Abstract
Brain responses to feed flavors with or without a feed additive (FA) were investigated in piglets familiarized or not with this FA. Sixteen piglets were allocated to 2 dietary treatments from weaning until d 37: the naive group (NAI) received a standard control feed and the familiarized group (FAM) received the same feed added with a FA mainly made of orange extracts. Animals were subjected to a feed transition at d 16 post-weaning, and to 2-choice feeding tests at d 16 and d 23. Production traits of the piglets were assessed up to d 28 post-weaning. From d 26 onwards, animals underwent 2 brain imaging sessions (positron emission tomography of 18FDG) under anesthesia to investigate the brain activity triggered by the exposure to the flavors of the feed with (FA) or without (C) the FA. Images were analyzed with SPM8 and a region of interest (ROI)-based small volume correction (p < 0.05, k ≥ 25 voxels per cluster). The brain ROI were selected upon their role in sensory evaluation, cognition and reward, and included the prefrontal cortex, insular cortex, fusiform gyrus, limbic system and corpus striatum. The FAM animals showed a moderate preference for the novel post-transition FA feed compared to the C feed on d 16, i.e., day of the feed transition (67% of total feed intake). The presence or absence of the FA in the diet from weaning had no impact on body weight, average daily gain, and feed efficiency of the animals over the whole experimental period (p ≥ 0.10). Familiar feed flavors activated the prefrontal cortex. The amygdala, insular cortex, and prepyriform area were only activated in familiarized animals exposed to the FA feed flavor. The perception of FA feed flavor in the familiarized animals activated the dorsal striatum differently than the perception of the C feed flavor in naive animals. Our data demonstrated that the perception of FA in familiarized individuals induced different brain responses in regions involved in reward anticipation and/or perception processes than the familiar control feed flavor in naive animals. Chronic exposure to the FA might be necessary for positive hedonic effects, but familiarity only cannot explain them.
Highlights
In many species including humans, food intake can be stimulated by the use of food additives
Piglets familiarized with the feed additive (FA) from weaning had significant brain activations in the insular cortex, the amygdala and the striatum
The aim of our study was to demonstrate that the sensory perception of a feed additive (FA) can modulate brain activity in areas involved in hedonic and motivational processes or in learning and memory, in relation to and/or independently from familiarization with this additive in the pig model
Summary
In many species including humans, food intake can be stimulated by the use of food additives. These dietary substances can modulate the food organoleptic properties and food palatability, as observed for specific flavors [1], but they can influence satiety signals via the modification of post-ingestive visceral information [2]. Many authors have described the positive impact of feed additives such as flavors to improve feed intake and growth in piglets during post-weaning feed transitions [3,4,5,6]. The characterization of eating behavior modifiers might help to support or even improve feed intake during critical feed transitions or stressful conditions, notably in reproductive sows and growing piglets
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