Investigating the Effects of Enzyme Inclusion Rates in Reduced Protein Diets to Improve Nutrient Digestibility in Laying Hens

Enzymes have the potential to enhance nutrient utilisation and provide economic and environmental benefits in reduced protein (RP) diets; however, responses to different inclusion levels of phytase and carbohydrase enzymes remain inconsistent. Therefore, the present study aimed to evaluate the effects of phytase, xylanase, and β-glucanase inclusion levels in RP diets on nutrient digestibility and performance in laying hens. A total of 8 dietary treatments were allocated to 13 replicate cages of two hens per cage per treatment (n = 208) from 35 to 57 weeks of age. Experimental diets comprised two protein levels (standard protein (SP) at 16.5% crude protein versus RP at 14.5% crude protein), two phytase levels (600 and 1200 FTU/kg), and two XB levels (xylanase, β-glucanase 100 g/ton and 150 g/ton) were examined via a 2 × 2 × 2 factorial design. Between 35 and 57 weeks of age, no significant interactions were observed in laying performance parameters. However, RP diets significantly decreased egg weight across all periods, 35–47 weeks (p = 0.049), 48–57 weeks (p = 0.045), and overall, from 35 to 57 weeks (p = 0.044). Reduced protein diets also decreased egg mass from 35 to 47 weeks (p = 0.035). High Xylanase and β-glucanase (XB) inclusion (150 g/ton) lowered hen day egg production during 48–57 weeks (p = 0.015). At 47 weeks, RP diets reduced yolk weight (p = 0.021) and increased egg shape index (p = 0.048). Additionally, XB at 150 g/ton with 600 FTU/kg PhyG improved shell breaking strength (p = 0.046) but reduced it at 1200 FTU/kg. At 57 weeks, RP diets decreased albumen weight (p = 0.016), albumen proportion (p = 0.006) and increased yolk proportion (p = 0.005). Xylanase and β-glucanase inclusion at 150 g/ton reduced shell breaking strength (p = 0.036), and XB reduced yolk colour score (p = 0.038) only in SP diets. Also, RP diets reduced excreta moisture (p = 0.015) and improved dry matter digestibility (p = 0.020). Notably, feeding RP diets increased apparent metabolisable energy digestibility (p = 0.003), decreased protein excretion (p < 0.001) and increased apparent protein digestibility (p = 0.013). It is therefore concluded that decreasing RP diets to appropriate levels may benefit the environment without affecting the feed efficiency of laying hens.