Feed Strategy - July 2018 - 8
8 ❙ FeedStrategy
IMPROVING EGG QUALITY
Poultry egg shells consist of
mostly calcium carbonate plus organic components. These matrix
proteins complex with calcium
carbonate and make a significant
contribution to the crystal growth
mechanism and, hence, the structural integrity of the eggshell. A
non-calcified organic cuticle covers
the shell, offering further protection
to the contents. A decline in egg
numbers combined with a deterioration in shell quality is the reason for
cycles lasting around 72 weeks.
To extend this, nutritionists need
to support the tissues and organs
involved in egg production.
Eggs display a very consistent
composition with regard to proteins,
essential amino acids, total lipids,
phospholipids, phosphorus, iron, etc.
They only differ slightly between
breeds and as the bird ages. However,
the viscosity of the protein-rich albumen decreases with age - Haugh
units decrease on average by 20 over
the laying period. This means that
the antioxidant status of the bird will
have a role to play in enabling protein
production throughout the cycle. The
egg white or albumen is encapsulated
in the first of the paired shell membranes, and the outer membrane is
the foundation for shell formation,
both of which require sufficient antioxidant protection.
Pigments are routinely added to
laying hen diets to ensure a brightly
colored egg yolks. They can be
synthetic (yellow: apo-ester, red: can-
Effect of egg weight on percentage of shell,
albumen and yolk weight
% shell weight
% albumen weight
% yolk weight
Percentage of egg weight
Eggshell and contents
Source: Sinha et al, 2017
Shell strength decreases over the laying cycle because the percentage
of shell weight decreases as egg weight increases.
thaxanthin or citranaxanthin); nature
identical (lutein) or natural (marigold
extract). The inclusion of corn in the
diet also influences yolk color as it
contains the orange pigment zeaxanthin. Access to foliage on the range
can also intensify egg yolk color.
Regional preferences for color intensity, as well quality assurance scheme
guidelines, will dictate the amount
and form of pigments added.
Controlling egg size
Influencing egg quality starts
before the hen lays her first egg.
The aims of diets are uniform pullets that meet target weights for
breed and are ready to start laying.
However, energy and protein ratio
between 11 and 16 weeks is key as
excess energy results in fat birds.
As egg weight increases, the percentage of shell decreases, which
is one of the reasons that shell
strength decreases over the laying
cycle. Similarly, as total egg weight
increases, the weight of egg yolk
increases. Particularly when increasing cycle length, egg size needs to
be controlled to prevent uneconomic
levels of downgraded eggs.
Egg size and number can be manipulated with management and nutrition. The heavier the hen is at the
onset of lay then the larger her first
eggs will be. Energy and protein levels through the cycle are important
to optimize egg production and control body weight, as any excess will
result in larger eggs. A hen consuming an extra gram of protein will lay
www.WATTAgNet.com ❙ July 2018