In the domestic environment, horses are often presented with foods to which they are not evolutionarily adapted, such as low fibre pellets. Horses may not have the ability to learn the consequences of consuming unnatural foodstuffs and adapt their selection accordingly. This study aimed to investigate the horse’s feeding preferences when presented with concentrate pellets differing in nutrient content. Using a choice test, the relative preferences of 12 horses for mint and garlic, in iso-caloric diets, was first assessed over 29 meals. A mint preference, calculated as the proportion of mint in the total food intake, was shown by 11 horses. The horses were then divided into two groups, approximately balanced on the basis of mint preference. Group A was exposed to a choice of a mint-flavoured lower energy food or a garlic-flavoured higher energy food, while group B was exposed to mint-flavoured higher energy food and garlic-flavoured lower energy food for 29 meals. Next the flavours were presented in iso-caloric foods, initially for 10 meals, then a further 40, before the flavour-energy pairings were reversed for 30 meals. A final iso-caloric test was carried out for 30 meals. Both groups showed a preference for mint in the initial iso-caloric choice test but no such preference was shown in later iso-caloric tests. Both groups showed a higher preference for mint when paired with higher energy (proportion of mint intake to total intake was 0·75 (s.e.0·02) and 0·73 (s.e.0·02) for A and B respectively). Group B also showed a preference for garlic when paired with higher energy (proportion of mint intake: 0·32, s.e. 0·02) whilst group A showed a significant decrease in preference for mint when paired with lower energy (by 0·21 (s.e. 0·03), T = 6·88, P 0·01). The results suggest that horses can select a higher energy diet over a lower energy one and that horses can form associations between foods and their nutritional composition, even if they do not resemble those found in their natural environment.