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KING’ORI within the shell gland area of the oviduct for a longer than normal period. During this time a very thin layer of extra calcium is deposited on the egg, producing a greyish, bleached outlook (Thear, 2005). Release of stress-related hormones will result in the production of pale brown-shelled eggs (Hughes et al., 1984). Relocation, such as movement from one type of housing to a completely new housing environment, stresses the hens and can produce severe visual defects of the egg. It is known to increase the incidence of calcium coated and checked (misshapen) eggs. Internal defects These include defects on the yolk and albumen. Assessment of Interior egg quality involves breaking the egg to inspect its contents. Two interior measurements in common use are the measurement of yolk color using the Roche Yolk Color Fan, and the measurement of Haugh units which also characterize the freshness of an egg (USDA, 2000; Or-Yehuda, 2007). The Roche Yolk Color Fan has 15 sample colors, ranging from 1 (the lightest) to 15 (the darkest), which are visually matched to the color of the yolk. Internal egg deffects occur in the form of blood and meat spots, double yolks, mottled and discoloured yolks, rotten eggs, watery whites, discoloured whites and round worms in eggs (Optimum egg quality, 2010). Occurrence of blood and meat spots is revealed by candling. Candling reveals most of the spots, but brown eggshell hampers selection in brown chicken lines. Estimated frequency of blood and meat spots in brown layers is about 18% whereas it is 0.5% in white egg layers (Honkatukia et al., 2011). Several factors are known to increase the incidence of meat and blood spots: genetic background, low level of vitamin A and/or D, stress or infections. Internal egg quality involves functional, aesthetic and microbiological properties of the egg yolk and albumen. Meat and blood spots in addition to being an aesthetic and ethical problem, they may increase the risk of infections such as salmonella (Smith et al., 2008) and reduce hatchability of eggs (Bermudez et al., 1993). Blood spots are droplets of blood found usually on the surface of the yolk (Shirley, 1965). Meat spots appear as red, brown or white spots in the albumen. They are either pieces of tissue from reproductive organs or blood spots that have changed colour due to dilution. They emerge during the ovulation process in the ovary or later in the oviduct. Blood on the yolk originates from bleeding of the small vessels in the ovary or in the oviduct (Shirley, 1965). Meat spots in the albumen can be formed from a bit of reproductive tissue while the egg is passing through the oviduct. As an egg ages, the yolk takes up water from the albumen, which in turn dilutes blood spots and makes them look like meat spots. In general the frequency of blood and meat spots is less than 1% in all eggs laid in commercial lines (Smith et al., 2008). The incidence of spots seems to increase when the hen ages (Bustanyet al., 1987). Increased frequency also appears at the start of laying. Different factors, including nutritional, environmental and heredity, trigger the incidence of spots. Probably the most important nutritional factor is a lack of vitamins A and D (Sauter et al., 1975; Bermudez et al., 1993; Sutcliffe et al., 1998). When the supply of vitamin A is sufficient, the chicken has a low probability of having blood spots (Becker et al., 1973). Environmental factors, like sudden loud noises, temperature changes and infections, induce an increase in the incidence of spots (Campo, et al., 1998; Deaton, et al., 1986). Double Yolk eggs appear when ovulation occurs too rapidly, or when one yolk somehow gets stuck before shelling and is joined by the next yolk (2011 PoultryHelp.com). Double yolk eggs may be laid by a pullet whose productive cycle is not yet well synchronized. They're occasionally laid by a heavy-breed hen, often as an inherited trait. They are usually bigger than the ordinary (normal) egg. No-yolk eggs (yolkless eggs) are called "dwarf", "wind" eggs. Such an egg is most often a pullet's first egg, produced before her laying mechanism is fully developed and is usually smaller than the ordinary egg. In a mature hen, a “wind” egg is unlikely, but can occur if a bit of reproductive tissue breaks away, stimulating the egg producing glands to treat it like a yolk and wrap it in albumen, membranes and a shell as it travels through the oviduct (2011 PoultryHelp.com). A double shelled egg or an egg within an egg appears when an egg that is nearly ready to be laid reverses direction and gets a new layer of albumen covered by a second 354 J. Anim. Prod. Adv., 2012, 2(8):350-357
EGG QUALITY DEFFECTS: TYPES, CAUSES AND OCCURRENCE … shell. Sometimes the reversed egg joins up with the next egg and the two are encased together within a new shell. Double shelled eggs are so rare that it is unknown exactly why they happen. Some eggs may have an unusual or unacceptable odour or taste, although their appearance is normal (Optimum egg quality, 2010). They differ from rotten eggs, which are obviously defective and smell putrid. Off odours and flavours are rare in fresh eggs stored correctly. They will occur due to poor storage conditions (long storage period, high temperature, and presence of strongly scented materials in egg store) and use of strongly flavoured ingredients in the feed. Hens that eat onions, garlic, fruit peelings, fish meal, and fish oil will lay eggs with an undesirable flavor. Eggs can also absorb odors that translate into unpleasant flavors if they're stored near kerosene, carbolic acid, mold, must, fruits and vegetables (2011 PoultryHelp.com). Certain bacteria and fungi growing either on the outside or the inside of the egg may give an undesirable odour or flavour to the egg contents without causing noticeable spoilage. Bacterial or fungal contamination of the egg can produce rots (black, red, green). The egg looks and smells putrid when broken out. Under conditions of good management, the incidence of rotten eggs is very low; such eggs must be eliminated during grading, as they have such a detrimental effect on product image (Optimum egg quality, 2010). Bacterial and fungal contamination will occur due to faecal contamination, improper washing procedures, high storage temperature and humidity, long storage period and infection of the hen’s oviduct. The development of watery whites is chiefly due to the increasing age of the egg. When an egg broken onto a flat surface has a watery, spread-out white, this usually indicates that the egg is stale. The yolk index and haugh unit are the best indicators of internal egg quality (Isikwenu et al., 1999). Yolk index is determined as a ratio of the yolk height to the yolk width. The height of the white and the weight of the egg are used to calculate a value in Haugh units on a scale of 0-110; the lower the value, the more stale the egg. The higher the yolk index (Ayorinde, 1987) and haugh unit the more desirable the egg quality. A minimum Haugh unit measurement of 60 is desirable for whole egg sold for the domestic consumer (Optimum egg quality, 2010). Oiling of eggs within 24 hours of lay is very effective in slowing down reduction in albumen quality, but does not replace the need for cool storage (Jacqueline et al, 2011). The normal colour of egg white is slightly yellow-green but may be discoloured to yellow, green or pink which is objectionable (Optimum egg quality, 2010). However, this problem is rare. Excess riboflavin in the diet causes egg white to turn green while cyclopropene fatty acids in cottonseed cause the white to turn pink after storage. Omission of xanthophylls in the diet will lead to pale yolks (Esonu, 2006). Pale yolks can result from any factor which alters or prevents the absorption of pigments from the diet or the deposition of these pigments in the yolk. The inclusion of more than 5% cottonseed meal in a layer diet will result in olive or salmon coloured yolks (Esonu, 2006). Mottled yolks (with many pale spots and blotches which vary in colour, size and shape), occur when the contents of the albumen and yolk mix as a result of degeneration and increase permeability of the vitelline membrane (Amiri Andi et al., 2006). The anticcocidial drug, Nicarbazin, has been shown to cause yolk mottling when fed at a concentration of 0.005% or greater in the diet. The degree of mottling is not the same in all eggs, and not all hens respond the same way to Nicarbazin. However, a direct relationship exists, however, between the duration of feeding Nicarbazin, the level of Nicarbazin in the diet, and the incidence of mottled eggs. Deworming drugs, such as Piperazine and dibutyltin dialaurate, have also been reported to cause yolk mottling (Jacqueline et al., 2011).Some eggs may contain one or more roundworms, though the incidence is quite rare. Roundworms are internal parasites and migrate from the cloaca to the oviduct, where they may be enclosed in the egg (Optimum egg quality, 2010). This egg defect can be prevented by regular deworming and good hygiene. Conclusions Egg quality is influenced by nutrition, breed, climatic factors, flock management (age, housing, disease control), and post-lay handling of eggs. Egg quality is determined by the external (shell) and 355 J. Anim. Prod. Adv., 2012, 2(8):350-357
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