Effects of Dietary Energy and Protein Levels on Free Force-Feed Peking Ducks

This study aimed to determine the dietary energy and protein levels for optimal growth performance and carcass characters of free force-feeding Peking ducks from 21 to 38 days of age. A total of 1,440 21-d-old Peking ducks were randomly assigned to 4 dietary metabolic energy (ME) and crude protein (CP) treatments: low nutrient (ME 11.93 MJ/kg, CP 16.0%), normal nutrient (ME 12.35 MJ/kg, CP 16.6%), moderate nutrient (ME 12.77 MJ/kg, CP 17.1%), and high nutrient (ME 13.19 MJ/kg, CP 17.7%), respectively, each containing 6 replicates with 30 males and 30 females per pen. At 38 d of age, performances, the carcass characteristics, serum biochemical indices, and hepatic and intestinal mRNA gene expression of ducks were measured. Body weight gain (BWG) and feed conversion rate (FCR) were improved linearly with increasing dietary nutrient. Skin percentage showed a quadratic trend and relative liver weight had a quadratic relationship with dietary nutrient. Serum lipase increased linearly while lipoprotein lipase (LPL) decreased linearly as dietary nutrient increased. Liver microsomal triglyceride transfer protein (MTTP) mRNA expression had a quadratic correlation with dietary nutrient. Besides, the intestinal neutral amino acid transporter SLC1A4 mRNA expression had a quadratic trend with dietary nutrient. Both low nutrient diet (ME = 11.93 MJ/kg, CP = 16.0%) and the high nutrient diet (ME = 13.19 MJ/kg, CP = 17.7%) are suitable for free force-feeding Peking ducks based on skin percentage, growth performance, and gain feed cost.