Estimation of dietary tryptophan requirement for laying duck breeders: effects on productive and reproductive performance, egg quality, reproductive organ and ovarian follicle development and serum biochemical indices

This study aimed to determine the dietary tryptophan (Trp) requirement for laying duck breeders. A total of 504 Longyan duck breeders (body weight: 1.20 ± 0.02 kg) aged 22 wk were randomly allocated to 6 treatments, each with 6 replicates of 14 ducks. During the next 16 wk, birds were fed the basal diet with total Trp contents of 1.00, 2.00, 3.00, 4.00, 5.00 and 6.00 g/kg, respectively. Dietary Trp levels increased egg production, egg mass and feed intake of duck breeders from 22 to 37 wk (P < 0.05), and there were linear and quadratic effects of Trp level (P < 0.05). The feed conversion ratio (FCR) quadratically decreased with dietary Trp levels (P < 0.05). Dietary Trp levels decreased (P < 0.05) egg albumen height and Haugh unit at wk 8 or 12, and the responses were linear and quadratic (P < 0.05). The body weight of breeders, absolute and relative weight of oviduct, number and total weight of preovulatory follicles (POF), and its proportion relative to ovarian weight were increased (P < 0.05), and the responses were linear (P < 0.01) and quadratic (P < 0.001). Ovarian weight increased quadratically (P < 0.05), and the mean weight of POF increased (P < 0.05), linearly and quadratically. The proportion of small yellow follicles relative to ovary weight decreased (P < 0.01) linearly and quadratically. At wk 16 of the trial period, the serum albumin content and alanine aminotransferase activity decreased (P < 0.05) and the creatinine content increased (P < 0.01) linearly and quadratically. The Trp requirements were estimated to be 3.14 g/kg for optimizing egg production, 2.93 g/kg for egg mass, and 2.92 g/kg for FCR. Overall, dietary Trp levels (1 to 6 g/kg) affected productive performance, egg quality, reproductive organ and ovarian follicle development, and serum biochemical indices of layer duck breeders, and a diet containing 2.9 to 3.1 g Trp per kg feed was adequate during the laying period (22 to 37 wk of age).