Induction of low-nutritious food intake by subsequent nutrient supplementation in sheep (Ovis aries)

Abstract

Acceptance of and preference for a particular food depends not only on its intrinsic (e.g. nutritional) properties but also on expected or recent food experiences. An instance of this type of phenomenon has been called induction effect, which consists of an increased intake of a type of food when it precedes a hedonically preferred food in a sequence familiar to the animal, relative to controls that have access only to the less-preferred food. The purpose of our study was to assess intake induction of a low-nutritious food when followed by different high-nutritious supplements in sheep (Ovis aries). In this experiment, we ran a supplemented phase where animals fed oat hay (a low-nutritious food) in the first part of the daily feeding sessions followed by a supplement with either a high (soya bean meal; group GS) or a low (ground corn; group GC) protein-energy ratio in the second part ate more oat hay than controls that were fed oat hay in both parts of sessions (group GH). In addition, supplemented animals presented a stronger preference for oat hay over alfalfa hay than controls in a subsequent choice. When all animals received no food in the second part of the sessions (Non-supplemented phase), intake of oat hay converged to the control's intake level in all the groups, suggesting that the presence of supplements after access to oat hay was responsible for intake induction. Lastly, we repeated the supplemented phase with a different control group where animals received oat hay in the first part of the sessions and no food in the second part (group NF), thus equalizing groups in terms of the time of access to oat hay in a session. Groups GS and GC still developed higher intake of oat hay than group NF. In both supplemented phases of the experiment, we estimated animals' daily metabolizable energy (ME) and crude protein (CP) intake. CP intake was higher in group GS than in groups GC, GH and NF, but there was no difference between group GC and the controls. In turn, groups did not differ in ME intake in the First supplemented phase, and only group GS presented higher ME intake than the rest of the groups in the Second supplemented phase. Therefore, a nutritional account of the present induction effect seems insufficient. We propose that a learned association between oat hay and the post-ingestive feedback from the subsequent high-nutritious supplements underlay sheep's intake induction and increased preference for oat hay.

Use of Unpalatable Forages by Ruminants: The Influence of Experience with the Biophysical and Social Environment

“…For instance, intragastric infusion of nutrients can condition a preference towards a low-quality feed (e.g., wheat straw) in sheep [ 58 , 59 ]. Sheep showed enhanced intake of, and developed a preference for, oat straw when its consumption was immediately followed by consumption of nutritious food (e.g., soybean meal or corn) [ 6 , 7 ]. In the latter studies, the design of the experiments suggested that a learned association between oat straw and the post-ingestive feedback from the nutritious supplements was the fundamental reason for the sheep’s intake induction and increased preference for oat straw.…”

“…Animals deal with this problem through evolved morpho-physiological mechanisms [ 1 , 2 ] and by means of experience. Experience can alter both the morpho-physiological and psychological (learning) mechanisms to better cope with unpalatable forages [ 3 , 4 , 5 , 6 , 7 ].…”

“…On the other hand, the context in which animals experience unpalatable forages can result in learned associations that enhance consumption of and preference for them [ 20 , 21 , 22 ]. For instance, sheep can develop a preference for either low-quality [ 6 , 7 ] or toxin-containing [ 23 ] food when this food precedes a highly nutritious and preferred food in a sequence familiar to the animal.…”

Assessing the impact of supplements, food aversions, and silica on medusahead (Taeniatherum caput-medusae (L.) Nevski) use by sheep

“…The intake induction effect consists of increased consumption of the low-valued meal relative to controls where animals do not have access to the preferred food (e.g., Flaherty and Grigson, 1988;Freidin et al, 2011Freidin et al, , 2012. This induction may be a consequence of animals partially attributing the postingestive effects of the preferred food to the low-palatable food because of the close temporal proximity between both ingestive events (Yearsley et al, 2006).…”

“…Preference for a particular food depends not only on its intrinsic (e.g., nutritional, toxicological) properties, but also on the nutritional context where that target food is ingested. An instance of this type of phenomenon has been called induction effect, which consists of an increased intake of an unpalatable food when it is associated with the ingestion of a preferred food in a sequence familiar to the animal (Flaherty, 1996;Freidin et al, 2011Freidin et al, , 2012. It was hypothesized that preference for medusahead by herbivores is influenced by their experiences with the nutrients consumed in association with the weed.…”