Trace Elements

  • Fe and Zn (J. Nutr. 116:927, 1986)
    1. Excessive Fe may aggravate borderline deficiency of Zn
    2. High dietary Zn can clear up or prevent Cu deficiency induced Fe accumulation in the liver
    3. Zn can prevent Fe induced free radical damage presumably by displacing Fe at sensitive molecular sites (Free Radical Biol. Med. 8:281-291, 1990; J. Nutr. 125:823-829, 1995, J. Exp. Med. 185:71-79, 1997)
  • Increased dietary Zn reduces toxicity of lead
    1. Marginal Zn deficiency may increase body burden of Pb
    2. Zn reduces Pb absorption
  • Cadmium greatly reduces Zn absorption and is also a strong antimetabolite of Zn
    1. Cd competes with Zn at active sites
    2. Cd exposure enhances the Cu, Zn, and Cd content of metallothionein
    3. Incorporation of metals other than Zn into metallothionein may require prior synthesis of Zn thioneine with subsequent displacement of Zn by other metals
  • Phosphorus in the form of phytate reduces Zn absorption in nonruminants (J Nutr. 119:211, 1989)
    1. Phytate reduces apparent absorption of Zn in ruminants only when the rumen is bypassed (J. Nutr. 93:386, 1967)
    2. Calcium increases stability of the Zn-Phytate complex in nonruminants further reducing Zn availability
      1. Ca must be present in available form when complex is formed since feeding Ca Phytate does not affect Zn utilization
      2. Ca does not affect Zn absorption in the bovine (J. Dairy Sci. 62:1081, 1979)
  • Clay and possibly other substances consumed by persons who practices geophagia may inhibit the availability of Zn for intestinal absorption
  • Other organic substances inhibiting Zn absorption
    1. Component of dietary fiber in human diet
    2. Products formed during food processing
      1. Amino acid-phytate products
      2. Products of the Maillard reaction

    • VI.  Requirements

    1. A.          NRC recommendation for cattle is about 40 ppm Zn
    2. B.           For poultry and swine, 40-100 ppm is recommended
    3. C.           RDA for humans
      1. Infants -1 yr...........................................3-5 mg/d
      2. Children 1-10 yrs..................................l0 mg/d
      3. Adult males..........................................15 mg/d
      4. Nonlactating, nonpregnant females.....15 mg/d
      5. Pregnant females.................................20 mg/d
      6. Lactating females.................................25 mg/d

    VII.  Dietary Sources of Zn

    1. Zn is widely distributed in most feeds
      1. Legume forages are generally higher than grasses in Zn
      2. High protein feeds contain substantial amounts of Zn but availability of Zn must be considered in plant protein sources
      3. In areas where soil is very low in Zn (such as western Australia) some widely used feeds may be very deficient in Zn
      4. Egg white is very low in Zn

    VIII.  Zinc Deficiency

    1. Changes in agricultural practices may have increased probability of borderline Zn deficiency when no supplemental Zn is fed
    2. Causes of Zn deficiency in humans (J. Am. Col. Nutr. 4:49, 1985)
      1. The most severe manifestations of human Zn deficiency occur in infants with the genetic disease acrodermatitis enteropathica
        1. Transmitted by an autosomal recessive gene
        2. Symptoms usually begin after infants have been weaned from breast milk
        3. Symptoms-rash that usually begins around body orifices, diarrhea, failure to thrive, infections, death
        4. Condition appears to result from a defect in ligands involved in Zn absorption. (Evans says that defect is in the tryptophan metabolizing pathway proximal to synthesis of picolinic acid.
        5. Treatment
          1. Oral administration of pharmacologic doses of Zn Sulfate
          2. Physiological levels of Zn as Zn picolinate
      2. Malabsorption syndromes and inflammatory diseases of the bowel
      3. Liver disorders - alcoholic cirrhosis, hepatitis
      4. Renal dysfunction
      5. Injury, inflammation and stress
      6. Parasitic diseases
      7. Parenteral or enteral alimentation without adequate Zn
      8. Nutritional
        1. Alcoholism
        2. Protein-energy malnutrition
        3. High dietary fiber and phtate
        4. Pica
        5. Pregnancy
    3. 0.1% ZnS04-7H20 in distilled water on tongue is a test for subclinical Zn deficiency
      1. If individual is Zn deficient, he doesn't taste it
      2. If Zn is adequate, it tastes bad; the more adequate Zn is, the worse it taste
    4. Effects of Zn deficiency or protein and nucleic acid metabolism
      1. Utilization of amino acids for protein synthesis is impaired
      2. Increased protein catabolism results in increased urinary nitrogen
      3. RNA is reduced in certain tissues (RNA polymerase is a Zn enzyme)
      4. DNA synthesis is impaired almost immediately in Zn deficiency (DNA polymerase and thymidine kinase are both Zn enzymes)
      5. In addition to an enzyme role, Zn may have a role in maintaining structure of RNA, DNA, and ribosomes
    5. Effects of Zn deficiency
      1. Male reproduction
        1. Impaired spermatogenesis
        2. Testes, epididymis and prostate do not develop normally
        3. Reduced serum testosterone
      2. Females reproduction (see J. Anim. Sci. 60:1530, 1985)
        1. Rat - fetal resorption, abnormal fetal development, dystocia, prolonged labor, excessive bleeding, frequently maternal death
        2. Swine - prolonged labor, reduced litter size
        3. Hens - decreased hatchability of eggs, abnormal development of embryo, high mortality of embryo
        4. Cattle - reduced conception
        5. Sheep - reduced number of lambs per ewe.
        6. Humans - prolonged gestation, inefficient labor, atonic bleeding at delivery, possible risk to fetus
      3. Zn deficiency and keratogenesis (hyper-keratinization or thickening of epithelial tissue)
        1. Swine: parakeratosis-skin becomes rough with loss of hair and possible bleeding mostly around the mouth, eyes and legs
        2. Sheep: wool fibers lose their crimp and become thin and loose
        3. Birds: poor feathering and dermatitis
        4. Humans: acrodermatitis enteropathica
      4. Zn deficiency and wound healing
        1. Zn accumulates at the site where a wound is healing.
        2. When Zn is deficient, DNA and subsequent collagen synthesis are impaired resulting in wounds not healing or healing at a slower rate
      5. Immune system does not operate properly during Zn deficiency
        1. Atrophy of thymus
        2. Decreased lymphocytes
        3. Decreased thymic hormone production
      6. Zn deficiency in the young can permanently affect binding function
        1. Decreased brain size and learning ability
        2. Probably relates to effect of Zn on DNA and RNA synthesis
      7. Skeletal changes - collagen synthesis and turnover is reduced
      8. Abnormal prostaglandin metabolism
        1. Platelet aggregation is abnormal
        2. Prolonged bleeding time can be reversed within 4 hr by oral administration of Zn
      9. Crystalline insulin contains 0.5% Zn. Release from pancreas and physiological potency of insulin maybe reduced by Zn deficiency
      10. Zn deficiency impairs mobilization of vitamin A from liver resulting in decreased circulating vitamin A levels
    6. Manifestations of Zn deficiency in humans
      1. Anorexia
      2. Dermatitis
      3. Poor wound healing
      4. Impaired immunity
      5. Growth failure
      6. Hypogonadism
      7. 7Oligospermia (Oligo means few, scant)
      8. Impotence
      9. Hypogensia (poor sense of taste)
      10. Poor dark adaptation
      11. Neurophysiological dysfunction
    7. Manifestations of Zn deficiency in farm animals
      1. General, nonspecific
        1. Reduced feed intake, feed efficiency, and growth
      2. Clinical appearance
        1. Inflammation of mouth and nose with submucous hemorrhages
        2. Skin parakeratosis, loss of hair (mammals), decreased feather pigmentation and frizzled feathers (birds)
        3. Slow wound healing (if at all)
        4. Stiffness of joints, decreased bone mineralization, bone deformities
        5. Grinding of teeth and excessive salivation
        6. Retarded testicular development (reversible in calves but not in rats)
      3. Biochemical changes (not very effective in identifying borderline Zn deficiency
        1. Decline in plasma Zn in a few days
        2. Small decline in liver and kidney Zn
        3. Decline in hair Zn over a long period
        4. Increased in vitro uptake of 65 Zn by erythrocytes
        5. Moderate reduction in carbonic anhydrase
        6. Larger reduction in serum alkaline phosphatase
      4. A hereditary Zn deficiency occurs in a small percentage of Dutch Friesian cattle
        1. Clinical and biochemical changes almost identical to that produced with a low Zn diet
        2. Similar to acrodermatitis enteropathica in humans
        3. Defect may be due to absence of a transepithelial transport mechanism for Zn
        4. When Zn intake is high enough, diffusion may allow sufficient Zn to pass without the transport mechanism

    IX.  Toxicity

    1. Low levels
      1. Adverse physiological effects not usually observed when dietary Zn concentrations are below 600 ppm
      2. Minimum Zn levels at which decreases in weight gain or body weight loss have been reported
        1. Cattle..........900 ppm
        2. Sheep.........1,500 ppm
        3. Swine.........2,000 ppm
        4. Chicks........800 ppm
        5. Turkeys......4,000 ppm
    2. High levels: > 1000 ppm Zn in diet usually causes some adverse effects
      1. Reduced weight gains
      2. Anemia
      3. Reduced bone ash
      4. Decreased tissue Fe, Cu, Mn
      5. Diminished utilization of Ca and P
      6. Diarrhea
      7. Arthritis and severe bone and cartilage
      8. 8In humans, unpleasant taste, gastrointestinal discomfort, and dizziness
      9. Death

    Trace Elements




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