Dose-response relationships for valine in the growing White Pekin duck

The response of White Pekin ducks to supplements of L-valine was studied during 3 wk posthatching. The basal valine concentration was 6.8 g/kg in a diet containing 18% CP and 2,990 kcal ME/kg (12.5 MJ ME/ kg). L-valine was supplemented in eight graded levels up to 12.7 g/kg at the expense of L-glutamic acid. Three pens of 14 ducks were allocated to each valine level. Diets were offered ad libitum. Body weight gain and feed/gain ratio were studied. At the end of wk 3, ducks were killed, processed to a homogenous mass, and analyzed for total body CP and amino acid content. Accretion of protein and amino acids was calculated. Additionally, a 5-d N balance study was conducted with separate ducks of the same hatch beginning on d 11 (6 ducks per treatment). The response of ducks to increasing valine concentration was described by exponential functions. Ducks significantly responded to the increasing valine concentration in growth, feed/gain ratio, and protein accretion. Ninety-five percent of y(max) in BW gain and protein accretion were achieved with 8.0 and 7.9 g valine/kg, respectively. The content of protein in gained BW was, on average, 149 g/kg without a significant valine effect. The valine content in accreted body protein was also unaffected by dietary valine (4.1 g/16 g N on average), which suggested that a major shift in body protein fractions did not occur. The overall efficiency of valine utilization was affected by dietary valine concentration and showed a maximum of 49%. Data from the balance study showed basically the same response of ducks, but the estimated optimum in dietary valine concentration was lower (7.0 g/kg). A comparison with published broiler data indicated that ducks and broilers in this age period were similar with regard to the valine content in gained protein and the efficiency of utilization of supplemented valine.