Growth curve analyses in selected duck lines

1. Growth patterns of male ducks from 4 lines (lines A, B, C and D) selecte d for market weight were analysed and compared to growth patterns of ducks in the respective line 7 generations earlier. Growth curves were analysed u sing procedures derived from the Weibull sigmoidal function and the linear- linear relative growth rate model and simple allometry. 2. The ducks were fed ad libitum under 24-h lighting throughout the experim ent. At weekly intervals from the time of hatch through 70 d of age, 16 duc ks from each line were killed to determine body, carcase, breast-muscle, le g and thigh-muscle, and abdominal fat weights. 3. Line A was the heaviest line, followed by line B, line C and line D. How ever, body weight, carcase weight and breast-muscle weight at 49 d of age w ere not significantly different between lines A and B. After 7 generations of selection, the breast-muscle yield was increased to >19% and the abdomin al fat percent was reduced to <1.4% in all lines. 4. The Weibull growth curve analysis of body weight showed an increase in t he asymptotes during selection, while the age of the inflection point remai ned constant in all lines (21.3 to 26.0 d). For breast-muscle growth, ducks reached the inflection point 12.8 to 14.3 d later than for body weight. Be tween line A and line B, asymptotes for body weight, asymptotes for breast- muscle weight and allometric growth coefficients of breast muscle and leg a nd thigh muscles from 14 to 49 d were not significantly different. 5. The relative growth rate model discriminated body and breast-muscle grow th patterns of line A and line B. The initial decline in the relative body growth rate was less and the time to reach the transition was longer in lin e A than line B. On the other hand, the initial decline in the relative bre ast-muscle growth rate was greater in line A than line B.