Effects of rumen-protected tryptophan on performance, nutrient utilization and plasma tryptophan in cashmere goats
Thirty-six Liaoning cashmere goat wethers (28.72 ± 0.59 kg) were used to determine the effects of rumen-protected tryptophan (RPT) on performance, nutrient utilization and plasma tryptophan (Trp) during the cashmere fast-growing period. The goats were randomly assigned to the following treatments: Control (without RPT), LRPT (RPT – low), MRPT (RPT– medium) and HRPT (RPT – high) at RPT levels of 0, 2.0, 4.0 and 6.0 g per goat per day, respectively. RPT-medium supplementation improved average daily gain and feed efficiency (P < 0.05) when compared with the control and HRPT. RPT supplementation increased (P < 0.05) the length and growth rate of cashmere fiber, whereas no differences were observed among the LRPT, MRPT and HRPT treatment groups (P > 0.05). RPT-medium supplementation decreased urinary nitrogen (N) excretion and increased N retention when compared with other groups (P < 0.05). Plasma Trp concentration was higher for HRPT treatment group when compared with other treatments (P < 0.05). In conclusion, RPT supplementation potentially improved growth performance, N utilization and cashmere fibre growth in Liaoning cashmere goats. In the experimental conditions of the current trial, the optimum RPT supplementation level was 4.0 g per goat per day during the cashmere fast-growing period.
Key words: Rumen-protected tryptophan, growth performance, fibre characteristics, nutrient utilization, plasma tryptophan, cashmere goats.