1. bone mineralization

Lack of vitamin D3 or lack of its metabolites can cause obstacles to the calcification process, which can lead to weak bones, especially in fast-growing chickens. The so-called "weak leg syndrome" in commercial broiler flocks is due to a certain extent that the biosynthesis of calcitriol is insufficient to meet the physiological needs of bone development. The most common symptoms in broiler flocks are tibial chondrodysplasia and femoral degeneration.Cage layer fatigue in commercial layer flocks is a direct consequence of damage to mineral metabolism. It is the result of insufficient minerals in the long bones of the hens before they reach the peak of laying. Cage layer fatigue occurs in older flocks It is caused by insufficient calcitriol synthesis. The affected chicken flocks characteristically produce eggs with inferior eggshell quality and exhibit low egg production to compensate for the loss of body calcium reserves.
 

2. Reduced hatchability

Breeding hens only transfer vitamin D3 into the egg yolk to meet the needs of embryonic development, and do not transfer vitamin D3 into the egg yolk. The embryo's kidney produces enzymes and ascorbic acid, which convert vitamin D3 into calcitriol. When the hen lacks vitamin D3, the amount of vitamin D3 transferred into the egg yolk will be reduced, thereby indirectly reducing the synthesis of calcitriol. If a sufficient amount of calcitriol is not synthesized, the embryo can not use the calcium and phosphorus reserves in the eggshell and regulate the calcification process. Poor calcification of embryonic bones can lead to soft beaks, and when the chicks are hatched, the chicks cannot peck their shells.
 

3. Growth rate and feed utilization

The adverse effect on growth rate and feed utilization rate is mainly due to the damage of long bones caused by mineral metabolism obstacles, which in turn will affect the chicken's exercise ability, which is not conducive to its search for feed and drinking water. The most sensitive stage for broilers is within 3-4 weeks of age, because this stage is the stage where broilers grow the fastest and use the most effective feed.
 

4. Decline in egg production

Commercial laying hens will experience a sudden and sharp drop in laying rate due to the short-term exhaustion of body calcium reserves after the peak of laying. Such a drop in egg production rate can last for 3-4 weeks, and then it can gradually return to nearly normal with the reconstruction of body calcium reserves.
 

5. Hypocalcemia

Insufficient intake of vitamin D3 will lead to a decrease in calcitriol synthesis, and a decrease in plasma calcitriol level will harm the calcium balance in the body and cause hypocalcemia. This disease has been observed in commercial layer flocks and breeder flocks, and is characterized by ataxia and paralysis.
 

6. Embryonic death

The skeletal development of the embryo is directly related to the vitamin D3 status of the breeding hens, especially the metabolites of vitamin D3, which are preferentially deposited in the egg yolk, so as to meet the needs of vitamin D3 for embryo development. During embryonic development, vitamin D3 in the egg yolk is converted into calcitriol in the embryo's kidney. Calcitriol can promote the body's use of calcium and phosphorus in eggshells, and regulate the calcium balance in the body and the calcification process of embryonic bones.