Day-night behaviour and performance of barrows and gilts (70-100Â kg) fed low protein diets with different levels of tryptophan and B6 vitamin

Tryptophan (Trp) is involved in regulation of animal behaviour, since it originates serotonin and melatonin, especially in low crude protein diets, and Trp metabolism requires B6 vitamin (B6) as enzymatic cofactor. The objective of this study was to feed low protein diets with different levels of standardized ileal digestible (SID) Trp and B6 for barrows and gilts (70-100 kg) and to measure day-night behaviour, performance and carcass traits. In experiment 1 (Exp. 1) sixty four barrows (initial BW = 70.77 ± 2.07 kg) were used, and in experiment 2 (Exp. 2) sixty four gilts (initial BW = 70.52 ± 2.95 kg) were used. In both experiments a 2 × 4 factorial arrangement of treatments was used: two B6 levels (1 and 5 mg kg−1) and four levels of SID Trp (Exp. 1: 0.130, 0.155, 0.180, 0.205%; and Exp. 2: 0.140, 0.167, 0.194, 0.221%). Day-night behaviour was recorded at the end of weeks 1, 2 and 3 (days 7, 14 and 21) during 24 h. Scan-sampling was used to determine time-budget behaviour. Growth performance and carcass traits were measured at the end of the experimental period, when animals reached about 100 kg BW (in average 26 days). In Exp. 1 (barrows), stationary behaviour in daytime period (from 6:00 h to 18:00 h) increased quadratically (P = 0.005) as Trp content in diets increased from 0.130 to 0.165%, but it decreased until 0.205% of SID Trp. Interacting behaviour in night-time period (from 18:00 h to 6:00 h) was affected by B6 (P = 0.031). Sleeping behaviour decreased linearly (P = 0.003) as Trp content in diets increased from 0.130 to 0.205% and feeding behaviour showed quadratic response (P = 0.008) to SID Trp (0.161%). In Exp. 2 (gilts) sleeping behaviour in daytime period decreased quadratically (P = 0.001) as SID Trp content in diets increased from 0.140 to 0.179%, but it decreased until 0.221% of SID Trp. Feeding behaviour was affected by the interaction Trp × B6 (P = 0.030) as supplementary B6 (5 mg kg−1) decreased visits to feeder up to 0.194% Trp content. Sleeping behaviour in night-time period was affected by the interaction Trp × B6 (P = 0.030) once supplementary B6 (5 mg kg−1) markedly decreased time spent sleeping when compared to basal B6 (1 mg kg−1) as Trp levels increased in diets. Feeding behaviour responded quadratically (P = 0.001) to Trp (0.173%). In both experiments performance variables and carcass traits were not different (P > 0.05) neither for Trp nor B6. SID Trp levels from 0.130 to 0.205% (barrows) and 0.140 to 0.221% (gilts) even as B6 content (1 or 5 mg kg−1) in diets had no consistent effects on behaviour and did not alter performance of pigs.