But achieving good eggshell quality becomes more difficult during the late stages of a layer’s production when hens’ shells become thinner while their eggs become larger. This challenge can prompt farmers to replace aging layers with younger hens, compromising economics and environmental sustainability.
Feed and farm factors
Good eggshell formation requires critical macro minerals and essential trace minerals supplied in the feed. Calcium in feed is absorbed into the hen’s bloodstream where it is deposited in medullary bone or used directly by the bird. As a calcium reservoir, medullary bone is a buffer between hens’ calcium uptake in the day and calcium deposition around the eggshell at night.
Older hens metabolise calcium in feed less efficiently than younger birds, leading to thinner eggshells. Several studies have shown that increasing calcium in older hens’ diets can support eggshell integrity and reduce the number of broken eggs.
Timing of nutrient utilisation
Studies also show that time of day matters when it comes to hens’ utilization of nutrients. Researchers observed that when birds were freely able to select dietary intake, hens under-consumed calcium in the morning and consumed much more of it in the afternoon. These intake patterns reflect physiological processes in the bird required for egg production. Research suggests a split-feeding strategy in which birds receive one-third of their calcium in the morning and the remaining two-thirds in the afternoon feed can optimise hens’ calcium intake.
Phosphorous
While most of an egg’s phosphorous is not found in the shell ultrastructure, phosphorus intake has a major influence on calcium metabolism. High levels of bloodborne phosphorus inhibit calcium mobilisation from bone. A meta-analysis found that dietary non-phytate phosphorous (NPP) could be decreased to meet laying hens’ requirements and maintain health and productivity at lower than recommended levels of supplementation. The typical recommendation to feed 350 to 450 mg NPP per hen per day is nearly twice the required level informed by research.
Bioavailability
Bioavailability is another factor to consider. The inclusion of a nutrient in a premix does not guarantee that it will be absorbed into the hen’s system. For example, phytase – an enzyme used in 90% of poultry feed – can degrade phytate. Phytic acid levels will define the possible phosphorous release and the potential for interaction with other ingredients in the feed.
Without eggs, the centre does not hold
Trace minerals are a good example of ingredients that can interact with phytate. Trace mineral sources with lower solubility, such as hydroxy copper, zinc and manganese, remain intact in feed and prevent soluble trace mineral ions from releasing and inhibiting the efficacy of phytase.
Absorption and availability
Although small fractions of the hen’s overall diet, zinc, manganese and copper must be supplemented because raw materials in feed don’t supply adequate levels of these essential nutrients required for eggshell formation. Zinc is required to activate carbonic anhydrase, essential for the deposition of calcium carbonate and the basis for a strong eggshell. Research has shown that supplementing hens’ diets with zinc reduces defects, such as soft, broken or deformed shells. Manganese helps increase the degree of effective thickness and total thickness of eggshells. Copper synthesises collagen for egg production.
Mineral source stability and solubility explain the wide variation between how trace minerals interact with other feed ingredients and influence oxidation reactions in the bird. The availability of the mineral following intake and the bird’s ability to metabolise the mineral are both affected by the mineral source.
Trace minerals in feed are not inert but chemically active and many inorganic sources are highly soluble, disassociating during the digestion process. Once the soluble trace metal has separated from its ligand (commonly sulphate) this soluble ion (for example, Cu2+) can bond with dietary antagonists in the feed and in the bird’s gut. Replacing sulphate sources of trace minerals with hydroxy trace minerals can reduce this risk, as hydroxy minerals have a crystalline matrix structure, containing layers held together by covalent bonds which are not reactive or soluble until a pH of less than 4. This design keeps the minerals intact until they reach the proper area within the bird’s gastrointestinal tract. As each trace mineral responds differently to varied antagonists, this may explain an NRC report stating that the absorption coefficients of inorganic trace elements is only 5-20% absorption.
Trace minerals during late lay
A study conducted in Australia examined the use of different trace mineral types during late lay. A total of 600 45-week-old laying hens were fed one of two diets and exposed to cycling heat stress. Diets included sulphate-based minerals or hydroxy minerals. The birds were checked for daily feed intake, FCR, egg production, egg weight and egg mass.
Birds receiving the hydroxy trace mineral diet produced eggs with a higher mass, improved feed conversion and better hen-day egg production. Analysis of the heat-stress-related data indicated that use of hydroxy minerals modulated the effects of high temperatures, while birds receiving a sulphate-supplemented diet showed a negative correlation between daily egg production and maximum temperatures.
A study conducted at Texas A&M University tracked 506 birds for 51 weeks, assessing egg production, egg feed conversion, shell thickness and shell strength. Birds were given various diets including a hydroxy mineral control – 60 ppm zinc and 80 ppm manganese – with another treatment looking at the use of an additional 40 ppm zinc and 40 ppm manganese from hydroxy sources for weeks 48 to 52.
The findings showed that swapping oxide-based minerals for hydroxy minerals improved egg production and egg feed conversion (Figure 1) and, additionally, feeding higher levels of zinc and manganese in the late lay period can significantly improve eggshell thickness and breaking strength (Figures 2 and 3).
Extrapolating from the data, just changing the 2 mineral sources could reduce feed use by 3.4 tonnes for every million eggs produced.
Recommended premix nutrient levels (plus energy and macro materials) in laying hens’ diets when aiming to improve eggshell quality are presented in Table 1. These are complete levels. An increase in mineral levels is advised when eggshell problems are detected.
The dietary levels indicate a 110 g daily intake to be sufficient and can be adjusted when feed intake differs. As the trend towards extended laying phases continues, tailoring trace mineral supplementation to optimise availability, implementing split feeding strategies on the farm and assuring best practices for health management can help producers in their efforts to achieve more first-grade eggs, boost the lifetime productivity of their layers and support sustainability by cycling through fewer hens.
