Optimizing egg size in laying hens

Optimizing egg size or weight means adjusting it to market conditions to generate the most favorable economic return. Egg market conditions, along with the marketing characteristics of the particular country, are what determine the economic convenience of producing larger or smaller eggs. Markets that sell eggs by unit with weight classification favor the production of larger eggs, especially in the first third of the production cycle – which is not usually the case when eggs are sold by weight. On the other hand, it is common for producers to want to reduce an exaggerated egg size toward the end of the laying cycle – especially now, with hens that have much longer production cycles. This is because egg weight has a negative correlation with shell quality, which means an increase in the number of broken eggs or eggs with fragile shells that cannot be marketed.

For fertile egg producers, it is important that breeder hens produce eggs large enough to be incubated as soon as possible. For table egg producers, the goal is to achieve an optimal egg size to yield the greatest economic benefit according to market conditions. In both cases, it is important to understand the factors that control egg size. The most important factors are: genetics; body weight and sexual maturity; environmental conditions; medications and contaminants; and nutrition.

Genetics

Egg weight is ultimately determined by the size of the ovum released by the ovary; thus, the bird will produce a larger egg around a larger yolk. Egg size is a genetic factor that has always been considered in the selection of different commercial strains. Today, however, each genetic line has its own parameters for this trait. Differences in egg size between strains tend to diminish or disappear after 50 weeks of age.

Body Weight and Sexual Maturity

Body weight at sexual maturity is the most important factor influencing egg size at the beginning of laying and throughout the rest of the production period. Body weight directly affects the size of the yolk that enters the oviduct, which ultimately determines the size of the egg. Within the same flock, the heavier the hen, the larger the egg she produces. Therefore, the more uniform the flock is in body weight, the more uniform the egg size will be.

Environmental Conditions

It is important to avoid exposing the hens’ feed to nicarbazin, gossypol, and fumigants – as all of these affect egg weight negatively. Feed contamination with mycotoxins – especially aflatoxin and, to a lesser extent, T-2 toxin – also affects egg size. The reduction in egg weight is most characteristic of aflatoxin toxicity, which impairs normal fat mobilization from the liver to the ovary and occurs after 7 days of exposure, well before other production parameters are affected.

Nutrition

Nutrition has a very significant influence on egg size. Properly formulated diets that ensure effective nutrient intake are needed to maximize egg weight at the beginning of the production cycle. The main nutritional factors that affect egg size are: linoleic acid; energy level, fat and phospholipids; protein and amino acids.

Deficiency of linoleic acid (which is found in corn and vegetable oils) affects egg weight. This situation can occur in barley, wheat, or sorghum-based diets, where the greatest response to supplementation is also obtained. The response to linoleic acid depends on the amount stored during the growing period. Maximum response is achieved with around 1.5% linoleic acid in the diet of hens without reserves and around 1.0% in the diet of hens with reserves.

To ensure adequate egg size, hens need a minimum daily intake of 280 kcal/kg of metabolizable energy. Energy intake below this minimum affects egg weight, especially in flocks that enter into production prematurely.

It has been shown that adding fat to the diet improves egg weight and that this effect is independent of the level of energy and linoleic acid: there is a positive effect of fat per se. Vegetable oils, especially corn and soybean, have a greater effect on increasing egg size than animal fats, and the response is obtained with supplementation of at least 2% and up to 4%.

An increase in egg size is also obtained by including at least 10% cooked soybeans in the diet. In addition to the contribution of oil and linoleic acid, the effect is due to the lecithin present in soybeans, which is an important phospholipid component of the yolk.

Adequate supply of protein and amino acids is critical to producing good egg size, since 50% of the solid portion of the egg is made up of protein. Protein intake is linearly related to egg size; however, the response is due to a balanced intake of essential amino acids. When limiting, the amino acids with the greatest impact on egg weight are: methionine, threonine, valine, and lysine – with methionine having by far the greatest effect.

It is not advisable to use high levels of protein to improve egg weight, as this not only adds an additional cost but it also creates pollution and can affect the birds’ productive performance. To meet the daily requirements of essential amino acids in practical diets, it is recommended to use a minimum of 14% protein, with appropriate supplementation of pure amino acids (Table 1).

To maximize egg weight, it is recommended to use high levels of amino acids (800 mg/day of digestible lysine) and increase the ratio of sulfur amino acids to lysine (reaching up to 92%), which means a daily intake of up to 735 mg/day.

Recommendations to Optimize Egg Size

With today’s laying hens, it is not advisable to reach the beginning of laying with heavy birds: it is less complicated to increase egg size in light hens at the beginning of laying than to reduce egg weight in heavy birds.

The suggested adequate body weight at the start of laying is one that reflects a feed intake between 95 and 100 grams/hen/day. In addition to favorable environmental conditions and an effective prevention of mycotoxicosis, the resources to increase egg size in the initial phase include the use of high levels of digestible amino acids (800 mg/day of digestible lysine), with a high ratio of methionine + cystine (92%) equivalent to 735 mg/day. Moreover, use high levels of linoleic acid (1.5%) and add extra vegetable oil (minimum 2%) and/or include cooked soybeans (minimum 10%) or lecithin (minimum 2%) in the diet. Once the desired egg weight is achieved, it is recommended to suspend the measures used to obtain it.

After 60 weeks of age, it is difficult to reduce egg weight without affecting production. The best way to control excessive egg size toward the end of the laying cycle is by controlling pullet weight at sexual maturity.

It is possible to reduce egg size by manipulating environmental temperature. Temperatures between 28°C and 29°C first depress egg weight before affecting egg number or shell quality. However, this measure is only recommended if it is economically feasible and completely safe to manage.

Egg size can also be reduced by lowering the level of protein (14%), essential amino acids (750 mg/day of digestible lysine), and, in particular, the level of methionine in the diet. A safe reduction of methionine and methionine + cystine would be between 75% – 80% (280 to 300 mg/day of MET and 495 to 530 mg/day of MET+CYS) to avoid the risk of production losses. Note that the practical application of this measure requires precise knowledge of the amino acid composition of the ingredients and of feed intake.

With today’s high-performance layer strains, it has become necessary to provide sufficient nutrients to allow the full expression of their genetic potential, including egg weight. However, the maximum productive response does not necessarily correspond to the most profitable results. It is essential to analyze market conditions and feed costs when making decisions regarding the specific nutrient levels to be used.