7International Hatchery Practice • Volume 31 Number 6

The modern broiler chickspends 50% of its life in anembryonic state. It is therefore

important to ensure that adequatenutrients are available to the devel-oping embryo, which is completelyreliant on the diet fed to thebreeder hen. Consequently, thephysiological status of the chick athatching is greatly influenced by thenutrition of the breeder hen.

by Aziz Sacranie,Technical Director,

Global Poultry Services, Alltech.www.alltech.com

The nutrient supply to the broilerbreeder is a sum of the actual nutri-ent content of the diet and thequantity or volume of feed suppliedto the breeder birds. Both partsneed to be balanced to ensure correct daily nutrient supply. This islikely the main difference betweenproducing a broiler hatching eggand a commercial egg.The cost of feeding the breeder

appropriately to ensure good nutritional status of the chick is lowwhen viewed on a per-chick basisand compared with the total feedcost of raising a broiler to slaughterweight.Poultry nutrition advisor Franco

Calini calculated that the cost ofbreeder feed contributing to theproduction of a chick is equivalentto only 7% of the total feed cost for

a broiler grown to 2.5kg. This illus-trates the value of ensuring the bestpossible nutrition of the breeder,even at 2017 feed costs.

The hatching egg

The hatching egg is essentially anembryonic chamber. As such, it provides its contents with physicalprotection against any externaltrauma as well as satisfying thenutritional requirements of thegrowing embryo.The shell is provided with differ-

ent markings and colour in order tocamouflage it from any potentialpredators and to help the henrecognise her eggs. The egg formation is a challenging

process, requiring energy and nutrients. If limited or deficient, thehatching egg is not able to fulfil thefull potential of its function or itsstructure.

The yolk

The yolk mass, composed of tightlypacked yolk spheres containinglipoprotein, is deposited in a concentric manner 6-11 days beforeovulation. The developing ovum (yolk) grows

and matures within follicles on theovary. The follicle, when mature,ruptures and releases the ova intothe oviduct (ovulation). Ovulation usually occurs immedi-

ately after the hen has laid the previous egg; the yolk undergoes nofurther development after ovula-tion.At ovulation, the largest yolk in

the follicle hierarchy within theovary, together with its attachedblastodisc, moves into the upper,funnel-shaped portion of theinfundibulum, where fertilisationtakes place.The follicular hierarchy is impor-

tant, particularly in broiler breeders.Overweight or overfed hens tend todevelop multiple follicular hierar-chy, which may result in doubleyolk eggs, prolapse and peritonitis.Sperm migrates from the vagina to

the first sperm storage tubule (SST),located in the uterovaginal junction.After a period of natural selection,the surviving sperm are propelledalong the tract to the second SST,located in the infundibulum (Fig. 2). Thereafter, the sperm is able to

penetrate the vitelline membrane,which encapsulates the yolk. Only afraction of the sperm populationsurvives the journey. In order to guarantee the fertilisa-

tion of a given ova, a minimum of2,000 sperms are required in theinfundibulum. The quality and survivability of the sperm, and itsability to penetrate the vitellinemembrane, are enhanced byincluding quality organic trace

minerals in the male and femalediets. The yolk is rich in energy,comprised of 21-36% lipid and 16-22% protein. Immunoglobulins, pri-marily Immunoglobulin G (IgG), arealso transferred as the yolk matures. The yellow colour of the yolk is

due to the presence of carotenoids,which protect the vulnerableembryonic tissues against damagecaused by free radicals. This processis also facilitated by the presence ofvitamin E, which is enhanced by thepresence of organic selenium (Se).The nutrient composition of the

yolk is entirely dependent on thematernal diet and is of vital impor-tance to embryonic well-being. Age,diet and environment each play arole in the quality of the embryonicchamber and its contents.

Formation of the egg

The yolk, once captured by theinfundibulum, makes its way alongthe ovary to the cloaca. The firstlayer of thick albumen is secretedhere, as well as the precursors tothe chalazae, which anchor the yolkin the centre of the egg.The albumen, or egg white, is

multi-layered and is largely produced in the longest region ofthe oviduct, the magnum.

Feeding the breeder hen for quality hatching eggs

Continued on page 9

Fig. 1. Left, ideal follicle hierarchy of 6-7 ova. Right, multiple follicle hierarchy, potentially leading to double yolk eggs, peritonitis and prolapse.

Fig. 2. Sperm migration in the avian oviduct (Brillard et al., 2005).

Ovary

Infundibulum

Magnum

Isthmus

Uterus

VaginaActive

Passive

Sperm storage tubules(main site)

Sperm storage tubules(secondary site)

The four layers of albumen, whichare visible at oviposition, consistprimarily of water (90%) and protein(10%). A rich source of biologically

active material, the albumen is crucial to embryo protection, withits antibacterial proteins serving as amechanical buffer between theexternal environment and thedeveloping chick. Most importantly, the albumen

also functions as a support for thedeposition of the inner and outershell membranes.The albumen’s thickness and

turgidity (assured by sulphatedmucosubstances) play a crucial rolein ensuring shell quality as well asHaugh units, both important inhatching or commercial eggs. The structure and well-being of

the cilia in the magnum assist inmaintaining the turgidity and thethickness of the albumen as theyolk progresses along the oviduct.Respiratory diseases, such as

infectious bronchitis, affect thestructure and well-being of the ciliain the lower magnum, resulting inwatery albumen. This leads to a lack of support for

the deposition of the membranes,which could fold and get distorted,compromising the calcium carbon-ate deposition and resulting in awrinkled shell.Age, stress and oxidation will also

impair the magnum’s ability to pro-duce the necessary proteins anddamage the cilia, resulting in wateryalbumen. Fig. 3 illustrates healthy cilia in the

magnum and unhealthy cilia, which

would result in poor shell construc-tion and quality.Various researchers have reported

that a total replacement of inor-ganic trace minerals with organicproteinate minerals resulted inhealthy cilia in the magnum and theisthmus, improving shell quality.

The eggshell

The egg takes an average of 24hours to form from ovulation tooviposition. Of this cycle, 20 hoursare spent forming the shell mem-branes and the ‘true’ shell (the calcified portion of the shell). Thismulti-layered structure consists of95% calcium carbonate plus anorganic matrix (3.5%), which con-tains proteins, glycoproteins andproteoglycans. This matrix influences calcium car-

bonate deposition during all stagesof shell formation, controls crystalgrowth, shape and the resultingshell.The structure of the shell can be

affected by disease, nutrition andenvironment. The total thickness ofthe shell represents the main barrierto bacterial penetration, althougheach layer has a specific role toplay. The presence of cuticle on the

surface of the shell is important; it isthe first physical and chemical bar-rier against bacterial penetration,partially blocking the gas exchangepores. Beneath the cuticle lies the verti-

cal crystal layer, along with organicmatrix proteins. The honeycombedpalisade layer, beneath the crystal

layer, forms the bulk of the shell.The matrix proteins throughout

the thickness of the shell influencethe shell’s mechanical properties.Shells with a poorly formed organicmatrix layer will be more brittle andare prone to breakage.Each layer of the shell supports a

variety of protein types, some classified as ‘egg white proteins’ andothers as ‘shell-specific proteins’.Ovocleidin-17 is one such shell-specific protein identified bothwithin the palisade layer and thebase, the mammillary nucleate layer.

Mammillary layer

This basal layer is a specific nucle-ation site on the outer surface ofthe outer membrane, attracting calcium salts to initiate the forma-tion of the mammillary layer in thetubular shell gland.Poor mineralisation of mammillary

nucleates will lead to poor con-struction of the subsequent shelllayers. The formation of the mam-millary nucleates may be influencedby the diet, age and environment.Pore formation begins at the

mammillary layer level.

Palisade layer

The palisade layer is the thickestpart of the shell. Each palisade col-umn grows perpendicularly from amammillary nucleate, fusing as cal-cification progresses. The palisade

layer is covered with a crystal layer,followed by pigment and cuticle.The hatching eggshell displays, at

any one time, a variety of crystalmodifications in its mammillarylayer. The incidence and nature of the

variations from the calcitic growthpattern are made worse by stress,disease, housing and diet, and theimpact on the shell as an embryonicchamber or table egg is compro-mised.Ideally, the following factors are

important for hatching eggshellquality:l Uniform shape and weight.l Effective thickness of the shell(making it resistant to damage).l Integrity of the shell ultra structure.

Mineral nutrition and eggformation

M. Kidd (2003) reported trace min-eral deficiency in adult broilerbreeders could cause embryonicdefects and mortality, impactingoverall hatchability. Trace minerals in their inorganic

form are limited in the ability of thebird to absorb and utilise. This further diminishes as the bird

ages or its health status is compro-mised. However, the demand forthese nutrients increases as the birdgets older.The role of trace minerals in the

process of shell formation, as well

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International Hatchery Practice • Volume 31 Number 6 9

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Fig. 3. Left, Healthy cilia in the magnum. Right, lack of or matted cilia inthe magnum.

Normal mammillary layer showingthe mammillae randomlyarranged.

Masses of spherical calcite situated between normal mammillae at the beginning of lay.

Structural modifications ineggshells from birds at 60 weeksof age.

Confluence in eggshells from thetreatment date to the end of layperiod.

Pores

CuticleShell pigment layerVertical crystal layer

Crystalline palisade layer

(Organic matrix layer)

Mammillary bodies

Mammillary layerShell membrane

Egg interior - albumen

Fig. 4. Structure of the eggshell (Hy-Line International).

as being an integral part of the shell,has been well documented. Zinc (Zn) and manganese (Mn) are

both co-factors in producingenzymes for calcium metabolism.Manganese deficiency reduces shellweight, and shell membranes con-tain manganese, zinc and selenium.In 2010, Solomon, Bain and

Stevenson conducted an investiga-tion to determine whether theinclusion of Sel-Plex (Alltech) orBioplex (Alltech) minerals in thelayer diet influences the shell formation of commercial eggs. They used 400 laying birds with

four treatment groups (20 cages pertreatment, five birds per cage). The treatments were:

l Treatment A: Inorganic Se (0.3ppm) and inorganic55ppm Zn, 15ppm copper (Cu),70ppm iron (Fe) and 80ppm Mn.l Treatment B: No Se supplementation (control).l Treatment C: Sel-Plex (0.3ppm Se).l Treatment D: Sel-Plex (0.3ppm Se) + Bioplex Zn,Fe, Cu and Mn (20, 5, 5, and 20ppm,respectively).They examined shell structures at

22, 46, 60 and 72 weeks of age.The results showed: At the beginning of lay, structural

diversity was most pronounced in

the mammillary layer of eggshellsfrom birds fed inorganic Se or thecontrol.At mid-lay, the mammillary layer

of eggshells from birds fedTreatment C or D demonstratedextensive confluence.Also at mid-lay, physical data

showed a trend for improved shellstrength in eggs from birds fedTreatment D.The mammillary layer of eggshells

from layers fed Treatment D main-tained their fused configuration atthe end of lay.The trend for increased breaking

strength values persisted ineggshells from birds fed TreatmentD at the end of lay (Fig. 5).In all cases, inorganic mineral

Treatment A showed the worstbreaking strength. Even Treatment Bwith no supplement performed better.These morphologic variations

suggest that albumen quality and itsstructure are better maintainedwhen fed only organic minerals(Treatment D). Well-structured, turgid albumen

due to healthier cilia in the magnumand isthmus guarantees a suitable

base for shell membrane depositionand subsequent shell growth.The researchers concluded that

whilst commercial eggs were used,the results can also be applied tohatching eggs. The results indicate that supplying

trace minerals in an organic proteinate form have a positiveinfluence on shell construction andshell performance.These results are consistent with

the findings of Eden (1999), Ranema(2002) and Rutz (2010). Each of themreported improved performance inbroiler breeders when only organicminerals (Bioplex) were supplied inthe laying diets.The improvements they observed

were improved hatchability, by asmuch as 2%, and better albumenquality, shell thickness and weight.These results – combined with

better understanding of the eggshellconstruction – strongly point in thedirection of replacing inorganictrace minerals in breeder diets withorganic proteinate trace minerals,such as Bioplex.This will ensure high-quality

hatching eggs that meet the geneticpotential requirements of modernbroiler breeders. n

References are availablefrom the author on request

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10 International Hatchery Practice • Volume 31 Number 6

Fig. 5. Breaking strength eggshell at 46 (mid-lay) and 72 (end of lay)weeks of age.

36.0

34.5

33.0

31.5

30.0

Mid lay End of lay

New

tons

n Inorganic(treatment A)

n No added minerals(treatment B)

n Sel-Plex(treatment C)

n Sel-Plex + Bioplexes(treatment D)