Serum vitamin D concentrations in rabbits (Oryctolagus cuniculus) are more affected by UVB irradiation of food than irradiation of animals

Mäkitaipale J, Opsomer H, Steiner R, Riond B, Liesegang A, Clauss M, Hatt J-M.

Vet J. Published online May 28, 2024. doi:10.1016/j.tvjl.2024.106149.


Rabbits kept under ultraviolet B (UVB)-irradiation respond with increasing serum vitamin D (25(OH)D) concentrations, but it is unknown whether irradiation of the animals or their feed contributes more. Twenty-four New Zealand White rabbits were divided into three groups for a four-week period: the control group (C) received no UVB-exposure and non-irradiated hay (ergocalciferol (vitamin D2) concentration 2.22 µg/100 g dry matter). The direct exposure group (D) was provided with 12 hours of UVB-irradiation daily and fed the same hay as group C in shaded areas to prevent UVB-irradiation thereof. The indirect exposure group (I) did not receive direct UVB-irradiation but was fed hay of the same batch that was exposed to 12 hours of UVB-irradiation (vitamin D2 6.06 µg/100 g dry matter). Serum 25(OH)D2, 25(OH)D3, ionised calcium, total calcium, phosphorus, and magnesium concentrations were measured weekly. There was no systematic effect on serum mineral concentrations. The serum 25(OH)D2 concentrations were significantly higher in group I compared to groups C and D from the second week onwards. 25(OH)D3 concentrations increased only in group D, with significant differences to both other groups from the third week onwards, yet at lower magnitudes than the noted increase of 25(OH)D2 in group I. Total 25(OH)D concentrations were highest in group I, intermediate in group D and lowest in group C.

Serum total 25(OH)D concentration was more affected by UVB-irradiation of rabbits’ feed than by direct irradiation of the animals themselves. If rabbit serum total 25(OH)D concentrations should be managed, diet manipulation rather than animal UVB-exposure appears to be more effective.