Egg Quality
1. Introduction: The Importance of Egg Quality
- Why is Egg Quality Important?
- For table eggs, quality directly affects marketability.
- For hatching eggs, good quality hatching eggs are crucial for producing good quality chicks.
- Egg quality cannot improve once the egg is laid.
- Modern Trends:
- Modern poultry production uses bigger farms with more automated processes, including egg collection and packing, and this is also true for hatcheries.
- Automation means less attention is given to individual egg selection.
- This increases the importance of having the right conditions at each step of the process to get predictable results.
2. Egg Formation
- How Eggs are Formed: The egg is formed gradually inside the hen over a period of about 24 hours.
- Factors Influencing Egg Formation and Quality:
- Health status.
- Nutrition.
- Genetic attributes of the breeder hens.
- Temperature the eggs are exposed to after laying.
3. Factors Affecting Egg Quality
- As mentioned, health status and nutrition are the most important factors, along with genetics and temperature after laying.
- Let’s look at some specific factors and their impact:
- Health: Diseases like infectious bronchitis and egg-drop syndrome can affect the oviduct and ovaries, leading to problems like thin or wrinkled shells, flat-sided eggs, misshapen eggs, discolored, small, deformed, and easily broken shells, and watery egg white. Other infectious causes include infectious laryngotracheitis or avian encephalomyelitis (rough shells), typhosis (heterogeneous size, small/shell-less eggs, soft shells, deformed eggs), and Mycoplasma synoviae (eggshell apex abnormalities).
- Nutrition: Poor nutrition, especially lacking calcium and vitamin D3, can cause reduced shell strength and thin-shelled eggs. An inadequate balance of minerals like calcium and phosphorus results in poor shell quality. Nutrition can also influence feces production, potentially increasing dirty eggs.
- Age: Older breeders can be associated with reduced shell strength, pinholes, and calcified material (pimples) on eggshells.
- Water Quality: Saline water can contribute to reduced shell strength and thin-shelled eggs.
- Stressors: Stressors like frights, disturbances, and crowding can cause flat-sided eggs, misshapen eggs, and can even abruptly stop egg formation, leading to breaks and repairs in the shell, often when the flock is disturbed late in the afternoon.
- Management Practices:
- High barn temperature can reduce shell strength.
- Mechanical damage from birds (beak and toenails), collisions between eggs, or pressure from poor cage floor design can cause cracks. Toenails or other sharp projections can cause pinholes.
- Infrequent egg collection and rough handling can lead to mechanical damage like cracks.
- Incorrect or significant changes in lighting programs can contribute to rough shells and blood spots.
- Water shortages can lead to rough shells.
- Overcrowding can be a stressor leading to misshapen or flat-sided eggs.
- Early Maturation/Over-stimulation: In broiler breeders, feeding and lighting programs just before and during early lay influence maturation. Early maturation and over-stimulation cause erratic ovulations.
- Erratic ovulation means the ovary releases yolks too frequently, potentially resulting in more than one yolk in the reproductive tract simultaneously.
- This increases the chance of double and triple yolks, disturbs the 20-hour shell deposition period, and leads to slab-sided eggs, wrinkled eggs, and potentially internal laying.
4. Egg Defense Mechanisms Against Bacteria
- Eggs have several ways to protect themselves from bacteria.
- Rigid Shell Structure: A strong shell is an obvious defense. (However, for hatching eggs, a very thick shell can be a problem for gas exchange and moisture loss).
- Albumen pH Increase: Within a few days after laying, the albumen (egg white) pH increases from 7 to 9.3 due to carbon dioxide release. This higher pH provides effective protection against microorganisms.
- Note: This pH increase takes 2-3 days, so the albumen defense is not very effective immediately after laying.
- Temperature Drop and Air Cell Formation: Immediately after laying, the egg temperature drops, and an air cell forms as air enters the egg. This air entry is a potential risk for contamination if the shell is dirty.
5. The Laying Environment
- Eggs are typically produced in laying nests.
- Traditional Nests: Small wooden boxes with thick litter (oat/rice hulls, straw, wood shavings). Eggs are protected until collected by hand.
- Challenge: Eggs rest on insulating litter, keeping them warmer, especially if other hens use the nest. To avoid embryonic development starting, eggs in these nests must be collected at least four times a day, particularly in warm weather.
- Roll-away Nests: Eggs roll away to a central belt after being laid.
- Benefits: Automates collection, provides optimal collection conditions, reduces labor costs. Improves egg cooling, which helps hatchability, especially in older flocks.
- Floor Eggs: Eggs laid outside nests or in nests with insufficient clean material have an increased risk of contamination.
- Why? As the egg cools after laying, the contents shrink, creating a vacuum that draws air (and potential contaminants like bacteria, molds, or droppings) through the pores.
- Even if visually clean, floor eggs should be considered second-grade and labeled as potentially dirty for the hatchery. Washing/disinfection helps but can’t totally eliminate contamination that happened right after lay.
6. Common Egg Defects and Their Causes
- Defects can have a mechanical origin (after laying) or a biological origin (affecting formation).
- Star Cracks: Fine cracks radiating from a central impact point. Causes are the same as visible cracks.
- Hairline Cracks: Very fine cracks usually running along the length of the egg. Causes are the same as visible cracks, plus possible collisions between eggs or pressure from cage floor design. Detected by candling (placing over a bright light).
- Visible Cracks: Often result in a broken shell membrane. Reduced shell strength leading to cracks can be due to older breeders, poor nutrition (calcium, Vit D3), saline water, infectious bronchitis, high barn temperature, mechanical damage (beaks, toenails), infrequent collection, or rough handling.
- Pinholes: Very small holes. May be flaws in shell formation or pimples knocked off. Associated with older breeders, poor nutrition, strain of bird, or damage from toenails/sharp objects.
- Flat-sided Eggs: Part of the shell is flattened or indented, often with a wrinkled adjoining part. Traditionally linked to infectious bronchitis, but also caused by stressors (frights, disturbances, crowding), or incorrect/changed lighting programs. Can result from erratic ovulation.
- Thin Shelled Eggs and Shell-less Eggs: Commonly produced by pullets starting lay, especially early maturing birds. Causes: immature/defective shell gland, poor nutrition, saline water, diseases (infectious bronchitis, egg-drop syndrome). Can result from erratic ovulation.
- Calcified Material (Pimples): Small lumps of calcified material on the shell. Some easily removed, others leave a small hole. May be caused by foreign material in the oviduct, associated with age (older breeders), poor nutrition, and strain of bird.
- Misshapen Eggs: Shells are obviously different from the expected smooth, normal shape. May occur with immature/defective shell gland, diseases (infectious bronchitis), or stresses (frights, disturbances, overcrowding). Can result from erratic ovulation.
- Rough or Sandpaper Shells: Rough-textured areas, often unevenly distributed. Causes can be infectious (Infectious bronchitis, infectious laryngotracheitis, avian encephalomyelitis) or management-related (disturbances at laying time, incorrect/changed lighting, water shortages).
- Eggshell Apex Abnormalities (EAA): Altered shell surface, thinning, increased translucency, cracks, and breaks at the egg’s apex. Associated with Mycoplasma synoviae infection.
- Dirty Eggs: Eggs with visible dirt. Increased risk from floor laying or insufficient nesting material. Can also be influenced by nutrition affecting feces. Eggs must be clean to be marketed.
- Scratches: Damage to the shell surface. Egg cleaning should avoid scratching, as it can remove the cuticle.
- Blood Spots: Caused by rupture of blood vessels in the ovary or oviduct. Causes include fungal toxins, vitamin K antagonists (like sulfaquinoxaline), avian encephalomyelitis, and wrong lighting programs.
7. Hatching Egg Selection
- Why Select? Eggshell quality is important because eggs with poor shell conditions do not hatch as well. They are also more easily penetrated by bacteria.
- Culling Decisions:
- Eggs with moderate or severe shell defects should be culled during collection.
- Unclean eggs should also be culled.
- Setting defective or unclean eggs decreases chick quality and increases the number of exploders (contaminated eggs with gas-forming bacteria).
- Exploders are a significant risk as they can contaminate many other eggs and dramatically increase bacterial load in the hatcher. They should be avoided.
- Acceptable Eggs: Eggs with minor defects or small stains can be used.
- Decision Maker: It’s up to the person collecting the eggs to decide what is acceptable for setting.
- Communication: Good communication between the hatchery (wanting clean eggs) and the breeder farm (wanting to deliver many eggs) is essential to agree on acceptable quality. Routine reporting of chick and egg quality from the hatchery to the breeder manager is crucial for constructive discussions.
8. Egg Washing and Disinfection
- Washing:
- Good washing procedures exist for dirty eggs but have limitations.
- Washing helps remove dirt and may prevent further contamination, but cannot completely remove contamination that occurred immediately after lay.
- Egg washing cannot replace good hatching egg management; it can only support it.
- Poor procedures or reusing water/detergent can cause cross-contamination.
- Good washing needs controlled temperature, time, detergent, and a water replacement protocol.
- Washing removes the cuticle, the wax-like shell cover. The cuticle is a barrier against microorganisms, especially when albumen pH is still low. It can also limit gas conductance. Removing the cuticle might slightly benefit hatchability if shells are very thick or cuticles rigid, particularly for duck and turkey eggs.
- Disinfection:
- Disinfecting eggs as soon as possible after collection is recommended to prevent spreading pathogens and cross-contamination.
- Formaldehyde is a preferred method but is a health/environmental hazard.
- Alternative liquid sprays (hydrogen peroxide, quaternary ammonium) are effective but need careful application.
- Farm disinfection has had limited success in commercial broiler operations.
- Hatchery disinfection is crucial as a critical biosecurity control point. Farm disinfection should not replace it.
- Avoid disinfecting twice too close together: Allow at least 24 hours between disinfectant applications at the farm and hatchery.
9. Egg Storage
- Effects of Storage: Egg storage reduces hatchability and chick quality, especially with older flocks and storage exceeding 5-7 days.
- Hatchability typically drops by about 0.5% per extra day after 5-7 days. The longer the storage beyond 7 days, the greater the impact.
- Storage also adds to incubation time. A general rule is one day of storage adds one hour to incubation, possibly due to a weaker embryo needing more development time.
- Short Storage: Setting eggs immediately after lay also reduces hatchability, although the reduction is limited (max 1-2%).
- It is advisable to store eggs for at least 24 hours, preferably 48 hours, before setting. This likely relates to the need for albumen pH to increase for optimal embryo development.
- Exposing eggs to ammonium gas briefly can rapidly increase albumen pH and reduce the negative effect of very short storage.
10. Egg Storage Conditions
- Temperature: To limit negative storage effects, reduce storage temperature for longer periods.
- Up to 4-5 days: 20-22°C.
- 4-5 to 8-10 days: 18°C.
- Up to 14 days: 16°C.
- Exceeding 14 days: 14°C or lower.
- Keeping eggs too cold for short periods can make it harder for incubators to warm them uniformly and quickly. This is significant with large numbers of eggs (e.g., 100,000 eggs = 6000 kg mass comparable to water).
- Risk of Condensation (“Sweating”): This happens when egg temperature is below the dewpoint of the room they enter. Condensation increases bacterial contamination and should always be avoided.
- Preventing Embryonic Development: Eggs must be stored below the physiological zero (approx. 26-27°C), the temperature below which no development occurs.
- If eggs aren’t cooled fast enough or are exposed to high temperatures (e.g., in the sun), embryo development starts. Recooling these embryos increases early mortality.
- Continuously controlling storage temperature is crucial.
- Uniformly cooling eggs to air temperature is vital. This can be done using air velocity in the storage room to increase heat transfer. Once desired temperature is reached, minimal air velocity is needed, just enough for even temperature distribution.
11. Advanced Storage Considerations
- Long Storage (over 10 days):
- Turning eggs once or twice a day (90-degree angle) is beneficial.
- Alternatively, storing eggs with the pointed end facing up is helpful.
- These practices prevent the blastoderm from sticking to the shell membrane.
- Eggs from Young Flocks: Embryos have an optimal development stage for storage. Eggs from very young flocks might not have reached this stage.
- Temporarily warming these eggs is reported to have beneficial effects.
- Warning: This is risky because eggs that develop beyond the optimal stage will have reduced hatchability, and it’s difficult to predict the correct stage without extensive examination.
- Moisture Loss:
- High relative humidity (RH) in storage rooms is often used to prevent moisture loss, which decreases egg weight. The effect on hatchability is not clear.
- Increasing RH (e.g., by spraying water) carries a risk of egg contamination, similar to condensation.
- Lower storage temperatures naturally reduce moisture loss because the water vapor pressure difference between the eggshell and air (the driving force for loss) is smaller.
- Preventing Moisture Loss without Spraying: Keep the storage room closed (no ventilation). Separate it from the handling room and only open to move eggs. The evaporated moisture from the eggs will stay in the room, maintaining higher humidity without spraying.
- Closing the room also decreases energy costs by reducing cooling/heating needs.
- Air velocity does not influence moisture loss significantly; the eggshell’s restriction of loss is much more important.
12. Internal Egg Quality
- Beyond shell condition, the internal quality matters.
- Infectious bronchitis can negatively impact internal quality.
- Affected eggs may have a watery egg white with no distinct inner albumen ring, unlike normal eggs which show light reflected from an outer ring and an internal ring.
13. General Egg Appearance
- Ideally, a good quality egg shell should be smooth, clean, and free of cracks.
- Chicken eggs should ideally be uniform in color, size, and shape. (Though sources list many conditions that cause deviations from this ideal).
