Can goats learn about foods through conditioned food aversions and preferences when multiple food options are simultaneously available?

Abstract

The objective of this study was to determine the extent to which herbivores are able to use conditioned food aversions and preferences to learn about the nutritional and toxic properties of food plants, when food options are simultaneously available. Conditioned food aversions and preferences have been invoked as important mechanisms by which free-ranging herbivores optimize food selection by learning about the negative and positive consequences of consuming particular plant species through a series of encounters. In most previous tests of this hypothesis, access to individual test foods has been separated in time, giving animals the opportunity to associate particular foods with particular post-ingestive effects. We presented animals with a more complex scenario by offering test feeds simultaneously during the learning phase. Such a test is an important step in assessing the importance of conditioned food responses as mechanisms by which herbivores learn to select an optimal diet. We first assessed the ability of goats to learn about test foods and their post-ingestive effects, when different conifer species were offered on separate days during the learning phase and animals were dosed with compounds eliciting positive, negative, or neutral post-ingestive effects. We then investigated the ability of animals to learn to make appropriate choices when all potential test foods were simultaneously available during the learning phase. The results confirmed that goats can learn to associate particular foods with particular post-ingestive effects and adjust their diet selection accordingly. The success with which animals made such associations was greatly reduced when they were presented with test foods simultaneously during the learning phase. When test foods were simultaneously available, animals tended to select a mixed diet, thereby reducing their opportunity to learn about the post-ingestive effects of particular foods. The results suggest that caution is required in extrapolating results of artificial conditioning experiments to free-ranging herbivores. The results also suggest that reducing the risk of toxicity through selection of mixed diets is an important component of a successful foraging strategy.

Sheep deficient in vitamin E preferentially select for a feed with a higher concentration of vitamin E

“…These results support the notion that ruminants do not instinctively detect the needed nutrients (or medicines) available in the feeds but they take time to learn about their feeds by associating the sensory properties of feeds with post-ingestive feedbacks (Provenza and Balph, 1990). The association, by animals, of post-ingestive effects with food flavours has been identified as a means through which herbivores learn about the consequences of feeds (Duncan and Young, 2002). Learning about components of the feedbase is an important tool that herbivores use to modify foraging behaviour (either to prefer or to avoid feeds) in order to cope and adapt quickly to the changing internal and external environments for the achievement of nutritional homoeostasis (Villalba et al, 2006a;Howery et al, 2010).…”

“…In this study, where sheep were confined in individual pens and social interactions between animals were restricted, the sheep had to learn about their feeds by themselves and this may have delayed their learning process. In addition, recent research has demonstrated that process of learning about diets is delayed when experimental procedures become complex (Duncan and Young, 2002) by offering several feeds simultaneously (Duncan et al, 2007) and by increasing the number of consequences associated with the ingestion of feeds (Ginane et al, 2005). The complexity of the feeding procedure in this study and the novelty of flavours to the sheep might have contributed to the delayed association of the flavours with the post-ingestive signals.…”

Self-medication and homeostatic behaviour in herbivores: learning about the benefits of nature’s pharmacy

“…For instance, lambs and goats fed diets low in energy and protein prefer flavoured lowquality foods previously paired with intra-ruminal infusions of energy (starch, propionate, acetate) or nitrogen (urea, casein, gluten), respectively Provenza, 1996, 1997a, b andArsenos et al, 2000;Duncan and Young, 2002). Given pre-loads of energy or nitrogen, lambs prefer flavours previously paired with nitrogen or energy, respectively, during the ensuing meals (Villalba and Provenza, 1999).…”

Food sensory characteristics: their unconsidered roles in the feeding behaviour of domestic ruminants

“…Studies concerning the food learning theory have proved that ruminants, as other animals, can associate sensory characteristics and post-ingestive consequences during food learning processes (Provenza, 1995;Forbes and Provenza, 2000). They can learn both positive (Villalba and Provenza, 1997;Duncan and Young, 2002) and negative (Zahorik et al, 1990) consequences when presented experimentally with simple conditioning procedures (i.e. one pre-and post-ingestive association at a time).…”