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Understanding the Role of the Skeleton in Egg Production. Part 3

13 May 2014

Hy-Line International

The third and final part of this Technical Update discusses the roles of nutrition and disease in the formation and maintenance of a healthy skeleton of pullets and laying hens.


Feed consumption and nutrition always go hand in hand. All diet formulations must be based on feed consumption to ensure proper intake of the critical nutrients. As a result, all Hy-Line diets are recommended on the basis of total daily feed intake. Focusing on calcium and available phosphorus, as examples, the Hy-Line Brown and Hy-Line W-36 need to consume the following amounts each day in her ration:

 Peaking dietLay diet #2Lay diet #3Lay diet #4
 Hy-Line BrownHy-Line W36Hy-Line BrownHy-Line W36Hy-Line BrownHy-Line W36Hy-Line BrownHy-Line W36
Calcium (g/day) 4.00 4.00 4.40 4.20 4.70 4.35 4.90 4.50
Available phosphorus (mg/day) 440 500 400 480 360 460 350 400

Attaining the required levels for these nutrients is significantly dependent on daily feed consumption. A sample calculation for a bird recommended to have 4.00 grams of calcium per day and with an observed feed consumption of 95 grams is as follows:


Limestone particle size is also important for optimum shell quality. Pullets should have fine particle calcium, ideally less than 1.1mm (1100 micron) average. It is best to use limestone flour for pullets as the smaller particles are more easily absorbed.

Layers should ideally receive a 50:50 ratio of large and fi ne particle limestone at the start of lay and transition to a 70:30 ratio (large: fine) by the end of lay. Changing the particle size ensures that more calcium will be available at night from the diet instead of from the bone.

Further measures to increase night calcium availability include ensuring a last feeding one to two hours before lights are turned off and adjusting the feeding regime to 40 per cent in the morning and 60 per cent in the afternoon.

The large particle fed during lay should be around 2mm to 4mm (2,000 to 4,000 microns) average size with an ideal 3mm (3,000 micron) size. When calcium particle size is above 3.5mm (3,500 micron), the solubility rapidly decreases. If the hen is not effectively absorbing the calcium in the diet, she can be deficient (even with an accurate 'calculated value' of the ration).

Additionally, the source of limestone should be checked. Low calcium content limestone (less than 37 per cent) may contain other minerals that reduce the solubility and, therefore, the calcium availability. Depending on geological formation, different limestone structures exist which may also affect solubility and availability.

Phosphorus intake is similarly calculated, although the requirement definition is more complex due to different systems used to express available and digestible phosphorus. Care needs to be taken that requirements and the availability matrix are being expressed on the same system. There are ongoing projects in the US and the EU to review the phosphorus nutritional systems and create a more universal standard.

The use of phytase enzymes must be considered when formulating the diet. Phytase is an important tool in reducing both the cost and environmental burden of animal feeding; however care needs to be taken when applying matrix values. Matrix contributions need to be accurate for the phytase being used, the diet in which it is being used and the dosage being applied. The matrix contribution must not exceed the concentration of phytate phosphorus potentially available for release. This differs by phytase source, inclusion rate and the ingredient makeup of the diet.

Vitamin D3 (cholecalciferol) is a critical nutrient that aids in calcium and phosphorus uptake in the small intestine, bone mineralization, inhibition of calcium excretion in the urine and immune system modulation. Vitamin D is typically included in the feed as vitamin D3. It is absorbed in the small intestine and converted to 25-hydroxycholecalciferol in the liver. This metabolite is then converted to the active form of 1, 25-hydroxycholecalciferol in the kidneys. In addition to vitamin D3, there are commercial products that contain 25-hydroxycholecalciferol which cut down on a conversion step in the hen and have a higher biological value.

Other dietary factors are also important to consider in the efficiency of bone calcification and eggshell formation. This includes the acid base balance of the diet (or dietary electrolyte balance - DEB), vitamin K, zinc, copper, iron, manganese and magnesium. Some essential amino acids which are often limiting in laying diets (valine and arginine) may be important due to their role in calcium transportation and formation of the bone matrix.

Feed Consumption

Consumption volumes at the start of lay change quickly; for example, the Hy-Line Brown eats 80g to 90g per day at the start of lay and soon eats 110g to 115g per day in about four to six weeks at peak production. Often, feed mills may only have one Peaking Diet that is formulated for 110g to 115g per day intake for brown birds and 100g to 105g per day for white birds.

When intake at the start of lay is only 80g to 90g per day, there will be deficiencies of 20 to 25 per cent in calcium, phosphorus, essential amino acids and other nutrients. Creating a diet matrix can help ensure that the correct dietary formulation is used. Not all diets will be used, but it will simplify ordering feed for a farm.

Daily feed consumption
 Peaking dietLay diet #2Lay diet #3Lay diet #4
90g per day X      
95g per day        
100g per day X      
105g per day        
110g per day X X X X

The bird is still growing until about 32 weeks and is adding muscle mass and bone density. If there are deficiencies in the diet, the impact may not be immediate but can be felt late in lay when hen body reserves have been depleted.


Nutritional issues are usually the primary cause for decreased skeletal integrity and resulting shell quality problems. However, many subclinical respiratory and enteric diseases may have the same effect.

A decrease in feed consumption or nutrient absorption can have a dramatic impact on shell and bone quality as described previously.

Bacterial, viral or protozoal pathogens may cause temporary or permanent damage to the intestine and reduce the absorption of key nutrients. The duodenum in particular is the location in the intestine where calcium is actively absorbed in response to increased demand under hormonal influence involving vitamin D3.

Diseases such as focal duodenal necrosis can damage the duodenum and may decrease the efficiency of absorption. Additionally, there are many diseases that cause shell quality issues by affecting the oviduct, including infectious bronchitis, Newcastle disease, Mycoplasma synoviae, egg drop syndrome (EDS) and avian influenza.

Actions When Skeletal Issues Are Identified

During routine handling, if soft bones or crooked keels are detected during lay, there are steps that can be taken to correct the issue.

General measures

These should only be used until specific measures can be taken.

  • Add water-soluble vitamin D3 or 25-hydroxycholecalciferol to the drinking water once or twice a week to increase calcium and phosphorus metabolism
  • Add 2- to  4-mm particle limestone or oyster shell to increase the level of calcium in the gizzard overnight and provide calcium for egg shell and strengthening bones.
  • Review, and if necessary increase, the level of available phosphorus in the diet to help with bone strength and metabolism.

Specific measures

  • Verify or determine feed consumption of the flock
  • Check the feed formula to ensure the correct amounts of calcium, phosphorus and vitamin D are specified
  • Ensure that the daily levels of consumption meet the dietary needs of the hen
  • Send feed samples for analysis to determine if calcium and total phosphorus levels are consistent with formulated values. When sampling, it is important to obtain a representative sample of the feed to minimise sampling error. A standard procedure for collecting accurate feed samples is to collect multiple sub-samples and mix them together. Use a portion of this mixed sample to send in for analysis.
  • If a deficiency is found, work with the feed mill to prepare the correct formulation based on daily consumption
  • Check the flock to see if there are any disease issues that are minimizing absorption or reducing feed consumption.

Ensuring good skeletal development from rear into lay through best management and nutritional practices is essential to reach the genetic potential of the Hy-Line layer.

Understanding the importance of the skeleton in laying hen production will help producers implement best practices. Formulating the diet to consumption and monitoring the skeletal quality will create the environment to attain the best and most economical production.

Further Reading

Go to our previous chapter on this story by clicking here.

May 2014

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