The Potential of an Artificially Ultraviolet B Irradiated Hay as a Source of Vitamin D

Roughage can be a significant source of vitamin D in herbivore diets. The vitamin D content of forages can vary considerably and depends, among others, on plant species, plant maturity and climate fluctuations. Ultraviolet B (UVB) exposure causes conversion of provitamin D to vitamin D and thus represents the most important influence. To characterise this effect, two batches of a young-cut roughage of high hygienic and nutritional quality were exposed to constant artificial UVB-irradiation up to 192 h and were sampled at regular intervals. In previous studies, both ergocalciferol (vitamin D₂), cholecalciferol (vitamin D₃) and/or their metabolites have been detected in plants. Therefore, the present roughage was analysed for both D₂ and D₃. Whereas cholecalciferol never exceeded the detection limit of 0.25 µg/100 g, ergocalciferol increased from 2.22 µg to 19.15 µg/100 g dry matter in a time-dependent manner. Additionally, the values indicate an interplay with other factors not investigated in this study, for example, leaf-stem-ratio in the different samples. The high amounts of ergocalciferol in the experimental roughage after UVB-exposure confirm the value of hay as a vitamin D source for managed herbivores. The quick rise with time cautions against neglecting UVB-irradiation's effect on feed, both in practical as well as in experimental settings.