Metabolic studies on lean and fat Pekin ducks selected for breast muscle thickness measured by ultrasound scanning

Female Pekin ducks selected for high (lean) or low (fat) breast muscle:tota l breast thickness ratio (MT:TOT), measured with ultrasound scanning, were used in metabolic studies to determine the metabolic differences and assess the effects of feed withdrawal and refeeding on plasma parameters. Lean an d fat ducks had similar body weight changes throughout the studies. Lean du cks had significantly lower fat and higher CP and ash carcass contents. The y also had higher (P < 0.05) plasma glucose after feed withdrawal but less (P < 0.05) plasma glucose after feeding. Fat ducks had similar plasma trigl ycerides (TG) after feed withdrawal but higher (P < 0.05) TG concentration after feeding and higher (P < 0.05) plasma uric acid than the lean females after feeding. Feed deprivation resulted in higher (P < 0.05) plasma choles terol than did feeding. Lean ducks fed the test diet retained more (P < 0.0 5) N than the fat birds. Lean and fat Pekin ducks had similar (P > 0.05) AM E, AME(n), TME, and TME,. Lean ducks lost less (P < 0.05) N than far birds. Plasma cholesterol was not significantly correlated (P = 0.06) with nitrog en retention (NR); NR was negatively correlated (P < 0.05) with plasma TG, and TC was positively correlated (P < 0.05) with total energy excreted. The re was a positive correlation (P < 0.05) between MT:TOT and NR. The MT:TOT correlated (P < 0.05) negatively with carcass fat, and positively with carc ass CP and plasma insulin-like growth factor I (IGF-I) concentration. The r esults we obtained demonstrate the usefulness of ultrasound scanning in liv e bird selection for leanness and greater breast muscle thickness and are r elated to metabolic differences between lean and fat female Pekin ducks sel ected for high or low MT:TOT ratios.