Abstract
This study evaluated the optimal concentrations of dietary ME and CP for the productivity, reproductive performance, and fat deposition in laying duck breeders aged from 29 to 45 wk. Using a 3 × 3 factorial arrangement of treatments, 648 Longyan laying duck breeders with similar BW were randomly assigned to experimental diets of 2,600 (HME = high ME), 2,500 (MME = medium ME), or 2,400 (LME = low ME) kcal of ME/kg, each containing 19% (HCP = high CP), 18% (MCP = medium CP), or 17% (LCP = low CP) CP. Each dietary treatment contained 6 replicates of 12 birds each. Compared with birds fed the LCP diet, the egg production and egg mass were higher in birds fed HCP and MCP (P < 0.01), with better feed conversion (P < 0.01). Interactions were detected between ME and CP levels in egg production, egg mass, and feed conversion ratio as the LMEMCP diet was the best (P < 0.05). The birds fed MME (P < 0.05) had the lowest abdominal fat. The percentage of healthy ducklings was affected by maternal dietary CP (P < 0.05) with the HCP being the highest. The weight of large yellow follicles/ovarian weight was higher in birds fed HCP and MCP (P < 0.05), whereas the weight of small yellow follicles/ovarian weight was higher in birds fed HCP and LCP (P < 0.05). The hepatic transcript abundances of genes for very low density apolipoprotein-II and carnitine palmitoyltransferase-1A (CPT-1A) were lowest in birds fed MCP, whereas the highest abundance of CPT-1A transcripts was found in birds fed MME. These results revealed that the diets containing ME of 12.9 kcal/g protein optimized both egg production and egg mass, while the feed conversion was optimized at 12.8 kcal ME/g protein. Using ME to CP ratio of 12.9 kcal/g protein, i.e., 2,451 kcal ME/kg at 19% CP, maximized the reproductive performance and hatchling outcome of Longyan laying duck breeders.