Ruminal disappearance, intestinal digestibility, and plasma tryptophan response of rumen-protected tryptophan in Cashmere goats

The objectives of this study were to evaluate the ruminal disappearance and intestinal digestibility of a rumen-protected tryptophan (RPT) product; and to assess the response of plasma tryptophan (Trp) concentration to the RTP product supplementation during the cashmere fast growth period (July–November 2009) and the cashmere non-growth period (February–June 2010). Four Liaoning Cashmere goat wethers were used to study ruminal digestibility using the Dacron polyester bag technique, and intestinal digestibility of the RPT product was evaluated by the in vitro modified 3-step technique. Liaoning Cashmere goat wethers (n = 36; 24.5 ± 0.27 kg) aged 1.0 year-old were stratified by weight and assigned at random to three treatments: control, group I and group II fed 0, 2.0 and 4.0 g RPT product per head per day, respectively. Blood samples were collected twice per day at 10.00 h and 22.00 h prior to the start of the RPT product supplementation and at the end of every month in each experimental period. Assay of the RPT product supplement showed that it contained 33% L-Trp in a protected form. Less than 30% of the Trp disappeared during rumen incubation for ≤12 h. Intestinal digestibility of Trp ranged from 78 to 89% with an average value of 85%. The RPT product supplementation increased plasma Trp concentrations and the increases were significant for the sample taken at 22.00 h during both periods of the experiment (P < 0.05). In conclusion, the RPT product used in this study was an effective means of increasing the supply of Trp post-ruminally to Cashmere goats. Under the conditions of this trial, the optimum level of the RPT product supplementation observed was 2.0 g/goat/d during the cashmere non-growth period, and 4.0 g/goat/d during the cashmere fast growth period.