Taste in domestic pig, Sus scrofa

Introduction The fact that taste is not even indexed in ‘Swine Production and Nutrition’, a major textbook on swine nutrition (P ond and M aner 1984), supports the notion that taste is considered to be of no consequence in pig production. Not only does this omission underestimate the consequences of millions of years of evolution of the chemical senses, it also neglects the existence of a sensory apparatus for high taste acuity in the pig (T uckerman 1888; C hamorro et al. 1993) as will be shown in the following. Oral compounds stimulate the taste buds. In the pig, as in most mammals, these are located in fungiform papillae on the tip of the tongue, and foliate and vallate papillae on the back of the tongue. The pig differs, however, from most mammals in the number of taste buds, which exceeds most species, including the human (B radley 1971). Thus the domesticated pig possesses at least 10 000 vallate taste buds, whereas the human has 6000 (C hamorro et al. 1993), and about 4800 foliate taste buds (T uckerman 1888), compared with 3000 in human. The discrepancy between the human taste apparatus and that of the pig becomes even more evident when one compares the 1600 human fungiform taste buds with the 5000 found in pig (M iller 1986). As a result of this, the pig tongue has three to four times more taste buds than the human tongue. In humans there is a positive correlation between the number of fungiform taste buds and ability to taste (M iller and R eedy 1990; B artoshuk et al. 1996). Provided a similar relationship exists between species, with regard to number of taste buds and tasting ability, then the pig’s ability to taste is superior to that of humans. It thus seems that if it is assumed that the sense of taste plays no role in the feed consumption of pigs, the same conclusion will have to be drawn on its role in human consumption. Taste information from the fungiform taste buds is conveyed in the chorda tympani nerve (CT) and from the foliate and vallate taste buds through the glossopharyngeal nerve (NG). Recordings of nerve impulses in these nerves have been used in many species to assess a species’ ability to taste. If one considers the above data, suggesting an excellent sense of taste in the pig, coupled with the importance of unperturbed growth of the pig, one would expect a large number of recordings from the pig’s taste nerves in the literature. However, this is not the case. There are only three published studies which include recordings of the pig’s CT nerve (K itchell 1963; H ellekant 1976a, b) and one from its NG (K itchell 1963). The number of tastants used is also limited to the four standard taste stimuli: NaCl, quinine hydrochloride (QHCl), citric acid and sucrose, with the exception of an earlier study by the present authors which included thaumatin (H ellekant 1976a). No commercial feed additives nor any of the many new sweeteners, such as acesulfame-K, alitame, aspartame, etc., which, due to their high potency and pig’s sweet tooth (A umaitre 1980) could have potential use in the diet of the pig, have been included. Ten years ago one might think that data from other species could be applied to the pig’s sense of taste. However, there are large differences in the sense of taste between species. This was pointed out already by K are and K itchell some 30 years ago (K are 1960, 1961; K itchell 1963, 1965; K are et al. 1965; K are 1966) and has been increasingly documented when taste stimuli outside the usual array above have been used (J akinovich and S ugarman 1988; H ellekant and D anilova 1996; D anilova et al. 1998). For example, in an array consisting of 13 compounds that are sweet to humans, three were found to be sweet, three marginally sweet, and seven not-sweet to the pig (H ellekant and D anilova 1996). Data are presented of whole nerve and single taste fibre recordings from both the CT and NG nerves during taste stimulation with approximately 30 compounds. The data presented here show that conclusions on how a compound tastes to the pig have to be based on data acquired in pigs. Data from humans or other species are not sufficient.