Each commercial variety has a genetically determined range of egg size, and within this range,environment plays an important role in the expression of egg size. Genetics, body weight management, nutrition, and lighting programs are the four pillars of egg size and are useful tools for the egg producer to change egg weight profiles to best supply the optimum egg size to a market.
1. Genetics/Breed-Some smaller breeds produce small eggs due to their body size, while some chicken breeds produce medium to large eggs.
Egg weight is a heritable trait (~40%) that responds well to genetic selection. About 60% of egg size variation, however, is due to non-genetic factors (nutrition, management, etc.). These non-genetic factors can be manipulated by egg producers to achieve the desired egg size profile. Egg numbers and breaking strength have a negative correlation with late egg weight.
2. Body wt-Hen body weight is the key to increased egg size. Bigger hens produce larger eggs than smaller hens and bigger breeders produce larger eggs than smaller breeders. An important factor in egg weight is the pullet‘s body weight at maturity. Heavier hens tend to lay more eggs throughout the production period and will have greater flexibility in adapting different egg size profiles. Body weight is affected by many factors, including beak trimming, vaccination program, transfer, disease challenges, pullet lighting program, space allotment, and nutrition.
3. Lighting- Chickens are responsive to changes in day length, and this has a significant effect on egg production and egg size. At the same time, these slow step-down lighting programs can also delay maturity and increase egg size.provide fewer light hours and slower growth but earlier sexual maturity with smaller egg size.
Age of light stimulation and body weight are interacting factors that help determine the onset of egg production, as well as egg size. As egg weight is changed, the egg number tends to change inversely to keep the egg mass constant.
4. Nutritions-Nutrition during the rearing and laying period has a critically important role in egg nweight. Proper rearing nutrition allows the hen to achieve or exceed the standard body weights.
The most important nutrients for control of egg size are linoleic acid, protein and some specific amino acids. Reducing the level of one, or a combination of these nutrients in the diet will reduce egg size. Protein level in the feed can be used to alter egg size at different stages of production. In the first couple of months of egg production feeding a high, 18% to 20% protein layer ration will increase egg size.
During the laying period, the specification of diets can be used to manage egg size. Energy, methionine/cystine, other digestible amino acids, linoleic acid, and total fat can directly affect the egg size.