
Methods for evaluating the bioavailability of minerals
• In vivo techniques, which are expensive
• In vitro techniques, which are relatively cheap
• Semi In Vivo Techniques, cell cultures and tissues
• Using chamber, adopted from rumen absorption studies
• Closely linked with those biological parameters and inexpensive
• Lead to tabulated values that can easily be applied in practice, or fit in an existing evaluation system.
In vivo experiments
• Animal performance (average daily gain, feed intake, feed conversion ratio, reproduction characteristics);
• Digestion/absorption coefficients;
• Concentrations in several tissues (bone and organs, such as liver, kidneys, muscle, spleen);
• Total mineral content in the animal’s body;
• Morphological characteristics in several tissues;
• Blood parameters (concentrations of the minerals, enzyme activities, hormones);
• Concentrations in secretory fluids (bile, pancreatic fluid);
• Concentrations in urine.
In vitro techniques
• This approach has not resulted in satisfactory results
• Difficult to simulate the gastric and intestinal conditions properly
• Guéguen (1976, 1977) developed the citric acid solubility of phosphorus sources
• Solubility in water and solubility in 2% citric acid were not discriminative
• TNO Intestinal Model (TIM) that simulates gastro-intestinal conditions
Terms used to express the bioavailability of minerals
• Digestibility/absorbability- gastrointestinal tract (feed – faeces).
• (Bio) availability or bio efficacy- retained in the body [feed – (faeces + urine)]
• Compared with a reference that is assumed to be 100% available
Absorbability:————-
• Absorbed from the intestinal tract – terms absorption and digestion can be used
• Scientific point of view – fraction that is absorbed from the gastrointestinal tract, in this case, digestibility is not the right term when related to minerals
• Measures not related to disappearance of minerals from the gastrointestinal tract
• Nutritive value of a mineral is related to a reference mineral, the term relative (bio) availability should be used
Factors affecting mineral content of forages————
• Soil
• Plant species
• Stage of maturity
• Yield
• Pasture management
• Climate
• Young and alkaline geological formations more abundant in most trace elements than the older, more acid, coarse, sandy formations.
• Leaching and weathering of soils in tropical regions, under conditions of heavy rainfall and high temperature, accentuate mineral deficiencies
• Legumes are richer in a number of minerals than are grasses
• As plants mature, mineral content declines due to the natural dilution processes and translocation of nutrients to the root system
• Micro mineral concentration of forages across growing seasons is generally less variable than macro mineral concentrations
• Mineral content in soil keeps on changing due to pressure on land for maximum crop production, fertilizer application and natural calamities, which may alter the nutrient contents in feeds and fodders thereby affecting the mineral status of animals.
• Knowledge of the level of minerals in feeds and fodders of a particular area is essential for balancing dietary mineral requirements and formulating the area specific mineral mixture, which will be practical as well as cost effective
Bioavailability of calcium ———
• Present in bone tissue as the hydroxyapatite form of calcium phosphate (99%) and Soft tissues of the body (1%)
• Bioavailability – vitamin D concentration, Ca/P-ratio, phytate or oxalate complexes, anion/cation-ratio, dietary magnesium and aluminium, particle size, etc
• Sources – calcium carbonate, limestone, oyster shells, calcium phosphates, calcium sulphate and bone and meat meals
• Particle size of calcium sources has a distinct influence on the rate of solubility of the calcium
Bioavailability of magnesium ————–
• Structural role in the skeleton associated with hydroxyapatite crystals (60 to 70% of total magnesium of the body)
• Functional roles such as nerve function and muscular contraction.
• Component of several enzymes implicated in the metabolism of carbohydrates, lipids and proteins
• In ruminants, magnesium absorption occurs predominantly in the reticulo- rumen section of the gut
• Usual recommendation is to provide dairy cows with additional 25 g magnesium a day
Bioavailability of sodium———
• Sodium (and chlorine) maintain osmotic pressure, regulate acid-base equilibrium and control water metabolism in the body
• Addition of salt to a feed replete with sodium can lower feed intake
• According to the type of diet, practical diets require less or more supplementary sodium
• Common salt (NaCl) is mostly used for sodium supplementation, although for regulating acid-base balance and to optimise chlorine levels sodium bicarbonate is used.
• Other sources of sodium are sodium-containing phosphates and sodium sulphate
• No publications suitable for the study of sodium bioavailability of ruminants
Bioavailability of phosphorus ———–
• Present in the skeleton (80%)
• Nucleotides, such as ATP, nucleic acids, phospholipids, and many other phosphorylated compounds(20%)
• Absorption takes place predominantly in the small intestine
• Large differences in absorption and utilisation of phosphorus can be found, depending on the nutritional status of the animal
• Factors – intake level, age of the animal, levels of dietary mineral compounds, e.g., calcium, phytic acid and phytase, magnesium and intestinal pH.
• Phosphate sources include dicalcium phosphate (anhydrous or hydrated), monocalcium phosphate, or mono-dicalcium phosphate
• Lactating animals have higher levels of addition of phosphorus in their diets compared with pregnant animals
Bioavailability of cobalt –————
• Component of vitamin B12
• Vitamin B12, also known as cobalamin contains about 4.5% cobalt
• Cobalt deficiency leads to “wasting diseases” as a result of inadequate synthesis of vitamin B12 from dietary cobalt
• Deficiency – particularly in grazing animals
• Distributed throughout the body with high concentrations in liver, bone and kidney. Supplemented as cobalt sulphate
Bioavailability of copper —————-
• Essential component of several metallo enzymes.
• Copper deficiency is a serious problem for grazing ruminants in many countries of the world.
• Due to both low concentrations of the element in forage as well as to elevated amounts of molybdenum and sulphur, which interfere with copper utilisation. Supplemented in the range of 10 to 30 mg/kg
Bioavailability of iron ————-
• key role in many biochemical reactions
• all of the iron in the animal’s body is organic in nature and only a very small percentage is found as free inorganic ions
• Haemoglobin (blood) iron (60%)
• Myoglobin (3%)
• Iron content of the body varies with species, age, sex, nutrition and state of health and is controlled by adjustment in absorption rate
• Ruminant diets are usually not supplemented with iron, because roughage contains already a high amount of iron due to contamination with soil particles.
• Supplemented as ferrous sulphate heptahydrate (FeSO4•7H2O) in animal diets.
• No publications suitable for the study of iron bioavailability of ruminants
Bioavailability of iodine-————–
• Tissues concentration – 0.1 μg/g body weight
• Thyroid gland – 400 μg/g body weight
• Integral part of the thyroid hormones thyroxin (tetraiodothyronine) (T4) and triiodothyronine (T3)
• Plants, water or other animal feedstuffs have highly variable concentrations of iodine.
• Differences in species and strains, climatic and seasonal conditions, the type of soil, the fertiliser treatment or possible interactions
• Thyroid gland – up to 90 % of the iodine is captured by a Na/K-dependent ATP-ase.
• Predominant sources are calcium iodate and ethyl diamine hydro iodide (EDDI) or organic forms of iodine Potassium or sodium iodide are less stable sources
Bioavailability of manganese-——————
• Important function in blood clotting and lipid and carbohydrate metabolism
• Deficiency lowers the activity of the manganese superoxide dismutases
• Abnormal male and female reproductive functions
• Absorption is affected by manganese source, dietary antagonists (fibre, phytate, high levels of calcium and phosphorus, iron, magnesium) and depends on the concentration in the diet
• Most diets for ruminants are likely to be deficient in manganese
• Supplemented as manganese sulphate, manganese oxide or various organic forms
Bioavailability of molybdenum—————
• Considered as a toxic element because of its interference with the copper metabolism in ruminants.
• As a component of the enzymes xanthine oxidase, aldehyde oxidase and sulphite oxidase.
• Xanthine oxidase and aldehyde oxidase – electron transport chain
• Aldehyde oxidase – niacin metabolism
• Sulphite oxidase – sulphite to sulphate conversion for excretion in urine.
• No evidence of characteristic symptoms of molybdenum deficiency in ruminants
. • Supplementation of ruminant diets is not usual for molybdenum but added to counteract toxicity risk due to high levels of copper supply.
Bioavailability of selenium-————–
• Toxic element causing the lost of hair, nails and hooves.
• Chronic selenium toxicity have been related to consuming selenium- accumulating plant.
• Chronic toxicity from (mg/kg)
• Acute toxicity needs a much higher selenium level in the diet
• Main constituent of glutathione peroxidase which, associated with vitaminE plays a role of “cellular scavenger” protecting cellular membranes from oxidative effects (peroxides and free radicals)
• Concentration depends on the soil concentration of selenium
• Seeds and by-products have generally higher selenium content than forages
• Animal by-products including fish meals, but with the exception of milk products have high concentration of selenium.
• supplemented as sodium selenite.
Bioavailability of zinc ————–
• Activates several enzymes and is a component of metalloenzymes
• Most abundant intracellular trace mineral in animals
• Primarily absorbed from the small intestine
• Animal diets require supplementation with zinc because of either low dietary levels or the presence of dietary factors that decrease bioavailability of the mineral (e.g. phytic acid)
• Supplemented in diets for all species of livestock in the range of 30 to 250 mg/kg to cover their requirements
• Supplemented as zinc sulphate (ZnSO4•xH2O) or as zinc oxide
Factors affecting Trace Mineral Bioavailability in Ruminants—————–
• Dietary factors that affect bioavailability of minerals differ greatly between ruminants and non-ruminants.
• In ruminants, microbial digestion in the rumen and reticulum precedes mammalian digestion in the abomasum and small intestine.
• Ruminant diets are usually high in fibre, and considerable digestion of fibre occurs via microbial fermentation in the rumen.
• The pH in the rumen environment is only slightly acidic (6.0–6.8), and in the rumen, many trace minerals exist largely in an insoluble form
Identifying Mineral Needs————
The first challenge with a mineral program is knowing what your cows need. This is driven by the feeds they eat as well as the water they drink and it changes throughout the year. Oftentimes, we may not think about the mineral contribution of the water to the diet, but it is very important, especially when water could be high in salt and sulfates. Ideally all feeds and water should be tested for mineral content to determine deficiencies, toxicities and interactions that may exist. Once this is determined, then mineral supplements can be sourced. Many companies have formulated minerals for specific regions or are willing to develop custom formulations for ranches. If you choose to use a mineral that has been formulated for a region, reading and understanding the feed tag becomes more critical.
Analyzing the Mineral Tag-———–
As you analyze the mineral tag, there are a few key items to look at initially. How much salt does the product contain? Products that contain 10% salt or more don’t need additional salt and will result in an adequate daily intake of 3 to 4 oz. Mineral supplements that contain less than 5% salt are considered mineral concentrates with cattle consuming approximately the recommended 2 oz. per day. If using a mineral concentrate, free choice salt must be provided.
Next, take a look at the ingredient list to determine the type of mineral used in the supplement. Not all sources of minerals have the same bioavailability to the animal. For example, you could be spending extra money for a high copper mineral, but the copper is being provided by copper oxide, which is only 15% bioavailable. Therefore, the mineral tag may show that the supplement has 5000 ppm Cu, but the cattle will only utilize 750 ppm (15%) because it is supplied as copper oxide. On the other hand, if tribasic copper chloride is a source of Cu, its relative bioavailability is 115 which means Cu is 15% more available to the animal than that in copper sulfate, which is used as the standard (100%). A product with tribasic copper chloride will provide more Cu to the animal than a product with copper oxide or copper sulfate.
Inorganic & Organic Mineral Sources
Mineral sources are divided into two groups: inorganic and organic. Inorganic will be less expensive mineral sources, but are also typically less bioavailable than their organic counterparts. Generally speaking inorganic sulfates and chlorides are more available than oxides and carbonates. The exceptions to this are zinc oxide and magnesium oxide, both of which have a bioavailability of 100. Chelated minerals are those that are bound to an amino acid or other organic molecule, and their bioavailability exceeds 100. If animals are stressed or mineral antagonists are present in large amounts the extra price paid for chelated minerals may be justified. Chelated minerals will provide more value to cattle during weaning or other stressful periods, but their cost will likely exceed the benefits in a standard mineral program. See Table 1. below for a sample of mineral supplements, mineral concentration, bioavailability and mineral availability.
Table 1. Mineral concentrations and relative bioavailabilities of common mineral sources.
Supplement Mineral concentration
(MC, %) Relative Bioavailability*
(RV, %) Mineral Availability
(MC x RV)
Calcium
Calcium carbonate 38 100 38.0
Calcium chloride 31 125 38.75
Dicalcium phosphate 20 110 22.00
Limestone 36 90 32.40
Monocalcium phosphate 17 130 22.10
Cobalt
Cobaltous sulfate 21 100 21.00
Cobaltic oxide 73 20 14.60
Cobaltous carbonate 47 110 51.70
Cobaltous oxide 70 55 38.50
Copper
Cupric sulfate 25 100 25.00
Cupric chloride (tribasic) 58 115 66.70
Cupric oxide 75 15 11.25
Copper
(organic form) 130
Iodine
Potassium iodate 69 100 69.00
Calcium iodate 64 95 60.80
Ethylenediamine (EDDI) 80 105 84.00
Magnesium
Magnesium sulfate 20 100 20.00
Magnesium oxide 55 100 55.00
Manganese
Manganese sulfate 30 100 30.00
Manganese carbonate 46 30 13.80
Manganese
(organic form) 176
Phosphorus
Defluorinated phosphate 12 80 9.60
Dicalcium phosphate 18 85 15.30
Selenium
Sodium selenite 45 100 45.00
Sodium
Sodium chloride 40 100 40.00
Sodium bicarbonate 27 95 25.65
Zinc
Zinc sulfate 36 100 36.00
Zinc carbonate 56 60 33.60
Zinc oxide 72 100 72.00
Zinc (organic form) 159 to 206
Conclusion –——–
• Locally available feeds and fodder are varying in mineral content and mineral deficiency is an area specific problem.
• Mineral status of locally available feedstuffs is essential.
• Mineral content dependent on the soil, which nourishes the plants
• Availability decreases with maturity of fodder
• Agro-climatic conditions – mineral content in green vegetation depends on physical and chemical properties of soil, soil erosion, cropping pattern, fertilizers and chemicals application, species and genetic differences among plants, stage of growth, presence of other minerals etc
• Understanding the bioavailability of various mineral sources effective mineral mixture supplementation can be provided
Reference-On request.
Dr Manoj Kumar Jha,Dairy consultant.Delhi.
