Abstract
Lohmann Brown hens (n = 420), at 28 weeks of age, were divided into five dietary treatments, and each treatment included six replicates of 14 laying hens. Dietary crude protein (14%) was presented as the control diet. Dietary L-Thr was added to the control diet for 12 weeks. Dietary Thr levels are 0.43%, 0.49%, 0.57%, 0.66%, and 0.74%, based on digestible base. From 28 to 40 weeks, hen-day egg production presented a quadratic trend to supplementing dietary Thr (R
= 0.96,
= 0.02), and reached a maximum level at 0.58%. Serum uric acid demonstrated a quadratic trend (R
= 0.62,
= 0.02) at 0.59%. Both serum total cholesterol and 3-hydroxy-3-methylglutaryl (HMG-CoA) reductase showed lower levels (
< 0.05) at 0.66% Thr. Serum CuZn-SOD elevated (
< 0.05) at 0.49%, 0.57%, and 0.66% Thr, as compared to the control group, and showed a quadratic trend (R
= 0.87,
= 0.003) at 0.56%. Supplemental L-Thr decreased (
< 0.05) the expression of ileal HSP70 at 0.66% Thr. In summary, the optimal dietary Thr requirements to optimize egg production, serum uric acid, and serum CuZn-SOD were 0.58%, 0.59%, and 0.56%, respectively, by regression analysis.