Abstract
This study investigated the effects of dietary crude protein (CP) levels on body weight (BW), laying performance, egg quality, and nitrogen (N) balance in laying hens from 18 to 62 weeks of age. A total of 84 Hy-Line Brown hens at 18 weeks old were randomly assigned to two groups, each with six replicates. The control group (CON) received diets with 17.5%, 16.5%, 15.5%, and 14.5% CP from weeks 18-38, 39-46, 47-54, and 55-62, respectively. The reduced protein group (RP) was fed diets with 1.5% less CP than the CON group during the same periods (16.0%, 15.0%, 14.0%, and 13.0%, respectively). The RP group showed significantly lower BW from weeks 30-62 (p < 0.05) and reduced hen-day egg production during weeks 18-38 and 54-62 (p < 0.05). Egg weight (EW) was significantly higher in the CON group than the RP group during weeks 54-62 (p = 0.003), and feed efficiency was also reduced in the RP group across multiple phases (p < 0.05). At week 38, Haugh units (HU) were lower in the RP group (p = 0.034), and yolk color was lighter at week 62 (p = 0.006). N balance parameters showed that the RP group had significantly lower N intake at weeks 46, 54, and 62 (p < 0.01), and N excretion was reduced throughout the trial (p < 0.05). Total N retention was lower in the RP group at weeks 26, 38, 54, and 62 (p < 0.05), and N retained in eggs was also reduced at weeks 26, 38, and 62 (p < 0.05). In summary, lowering dietary CP levels by 1.5% decreased N excretion, suggesting environmental benefits. In summary, reduction of dietary CP levels by 1.5% reduced N excretion but also compromised BW, laying performance, HU, and N retention. These findings highlight the need for further refinement of amino acid formulations to achieve both environmental and production goals.