Vitamin D plays many important functions in the animal, as it is necessary for proper calcium (Ca) absorption and use in different biological processes. The aim of several recent experiments with poultry was to evaluate the efficacy of different forms and levels of vitamin D3 in the diets for broiler chickens and laying hens. The results of these studies are presented and discussed in this review paper. Based on these results, the modern high-performing poultry requirement for supplemental vitamin D to maximise mineral digestibility, performance and immunity indices, bone health, and eggshell quality is about 3,000 IU/kg, i.e. much higher than NRC (1994) recommendations. The results of several recent poultry studies have shown that 25-hydroxycholecalciferol (25-OH-D3) is more efficient in commercial poultry nutrition than the basic form of vitamin D3 (cholecalciferol).
