Long-term effects of tryptophan on behavioural response and growing-furring performance in silver fox (Vulpes vulpes)

The effects of dietary tryptophan (TRP) supplementation on behavioural resp onse, body weight, feed consumption, and winter fur development was assesse d on silver fox pups from July 28 until December 5. Ten males and ten femal es received a commercial fox ration (control) and 10 males and 10 females t he same ration supplemented with TRP (1.2 g/MJ ME). Dietary TRP supplementa tion increased the consumption of protein and gross energy in September and November and total DM in September. The male foxes also consumed more feed and gained more weight than the females throughout the trial. Dietary TRP supplementation did not affect body weight gain, initiation of winter fur g rowth or fur quality in the test groups. There was a trend toward later pri ming of fur in the TRP supplemented group. The number of contacts with the novel object increased and the latency time until contact with the tidbit a nd the novel object reduced towards the end of the experiment. In the tidbi t test, dietary TRP supplementation reduced the latency time of the females (40.4 s) compared with the non-supplemented females (58.0 s), the TRP supp lemented males (51.7 s), and the non-supplemented males (47.6 s, P = 0.001) . In the novel object test, the latency time of the TRP females (32.5 s) wa s likewise reduced compared with the control group females (46.9 s) and TRP group males (44.0 s) being comparable to the control group males (38.5 s, P = 0.029). It appears that dietary TRP supplement reduces fear and enhance s exploratory behaviour in the female silver fox. This is likely due to the female being more sensitive to the imbalance between TRP and other large n eutral amino acids, the supplement leading to increased brain serotonin syn thesis. Further research needs to elucidate the effects of dietary TRP on t he pineal function due to potential interference with seasonal breeding and furring controlled by the photoperiod. (C) 1999 Elsevier Science B.V. All rights reserved.