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Highlights (for review):-The effect of odour, taste and nutrients on diet intake by horses was examined.-Two-choice and multiple-choice tests were used to evaluate feeding behaviour.-Nutrient content appeared to be the main driver for diet choices.-Taste appeared secondary to nutrients in determining the diet selected.-The multiple-choice test was able to more clearly differentiate in diet ranking. AbstractWhile 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)

Compared to ruminants little is known about how horses modulate food intake and learn about flavour-to-post-ingestive consequences. While it has been suggested that due to hindgut fermentation horse's foraging preferences may be largely influenced by sensory input (e.g. volatiles), it has been established that horses are able to differentiate and select familiar foods (e.g. concentrates and hay) based on nutritional content. Yet it remains unclear how this translates to the acceptance of nutritious novel foods (NF). Therefore, the influence of food cues and nutrient composition on NF acceptance were examined in two experiments using 11 adult mares. In experiment 1, we investigated the influence of a familiar odour (FO) on the acceptance of a nutritious NF and in experiment 2, we determined if horses have the ability to select nutritious NF based on the nutritional content, regardless of sensory preferences. In experiment 1 horses received identical NF in a two-choice test with one of the choices being masked with a FO over a 9-day period. In experiment 2 horses were offered a high or low protein option of an otherwise identical NF in a two-choice test in which the NFs were paired with two unfamiliar flavours (odours). The two-choice test lasted for 14 days and the flavour-protein pairing was switched after 7 days. NF intakes were recorded over a 10 min test period on each test day and analysed using Bayesian hierarchical models. The results of experiment 1 indicate that a FO had a strong positive influence on the NF intake for the first 5 days (90-100% of total consumption and strong evidence for nonzero temporal effects (Bayes factor B 12 =110)). This was followed by a more even distribution of intake for the remaining period. In experiment 2 horses had a greater intake of high protein NF regardless of the flavour on days 4, 6 and 7 (80-87% of total consumption) and this continued after the switch over (Day 9 to 14; 57-81% of total consumption). However, 4 out of 11 horses showed neophobia throughout the testing period, which could have been associated with the novel odours as horses scanned the buckets with little to no sampling. The results suggest that pre-ingestive cues (e.g. smell, taste) of foods play an important role in diet selection and that a FO can increase the acceptance of NF. This new knowledge could be applied by the horse industry to encourage the consumption of new food or forages by horses.

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The horse-keeping profile in this study should be considered in the public communication of guidelines as well as interactions between veterinarians and clients.