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 = lowME)
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.