Vitamin D is a fat-soluble vitamin that can be supplied through the diet or produced in the body through sunlight exposure, where precursors in the skin are converted into the active form. There are several compounds with vitamin D activity; for example, Vitamin D2 (ergocalciferol) is found in plants, while Vitamin D3 (cholecalciferol) is found in animals. In poultry, Vitamin D3 is about 30 times more active than Vitamin D2, which is why Vitamin D3 is used specifically in poultry diets.
After intestinal absorption, Vitamin D3 undergoes conversion through the liver and kidney pathways and is transformed into its biologically active metabolic form, 1,25-dihydroxycholecalciferol. Under conditions such as disease, intestinal disorders, or the presence of stress factors, birds may not be able to absorb and convert Vitamin D3 into its active form sufficiently.

In chicks, Vitamin D deficiency is associated with the following:

Reduced calcium and phosphorus deposition in bone, leading to progressive bone softening and bending—especially in the shank and thigh—along with beak softening

Enlargement of the knee and shank joints and stunted bone growth

Leg dragging while walking

Deformity of the rib cage and beaded ribs (“rosary” appearance)

Reduced growth rate

Weakened immune response

This Vitamin D3 product from Weishi (China) is supplied as a yellow powder with a potency of 500,000 IU per gram.