Why egg quality impacts the health of day-one-chicks? | PlusVet Animal Health
The main goal of every breeder farm is to get the maximum number of qualified eggs and live chicks per hen and the highest proportion of top quality day-one-chicks. In order to obtain the maximum number of healthy, highly productive chicks, we need to consider not only the variables related to the breeders but also the elements related to the eggs.
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Why egg quality impacts the health of day-one-chicks?

The main goal of every breeder farm is to get the maximum number of qualified eggs and live chicks per hen and the highest proportion of top quality day-one-chicks.

In order to obtain the maximum number of healthy, highly productive chicks, we need to consider not only the variables related to the breeders but also the elements related to the eggs.


Physical characteristics of fertile eggs play an important role in embryonic development, hatchability and status of the chicks. The quality attributes can be divided in two groups:

1. Factors related to internal quality

Internal quality factors will indicate the freshness of the egg.

The quality decline begins immediately after the egg is laid, mainly because of the loss of water and CO2. Losing carbon dioxide leads to an increase in the pH of the egg, that produces changes in the three-dimensional structure of the proteins.

The quality of the albumen is one of the main indicators related to freshness. The height of the albumen and the weight of the intact egg are used to calculate the Haugh Unit value. A Haugh Unit value of 70-80 is ideal for the fertile eggs and it will fall quickly after 3-5 days if the egg is not stored properly (Ahmadi, 2011).

Internal quality is optimal immediately after being laid; however, in practice, the best results are obtained by incubating eggs that have been stored for one to two days.

2. Factors related to external quality

The eggshell is about 0.3 mm thick and consists of more than 95% of calcium carbonate stabilized by a protein matrix. The cuticle atop and the membranes below the shell operate as barriers. It is covered by up to 20,000 pores that allow the exchange of gases and water between the developing embryo and the environment (La Scala et al, 2000).

There are many factors that determine the quality (thickness and strength) of the shell, among others:

  • Diseases and stress.
  • Nutritional factors, generally related to minerals and vitamins.
  • The length of time that the egg remains in the uterus and the rate of calcium deposition during its formation.
  • Some breeds are able to deposit calcium at a faster rate than other breeds.
  • As the hen ages, the eggshell quality declines.


The presence of visible cracks or micro-cracks due to deficient formation inside a hen or mishandling is quite common. While the eggs with visible cracks are discarded, detecting small cracks is not easy and very often eggs with star-crack and hairline-cracks are sent to the hatchery.


Micro-cracked eggs loose more moisture than normal eggs during incubation and show higher embryo dehydration and mortality, as well as worse quality of day-one-chicks. 

Table extracted from Moosanezhad Khabisi et al, 2011.


A thin-eggshell, abnormally big pores or the presence of micro-cracks may lead to the penetration of pathogenic bacteria inside the egg.   The porous shell is not a significant obstacle to bacterial penetration, although the underlying shell membranes and the cuticle are a more effective barrier.

There are two main routes for bacterial infection of the fertile egg (Gast, 2005):

1. Vertical transmission During the egg formation, the albumen or the egg membranes (rarely the yolk itself) are contaminated as a result of an existing infectious disease of the ovaries or the oviduct. The existing infectious disease of the reproductive organs may originate from systemic infections or it can be an ascending infection from a contaminated cloaca to vagina and then to oviduct.

Some bacteria that produce systemic infections (E.coli, Salmonella) are introduced to the hens via the gastrointestinal tract. After oral ingestion, these bacteria colonize several regions of the digestive tract, particularly crop and caeca in the case of Salmonella, disrupt digestive epithelium, enter the bloodstream and spread through the body of the bird to many organs including the reproductive system (Gast and Beard, 1990; Humphrey et al, 1993).


2. Horizontal transmission

In the horizontal infection, pathogens arrive inside the egg from the outside by penetrating the eggshell.

Although huge microbial contamination of shell is not common at the time of oviposition, avian faecal material and other environmental sources in the laying house, during transport, storage or incubation can rapidly introduce bacteria onto eggs (Board and Fuller, 1994; Davies and Breslin, 2003).


The major contaminants found inside the fertile egg are Gram-negative bacteria such as Escherichia coli, Salmonella, Pseudomonas, Aeromonas, Proteus and Alcaligenes sp; Gram-positive bacteria like Staphyloccocus and Bacillus. It has been found that most contaminated eggs contain a mixed colonization by several species (Mayes and Takeballi, 1983; Board and Tranter, 1995; De Reu et al, 2008).

Salmonella and E.coli

Salmonella species and E.coli are the maybe best studied egg bacterial contaminants that impact DOC quality. These bacteria may arrive to breeding flock and fertile eggs through several potential sources:

  •  The replacement pullets, which are carriers of pathogenic bacteria.
  • Laying house environment:  Environmental contamination of Salmonella and E.coli has been found to persist in the houses even after cleaning and disinfection.
  • Vectors: insects, reptiles, wild birds, rodents, livestock, pets and humans.
  • Feed and water
  • Hatcheries: chicks acquire the infection in two ways:  either during incubation, by penetration of the bacteria through the egg shell; or at hatch, by ingestion of contaminated dust and aerosols (Davies et al, 2001).



Omphalitis, also called yolk sac infection, is the most obvious consequence of bacterial contamination of the egg and a major cause of mortality in broilers during the first week (Husseina et al, 2008). Specific signs are (Jordan, 1990; Sainsbury, 1992; Anjum, 1997; Barnes and Gross, 1997):

  • Birds with distended abdomen.
  • Navel inflammation and swelling, that be observed in approximately in 30% of the affected chicks.
  • Unabsorbed yolk sac, that appears enlarged because the yolk has not been utilized by the chick. If the yolk sac contains inflammatory waste products, it is abnormally colored and has fetid odor.
  • Unabsorbed yolk sac is very often accompanied by pericarditis and perihepatitis.

Unspecific signs ((Kahn et al, 2008) are:

  • Diarrhea and pasted vents.
  • Dehydration, loss of weight.
  • Depression, drooping of the head and tendency to aggregate near the heat source.
  • Low maternal antibodies, poor immunity.
  • Poorer intestinal absorption of nutrients.
  • Mortality (5-10%) usually begins within 24 hours of birth and peaks by 5 – 7 days (Wray et al., 1996, Gross, 1964; Coutts, 1981; Mosqueda and Lucio, 1985).

Several bacteria such as E coli., Salmonella spp., Proteus spp., Enterobacter spp., Pseudomonas spp., Klebsiella spp., Staphylococcus spp., Streptococcus spp., Clostridium spp., Bacillus cereus and Enterococcus have been isolated from the yolk sac of infected birds (Pysniak, 2010; Cortes et al, 2004; Iqbal et al, 2006).

Consequences that last a life time

If chicks survive more than a few days, they show lower weight and poor growth.  On necropsy, usually an infected yolk sac remnant can be found, even in birds older than 10 days. Quality of the carcass will be deficient and these animals are very often condemned in the slaughterhouse (Giovanardi et al, 2005; Kabir et al 2010).

Several authors ((Phillips and Opitz, 1995; Gast and Holt, 1998) proved that pathogenic bacteria are likely to remain in the intestine and yolk sac remnant of the surviving birds during all the life of the animals, may spread to other organs and ultimately result in death.

Affected birds are more likely to develop infectious diseases, especially chronic respiratory diseases.


 There is no specific treatment for yolk sac infection in young birds. The use of antibiotics to treat the pathogenic bacteria may be useful in some cases in accordance with susceptibility testing, but generally speaking is of little value (McMullin, 2004).

Prevention is the only possible solution and involves the identification of the causative bacteria and a comprehensive and multilevel biosafety and management plan to eliminate the sources of pathogens in the breeder farm and the hatchery. We can help you with the establishment of this prevention plan, following biosafety and management criteria established by European and USA authorities. Do not hesitate to get in touch with us through for more information. 


In addition to reducing the sources of bacterial contamination, it is possible to mitigate the problem by using nutritional products based on vitamins and phyto-active ingredients.

  • Vitamin cocktails containing vitamins C, D3 and E have been proven highly effective to improve the quality and strength of the eggshell, cutting down the number of cracked eggs and reducing the possibility of bacterial penetration inside the egg. Some manufacturers include vitamin A, but experience shows that even low levels of extra-supplementation of vitamin A intensify the incidence of blood spots in the egg, decreasing internal quality.
  • There are phytoactive ingredients, such as ginger, extraordinarily rich in antioxidants.  Feeding ginger to egg-producing hens has been proven to improve the quality of the egg (Zhao et al, 2011) and egg production parameters (Malekizadeh et al, 2012).
  • Some vitamins (like vitamins C and E) and phytoactive ingredients such as sweetbay oil reduce the negative consequences of stress in hens. Stress is one of the leading causes of the presence of cracks in the freshly laid eggs.
  • Phytoactive ingredients such as cinnamon, marjoram or ginger are able to maintain the optimum functioning of digestive system, avoiding diarrhea or sticky droppings, thus reducing the percentage of dirty eggs. Some phytoactive ingredients are powerful microbiocides and are able to abate the populations of pathogenic bacteria in the intestine of the breeder, reducing the possibility of egg contamination through droppings and the spread of the infection from intestine to ovary and oviduct

Products of choice

PhytoMax© is a combination of vitamins, chelated calcium, microminerals and essential oils to be given through drinking water. It is intended for layers and breeders to:

  • Maintain the levels of calcium and magnesium needed for optimal egg production.
  • Reinforce skeletal health.
  • Prevent cage fatigue.
  • Stimulate the hepatic metabolism and the immune system.
  • Improve the quality of the egg and the health of day-old chicks.
  • Avoid the drop of the laying rate produced by stress (management, vaccines, hot weather, etc…)
  • At the start of the laying period, to boost productivity.
  • Prolong the productive life of the hen.


GrowthPlus© is added to feed to maintain and improve digestive health. It is formulated with synergistic ingredients:

  • Bactericidal and fungicidal plant extracts, combined with organic acids for better effectiveness, that reduce the number of pathogenic microbes in the digestive system.
  • Plant extracts with prebiotic effect, that promote the growth of beneficial bacteria in the gut.
  • Immunostimulant and antioxidant plant extracts.
  • Silicates with mycotoxin binding function.

It is especially useful in cases of gizzard diseases, necrotic enteritis, feed passage and other enteritis.  It is also used as a natural growth promoter and to replace antibiotic growth promoters.

PlusProtect Digestive© is intended for digestive health in birds and rabbits of all ages. It is formulated with synergistic ingredients:

  • Essential oils with bactericidal and fungicidal activity
  • Plant extracts with prebiotic effect.
  • Immunostimulant and antioxidant essential oils

PlusProtect Digestive© is useful to improve gut health in the following cases:

  • Candidiasis in beak, crop and gizzard
  • Bacterial infections in gizzard. In severe cases, it is better to give together with our PlusBind© line (mycotoxin binders)
  • Bacterial infections in the intestines (necrotic enteritis; E.coli; Salmonella sp.)
  • General digestive imbalances, such as feed passage.

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