Table eggs are an indispensable source of protein in many countries. They are preferred as a protein source due to high-quality protein content and versatility in cooking. However, the preferred egg size may vary significantly from one country to another. These varying demands in egg size are influenced by several factors such as cultural, culinary, economic and production factors that shape consumer choices and market dynamics. Local consumer preferences play a significant role.
In some markets, the price of eggs can correlate to size, influencing purchasing decisions. Larger eggs might command a higher price, affecting consumer choice based on budget considerations.
The profitability in table egg production industry largely depends on the ability of a layer flock to produce maximum numbers of first-quality eggs per hen housed that meet market demands, particularly in terms of size.
Table egg producers usually make their decisions in terms of layer breed based on their production target, considering the genetic potential of each strain to produce eggs within a given egg size range. Other major factors such as body weight at onset of egg production, density, lighting program during rearing period, heat stress and nutrition also significantly influence in the expression of egg size of each layer breed.
GENETIC ADVANCEMENTS
Historically, genetic companies have been developing their products to achieve longer persistency, maximum egg numbers, better feed conversion, better eggshell quality, eggshell colour and optimum egg size, taking into account consumer preferences and market needs. In addition, features such as durability, calmness, and production performance in different systems such a cage-free system which have gained increasing interest in recent years, are also among the selection criteria.
In order to match market demands, Novogen has decided for nearly two decades to adapt the egg weight profile of its products (Brown and White) by getting a rapid increase of the egg size during the first weeks of production to produce saleable eggs as soon as possible and at the same time by stabilising egg weight at the end of the production period, which contribute also to maintain a good eggshell quality and maximize profit of a longer production cycle.
Novogen is able to adapt its offer according to market demands whatever is the colour of the eggs. As an example, performances of NOVOgen White range of products are described in Table 1.
Table 1 – NOVOgen White strains
STRAINS | 25 WOA1 Bodyweight | 25 WOA1 Egg weight | 45 WOA1 Bodyweight | 45 WOA1 Egg weight | 65 WOA1 Bodyweight | 65 WOA1 Egg weight | 85 WOA1 Bodyweight | 85 WOA1 Egg weight | 105 WOA1 Bodyweight | 105 WOA1 Egg weight |
|---|---|---|---|---|---|---|---|---|---|---|
| WHITE | 1545 | 56,8 | 1688 | 63,1 | 1700 | 64,5 | 1725 | 65,4 | 1725 | 66,1 |
| WHITE LIGHT | 1510 | 55,4 | 1638 | 61,1 | 1662 | 62,3 | 1685 | 63,5 | 1685 | 64,5 |
| WHITE ULTRA LIGHT | 1480 | 54,7 | 1608 | 59,7 | 1620 | 60,7 | 1635 | 61,5 | 1635 | 62,1 |
BODY WEIGHT AT THE ONSET OF LAYING PERIOD
Pullets that have a greater body weight at the onset of lay are typically more physiologically mature. This maturity often means that their reproductive systems are fully developed, including larger ovaries and more substantial oviducts. A more mature reproductive system can produce larger yolks and, consequently, larger eggs. Also, heavier pullets generally have more body fat and muscle mass ( E.Lacin et al.,2008, Muir et al.,2023, Jian Lu et al.,2025). These nutritional reserves provide the necessary energy and nutrients for egg production and for growth until 33 weeks of age and onwards. Once hens establish a consistent laying rate and persistency, these reserves contribute to continued laying rate and size of egg maintenance. In two different studies by A.Perez-Bonilla et al., 2012 as shown in Table 2 and Table 3, hens with high and low initial weights of brown laying eggs had higher egg weights, had more egg mass but consumed more feed and higher FCR at 22-50 weeks and 24-59 weeks of age, respectively.
Table 2 – Effect of crude protein and fat content of diet on productive perfomance of brown egg-laying hens with different initial body weight ( A.Perez-Bonilla et al.2012)
| 22 – 50 WOA2 | Initial BW1 at 21 WOA2 (g) | Egg production (%) | Egg Weight (g) | Egg Mass (g/d) | Feed Intake (g/hen per d) | FCR3 (kg/dozen) | BW1 gain (g) |
|---|---|---|---|---|---|---|---|
| High | 1860 | 92,5 | 64,9 | 60 | 120,6 | 1,57 | 233 |
| Low | 1592 | 89,8 | 62,4 | 56,1 | 113,9 | 1,52 | 289 |
| P-value | P < 0. 01 | P < 0.001 | P< 0.001 | P <0.001 | P< 0.01 | P< 0.01 |
Table 3 – Effect of energy concentration of the diet on productive perfomance of brown laying hens differing in initial body weight and egg quality of brown egg-laying hens differing in initial body weight ( A.Perez-Bonilla et al.2012)
| 24 – 59 WOA2 | Initial BW1 at 21 WOA2 (g) | Egg production (%) | Egg Weight (g) | Egg Mass (g/d) | Feed Intake (g/hen per d) | FCR3 (kg/dozen) | BW1 gain (g) |
|---|---|---|---|---|---|---|---|
| High | 1733 | 91,2 | 64,2 | 58,5 | 114 | 1,49 | 313 |
| Low | 1606 | 90,5 | 63 | 57 | 111 | 1,46 | 307 |
| P-value | NS | P < 0.001 | P< 0.01 | P <0.001 | P< 0.001 | NS |
To support this, optimum body weight and development of body tissues should be ensured, especially in the first 5-6 weeks. The weight of the birds should be monitored from the beginning of the flock. Monitoring body weight in rearing period also allows changes in feed to be made according to the development of the bird, to change the management of the feed applied to the flock or to make nutritional changes in the feed. There will be no body development without a gradual and stable increase in feed consumption. The development of adequate feed intake capacity during weeks 10-16 of the pullet period is essential to ensure proper nutrient consumption at the onset of lay. Uniformity of flock of more than 85 % at beginning of lay can help to control average egg size of the flock throughout production period. Avoiding high stocking density prevents crowding, competition for feed, and stress, all of which can minimize having numbers of small eggs and keep standard laying rate.
Lighting program plays a crucial role in the development of pullets and performance of laying hens during the rearing period. The total hours of light provided each day determines the pullet’s growth rates. Pullets that experience longer light periods have increased feed intake, which promotes better body condition and can result in heavier eggs. Age at light stimulation and body weight are critical factors that help determine the onset of egg production, as well as egg size. Light stimulation should be done based on the flock’s average body weight and uniformity. Generally, early light stimulation at lighter body weights will accelerate maturity and decrease average egg size; while later light stimulation at heavier body weights will delay maturity and increase egg size.
Keeping hens in their thermoneutral zone (20°C – 24°C) should be a top priority at the farm. For an effective climate control, ventilation and cooling systems should be used. Heat stress has a direct negative impact on egg size, quality and production parameters. FAOSTAT 2010 reported that egg weight decreases 0.4 % per 1 ℃ between 23-27 ℃ and 0.8 % per 1 ℃ above 27 ℃
NUTRITION
An average egg weighing 60 grams contains 33-36 grams of egg white, 16-20 grams of egg yolk and 8-10 grams of shell. Approximately 10-11 grams protein and 0.3 % fat are found in albumen, while egg yolk has 17.5 % protein and 30 % fat. Carbohydrate and sugars are found in trace amounts. Eggshell is around 9-13 % of one egg. As laying hens age become older, the egg weight also increases, especially because the ratio of the weight of the egg yolk to the weight of the albumen increases. Fat deposition increases.
Linoleic acid is found in vegetable oils or animal oils. Linoleic acid supplementation in chickens provides metabolizable energy, which reduces the percentage of required feed intake. Many studies have shown that egg weight increases significantly as linoleic acid levels in feeds increase. This is because linoleic acid is an important component in the lipid structure that can enhance lipid deposition of egg yolk. According to these studies, linoleic acid may be optimized in feeds at around 1.1 -1.3 % for minimum egg weight and 2-2.2 % for optimum egg weight (Mendez et al., 1999, Grobas et al.,2001). To manage egg size in late laying period, a targeted reduction in the dietary linoleic acid content can be beneficial. The level of protein in the feed is a significant factor that can alter egg size. According to 24 different publications, increase of the protein content in the diet of laying hens by 1% is associated with egg weight increases by approximately 1.65 % and laying rate increases by about 1.50%. In addition, when calculating amino acid-based feed formulas, we must ensure that the 7 main amino acids are well regulated and that the remaining amino acids are provided with as little crude protein as possible. The proportion of amino acids needed in the egg does not change, but changes in the amount needed can be done to produce a larger egg. Therefore, a deficiency in any essential amino acid can limit the size of the egg.
Methionine, generally considered the first limiting amino acid, is identified as the most important amino acid in terms of its direct effect on egg weight. When optimizing egg weight, daily intake of methionine is usually considered together with cystine. Many researchers reported that these should be around between % 0.70-0.74 % methionine and cystine intake while optimum daily intake of other amino acids must be considered to provide optimum egg weight especially in 20-45 week of age. To reduce egg size, a strategic reduction in the levels of dietary protein, linoleic acid or particularly methionine + cystine and other specific amino acids can be effective. However, it is critically important that these nutrient limitations are not implemented prematurely, specifically before 45 weeks of age, as doing so will directly lead to a reduction in overall egg production. A general reduction in dietary protein can also negatively impact egg numbers in addition to egg size. Controlling total digestible amino acid intake, with studies suggesting that a reduction of all amino acids can be more effective in controlling egg weight than selectively reducing only methionine or methionine + cystine, is another viable strategy (Lemme, 2009; Macelline et al., 2021).
As branched-chained amino acids (BCAAs), isoleucine and valine are important for maintaining gut immunity, antioxidant capacity, and critical metabolic processes (Dong et al., 2016). Isoleucine is essential for growth, optimum egg mass, and egg production (Shivazad et al., 2002). Trial done in 2020 by Ilona A. Parenteau et al., a reduction of crude protein by 2 % with diets which have been fortified with synthetic amino acids, especially, a ratio of 90% Ile:Lys resulted in a greater proportion of large eggs (56 g ≤ EW > 63 g), suggesting that isoleucine might be used to manipulate egg weight, potentially at the expense of overall hen-day egg production. Beside optimal responses in egg production and quality were observed when the standardized ileal digestible SID ( Standardised ileal digestible) Ile ( isoleucine) : Lys ( lysine) ratio was between 82% and 88% as shown in Table 4.
Table 4 :Layers fed a low protein diet with varying levels of SID Ile:Lys to a control during 20-27 weeks and 28-46 weeks
| 20-27 WOA1 | Feed Intake (g/hen per d) | Egg Production (%) | Egg Weight (g) | Egg Mass (g/d) |
|---|---|---|---|---|
| CONTROL | 97 | 97.6a | 51.7a,b | 50.6a |
| SID Ile : Lys 702 | 95 | 94.3b | 51.3a,b | 48.6b |
| SID Ile : Lys 80 | 98 | 93.8b | 51.5a,b | 48.6b |
| SID Ile : Lys 90 | 96 | 95.4a,b | 52.1a | 49.9a,b |
| SID Ile : Lys 100 | 96 | 97.6a | 51.1b | 49.8a,b |
| P-value | 0.211 | < 0.001 | 0.004 | 0.003 |
| 28-46 WOA1 | Feed Intake (g/hen per d) | Egg Production (%) | Egg Weight (g) | Egg Mass (g/d) |
|---|---|---|---|---|
| CONTROL | 114a | 99.2a,b | 58.2a | 57.5 |
| SID Ile : Lys 702 | 113a,b | 97.7c | 58.6a | 57.2 |
| SID Ile : Lys 80 | 116a | 98.1a,b | 58.0a,b | 57 |
| SID Ile : Lys 90 | 110b | 99.6a | 58.2a | 58 |
| SID Ile : Lys 100 | 111b | 99.1a,b | 57.3b | 56.7 |
| P-value | <0.001 | < 0.0001 | <0.001 | 0.058 |
Layers use 60-65 % of energy of feed for maintenance, while the remaining part is used for egg mass. Energy for maintenance is spent for body weight of birds, physical activity, and feather cover. If hens are reared in cage-free system, they need more energy for maintenance due to additional physical activity than in cage system. Any lack of energy in the feed forces hens to use protein and amino acids for energy, reducing the amino acids available for egg size and potentially egg production. On the reverse, excessive energy in the feed can reduce overall feed intake and lead to lower egg weights. Maintaining optimal energy intake is crucial knowing that both deficient and excessive energy can negatively impact egg size and overall feed intake.
Feed presentation also plays an important role. If there is too much fine particles (less than 1 mm) in the feed, feed intake and egg weight will be reduced. “Empty feeders” method should be done once a day to consume all particles of the feed. To maintain optimum egg weight over an extended laying period, implementing phase feeding programs could be done. These programs should involve small, gradual reductions in energy and amino acid levels as the flock progresses through its production.
CONCLUSION
Egg size management is a dynamic process. Regular and systematic monitoring of laying rate, body weight, feed intake, and egg quality parameters are essential. This continuous data collection allows for timely and informed adjustments to management practices and nutritional formulations, ensuring that the primary goal of minimizing egg size without compromising laying rate is consistently met throughout the flock’s productive life.
