There are three biologically relevant forms of vitamin D used in animal feed supplements:
1. Vitamin D2 (Ergocalciferol)
This plant form is created when fungi or plants are exposed to UV light. Although useful, the bioavailability of D2 in animals is lower than that of D3. Therefore, this form is less often used in high-quality supplements.
2. Vitamin D3 (Cholecalciferol)
Vitamin D3 is produced in the skin of animals under the influence of sunlight. This form is more powerful and biologically active than D2. In animal feed supplements, D3 is therefore the most commonly used form, especially in pets, horses, cattle and poultry.
3. 25-Hydroxycholecalciferol (HyD)
This is a direct metabolite of D3 and is absorbed faster and more efficiently in the body. HyD does not need to be converted in the liver first, which ensures a faster effect. This form is ideal for young animals, animals in stressful conditions or with an increased need for calcium.