What happens with low calcium diets in laying hens?
Egg production in commercial laying hens has continuously improved in the past decades thanks to advances in modern breeding technologies.
Developing persistent “long-life” layer strains, is a major breeding goal. Obtaining hens that can produce 500 eggs or more within a 100-week production cycle (Bain et al., 2016).
The variety of “long-lived” layers can:
- Increase productivity
- Reduce the number of male chicks killed
- Optimize the use of resources, such as: land, water and food.
- Reduce waste(Bain et al., 2016).
Osteoporosis, or layer fatigue, is a common degenerative metabolic bone disease in caged laying hens.
Some of the disease’s characteristics and its impact on egg production and health include:
1- reduction of egg production and shell quality
2-increased bone loss,
3-degradation of bone microstructure,
4- bone fragility and increased fracture ratio
5-development of osteoporosis which can eventually lead to paralysis and in some cases mortality.
The majority of commercial laying hens worldwide are currently housed in conventional cages. Such is the case for China, the United States, India, Japan, Mexico, Brazil, Russia and Turkey, which are amongst the top 10 producing countries.
Skeletal problems are worsened with the extension of the egg production period in “long-lived” caged layers. This is due to the fact that:
A longer egg production period, requires greater amounts of Ca for the formation of the eggshell. Which in turn leads to the deterioration of bone quality.
Calcium is an essential mineral that must be absorbed from feed in order to maintain bone hemostasis and ensure normal cell function.
In laying hens, Ca does not only play an important role supporting bone remodeling, a lifelong process that balances activities between osteoblasts and osteoclasts. As it also is a critical component in eggshell formation.
Bones represent important Ca reservoirs. Where this mineral can be deposited and removed depending on the needs of the organism. Approximately 2.0 to 2.5 g of Ca are required to synthesize an eggshell within a 20 to 28 h period.
In order to meet eggshell formation requirements, an imbalance in bone remodeling occurs over time. With increased bone resorption, that leads to bone weakness or osteoporosis in laying hens. Also referred to as layer fatigue.
In the commercial poultry industry, regular layer diets contain 3.5% to 4.7% Ca.
The Ca found in the eggshell comes mainly from the diet through intestinal absorption. However, approximately 25% to 40% of Ca is obtained from resorption. This is particularly true during dark periods when hens temporarily stop eating( Ripe and Aygun, 2016 ).Hens experience physiological changes regarding Ca metabolism during sexual development.
Before sexual maturity, hens have 2 types of bones: cortical bone and spongy bone. After reaching sexual maturity, hens acquire a third type of bone, also known as medullary bone, which acts as a Ca reservoir for the formation of the eggshell. It is from this source that Ca is quickly released during laying.