TIPS FOR OPTIMIZING EGG SIZE IN COMMERCIAL LAYERS

The end users of table eggs today are looking for the best buy for their money. When it comes to groceries and a food staple like eggs, it’s Grade A Large Eggs that fit this scenario most of the time.

The genetic make up of a layer variety determines its range of possible performance results. Within this genetically defined range, we can alter the production characteristics through our management systems to optimize these traits which are most profitable for our market. Based on International market levels eggs are sold on the basis of egg size. Much preference is given to egg size, whereas in South Asian markets (especially the Indian Sub-continent region), usually, the eggs are not graded according to egg size. But still the consumer preference is towards large egg size. Hence poultry farmers have to give equal emphasis towards the production of large number of eggs with maximum egg size.

Size refers to the weight of an egg rather than the dimensions of the egg or how big it looks in appearance. For measuring the accurate egg size it is better to calculate the net weight per dozen eggs. In effect the factors affecting egg weight may be applied to egg size as well.

In the production cycle of the commercial layer, the hen will begin laying small eggs and in a matter of a few weeks will go to medium size and then to the desired large size egg. It is well known that the main factor that determines egg size is body weight; therefore the diet that supplies all nutrients can be used to manipulate and produce the preferred early egg size.

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.

THE FOUR PILLARS OF EGG SIZE

1. Genetics: 
   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.
2.  Body weight:

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. Due to the direct affect of body weight on egg weight, the achievement of flock target body weight with good flock uniformity is important for egg size management.

3. Nutrition:
   Nutrition during the rearing and laying period has a critically important role in egg weight. Proper rearing nutrition allows the hen to achieve or exceed the standard body weights. Changing the rearing diets based on attaining body weight standards (and not bird age) will best match the diet to the actual nutritional needs of the pullet. 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. These components can be specified in layer diets to influence egg size downwards or upwards. The protein content of the diet should be balanced to ensure the amino acids are utilized efficiently by the bird. Unbalanced protein can result in poor utilization of amino acids and suboptimal egg size. Breghendahl (2008) estimated the “ideal amino acid profile” and determined that the ratio of methionine to lysine should be a minimum of 47:100 to support maximum egg mass. All other amino acids should be balanced relative to lysine to ensure egg size is optimized as efficiently as possible. To avoid excessively large egg size and weak egg shells later in the laying period, these nutrients are gradually reduced after peak egg production (30 weeks of age). Pushing nutritionally for greater egg size could result in thinner shells and more cracked eggs if mineral requirements of the bird are not adequately provided for.
   Management for larger egg size should include nutritional considerations in rear for subsequent shell quality and bone strength (i.e. pre-lay diet). Egg weight can be regulated through use of a phase feeding regime. Optimal egg weight will be easier to achieve when formulating feed according to egg weight or egg mass and constantly updating the formulas according to these parameters. This tool can be very helpful either to increase egg weight on earlier production, or to control egg weight on late production. Be aware that not only nutritional levels, but all aspects of nutrition management can affect egg size. Feed particle size, water intake, water temperature, and feeding schedule can affect daily feed intake and nutrient intake as a consequence. Heat stress can depress egg weight. High environmental temperature above the thermoneutral zone (> 33°C) has a depressing effect on the bird’s feed intake. The result can be a shortfall in nutrients like protein (amino acids) and energy, which will decrease egg weight. It is common to see decreased egg size as a consequence of heat stress. Appropriate adjustments in feed formulation to match the actual bird feed intake and mitigation of heat stress conditions can minimize this depression of egg size. In environmentally controlled houses, lowering the environmental temperature will increase feed intake and support egg weight.

4. Lighting programs:

Chickens are responsive to changes in day length, and this has a significant effect on egg production and egg size. Slow step-down lighting programs (C and D) during the rearing period provide the pullet with more light hours to eat and grow. At the same time, these slow step-down lighting programs can also delay maturity and increase egg size. Faster step-down lighting programs (A and B) 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. Light stimulation should be done based on the flock’s body weight and uniformity. Generally, early light stimulation at lighter body weights will accelerate maturity and decrease egg size; while later light stimulation at heavier body weights will delay maturity and increase egg size. Generally, the hen has the ability to produce a certain egg mass. As egg weight is changed, the egg number tends to change inversely to keep the egg mass constant.

MANAGEMENT TIPS TO OPTIMIZE EGG SIZE IN A MARKET

Management for larger egg size:

1. Select a commercial variety with a heavier egg weight profile.

2. Use a slower step-down lighting program in rear. (12 weeks)

3. Light stimulation at a heavier pullet body weights.

4. Make smaller gradual reductions in energy and methionine/cystine during the phase feeding program.
a. Use feed formulation that provides 10–15% higher digestible amino acid intake (mg of digestible amino acid per bird per day. Increase the ratio of methionine + cystine to lysine to be >90%.
b. Linoleic acid has a positive impact on egg size. For increased egg size, use 1.5 g linoleic acid per bird per day. Use sources of supplemental oil which are higher in linoleic acid, like soybean oil or flaxseed.c. Increase total and supplementary fat content in the diets. Studies have shown that at the same linoleic acid levels, birds consuming a higher amount of total fat will produce larger eggs.

d. Keep an optimal energy intake. In situations of deficient energy intake, laying hens will utilize protein and amino acids as an energy source, resulting in less amino acids available for optimal egg size. Many situations of low egg weight are due to low energy intake. Overfeeding energy above recommended amounts tends to depress egg weights, as a consequence of lower feed intake.

Management for smaller egg size:

1. Select a variety that has a regular egg weight profile.

2. Use a faster step-down lighting program in rear. (7 weeks)

3. Light stimulation at a lighter pullet weight.

4. Make larger gradual reductions in energy, methionine/cystine, and total digestible amino acids during the phase feeding program.

a. Nutritional management for controlling egg size is more complex and generates slower results than managing for increased egg weight.

b. Reduce methionine + cystine to lysine ratio less than 84%

c. Control total digestible amino acid intake.

d. Limit linoleic intake to 0.9 g/day/bird

e. Start to control egg weight with phase feeding at least 2-3 gram before the desired weight gain.