Abstract Vitamin D 3 (Vit D 3 ) and 25(OH)D 3 are used as dietary sources of active vitamin D (1,25(OH) 2 D 3 ) in pig husbandry. Although acting primarily on intestine, kidney and bone, their use in pig nutrition has shown a wide range of effects also in peripheral tissues. However, there is an ambiguity in the existing literature about whether the effects of Vit D 3 and 25(OH)D 3 differ in attributing the molecular and phenotypic outcomes in pigs. We searched Web of Science and PubMed databases concerning the efficacy of Vit D 3 in comparison with 25(OH)D 3 on pig physiology, i.e. reproductive capacities, growth performance, immunity and bone development. Dietary intake of Vit D 3 or 25(OH)D 3 did not influence the reproductive capacity of sows. Unlike Vit D 3 , the maternal intake of 25(OH)D 3 significantly improved the growth performance of piglets, which might be attributed to maternally induced micronutrient efficiency. Consequently, even in the absence of maternal vitamin D supplementation, 25(OH)D 3 -fed offspring also demonstrated better growth than the offspring received Vit D 3 . Moreover, a similar superior impact of 25(OH)D 3 was seen with respect to serum markers of innate and humoral immunity. Last but not least, supplements containing 25(OH)D 3 were found to be more effective than Vit D 3 to improve bone mineralisation and formation, especially in pigs receiving basal diets low in Ca and phosphorus. The insights are of particular value in determining the principal dietary source of vitamin D to achieve its optimum utilisation efficiency, nutritional benefits and therapeutic potency and to further improve animal welfare across different management types.