The objective of the current study was to examine the effect of the inclusion levels of distiller’s dried grains with solubles (DDGS) which partially and fully replaced soybean meal (SBM) in laying hen diets with or without enzyme or vitamin E supplementation on nutrients digestibility and excreted nitrogen and phosphorous. For these purposes, a total of 180 Hisex Brown laying hens at 22 weeks of age were randomly distributed into 15 treatment groups in a 5 × 3 factorial design experiment including five levels of DDGS (0, 5.5, 11, 16.5 and 22% replaced for the same percent of SBM which represents 0, 25, 50, 75 and 100% respectively in the diet) and three levels of feed additives (without, 250 mg enzyme/kg diet or 200 mg vitamin E/kg diet) through 22–42 weeks of age. Results revealed that digestion coefficient values of nutrients including DM, OM, CP, EE, NFE and CF were more preferable in hens fed diets involved 25% DDGS instead of SBM than that of the control diet and other treatment groups. In contrast, hens fed 100% substitution of DDGS caused significant (P ≤ 0.01) decrease in digestibility coefficients of all nutrients. The amount of daily excreted N was decreased in hens fed 25 or 50% DDGS substitution, whilst feeding 75 or 100% DDGS led to an elevation in N excretion. The proportion of excreted phosphorous was statistically (P ≤ 0.01) decreased as the level of DDGS increased. Generally, neither enzyme nor vitamin E supplementation had any significant effect on the studied parameters. It could be concluded that DDGS could be used up to 50% as a replacement of SBM (11% of the diet) without any adverse effects on nutrients digestibility. Laying hen farms using DDGS up to 25 or 50% substituted for SBM in its diets (5.5 or 11% of the diet) will have clearer environment of nitrogen and phosphorous pollution than others whose diets free of DDGS.

The present study aimed to investigate the effect of the dietary levels of protein, methionine (Met), as well as probiotic on productive performance, feed utilization, and environmental pollution by N in Lohmann Brown laying hens. A total number of 160 Lohmann Brown laying hens at 20 weeks of age were randomly divided into 8 treatment groups using a 2 × 2 × 2 factorial design experiment. The experiment involved two levels of crude protein (16 and 18 %), two levels of Met (0.45 and 0.50 %), and two concentrations of probiotic (0 or 1 g/kg diet, with a concentration of 10¹⁰ CFU/g of Lactobacillus acidophilus) within 20–42 weeks of age. Results revealed that egg production parameters were significantly (P < 0.01) improved for hens fed diets of 18 % CP comparing with that of 16 % protein within the period from 26 to 30 weeks of age. Protein utilization and feed efficiency values were enhanced with 0.67 and 0.72 % Met during the period of 26–30 weeks of the age. For the N pollution, results showed that increasing crude protein in the diet from 16 to 18 % caused significant (P < 0.01) increase in the excreted N from 0.349 to 0.492 g/d. The methionine level of 0.72 % recorded the highest values of total consumed N being 3.98 g/d and excreted N being 0.527 g/d comparing with the other levels. It could be concluded that the best productive performance could be given by using 0.72 % total sulfur amino acids (TSAA). Furthermore, the dietary level of 18 % CP with 0.72 % Met is preferred in feeding laying hens through the whole experimental period. Ecologically, reducing the level of crude protein in layer diets to be 16 % along with the supplementation of Met can play an important role in minimizing the pollution with N from poultry excretion.