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Effects of protease addition on varying levels of CP/AA on performance, egg parameters and apparent amino acid digestibility in 50-70 wk old Hy-Line W36 laying hens

Hodge, V., K. Wamsley, K. Roberson and P. Adhikari

Supplementing exogenous protease may promote amino acid (AA) utilization in low crude protein (CP) diets. This study was conducted to determine the effects of reducing CP/AA in diets with or without a commercially available protease on post-peak laying hen performance, egg quality, and apparent ileal digestibility (AID). A 20-week study was conducted using 672 Hy-Line W36 laying hens (50-week-old at the beginning of the study), which were equally and randomly placed into 96 cages as experimental units (raised wire cages). There were 12 replicate cages per treatment with a stocking density of 871.4 cm2/hen. Each replicate cage (7 hens) was fed one of the 8 diets from the 4 AA levels (100, 95, 90, or 85% of breeder recommendation) x 2 protease inclusions (without or with). The adequate (100%) diet was based on corn, soybean meal, and DDGS and formulated based on digestible Lys: digestible AAs (dMet, dThr, dTrp, dTSAA, dIle, and dVal) for 100% of the Hy-Line W36 recommendation. Data were subjected to 2-way ANOVA (PROC GLM procedure, SAS 9.4). There were significant AA level x protease interactions for hen-day egg production (HDEP), percent yolk, and AID for CP, dMet, dThr, dIle, and dVal (P <0.05). For HDEP, 95% without protease was significantly higher than both levels of protease at 85 and 90%, along with 95% with protease (P=0.0069). The percent yolk for 100% with and 95% without protease were significantly higher than those fed 90% with and 85% without protease (P=0.0011). The AID for CP was significantly higher for 100% without protease than for 95% and 85% with and 90% without protease (P=0.0026). However, Met at 100% without protease was significantly higher than for 90 and 85% with and 85% without protease (P=0.0145). For both Thr and Ile, 100% without protease had higher AID than 95 and 85% without protease (P=0.0064 and 0.0022). Similarly, the AID of Val was higher for 100% without than 90% without protease. The main effect of the AA level significantly affected multiple parameters. As such, egg weight (EW) was higher in hens fed adequate AA level vs. those fed other AA levels (P=0.0003). A significant decrease in egg mass was observed when the AA level decreased from 90 to 85% (P<.0001). Furthermore, hens fed 85% AA level diets had a significantly higher FCR than those fed all other levels (P<.0001), and Haugh units significantly increased as the AA level decreased (P<.0001). No interactions or effects were found for feed intake, specific gravity, shell thickness, percent albumen, or total solids.

Since no main effect of protease was observed, it may not effectively promote AA utilization in low CP diets for commercial laying hens.