Horses show an aversion to bitter flavor experimentally highlighted using oral quinine solutions. Some vitamins B and minerals bitterness could decrease the acceptability of nutritional supplements. This study defined the effect of a lucerne versus water support on the aversion threshold of horses to vitamin B3 in comparison to quinine. Twelve horses were used to test 5 final concentrations of quinine or vitamin B3 (0, 10, 20, 40, 80mg/100mL water) in ascending order, with 6 horses for each molecule. Final concentrations were similar in water and lucerne supports. Horses had no access to food or water one hour before the tests. First, 850mL water support was offered, then a mixture of 300mL water + 100g lucerne support. After 10min, the support was removed and weighed to calculate the proportion ingested. For each molecule, the ingested proportions depending on the concentrations and the supports were compared using the non-parametric Kruskal-Wallis test. The same analysis was performed for comparing low (0+10) and high (40+80) groups for better significance (P < 0.05). The pair comparison was made with Dunn's test (Bonferroni correction). Our data (table) confirmed the quinine aversion threshold given in water between 40 and 80mg/100mL. This threshold was unchanged on lucerne support. Whatever the support, the vitamin B3 aversion threshold was higher than 80mg/100 mL, which on its own cannot explain the bitterness of supplements. Testing the additional effects of different vitamins or minerals would help understanding how horses perceive bitterness and accept feeding supplements. We observed a trend for a higher consumption of both molecules fed in lucerne suggesting a masking effect on the bitter taste. In contrast to all other horses, one horse was not sensitive to bitterness and drunk or ate the whole amount of water or lucerne mixture whatever the quinine concentrations. This reminds the polymorphism leading to disorders in human sensorial perception.