Protease supplementation in diets with varying crude protein levels: effects on production performance and blood biochemistry of aged laying hens

1. This study was conducted to evaluate the effect of dietary crude protein level and protease supplementation on production performance and blood biochemical traits of aged laying hens.2. Forty Lohmann Brown hens at 68 weeks of age were fed two diets differing in crude protein levels (CP, 120 g/kg or 160 g/kg), supplemented or not with protease at 50.0 mg/kg feed. Each treatment included ten replicate cages with one hen per replicate. The study lasted for a duration of 32 weeks. Egg production performance was measured every 4 weeks and blood chemistry and electrolyte variables were assessed at the end of the study.3. Results showed that there was no interaction (<i>p</i> > 0.05) between dietary crude protein level and protease supplementation on any production or blood measurements. Hens fed 120 g/kg CP diet had lower (<i>p</i> < 0.05) production rate, egg mass, feed intake, body weight and less favourable feed conversion ratio (FCR) compared to those fed 160 g/kg CP diet. Supplementation with protease, independent of dietary crude protein level, increased egg production (+4.8 points; <i>p</i> < 0.05) and mass (+3.3 g; <i>p</i> < 0.05), blood creatine kinase (+103%; <i>p</i> < 0.05) and decreased FCR (-0.51points; <i>p</i> < 0.05) and blood phosphorus (-18%; <i>p</i> < 0.05).4. The results demonstrated that protease supplementation enhanced egg production performance in aged laying hens, regardless of whether they were fed CP-adequate or deficient diets. This improvement could be partially associated with accelerating energy metabolism, as evidenced by elevated blood creatine kinase levels. These findings highlighted the potential of protease to reduce dietary protein inclusion while extending laying hens' productive lifespan and enabling the development of blood biochemical signatures for exogenous protease applications.