Abstract #W1

# W1
Tryptophan supplementation in calf milk replacers at weaning as an attempt to facilitate weaning.
M. Terré1, A. Bassols2, M. Vidal1, A. Bach*3,1, 1Institut de Recerca i Tecnologia Agroalimentàries, Caldes de Montbui, Barcelona, Spain, 2Universitat Autònoma de Barcelona, Bellaterra, Barcelona, Spain, 3Institució Catalana de Recerca i Estudis Avançats, Barcelona, Spain.

Tryptophan is a precursor of serotonin, a neurotransmitter that participates in the control of the affective state of the animal. We hypothesized that Trp supplementation could help dairy calves to cope with weaning stress. Twenty-seven Holstein male calves (48.2 ± 0.79 d old; 82.1 ± 2.57 kg BW) were used to evaluate the effects of Trp supplementation at the rate of 4.5 g/d via milk replacer (MR) on performance and behavioral parameters the weeks around weaning. All calves received the same feeding program (6 L/d at 15% DM from d 1 to 7, 4 L/d at 15% DM from d 8 to 14, and 2 L/d at 15% DM in one feeding until d 21 of study) and were weaned 21 d after the beginning of the study (around 63 d of life). Calves were fed starter feed (18% CP and 16.1% NDF) and chopped straw ad libitum. Animals were weighed weekly, DM intakes recorded daily, lying behavior was recorded using accelerometers throughout the study, and a scan sampling was performed twice a week, 1 h after the morning feeding to record behavioral activity (non-nutritive oral behaviors, suckling a neighbor calf, standing, resting, rumination, vocalizations, eating, and drinking). Data were analyzed with a mixed-effects model with repeated measures. Tryptophan supplementation did not affect calf performance nor concentrate and MR intake, but straw intake tended (P = 0.07) to be greater in non-supplemented compared with Trp-supplemented calves (153 vs 129 ± 9.0 g/d, respectively). Lying time decreased, lying bouts increased, and lying duration decreased when changes in the MR feeding program occurred, independent of treatment. Similarly, differences in behavioral observations occurred along days of study, with no impact of Trp-supplementation. The main changes observed in calf behaviors were an increase in vocalizations and standing time 1 h after the morning feeding at weaning, but again these changes were independent of treatment. Supplementing 4.5 g/d of Trp via MR between 48 and 62 d of life had no effect on performance and behavior in calves around weaning.

Key Words: calf, tryptophan, weaning