Week 4 Flashcards
egg production history
1900s:
chicken was a luxury
eggs were main protein source
80-150 eggs per year
1920-30s:
improved breeding, management and demand for more intensive farming
hens laid 250 eggs per year
1930-50s: semi intensive commercial egg production (100-1000s hens) housed in sheds with access to yards
1950s onwards
intensive production introduced
commerical farms can house 500, 000 hens
1980s egg boards deregulated and egg production is now a free market
2000s hens lay 371 eggs/year
free range eggs advantages
access to outdoors and ability to roam freely
interact socially
natural behaviours such as nesting, foraging for food
better bone strength due to better movement and activity
free range egg disadvantages
greater exposure to predators
harder biosecurity for farmers due to outside pathogens
increased likihiood of social stress and cannibalism
a greater occurrence of manure pron illness and parasites
increased need for antibiotics to treat sick hens
Cage eggs
- Automated feeding & watering, ventilations, lighting manure and egg collection - Climate control kept at 23C
- Produce eggs at low cost
cage egg benefits
hens rarely get sick
avoid injury from infighting as small groups allow them to establish stable pecking order
lower carbon footprint
less need to veterinary medications such as antibiotics
protected from predators
produce more eggs and cleaner eggs – cheaper
fewer occurrences of manure born illness, parasites and other exotic diseases
cage egg disadvantges
reduced social interaction
unable to roam freely
unable to practice natural behaviours
generally unable to perch, lower bone strength
barn laid eggs advantages
protected from treat
more free inside shed
increased social interaction with larger flocks
furnishings within barn allow hens to practice natural behaviours such as nesting, perching and dust bathing
barn laid disadvantages
greater occurrence of manure born illness
greater difficulty identifying and treating sick hens
higher likelihood of injury due to feather pecking and infighting
less stable pecking order due to the size of the flock
Free range chicken have poorer productivity, higher mortality and compromised health & welfare compared to conventional farms
Nutrition from eggs
- Source of protein 6.4g
- Rich in vitamin B2, B12, D, A, E
- Source of iodine and iron, calcium and zinc
Nutritional benefit form egg white
- Antimicrobial activity
- Thiamin transport
- Inhibiting cholesterol absorption
Nutritional benefit from egg yolks
- Contains liposoluble glycoproteins called lipovitellin
- Shown to prevent atherosclerosis, a condition by the buildup of cholesterol in
the wall of blood vessels
Egg formation - physical composition on the avian egg
- Self-contained raw ingredients for the formation of a check
- If fertilized, embryo floats on upper surface of yolk
- Shell of a chicken is porous, and the large end of the egg contains more pores
- Concentric rings of yold - not seen if hen has received a uniform diet - reflects consumption of foods with different pigments
- Albumen surrounds yolk and enclosed by two that are fused except at blunt end (air space)
- 32-35% yolk, 52-58% albumen, 9-14% shell
- 33% lipid, 17% protein and small amounts of mineral, vitamins and carbohydrates
The ovary
- Has only one functional ovary
- At the time of hatching, the female chick has up to 4000 tiny ova
(reproductive cells), some of which full-sized yolks may develop when
hen is mature - Each yolk (ovum) is enclosed in a thin-walled sac of follicle attached to
the ovary. - This sac is richly supplied with blood
The oviduct
- The mature yolk is released when the sac ruptures and is received by the funnel on the left oviduct
- The left oviduct is coiled or folded tube
- It is divided into five distinct sections
The defense mechanism of the eggs & quality assessment
The outsides of egg shells are not sterile and different microorganisms are associated with the surface of egg shells. A compromised barrier allows microbes on eggshell to enter eggs
Poultry frequently carry Salmonella & it may become part of the bacterial flora of the egg shell during ovulation
Mechanical barrier
- The crystalline eggshell (porous to allow gas) and the waxy hydrophobic, proteinaceous layer (cuticle) act as a barrier to liquid.
- The cuticle does not harden immediately, and washing can damage the layer making it permeable
- Cooling of the eggs post-lay creates a vacuum that can pull air & microbes through the pores
- Enzymes released by some bacteria (Pseudomonas or Salmonella) are able to damage the cuticle.
Biological barriers
- Contents of eggs are generally sterile - some vertical contamination form reproductive tract and after lay
- Egg white contains lysozyme, avidin, protease inhibitors, conalbumin-inhibitory effects on microorganisms
- High pH -9.3 makes it difficult from gram-positive bacteria and some yeasts to grow
Grading
The Food Standards Australia New Zealand (FSANZ) code stipulates cracked, and visually dirty eggs are unable to be sold to retailers or caterers for direct human consumption due to risk of infection
- Automatic candling technology (light spectrum analysis of the inside of the egg) detects internal defects
- Quality control on the grading floor also involves checking for tiny cracks that might not be visible to the human eye and measuring the height of the albumen (egg white) and shell thickness.
- Automatic acoustic crack detectors contain probes that gently tap the eggs at very fast speeds as they pass through the machine. If there is a crack in the eggshell, no matter how small, the tapping energy will be absorbed, resulting in a duller sound
Albumin
Albumin
- The height is an indicator of membrane integrity and structure of proteins
- As egg ages the proteins denature and can no longer retain moisture egg spreads
out and albumin height decreases
- Yolk ratio decreases as egg ages
- Haugh unit is a measure of eqq quality based on the height of its egg white - If pH of albumen becomes more alkaline it means microbial growth
Yolk colour
Fades during storage pigments become diluted by mouser passing through vitelline membrane
- Ass egg ages yolk width increases as yolk taken in moisture, yolk height decreases, and yolk weight increases
Environmental factors affecting egg quality
Heat stress
- reduced egg quality
- greater capacity for Salmonella contamination (vertical contamination)
Environment
- A contaminated environment, increased fouling of eggs, broken eggs
Animal behavior
- feather pecking, cannibalism, egg consumption
Diet quality
- protein quality, digestibility of feed, adequate level of calcium
Over time
- Egg weight decrease
- Yolk weight increases
- Albumen weight decreases - Albumen pH increases
- Albumen height decreases
Endemic disease
- Infection bronchitis virus, mycoplasma etc
