The influence of odour, taste and nutrients on feeding behaviour and food preferences in horses

While it has been established that nutrients and flavours (odour, taste) play an important role in diet selection by horses, previous studies have not always clarified what type of flavouring (e.g. non-nutritive or nutritive) was used. Therefore, the objective of this study was to determine the influence of distinct food characteristics (odour, taste, nutrients) on the preference of horses using different preference testing protocols. This experiment consisted of three phases; adaptation (P1), two-choice testing (P2) and multiple-choice testing using a chequerboard design (P3). Four pelleted diets equal in digestible energy, but contrasted in crude protein (LP; 14% and HP; 27%) and added non-caloric (natural) sweetener (i.e. LP, LP+, HP, HP+) were consecutively fed to each of sixteen adult horses. The diets were paired with four non-nutritive odours (coconut, banana, cinnamon, spearmint), with a unique odour and diet combination allocated to each group of four horses. In P1, each diet was presented solely for five days to facilitate pre and post-ingestive associations; in P2 a two-choice test was conducted with four diet combinations (contrasts) over three days; and in P3 the four diets were presented simultaneously in a checkerboard fashion over a 5-day period. Feed intake, bucket/zone visits and time spent foraging or moving were recorded. The key findings of this study were: (1) In P1 an initially large variation in intake was recorded with only some horses showing a neophobic response to a new odour/food, but variation declined within 2 days with the majority of the horses consuming over 90% of the diets. (2) Nutrient (HP) content appeared to be the main driver for diet intake in P2 (P < 0.05) and P3 (P < 0.001). (3) Taste appeared to be the secondary determinant of preference and this was more evident with the LP diet. (4) Consumption of diets linked to sweet aromatic odours (banana and coconut) was greater in P3 (P < 0.001). (5) The multiple-choice test, which was designed to promote patch foraging behaviour, showed more explicit differences in diet ranking compared to the two-choice test. These findings confirm previous studies that horses prioritise diets on nutrients, but this is the first equine study that shows the positive influence of a non-caloric natural sweetener on diet choice. A non-nutritive sweet taste or odour appears to encourage diet intake by horses, but more research is needed that examines different sweeteners coupled with and without odour and/or dietary nutrients and its long-term effects on food intake. (C) 2016 Published by Elsevier B.V.