Growth and IGF-I response to breast muscle selection by ultrasound and dietary protein programs in Pekin ducks

Four experiments were conducted to determine the reproductive, metabolic, growth and IGF-I response to ultrasound selection for increased breast muscle thickness (MT) in Pekin ducks. Selection for body weight had a negative ( P < 0.05) effect on the reproductive performance while the selection for greater breast muscle thickness resulted in egg production, fertility and hatchability similar to those of the control line (C). Males from the MT line reached market weight at 6 wk but the breast muscle thickness improved from 6 to 7 wk. Compared to females from the C line, MT females had higher (P < 0.05) carcass yield, plasma glucose, and body protein; lower fat and plasma uric acid; and no difference (P > 0.05) in plasma triglycerides and total cholesterol. Males responded more efficiently to increasing dietary protein than females, and males selected for greater MT can be slaughtered at an earlier age when a high protein feeding program (HP) was followed. Males receiving HP had greater (P < 0.05) pectoralis muscles yield, longer keel bone, and lower breast skin and total skin fat yields. Female dissection data show similar (P > 0.05) effects of high and medium protein programs. Increasing dietary protein reduced (P < 0.05) carcass fat and increased (P < 0.05) crude protein (CP). In vivo breast muscle measurement correlated positively (P < 0.05) with body weight, pectoralis yield, and keel bone length. Birds with higher pectoralis yield tended to have more CP and less fat in their carcasses. A low correlation (r = 0.19) was found for the caliper measurement of breast skin plus fat thickness and carcass fat. We determined the metabolic differences between lean and fat male and female ducks, associated metabolic parameters and body composition, and assessed the difference between two feeding solutions for the determination of metabolic endogenous losses. There was a positive correlation between breast muscle:total breast muscle thickness ratio (MT/TOT) and plasma IGF-I and with nitrogen retention. The MT:TOT correlated negatively with carcass fat and positively with carcass CP. Estimation of carcass fat or CP content were presented in prediction equations from carcass DM and ash content. The ducks with greater breast muscle thickness had higher (P < 0.05) plasma IGF-I concentration than the control ducks, and the high protein program resulted in higher (P < 0.05) plasma IGF-I Males exhibited higher (P < 0.05) IGF-I than females, and IGF-I concentrations decreased (P < 0.05) with age from 42 to 49 d. Plasma IGF-I of the High MT:TOT ratio ducks were more negatively affected by feed deprivation. These ducks had similar (P > 0.05) plasma IGF-I concentrations to low ratio ducks during fasting, but had higher ( P < 0.05) concentrations when fed. Collectively, these data contribute to an understanding of the response of growth and IGF-I response to the ultrasound selection for greater breast muscle thickness and dietary protein, complemented with the assessment of the selection on the reproductive and metabolic performance of the ducks. These results are of original value in the field of growth and carcass improvement in Pekin duck production.