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Trace Minerals For Laying Hens
Zinc is an
essential component of numerous enzymatic systems involved in metabolism
of energy, carbohydrates, nucleic acids and proteins. Zinc is also important
in maintaining the integrity of epithelial tissue, the protection of the
cells, cell division, and the transport and use of vitamin A. Moreover,
zinc plays a key role in the immune system and is involved in the function
of some reproductive hormones.
Function of Zinc in Egg Production
Zinc deficiencies can involve different consequences. A zinc deficiency
affects the quality of epithelium due to the role of zinc in mitosis,
protein synthesis and in the production of keratin (zinc helps the transformation
of cysteine into cystine). A zinc deficiency is characterized by a reduction
of cell division and replication resulting in an alteration in the quality
of the epithelium. Zinc also indirectly affects epithelial secretions,
by affecting the structure of epithelium, or directly during the synthesis
of eggshell membranes, uterine fluid or eggshell.
Zinc plays a role in the magnum
during the deposition of albumen (function of zinc in the protein
synthesis) and in the isthmus where eggshell membranes
are produced (proteins and chemical structure similar to keratin).
Further, zinc is important in the uterus where:
- Albumen is hydrated
- The four layers of the shell are produced (mamillary cores,
palissade, vertical crystals and cuticle) with the secretion of
uterine fluid.
- All the proteins of the shell are secreted inside the uterine
fluid (ovotransferrin, ovalbumin, lysozyme, osteopontin, OC-17,
OC-16, ovocalyxins). It is important to note the role of these
proteins in calcite deposition, and in the crystallography of
the eggshell. These represent a major parameter in the resistance
and strength of the eggshell
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Zinc and Carbonic Anhydrase
Carbonic anhydrase is a zinc dependent enzyme that plays a role in the
formation of carbonate anions for use in converting post absorption calcium
into calcium carbonate. Calcium carbonate is needed for eggshell manufacture
and deposition. Layer diets commonly have high dietary calcium (3.6 to
4.2% Ca) but this may not be effectively utilized in eggshell formation
if there is low carbonic anhydrase activity. In addition, high dietary
calcium can antagonize zinc availability to the hen, further decreasing
carbonic anhydrase activity. In order to prevent carbonic anhydrase from
being the weak link in calcium utilization, supplementation of layers
with zinc complexed to an amino acid, such as Availa®Zn,
will ensure a consistent supply of zinc for adequate carbonic anhydrase
activity and the production of calcium carbonate for eggshell formation.
Antagonists to Zinc and Recommended Dietary Inclusion Rate
Copper, cadmium, calcium and iron reduce zinc absorption and interfere
with its metabolism. Dietary concentrations of between 30 and 80 ppm are
typically included in layer diets. It is important to understand that
stress, trauma or any kind of pathology affects zinc status of the layer.
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