2008 Volume 11 Issue 2 Pages 61-66
In order to predict lysine and valine requirements in rabbits using the response of plasma free amino acid concentrations to the amounts of both amino acids in diets,17 Japanese white rabbits, aged 2months, were given experimental diets containing five levels of lysine and valine at 3 CP levels of 12,16 and 20%. Rabbits were fed each diet for successive 4 days. Blood was collected from the vein of the ear at 14: 00on day 4 and the free amino acid concentrations in the plasma were determined. Although the body weight gain, feed efficiency and apparent CP digestibility for CP 20% group showed the highest values, but no significant differences were recognized among 3 dietary CP levels. Metabolic fecal CP calculated by the extrapolation method was 0.88 g/d, resulting in similar true digestibility irrespective of dietary CP levels. Plasma lysine concentration only in the CP 12% group remained constant (basal line) when lysine intake was less than 0.6g/d, and then increased linearly in response to the increase in lysine intake. The lysine requirement at 12%CP was obtained as an intersection between the basal line and increasing line, leading to the value of 0.63%. Because plasma lysine at 16 and 20% CP levels as plasma valine at all CP levels increased linearly without the basal line, requirements of lysine and valine were not clear within the range of these CP levels.
