Effect of dietary protein levels and age on growth performance, total excreta and nitrogen balance of laying hens during the growing phase

This study examined the effect of a dietary protein level and age on growth performance, total excreta, and nitrogen balance in laying hen during the growing period for 18 weeks.A total of 96 Hy-Line Brown laying hens were divided into two treatments according to the experimental diets, with each group consisting of six replicates.The experimental diets included: 1) an adequate metabolizable energy and crude protein diet formulated to meet the age and breed specification for Hy-Line Brown containing 21, 18, 16, and 14% dietary CP during 0 to 6, 6 to 12, 12 to 15, 15 to 18 weeks, respectively (CON); 2) 2% CP deficiency from CON diet containing 19, 16, 14, 12% dietary CP during 0 to 6, 6 to 12, 12 to 15, 15 to 18 weeks, respectively (LP).Growth performance, total excreta, and nitrogen balance were investigated for 18 weeks every 3 weeks, and two-way ANOVA was used for statistical analysis of data.The LP group had lower total excreta and N intake than CON group in the whole period of the experiment (p < 0.001).Moreover, birds in the LP group showed lower N excretion than the CON group (p < 0.05).However, the CON group exhibited higher BW, ADG than the LP group (p < 0.001).Application of low-protein diet to laying hens during the growing period reduced N excretion, which contribute to the sustainable development of the laying hen industry by minimizing environmental pollution.