Behavioural mechanisms of diet selection by horses

Abstract

Compared to ruminants little is known about how horses modulate food intake and link the sensory properties (e.g. smell, taste) of foods with its post-ingestive consequences (negative and positive). While it has been suggested that horse’s foraging preference may be largely influenced by sensory input (e.g. volatiles, taste), because of hindgut fermentation, it has been established that horses are able to differentiate and select familiar foods (e.g. concentrates and hay) based on the nutritional content. However, there is a lack of knowledge of behavioural mechanisms related to olfaction, gustation and somatic sensory perception and their effects on diet selection by horses. In particular little is known of how these mechanisms may operate in pastured environments where horses are often exposed to a variety of plant patches, including familiar and novel species that may differ in flavour, nutrient concentrations and plant toxins throughout the year. The aim of this thesis was to further develop an understanding of behavioural mechanisms influencing diet selection by horses and in particular to determine how they identify and select amongst a variety of foods (familiar and/or novel) using sensory perception and post-ingestive feedback. A series of experiments examined: (1) The selection of familiar and novel forages using a checkerboard design to simulate patch foraging conditions. As changes in dietary preferences are largely influenced by the nutritional requirements of the animal and palatability of a food, it was of interest to investigate the effect of the nutritional status (energy intake) on novel forage selection by horses; (2) The influence of orosensory (smell) stimuli and post-ingestive feedback in the recognition of novel foods by horses. This was achieved by assessing the acceptance of a novel food with a familiar odour or with contrasting crude protein levels; and (3) The influence of different food characteristics i.e. nutrients, odour and taste, on the voluntary intake and preferences of horses exhibited when a number of foods were offered simultaneously (i.e. Smörgåsbord). In each experiment between 11 and 16 horses of Thoroughbred, Standardbred or Australian Stock Horse breeds were used. The findings of this thesis suggest that horses can respond to the nutritional content of foods, even if these are novel. There was a greater acceptance and intake of novel foods that contained a higher level of crude protein, and energy intake seemed to have a lesser impact on the intake of novel foods. It was also observed that the acceptance and intake of a novel food was largely influenced by the orosensory characteristics (smell, taste, texture), and possibly an individual’s experience. The thesis also shows that horses display patch foraging behaviour sampling from all foods on offer. When familiarised with diets horses clearly rank these based on nutrients, followed by taste and then odour. Further studies should assess the adoption of multiple-choice tests and nutritional geometric models to enhance our understanding of diet selection patterns by horses in different environments. In particular how individual animals may regulate the intake of multiple nutrients to meet dietary requirements. Whilst macronutrients may be the main driver for diet selection - the impact of the sensory perception on diet choice cannot be disregarded. This thesis highlights that familiar odour and taste cues could be applied in equine feeding management to increase food acceptance when forages/foods are scarce, during introduction of new foods or forage batches or when horses are moved to different environments.