This study aimed to evaluate essential traits of donkey’s milk and cow’s milk kefir during storage for 28 days at + 4 °C. The results showed that the pH decreases significantly during fermentation from 6.75 ± 0.045 to 4.22 ± 0.062 for cow’s milk and from 7.01 ± 0.011 to 4.28 ± 0.030 for donkey’s milk. Acidity values increased significantly during storage from 63 ± 2.08 °D to 170 ± 2.80 °D for cow’s milk and from 92 ± 1.0 °D to 163 ± 1.30 °D for donkey’s milk (p < 0.05). A significant variation in total solids was observed during storage. Stability in protein content was observed for kefirs during storage time. While the level of lactose decreased significantly during storage, the fat content did not vary in kefirs during storage time at 4 °C. For microbiological properties, donkey milk kefir presents a significant difference (p < 0.05) compared to bovine kefir. Donkey’s milk always contains the lowest average germs, suggesting a better microbiological quality than cow’s milk samples. The fermented milks showed an interesting antioxidant activity measured by the DPPH and ABTS assays, which were improved during storage. The Aeromonas hydrophila was the most sensitive bacterium to the action of kefir samples. Results from the sensorial test show that participants prefer kefirs freshly prepared than those stored after 28 days at 4 °C. In conclusion, related to its unique bioactive activities and microbiological properties, donkey’s milk could be an interesting kefir fermentation source materials alternative.
