Effects of oral administration of rumen-bypassed tryptophan on behaviour, blood constituents, growth and feed utilization of weanling beef calves

The present study was conducted to examine the behavior, blood constituents, growth rate and feed utilization of beef calves when the tryptophan was orally given over 14 days following weaning at 3 months of age. Ten naturally suckled Japanese Black calves were allocated to one of two treatments: tryptophan and control (water), 5 animals each after balancing the two groups for sex and weaning weight. Each calf in the tryptophan-fed group received the granules of rumen-bypassed tryptophan (80 mg kg(-1) of BW, including 30% L-tryptophan) on pre-weaning day (Day -1), weaning day (Day 0) and alternate days after weaning. Maintenance and social behaviors were recorded between 1300 and 1800 h using a video camera on Days 0, 1, 2, 4, 6 and 9, and blood samples were taken by jugular venipuncture on Days 1, 4 and 9 in order to determine the plasma glucose concentration, the percentage of eosinophils to total white blood cell counts and the neutrophils/lymphocytes ratio (N/L). Additionally average daily weight gain and feed conversion were calculated during the post-weaning period (14 days). There was a tendency for tryptophan-fed calves to spend more time in lying and less time in exploratory behavior than controls (P0.10). Agonistic behavior, social investigative behavior and play were markedly reduced by tryptophan administration (P0.05). Though the N/L of tryptophan-fed calves tended to be higher than that of controls on Day 1 (P0.10), there were no marked differences in plasma glucose, the percentage of eosinophils and N/L between treatments on other post-weaning days. Tryptophan-fed calves showed higher growth rate than controls (P0.01). These results indicated that the oral administration of tryptophan tended to increase lying behavior, and suppressed agonistic and social investigative behaviors, which might induce the improvement of growth even though the current tryptophan dose was reduced by half as much as our previous study