EGG QUALITY OF COMMERCIAL LAYER POULTRY
A.--Internal characteristics of eggs:
Albumen height and yolk colour
1.The height of the thick albumen is generally used as indication of internal egg quality
In the freshly laid fried egg the thick white (albumen) stands out and has clearly a firm jelly-like appearance.
The albumen of the Grade 1 egg still shows some firmness but not to the same extent as in the freshly laid egg.
The thick albumen starts to become more fluid and in the so-called old egg the albumen clearly has a watery appearance .It is thus mainly the height of the albumen (egg white) that declines with age.
The height (firmness) of the thick albumen is used as a characteristic of quality and is expressed in Haugh units. A Haugh unit takes into account the weight of an egg as well as the height of the albumen. The height of the albumen from a flat surface is measured with a micro-meter mounted on a tripod as shown in the picture.
During storage of eggs, especially under high environmental temperatures, the albumen becomes watery very rapidly and that results in a low Haugh unit value. This can happen within two days after an egg is laid, it can thus by far not be described as an old egg. The recommended storage temperature for eggs is 12 – 15 °C and a relative humidity of 70 – 80%.
2.The yolk colour is also used as indication of internal egg quality
Yolk colour has been standardised by the “Roche” colour fan, which is a set of yellow coloured blades varying from a very light yellow (number 1 on the fan) to a dark or almost reddish yellow (no 14) and values between 10 to 12 are acceptable.
Yellow maize is the main source of pigments for yolk colouring.
Layers on free-range would have a much higher level of the yellow pigments in their egg yolks due to the pasture to which they also have access to. Yellow pigments are covered with the green chlorophyll in leaves and therefore not visible.
Abnormalities of internal egg contents–—-
Blood and meat spots. These originate from the membrane surrounding the ovum. When this membrane rips open to free a fully developed ovum a fragment of tissue or a blood spot is included with the ovum in an egg. These are often mistaken for an embryo by a customer.
Double yolked eggs——
At the onset of production when a flock of pullets come into production a
higher number of double yolked eggs will be noticeable. This is because of unstable levels of hormones that have been involved in the stimulation of sexual maturity and had caused more than one ovum in the ovary to be ovulated, the ovums come free simultaneously. The situation reaches normality once the birds’ metabolic systems have settled down. More often is the cause of double yolked eggs a light program that was increased too rapidly. It also occurs where young pullets are placed with older hens in the same building in which the light program is already at the maximum number of hours, for example 16 hours.
Bacterial and fungal contamination of eggs——–
The greatest threat to internal contamination of eggs by bacteria is from the persons collecting the eggs and handling eggs during packing. Salmonella enteritidis is a bacterium that can be transmitted from human carriers to eggs and equipment. This bacterium causes diarrhoea in humans and it is most important that persons handling eggs should be aware of the importance to wash their hands after they have been to a toilet. Soap that contains a disinfectant and paper towels should be available in all toilets and rest rooms on an egg farm.
Other routes of contamination: —————
• The cloaca, if hens are suffering from scouring (diarrhoea).
• Egg collection belts, packing material and nests contaminated with faecal and egg contents from broken eggs.
• Poor handling during egg collection results in hairline cracks causing easy penetration and
access for bacteria to egg contents.
• Poor environmental conditions, such as dirty equipment, floors, clothing of workers, rodents, and cockroaches etc.
B.-External quality characteristics of eggs ——-
Factors affecting shell defects (Such eggs cannot be marketed) —
Age of the bird:—–
Shell thickness decreases with age because hens have lower calcium reserves and eggs from older hens should thus be handled with more care that eggs from younger hens.
Shell strength is related to the thickness of the shell. Shell thickness is typical to particular a breed. High environmental temperatures lead to decreases in eggshell strength probably because of lower feed (calcium) intake during hot weather.
Diseases such as EDS (egg drop syndrome) affect shell quality, picture on the right.
Factors affecting the appearance of egg shells (Not marketable) —–
Cleanliness of the shell. —–
It is a most important aspect from the consumer’s point of view that eggs will be clean without adhering dust or faecal matter. Dirty cage floors, egg collection belts, dirty nest material, used egg trays, hands that handle eggs can all contribute towards eggshells being contaminated with dirt (Washing of eggs removes the waxy layer and spoilage bacteria that can be drawn into the egg to cause rot).
Stained shells and fly marks. —-
Staining on the shell surface could be as a result of various substances such as blood caused by prolapsing, faeces and contamination from broken egg matter.
Open cracks —-
Are associated with the shell membranes being damaged or broken. The careless stacking of egg trays and the handling during collection all cause damage to the shell.
Hairline cracks, (left) —–
Are very fine cracks that are only detectable by candling. Main causes are rough handling during collection.
Pinholes, (right) —-
Are very small holes in the shell. Older flocks, poor nutrition and sharp objects in the cage system could be the possible causes.
Dr.Vinay Prasad, Technical manager, Srinivasa Poultry Farms
