I. INTRODUCTION
The transition in the layer industry from conventional cages to cage-free and even further into free-range production is rewriting the nutritional requirements of the laying hen. In the last 25 years, the number of eggs a hen can produce has increased by about 2 eggs each year while the amount of feed required to produce these eggs has been reduced by 18.6% in cages (Anderson, 1991; Anderson et al., 2013, Anderson, 2019). The result has been a high value protein source at the low cost the consumers pay for eggs today. During this time, the breeding companies began selecting laying hens that were better adapted to cages. This included smaller body weights, improved feed conversion, increased egg size and quality among a few of the traits selected for. The industry in the US is being pushed to transition from conventional cages to cage-free production systems at a rate which is 3 times faster than was taken to transition to cages originally. The breeding companies are trying to transition the hen into a more productive bird when destined to be in a cage-free setting. Currently in the US, brown egg layers are being used more in the cage free systems and almost exclusively in the free-range systems.
The industry is moving these birds to the cage-free egg production systems while relying on the nutrient requirements that were developed while the birds were housed in cages. Nutritionists are working on developing feed formulation models which will compensate for the increased locomotory movement within these systems while maintaining the same hen day production levels. However, what we are finding is that the variation in energy requirements between individual hens is increasing dramatically due to their activity levels. In addition, there are greater concerns related to egg safety.
The production systems I will be discussing were derived from industry needs in 2012 and were components of the North Carolina Layer Performance and Management Test (NCLP&MT). The research station transitioned with remodelled facilities from multi-level conventional cage systems that hold relatively small populations of hens in a simple environment with no enrichments. There was a brief period where the industry transitioned to either Enrichable or Enriched Colony Housing Systems. The systems in this comparison were large cages with hen populations ranging in size from 21 to 36 birds. The enrichable Colony Housing Systems was a cage with increased height so the birds would not hit their heads when standing normally with no other enrichments. The Enriched Colony Housing Systems included a nest area 270 in2 (1742 cm2) and 96 in (244 cm) of roost space and a scratch area. The Cage-Free Housing System was in a force-ventilated house with a slat litter flooring system. The pens were 12.1 ft x 6.6 ft (4 m x 2 m) density 177 in2 (1142 cm2), 1 nest/5 hens and 6 in (15.2 cm) of roost/hen and a dust bathing area. The Free-Range Housing Systems was a standard height curtain ventilated laying house with a slat flooring system with pens 12.1 ft x 6.6 ft (4 m x 2 m) density 177 in2 (1142 cm2 ), 1 nest/5 hens, and 6 in (15.2 cm) of roost/hen. The Veranda 10 ft x15 ft (3.04 m x 4.6 m) of shaded, bare dirt with access to a Paddock 30 ft2 /hen (2.78 m2 /hen) and rotated every 4 wks. This configuration and rotation system allows for a 50% forage cover to be maintained.
For this presentation I went back through the 39th and 40th NCLP&MT Rearing and Single Cycle Reports and used the feed consumption records which included the diets and the amounts fed. These records were maintained for each of the replicates in all of the production systems which consisted of a total of 410 replicates (13,860 hens). All of the birds were hatched on site and reared in the appropriate environments. They were transferred from rearing to the laying phase which commenced at 17 weeks of age. All of the birds were under the same management and dietary protocols with the only caveats being the environments and that each replicate’s feed was allocated independently based on feed intake and production. From the calculated nutrient profile of each diet and the feed consumption data, I calculated the nutrients discussed herein, on a hen basis for the 5 production environments. The data were segregated between 11 White egg Strains and 7 Brown egg strains.
II. PULLET REARING
As we shift production systems from cages to extensive systems such as enriched colony, cage-free (aviary) or range we have to start considering how we are rearing the pullets destined for these systems. Pullets should be grown in systems similar to those in which they will be placed for their productive life. This allows them to learn how to use the system and physically develop to better move within them. In order to accomplish this we have to provide them the proper nutrition. In addition, it affords them the opportunity to develop behavior patterns which will minimize floor eggs. In the 39th NCLP&MT, range reared pullets consumed 470 g of protein more than their cage reared hatch mates for both White and Brown egg pullets. Either by genetic selection for extensive production systems, recycling of nutrients, or improved range management by the 40th NCLP&MT, protein consumption via supplemental feed was significantly reduced and was lower than that required by the cage reared pullets. Total energy consumption followed the same patterns as protein consumption. We have no way of accounting for what the pullets consumed in the extensive systems. We have indications that range pullets consume about 11% of their total consumption from the range system on an as fed basis. When the moisture content of that component is accounted for, the birds get only about 3% on a DM basis of their consumption from the range paddock.
III. LAYER PERFORMANCE
Nutrient requirements for the laying hen are highly dependent upon the production characteristics of the hens and how this production varies among the different housing systems. In the 40th NCLP&MT overall, the Brown egg layers consumed more feed than the white egg layers in all of the production systems. Also, both the White and Brown egg layers had increased feed intake in the Colony system and in the range production systems. However, only in the White egg layers was feed conversion depressed in the Colony and Range systems. When comparing the Colony with the Enriched system, Hen-Day production percentage was significantly higher in the Enriched Colony. For each of the production systems, the White egg layers produced more eggs than did the Brown egg layer. Mortality was due primarily to trauma. In systems with the greatest ability to move, the result was more broken appendages as well as keel bone damage.
In the 40th NCLP&MT, both White and Brown egg layers had similar egg quality; however, the percentage of checked and loss eggs was greatest in the Colony and Enriched Colony systems with losses ranging from 8.3 to 11.2 %. Cost and income components were relatively consistent across all systems for both egg type layers with the one exception being the White egg layers in the Range system generating the least net income/hen.
IV. LAYER NUTRIENT CONSUMPTION
We have a relatively good estimate of nutrient intake (or feed disappearance) of the laying hen during the production cycle. The White egg layers in a single cycle flock consumed 96 to 108 g of feed/day in both cage and cage free systems. Brown egg layers consumption was 3.3% and 5% higher in cage and cage-free systems, respectively. On range the White egg and Brown egg layers feed consumption increased to 106.8 and 110.9 g/day, respectively. From that, they consume 21 g of protein, of which 57% is dedicated to egg production, 16,6% for body maintenance and growth and the remaining 21.4% for dealing with the environment. Energy consumption is about 300 kcal with 66% used for egg production, 11.3% for growth and body maintenance and the remaining 13.3% for dealing with the environment. If we look at Calcium 75.6% is used for egg production with the rest for skeletal maintenance and that lost to the environment. However, as we move into more extensive production systems, we really have not examined the shift in nutrient partitioning due to the additional needs of the production system. We have to formulate to compensate for the increase in activity levels of the hens, to increase bone density, and to provide the energy required to maintain homeostasis. We also have to deal with the nutrients robbed from the hen by the internal parasite loads such as Heterakis, Roundworms, and Tapeworms.
In all of the extensive production systems, the Brown egg layers consumed significantly more Protein on a daily basis than the White egg layers, except in the conventional cages where the protein consumption was not different. Interestingly, the protein consumed in the enrichable colony system was significantly higher by 7.2% than in the enriched colony system. The protein consumption of the range hens was intermediate to either of the colony housing systems. The energy, Calcium, Available Phosphorus, Lysine and Total Sulphur Amino Acids, as you would conclude, followed similar trends as seen in the protein consumption. However, due to the feeding of individual replicates, we were able to show the influence of environment on White and Brown egg layers.
We do not yet understand the recycling of the nutrients in the cage-free system or the true level of nutrition captured from the range paddocks. We know that additional nutrients are consumed from the range and in the cage-free system through the nutritional makeup of the eggs and yolk color through research at Pennsylvania State University and at North Carolina State University. However, we need to keep in mind that the hen’s consumption rates are higher than in cage–free or the conventional cage systems.
V. CONCLUSION
We have much to learn related to the nutritional needs of the laying hen in extensive production systems. We worked on the nutrition of the hen in cage systems for 75 years so the transition to extensive systems and how we can manage these systems to enhance the nutritional status of the hens is going to be vital. Some research areas are:
1. Understanding what level of nutrition is gained from foraging
2. What is the variation in hen activity levels in the range systems
3. Training hens to minimize floor eggs
4. Impact of internal parasites on performance and health (How to mitigate parasites)
We have a growing world population and, regardless of your viewpoint, there are production issues we have to face if we are going to feed this population. It is a work in progress and will continue long after me.
Presented at the 32th Annual Australian Poultry Science Symposium 2021. For information on the next edition, click here. 
