Abstract
Simple SummaryThe threonine (Thr) requirement of laying hens in a high-temperature climate is scarcely referred in the review of literature. Therefore, our aim was to estimate the dietary Thr requirement in low CP diets in a high-temperature environmental climate. Based on our findings, 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.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 (R2 = 0.96, p = 0.02), and reached a maximum level at 0.58%. Serum uric acid demonstrated a quadratic trend (R2 = 0.62, p = 0.02) at 0.59%. Both serum total cholesterol and 3-hydroxy-3-methylglutaryl (HMG-CoA) reductase showed lower levels (p < 0.05) at 0.66% Thr. Serum CuZn-SOD elevated (p < 0.05) at 0.49%, 0.57%, and 0.66% Thr, as compared to the control group, and showed a quadratic trend (R2 = 0.87, p = 0.003) at 0.56%. Supplemental L-Thr decreased (p < 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.
Highlights
High temperatures negatively affect protein utilization efficiency [1]
The results showed that both egg mass and hen-day egg production increased quadratically (p < 0.05) (Table 4)
Hens have selected for massive eggbecause production, It is important to formulate accuratelaying diets to meet the been requirements of laying hens feed resulting in are greater metabolic activity and reduced
Summary
High temperatures negatively affect protein utilization efficiency [1]. Diets that contain a high content of dietary crude protein (CP) will increase internal heat production by the elevated heat increment in a high-temperature climate [2]. Low levels of CP with supplementing limiting amino acids can overcome the bad effects of heat stress [3,4] and enhance protein utilization [5,6]. It has been reported that laying performance was equal among 14%, 15%, and 16% dietary. 14%, 15%, and 16% dietary CP [7]. Since synthetic dietary L-Thr became commercially available, it is CP [7]. Since synthetic dietary L-Thr became commercially available, it is possible to decrease CP
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