Vitamin D content in donkey milk: preliminary results

Vitamin D is an essential nutrient that plays a crucial role in the calcium homeostasis and bone metabolism and also acts as an hormone. Humans synthetize most of their vitamin D requirement from sunlight. However, an oral intake of vitamin D may be an important source in winter, when the UVB-related synthesis is limited and for people who may not be exposed to sunlight. However, only a few foodstuffs, mainly of animal origin, provide a considerable source of vitamin D thus limiting the possibility of fulfilling the requirements of this vitamin. Milk contains above all vitamin D3 and D2. Although there are several studies on the content of vitamin D in bovine milk, there is little information regarding donkey milk. Therefore, the aims of this paper is to carry out a preliminary evaluation of the vitamin D content in donkey milk and to investigate its seasonal modifications. Raw bulk milk samples were collected for 10 months, every 15 days, from a dairy farm that produces donkey milk for human consumption. All the samples were analysed for chemical composition and vitamin D content by HPLC after extraction by the partially modified Silva et al (1992) method. Donkey milk showed a higher vitamin D content (2.31 lg/100ml ± 0.83) compared to bovine and human milk. Vitamin D in donkey milk showedseasonal variations as reported in cows. In particular, vitamin D had a higher concentration in the summer than in winter, probably due to the different sun exposure of the animals. In conclusion, donkey milk shows a considerable vitamin D content, which could be useful to meet the deficiencies of this vitamin in humans. Further investigations are necessary to improve the vitamin D content in donkey milk through increasing its endogenous synthesis and transfer in milk and to clarify other variability factors.