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ANIMAL NUTRITION |
Department of Animal Sciences, Division of Animal Nutrition and Production Physiology, Technical University of Munich-Weihenstephan, 85350 Freising, Germany
2 Correspondence: Fachgebiet Tierernährung und Leistungsphysiologie, Technische Universität München, Hochfeldweg 6, 85350 Freising- Weihenstephan, Germany (phone: +49(0)8161713551; fax: +49(0)8161715367; e-mail: roth_fx{at}wzw.tum.de).
Abstract
The aim of the present study was to investigate whether pigs prefer diets varying in Trp content and whether these preferences change with time. To that end, a feeding trial was carried out over a 6-wk period. Piglets (equal proportion of males and females) with an initial BW of 8.20 ± 0.90 kg were randomly subdivided into four groups of 12 pigs each. Two reference groups were fed (as-fed basis) either 0.11% Trp (Trp-deficient) or 0.20% Trp (Trp-adequate) diets. Two other groups had a choice of two diets containing either 0.11 or 0.16% Trp (Trp-choice 1), or 0.11 or 0.20% Trp (Trp-choice 2). Average daily feed intake reached 335 and 366 g in pigs fed Trp-deficient and Trp-choice 1 diets, respectively. For Trp-choice 2 and Trp-adequate diets, a higher (P < 0.05) feed intake of 589 and 645 g/d, respectively, was observed. Piglets on Trp-choice 1 and Trp-choice 2, respectively, selected 87 and 93% of the higher Trp diet. Resulting Trp contents of total diets were 0.15 and 0.19% (as-fed basis) in Trp-choice 1 and Trp-choice 2, respectively. In wk 1, pigs on Trp-choice 2 chose lower proportions of the Trp-deficient feed (31% of total diet) than did pigs on Trp-choice 1 (44%), but at the end of the experiment, pigs of both groups almost exclusively chose the feed with the higher Trp content (96 and 98% for Trp-choice 1 and 2). Pigs on Trp-choice 1 had an ADG of 218 g, which was only slightly above the ADG of Trp-deficient pigs (198 g). Pigs on Trp-choice 2 and Trp-adequate diets had ADG of 404 and 458 g, respectively, which were higher (P < 0.05) than those observed for Trp-deficient and Trp-choice 1 groups. Plasma Trp concentrations in Trp-choice 2 and Trp-adequate groups (9.21 and 9.01 µmol/mL, respectively) were higher (P < 0.05) than in Trp-deficient and Trp-choice 1 groups (5.88 and 4.96 µmol/mL, respectively). Conversely, the sum of essential AA showed a higher (P < 0.05) concentration in plasma from pigs on the Trp-deficient and Trp-choice 1 diets than in plasma from pigs on Trp-choice 2 and Trp-adequate diets. Nutritional depletion of Trp influences the food selection behavior of piglets. Results of growth performance and the dietary preferences suggest that piglets are able to detect Trp-deficiency-induced metabolic changes and respond with an aversion against the Trp-deficient diet.
Key Words: Feeding Preferences • Piglets • Tryptophan
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