Mottled egg yolks are an infrequent, but when present a persistent problem for egg producers. Mottling refers to the appearance of pale or discolored patches or blotches on the surface of egg yolks.
This problem intensifies with prolonged egg storage, especially under inappropriate conditions, but feed also can play a part in controlling mottling. The following list of six areas should be checked when mottling appears as well as layer nutritional needs.
1. Poultry medications
Certain poultry medications are known to cause or intensify yolk mottling. These include anticoccidial nicarbazin, when used at high levels and during prolonged use. In addition, certain worming agents, like piperazine, also have been implicated with yolk mottling, but not when used under proper veterinary supervision at recommended dosages.
2. Cottonseed meal
Gossypol, which abounds in certain varieties of cottonseed, can cause total yolk discoloration (greenish hue), but also can lead to the appearance of blotches of various colors (from greenish to brownish hues). Removing or reducing cottonseed meal from layer diets and adding a gossypol binding agent, such as iron sulfate, usually resolves the problem.
3. Tannins
Tannins found in certain sorghum varieties also have been blamed for increasing the incidence of yolk mottling. Usually, changing the source of sorghum to a low-tannin variety resolves the problem of yolk mottling.
4. Calcium-deficient diet
A calcium-deficient diet will increase egg mottling. This is unlikely to happen in layers, but checking actual calcium levels should be considered when looking for the source of the problem causing mottling.
5. Weeds
Certain weeds, like shepherd's weed that grow along corn, are known to cause yolk mottling. Measures should be taken to control the weed or clean the corn before using it in layer diets. Other similarly offensive weeds exist in all cereals. This is something that should be taken seriously, especially when cereal and egg production is related with some form of business agreement.
6. Raw soybean meal
Raw soybeans will cause egg yolk mottling. Most likely, improperly (lightly heated) soybeans, especially full-fat soybeans or expelled soybeans, also may be responsible. This is not proven beyond doubt but it remains a concern in such cases.
Vitelline membrane
Egg yolk is separated from the albumen by a strong membrane called the vitelline membrane. Mottled eggs have a very thin and weak vitelline membrane. It is uncertain whether this is the cause or result of mottling, but prolonged storage tends to weaken this membrane. At the moment, there are no feed additives known with certainty to increase vitelline membrane strength, but it should not be excluded that such additives will be pursued by nutrition suppliers.
