Chicken embryo utilization of egg micronutrients

By S. Vieira. 2007

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IntroductionAvian embryos develop and grow from energy and nutrients storedin the egg by the hen. In this sense, breeder male contribution is notimportant. Follicular deposition of nutrients occurs over a wide range oftime, but becomes relevant during the week prior to ovulation. Amounts,but also forms, of nutrients deposited in the egg determine success ofembryo development and hatching of a healthy chick. To support theembryo during incubation, oxygen is the only nutrient not derived fromthe egg; however, adequate oxygen concentrations in the surroundingair and its free passage through well-established shell membraneporosities are essential. Developmental limitations and embryo mortalityare aggravated when any inadequacy in these conditions prevail.Macroscopically, the fertile egg has three components: shell, yolk,and albumen. Specific nutrients are mobilized by the embryo from eachof these parts. These typically have expected compositions, which arenotably affected by the hen’s nutrition.After oviposition, the egg may be submitted to changes due to inovo injection using the vaccination equipment routinely used inhatcheries. However, these injections are limited to small amounts, andpreferably done with more available forms of micronutrients. Researchon this matter is recent and usually directed to metabolic interventions,such as the role of substances which stimulate or mediate enzymetranscription.Egg ReservesMacroscopically, the egg is a simple structure with three majorcomponents (shell, albumen, and yolk), demonstrating uniquecharacteristics and playing specific roles during incubation. It is generallyagreed that each egg is built with a complete capacity to produce aperfect new organism. However, due to several reasons, this is notalways the case. In general, the composition of macromolecules in eggsis more constant than those elements usually found in a lower proportion,such as micronutrients. Since all egg constituents derive from the hen’sorganism, metabolic transformation of the hen’s feed is needed toobtain adequate embryo development and viable chicks at hatching.Egg shells consist of two main components: a matrix of protein fibersand col umns of calcium carbonate crystals in a proportion of 1:50 (Romanoff& Romanoff, 1949). A glycoprotein layer, the cuticle, covers the crystalsurface, and it is the last egg component to be deposited before oviposition.The cuticle has three main functions: prevention of excessive water loss(Peebles & Brake, 1986), protection from microbial infection (Roussel et al.,1988), and termination of calcite crystal growth (Dennis et al., 1996). Theshell matrix presents two regions: a mammillary region, connected to theouter shell membrane protein fibers, and a spongy one, associated to calcitecrystals deposited in layers on the mammillary matrix (Simkiss, 1968).

Subfields: Animal Science and Zoology, Biochemistry, Plant Science

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