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How to deal with bitterness for pigs
Bitter tasting ingredients can lead to pigs having a lower feed acceptability. These components could even trigger satiety signals, which in turn decrease feed intake and compromise animal performance.
BY GEMMA TEDO, PHD AND SOFIA MORAIS, PHD, INNOVATION DIVISION, LUCTA, SPAIN T
aste perception helps pigs assessing food quality through the recognition of at least five basic tastes: sweet, umami, sour, salty and bitter. The first four are identified by a small number and
types of taste receptors, whereas the latter is identified by a large number of bitter taste receptors from the T2R family (15 known in pigs). Bitterness is the most sensitive and com- plex of the tastes and is innately associated with an unpleas- ant and aversive sensation. It acts as a central warning signal to protect animals against the ingestion of potentially harm- ful substances, such as toxic secondary metabolites that are commonly produced by plants to deter its consumption. The binding of bitter compounds to T2Rs signals the brain, triggering aversive responses and the induction of anorexic signals, ultimately reducing feed intake (see Figure 1).
Bitterness in commercial feeds Some plant-derived ingredients used as raw materials in commercial feeds may contain non-toxic bitter compounds,
Figure 1 - Bitterness perception mechanism at the oral level.
such as anti-nutritional factors, that have been reported to decrease feed intake. In addition, certain commonly used phytogenic and pharmaceutical additives (see Table 1) con- taining a wide range of compounds with beneficial effects (e.g., improving enzymatic activity in the gut, showing anti- oxidant, anti-inflammatory or antimicrobial effects) can also trigger bitter taste receptors and cause behavioural aver- sions to feed. In an experimental model where piglets were already adapted to solid feed (21 days after weaning), the inclusion of common bitter additives in diets resulted in a fast reduction (about 8%) in feed intake (see Figure 2). An even worse feed acceptability would be expected in critical peri- ods, such as weaning.
bitterness
sweet umami bitter
8
sour salty
▶ PIG PROGRESS | Volume 34, No. 5, 2018
Great diversity of bitter taste receptors
Can bitter compounds be avoided? The complete avoidance of bitter compounds in pig feeds is particularly challenging because of the high prevalence and diversity of bitter tastants (ligands binding to a taste recep- tor), and the variability in bitter taste receptors. This is further complicated by: • The bitter complex: The bitter properties intrinsic to feed ingredients, derived from the presence of anti-nutritional fac- tors and other secondary plant metabolites that activate mul- tiple bitter taste receptors with different specificities are not always known. What is worse, complex, synergistic and un- predictable interactions occur between certain compounds, exacerbating the problem of bitterness perception.
PHOTO: HANS BANUS
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