The purpose of this study is to determine the impact of different levels of crude protein (CP) diets supplemented with dietary protease on the growth performance and nutrient digestibility of the weanling pigs. In a 5-week study, 100 crossbred ([Landrace × Yorkshire] × Duroc) of weaner pigs that have an average initial body weight (BW) of 7.17±1.06 kg were assigned to one of four dietary treatments with 5 replications and 5 pigs (3 gilts and 2 castrated male pigs) per pen in a randomized complete block design. The dietary treatments were as follows: Phase 1: CON: basal diets (20.60% CP); low protein (LP): CON - 0.30% CP; PLP1: (CON - 0.30% CP) + 0.05% protease; PLP2: (CON - 0.50% CP) + 0.05% protease. Phase 2: CON: basal diets (18.88% CP); LP: CON - 0.30% CP; PLP1: (CON - 0.30% CP) + 0.05% protease; PLP2: (CON - 0.50% CP) + 0.05% protease. The addition of protease to low CP diets significantly increased the feed conversion ratio (FCR) ( = 0.039), BW ( = 0.046), average daily gain (ADG) ( = 0.049), and average daily feed intake (ADFI) tended to increase ( = 0.053) in the young pigs during phase 1. However, FCR tended to increase throughout the experiment but did not change during phase 2, whereas BW, ADG, and ADFI stayed unchanged throughout phase 2 and overall. There was no significant difference in dry matter, nitrogen (N), and gross energy of nutrient digestibility in all phases and overall in weaned pigs with low CP when protease was fed. In contrast, adding protease to the low CP diets increased the tendency of N digestibility ( = 0.059) during phase 1. It is concluded that dietary protease supplementation tended to increase N retention during the first phase of the weaning period, hence increasing piglet performance.
