Unfolding the codes of short-term feed appetence in farm and companion animals. A comparative oronasal nutrient sensing biology review

Abstract

Roura, E., Humphrey, B., Tedo´, G. and Ipharraguerre, I. 2008. Unfolding the codes of short-term feed appetence in farm and companion animals. A comparative oronasal nutrient sensing biology review. Can. J. Anim. Sci. 88: 535Á558. The evolution of the chemical senses has resulted in a sensory apparatus for high taste and smell acuity in mammals and birds to ensure self-nourishment. Such peripheral chemosensory systems function as a code to unfold the nutritional value of feedstuffs. Food ingestion simultaneously evokes odor, taste and thermo-mechanical (somatosensing) sensations. Olfaction represents the capacity to identify feed volatiles that are predominantly derived from essential nutrients in plants.Comparative biology of olfaction shows that primates and chickens have a smaller olfactory epithelium and fewer olfactory receptor (OR) genes than non-primate mammals studied to date including farm and companion animals, such as the pig, the cow, the dog, the cat and the horse. A significant proportion of the total OR genes in mammals and birds have lost their functionality (pseudogenes) in a process that seems to reflect a decrease in the animal's reliance on the sense of smell, particularly in humans and cows. The taste system allows animals to recognize a diverse repertoire of nutrient (sugars, amino acids, salts, acids and fats) or toxic related chemical entities that provide valuable information about the quality of food. Taste senses non-volatile molecules in the oral cavity through taste receptors (TR). The TR are expressed in the sensory cells forming the taste buds of the tongue's papillae. Taste cells are linked to a network of solitary chemosensory cells diffused through many non-taste tissues involved in metabolic homeostasis. The number of functional taste receptor genes (TASR) in humans is equivalent to that in other mammals and superior to that in chickens. The TASR family 1 (TAS1R coding for umami and sweet TR) is conserved, in number and type, across the species evaluated, with the exception of the sweet receptor in chicken and feline species. The TASR family 2 (TAS2R coding for bitter TR) shows a strong adaptive capacity to dietary sources and digestive physiology across vertebrates. Pseudogenization (loss of gene functionality) in the TAS2R family seems to be a frequent strategy. The implications of oronasal nutrient sensing related to comparative animal feeding strategies and behaviors such as neophobia, feed refusal and hedonic preferences are discussed. Feed palatability and appetence might be one of the main driving forces in short-term feed consumption. Finally, practical applications relevant to animal production are outlined.Key words: Nutrient sensing, taste, olfaction, somatosensing, feed intake, farm, companion animals Roura, E., Humphrey, B., Tedo´, G. et Ipharraguerre, I. 2008. Le code de l'appe´tence a`court terme chez les animaux domestiques et de compagnie. Biologie comparative de la de´tection bucco-nasale des e´le´ments nutritifs. Can. J. Anim. Sci. 88: 535Á558. En e´voluant, ...

The Physiology of Taste in Fish: Potential Implications for Feeding Stimulation and Gut Chemical Sensing

“…Nevertheless, the T1R family shows a high degree of conservation across vertebrate evolution and its gene repertoire is practically constant in size across most vertebrates, except for the loss of the T1R2 gene in the sweet-insensitive chicken, its pseudogenization in cats (Li et al, 2005), the lack of T1R1 in panda bears (Li et al, 2010), and the absence of all T1R genes in the tongueless western clawed frog. This probably reflects the universal importance of sweet and umami tastes and the relative constancy in number and type of these tastants in most vertebrate species (Shi and Zhang, 2006;Roura et al, 2008). In contrast, orthologous T2R sequences are highly divergent and the T2R gene repertoire varies greatly among species, from only three functional genes in the chicken up to 49 in the frog, indicating that T2R gene families expanded after the separation of each lineage and that high variability exists in the number and type of bitter compounds detected by different species (Shi and Zhang, 2006;Oike et al, 2007).…”

“…Adapted from Marui et al, 1983 (© Springer International Publishing. Reproduced by permission of Springer International Publishing. Permission to reuse must be obtained from the rightsholder) (a, c, d) and broadly tuned L-amino acid sensor that is activated by most of the 20 standard AAs (depending on the species), but not their D-enantiomer forms, with responses being enhanced by purine 5 0 ribonucleotides (Li et al, 2002;Nelson et al, 2002;Roura et al, 2008). Another attractive taste modality, responding to several classes of sweet compounds (in mammals these include natural sugars, artificial sweeteners, D-amino acids, and sweet proteins) as fundamental sources of metabolic energy, is mediated by the T1R2/T1R3 receptor complex (Nelson et al, 2001;Li et al, 2002).…”

Effect of dose of thymol and supplemental flavours or camphor on palatability in a choice feedings study with piglets

“…Sensory neurons of the trigeminal nerve are part of the pain pathway and are involved in the detection of noxious stimuli such as low or high temperatures and pungent substances (e.g. acids, spices) (Roura et al, 2008). Transmembrane ion channel receptors of the transient receptor potential (TRP) family seem to be responsible for the detection of high (TRPVs) and low (TRPMs) temperatures and pungency or noxious cold (TRPAs) (e.g.…”

Attractants for wild pigs: current use, availability, needs, and future potential

“…Taste receptors of pigs can differentiate between the five taste sensations of sweet, salty, bitter, sour, and umami (savory) (Bachmanov and Beauchamp 2007;Roura et al 2008), giving them the ability to differentiate molecules within food items. Sweet and umami taste categories often represent sugars and proteins that are known to trigger gustatory preferences in pigs, while bitter compounds, which may signal rotten or rancid food items, are often rejected .…”