Simple SummaryNutrient waste management poses significant challenges associated with environmental concerns and feed expenses for the pig industry. Additionally, including high levels of crude protein in pig diets has been linked to postweaning diarrhea and protein fermentation in the large intestine compared to diets with a lower protein content, which can impair gut health. This study was conducted to assess the impact of low-protein diets on weaning to finishing pigs related to growth performance, nutrient digestibility, and meat quality. Our findings indicate that when supplemented with appropriate amino acids, low-protein diets do not negatively affect growth performance or nutrient digestibility in weaning to finishing pigs. Furthermore, the quality was superior in pigs fed low-protein diets as opposed to those fed high-protein diets. Consequently, employing low-crude-protein diets in weaning to finishing pigs is recommended.AbstractThis study aimed to evaluate optimal crude protein (CP) levels based on the National Research Council guidelines from 1998 and 2012 and their impacts on growth performance, fecal score, blood profiles, nutrient digestibility, and carcass characteristics of weaning to finishing pigs. Four diets were established in this experiment: high-protein (HP), medium-high-protein (MHP), medium-low-protein (MLP), and low-protein (LP). The HP diet followed the NRC (1998) guidelines, while the MHP diet reduced the CP content by 1%. The MLP diet had 1.5% lower CP content than the HP diet. The LP diet followed the NRC guideline of 2012, which suggests less protein than the NRC guideline of 1998. There were no significant differences in body weight, average daily feed intake, or nutrient digestibility. However, the average daily gain (ADG) of pigs fed the LP diet at 7–10 weeks was lower than in the other treatments, whereas the ADG of the pigs fed the LP diet was higher compared with that of pigs fed the other diets, showing compensatory growth in finishing periods (p< 0.05). The blood urea nitrogen of pigs fed the LP diet showed the lowest value, whereas the highest value was found in pigs fed the HP diet, and the other two diets were similar to the HP diet or positioned between the HP and LP diets (p< 0.05). Water holding capacity, cooking loss, shear force, and pH in the longissimus muscle were not influenced by varying dietary CP levels (p> 0.05), but the hunter values L and b were increased in pigs fed the LP diet (p< 0.05). Conclusively, a low-protein diet did not negatively affect growth performance, nutrient digestibility, or meat quality.