Effects of Graded Dietary L-Carnitine Levels on Growth Performance, Carcass Traits, and Physiological Responses in Pekin Ducklings

This study evaluated the effects of dietary LC inclusion (0, 50, 100, 200, and 400 mg/kg) in Pekin ducklings from 7 to 65 days of age on growth performance, carcass traits, metabolic profile, immune status, and economic efficiency. A total of 250 unsexed 7-day-old Pekin ducklings were randomly allocated to five dietary treatment groups, each comprising five replicates of 10 ducklings. The linear response plateau analysis estimated LC breakpoints of approximately 50 mg/kg diet for body weight gain and feed conversion ratio. Additionally, LC significantly improved carcass yield and crude protein content of the meat, as well as enhanced its antioxidant capacity. Physiologically, LC enhanced hematological indices, lipid metabolism, and thyroid hormone activity, without adversely affecting liver function. Moreover, LC favorably modulated the intestinal microbiota by increasing the abundance of beneficial Lactobacillus spp. and reducing pathogenic bacteria. Furthermore, it improved immune status, as indicated by higher immunoglobulin levels, lysozyme and phagocytic activities, and lymphocyte proliferation. LC significantly enhanced the mentioned parameters without inducing any adverse effects; however, the magnitude of the response plateaued and subsequently declined at higher inclusion levels (200–400 mg/kg). The improvements in performance and health status were attributed to the enhanced fatty acid oxidation, energy metabolism, antioxidant defense, and immunomodulatory effects of LC. In conclusion, including 50 mg L-carnitine/kg in the diet represents an effective and appropriate nutritional strategy under the conditions of the present study to optimize growth performance, carcass quality, nutrient digestibility, health status, and economic profitability in Pekin duck production systems.