Importance of Zinc SupplementationLayer Bird Nutrition

Zinc Pharmacological Role

› Zinc plays multiple roles in poultry nutrition.

› It is a component of various enzyme systems such as:

1. Glutamic dehydrogenase

2. Alcohol dehydrogenase

3. Alkaline phosphatase

4. RNA polymerase

› They enzymes are responsible for metabolism of carbohydrate, protein and lipids.

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› Zinc is essential and directly involved in catalysis and co-catalysis by the enzymeswhich control many cell process including:

1. DNA synthesis

2. Normal growth

3. Brain development

4. Behavioral response

5. Reproduction

6. Foetal development

7. Membrane stability

8. Bone formation

9. Wound healing

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› As a component of carbonic anhydrase, zinc helps in transport of CO2 from tissuesto lungs.

› Also it is required for utilization of vitamin A and conversion of pyruvic acid to lacticacid.

› Zinc is a component of hormone thymosin (produced by thymus cell) which isrequired for immunity purpose.

Zinc Deficiency

› Symptoms of zinc deficiency in young chicks includes:

1. Retarded growth

2. Shortening and thickening of leg bones

3. Poor feathering

4. Poor feed efficiency

5. Loss of appetite

6. Mortality in severe cases

7. Reduce bone ash

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› Zinc deficiency has been shown to decrease:

1. Cellular immunity

2. Thymus and spleen development

› Zinc is important for proper disease resistance and its deficiency has resulted in:

1. Bacteremia

2. Parasitic infections

3. Alteration in high-density lipoprotein cholesterol

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Zinc impacts immunity in poultry

– Zinc supplementation in breeder diets has been shown to enhance immunity of their progeny.

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› In layer and breeding poultry birds, zinc functions in formation of eggs.

› Zinc deficiency affects the quality of epithelium due to role of zinc in proteinsynthesis.

› It also indirectly affects epithelial secretion, by affecting the structure of epithelium ordirectly during the synthesis of egg shell membrane.

› Zinc plays a role in the magnum during the deposition of albumen and in the isthmuswhere egg shell membranes are produced.

› Dietary zinc source may have influenced hen day egg production and secretion ofreproductive hormones during sexual maturation.

› Majority of zinc and other trace elements in the egg are deposited in the yolk, andmuch smaller quantities are deposited into albumen.

› Approximately 86% of the zinc originally present in the fertilized egg is transferred tothe chicks.

› On increasing zinc concentration in egg, hatchability increased.

› The increased hatchability was primarily due to decrease incidence of late embryonicmortality when zinc level was increased in the egg.

› Supplemental zinc is essential in poultry diets to achieve normal reproductiveperformance.

Zn Availability

Zn Availability

› Zinc is widely available in food sources but its bioavailability from different foods ishighly variable.

› Zinc is commonly supplemented in the diets of poultry and livestock because manynatural feed ingredients are marginally Zn- deficient.

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Corn soya based diet

› It increases the demand of zinc in the diet.

› Cereal based diets including plant sources such as soya bean or cotton seed mealcannot deliver enough amount of zinc to the animals due to chelating effect ofphytate.

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Animal products

› They are the richest food sources of zinc, particularly the organs and flesh of beef,pork and shellfish.

› They do not contain phytase, they are good sources of available zinc.

› They tend to be expensive.

Zinc & Phytic Acid

› Zinc has been supplemented in animal diets using inorganic salts such as oxidesand sulphates.

› Trace minerals tend to dissociate in the low pH environment of upper gastrointestinaltract, leaving the minerals susceptible to various nutrients and ingredientantagonisms that impair absorption.

› Phytic acid is able to form complexes with trace minerals that are very stable andhighly insoluble, rendering the minerals unavailable for absorption.

Chelated Zinc

› The word chelation is derived from the Greek word ‘chele’, meaning claw.

– It refers to a bonding formed between a metal ion (mineral) and a ligand (proteinor amino acid chelating agent).

› A chelated complex is an organometallic compound consisting of a mineral +organic component (protein or polysaccharide)

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› It is produced by reaction of a mineral salt with an enzymatically prepared mixtureof amino acids and small peptides, under controlled conditions.

– The ligand binds the metal at more than one point such that the metal atombecomes part of a ring.

– The resulting ring structure protects the mineral from entering into unwantedchemical reactions.

– Certain amino acids and protein digestion products such as small peptides areideal ligands because they have at least two functional groups (amino andhydroxyl) that can form a ring structure with the mineral.

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› Organic mineral sources exist in the form of:

1. Metal amino acid chelates

2. Metal proteinate

3. Metal specific amino acid complexes

› The primary chelated minerals used in animal feed are the trace elements:

1. Iron

2. Manganese

3. Cobalt

4. Copper

5. Zinc

Zinc Bioavailability

Bioavailability is defined as:

› The proportion of the ingested element that is absorbed, transported to the site ofaction, and converted to a physiologically active form.

› Solubility is a critical factor for trace mineral absorption.

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Trace Mineral Stability

› To increase uptake, chelated minerals should be stable in digestive tract of animals.

› Chelates are stable, electrically neutral complexes, which protect trace minerals fromchemical reactions during digestion that would render the mineral unavailable to theanimal.

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Chelated minerals absorption

› Chelate minerals can be more effectively absorbed into the intestines than inorganicoxide and sulphate.

› Zn-methionine provides a source of zinc with greater biological availability than zincfrom inorganic sources.

› Gill (1997) reported that chelated minerals are more biologically available in animaldigestive system than inorganic minerals and that perhaps resulted in less mineralexcretion and pollution of the environment.

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› Clear indications of biological activity of zinc are:

1. The content of this element in liver

2. Accumulation of zinc in the bones

3. Levels of zinc in blood serum

› These are the indicators to ascertain the availability of this element in live animals.

Zinc Requirement

› Zinc requirement (mg/kg dry matter) are reported to be:

1. 40 for 0-8 weeks chicks

2. 35 for 8-18 weeks of age

3. 50 for laying hens and

4. 65 for parent stock

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› The NRC (1994) set the requirement of zinc at 40 ppm.

› But the research data on which NRC was formulated were more than 10 years oldand do not represent the needs of modern strain of commercial poultry (Leeson,2005).

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› The most commonly used zinc for supplementation in animal diet is inorganic zincinform of zinc sulphate due to:

1. Low cost

2. Commercial availability

› It is a common practice in the broiler industry to formulate diets to contain 100- 120mg supplemental zinc/ kg of diet.

Cont. …

› Burrell et al. (2004) reported improved performance when broiler consumed dietscontaining 110 mg zinc/ kg of diet while NRC (1994) recommendation is 40 mg zinc/kg of diet.

› Broiler and laying hens can tolerate 1-2 g/kg DM of zinc in their diet.

› Further increase in zinc concentration (up to 4 g/kg DM) leads to:

1. Loss of appetite

2. Retarded growth

Zinc Safety Margin

› NRC (1994) recommended 40 mg zinc/ kg of diet in broiler ration, but often diets areformulated to contain zinc level of 120 mg/ kg of diet.

› From a practical standpoint, wide safety margins are often used to avoid tracemineral deficiencies and allow birds to achieve their genetic potential.

› This higher level of addition possibly to reduce the deficiency under commercialcondition.

Zinc Excretion and Environment

› Excessive supplementation of inorganic zinc brings serious environmental pollutiondue to low utilization.

› Thus, broilers and breeders fed diets containing high concentrations of zinc arepotentially producing faecal waste that contains more zinc than field crops canutilize.

› Today, large scale commercial livestock production system have given rise to manyenvironmental concerns, since excess mineral concentrations in the manure canlead to mineral depositions that exceed crop nutrient requirement.

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› Enhanced bioavailability of mineral source can:

1. Potentially reduce the amount of a mineral that is added to a diet to meet nutritional requirement

2. Reduce the amount of mineral excreted by birds.

› Although organic form of trace minerals have increasingly been used by poultry feedindustry, the use of organic complexes of trace elements such as Zn-lysine andZnmethionine has received more attention because of their potential for greaterbioavailability.

Zn & Egg shell quality

Zn & Egg shell quality

› Egg shell quality is one of the most important problems in poultry industry,influencing economic profitability of egg production and hatchability.

› High egg shell breaking strength and lack of shells defects are essential forprotection against penetrating bacteria into the eggs.

› One of the main concerns is the decrease of egg shell quality with hen age, becausethe incidence of cracked eggs could even be more than 20% at the end of layingperiod.

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› Most of the studies on nutrition effects on egg shell and bone quality in laying henshave been focused on macro-minerals (Ca & P) and vitamin D3.

› In addition to this, some enzymes related with some microminerals are important formineralization process;

Cont. …

1. Carbonic anhydrase

– It is a zinc dependant enzyme that plays a role in converting calcium into calcium carbonatewhich is needed for egg shell formation.

– Activity of carbonic anhydrase, an essential enzyme for eggshell formation, has been directlyrelated to zinc status of hens.

2. Metalloenzymes

– Zinc and manganese, as cofactors of metalloenzymes, responsible for carbonate andmucoploysaccharides synthesis which implies their importance in egg shell formation.

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3. Egg shell mechanical properties

› Zinc, copper and manganese could affect mechanical properties of egg shell byeffect on calcite crystal formation and modifying crystallographic structure of eggshell.

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Inadequate zinc status of hen may reduce:

1. Egg shell quality

2. Hatchability

3. Embryonic development

4. Poor chicks’ quality