ENZYMATICALLY PREHYDROLYZED SOYBEAN MEAL FOR MINK (Mustela vison). II. EFFECTS ON BLOOD AMINO ACIDS AND ON BRAIN NEUROTRANSMITTERS
During postweaning growth and furring, 42 male Pastel kits were distributed into four groups. One group received a conventional diet made up of raw meat and commercial cereal mix; the other groups were fed diets containing, on a wet-matter basis, 10% soybean meal, 10% soybean meal prehydrolyzed with pepsin or 10% soybean meal prehydrolyzed with papain. Dry matter, protein and energy contents were approximately the same in all diets. Weight gain over 20 wk was significantly lower in soybean meal-fed groups compared with the one fed the conventional diet. Serum amino acids and brain biogenic amines were measured. When mink were fed pepsin-treated soybean meal, there was a significant increase in serum methionine, taurine, glycine and arginine contents compared with the groups fed the conventional or soybean diets. In the pepsin-treated group, the serum urea level was significantly lower than in the groups fed untreated or papain-treated soybean meal, suggesting that pepsin treatment decreases protein catabolism. In the papain-treated group, there was more tryptophan in the serum, suggesting a greater availability for the brain and for serotonin synthesis. In this respect, comparing papain and pepsin treatments, the serotonin content was significantly higher (P < 0.01) for the papain than for the pepsin group but in the same order of magnitude as the conventional or soybean-meal groups. A greater utilization of serotonin in the pepsin group and a greater mobilization of serotonin in the papain groups seemed to dissociate these two treatments on the basis of neurotransmitter synthesis as well as of the availability of amino acids. On the other hand, whole-brain noradrenaline content was significantly decreased (P < 0.01) with both pepsin and papain treatments compared with the conventional and untreated soybean-meal groups, suggesting greater noradrenaline utilization. Key words: Mink, neurotransmitter, amino acids, soybean meal