PREFERENCE FOR DIETS WITH FREE L-TRYPTOPHAN IN PIGS WITH DIFFERENT TRYPTOPHAN STATUS

The chemosensorial system of pigs has evolved to identify individual amino acids as indicators of protein in the feed, and therefore the palatability of the diet could be affected by the addition of free amino acids. A double choice test was conducted to determine the preference of diets with different free L-Trp levels in pigs under different Trp status. One hundred and eight piglets (17.7±1.4 kg BW) were divided into three groups and adapted for one week to diets that were either deficient (D), adequate (A) or excessive (E) in Trp (1.8, 2.4 or 3.0 g Trp/kg, respectively). After the period of adaptation, the animals were used in pairs to perform a series of double-choice tests (during 2 days) between diet D without free L-Trp (taken as reference) and three diets with increasing levels of free L-Trp to provide Trp in excess (E1, E2 and E3; 3.0, 3.6 and 4.2 g Trp/kg, respectively). All the diets had the same composition and only differed in their free L-Trp content, which was included at the expense of maize starch in the basal diet. For each double choice comparison and animal nutritional status, a total of six observations were obtained. Preference for each tested diet was expressed as its % contribution to total feed intake. No significant effects of pig’s Trp status (P = 0.924), free L-Trp inclusion (P = 0.995) or their interaction (P = 0.614) on feed preference were observed. Overall, the addition of L-Trp resulted in a preference value of 41%, which was significantly lower (P<0.001) than the neutral value of 50%, which should be expected to match an adequate Trp intake. These results indicate that pigs have an aversion for the diets with free L-Trp. In conclusion, the addition of L-Trp decreases feed palatability in pigs, independently of its inclusion level and nutritional status of the animals. tech.service.fad@lucta.com