This meta-analysis evaluates the impact of reducing crude protein (CP) levels in growing pig diets on manure nitrogen emissions to identify strategies for maximizing environmental benefits. A systematic search of PubMed, ISI Web of Science, and Scopus (2003 to 2024) yielded 56 observations from 10 studies. We employed random-effects models with restricted maximum-likelihood (REML) estimation and used Hedges’ g to calculate standardized mean differences (SMD). Additionally, meta-regression and broken-line regression analyses were conducted to investigate heterogeneity and emission breakpoints. The results indicate that low-protein diets significantly reduce both urinary nitrogen emissions (SMD = -5.09; p < 0.0001) and fecal nitrogen emissions (SMD = -0.79; p < 0.001). Substantial heterogeneity was observed for both fecal ($I^2$ = 81.6%) and urinary ($I^2$ = 81.7%) nitrogen emissions (p < 0.0001), highlighting the influence of varying study conditions. Broken-line regression analysis identified a significant breakpoint for urinary nitrogen emissions at 18.8% CP (p < 0.01), whereas no significant breakpoint was observed for fecal nitrogen emissions. Meta-regression analysis revealed that every 1% decrease in dietary CP was associated with increased supplementation of synthetic amino acids, including DL-methionine (p < 0.05), DL-tryptophan (p < 0.04), and L-threonine (p < 0.02), with L-lysine showing a tendency to increase (p = 0.10). Furthermore, economic analysis demonstrated that a moderate reduction to 15% CP, supplemented with four essential amino acids, yields a net cost saving of approximately $2.80 USD per metric ton; conversely, a drastic reduction to 13% CP incurs a net cost increase of approximately $14.30 USD per metric ton due to the high cost of valine and isoleucine. In conclusion, reducing dietary crude protein levels serves as an effective strategy for mitigating urinary nitrogen emissions, necessitating the precise supplementation of synthetic amino acids to balance environmental benefits with the nutritional requirements of growing pigs.

This experiment was conducted to evaluate the effects of migration frequency on growth performance, blood profile, pork quality and economical analysis in growing-finishing pigs. A total of 56 growing pigs [(Yorkshire×Landrace)×Duroc] with an initial body weight 28.01±4.09 kg were used in this experiment. Pigs were randomly allocated to one of two treatments in a randomized complete block design and 7 replicates with 4 pigs per pen. Experimental treatments were 1) 1 site: growingto- finishing at 1.24 m2/head, 2) 2 site: growing facility for 6 week at 0.81 m2/head followed by move to the finishing facility at 1.24 m2/head. Feeding trial was composed by two growing phase (0-3 week, 4-6 week) and two finishing phase (7-9 week, 10-12 week). As a result, different pig flows influenced on growth performance of growing-finishing pigs and 1 site treatment showed higher average daily gain, average daily feed intake, and G:F ratio on growing phase (0-6 week, p<0.01). The 2 site treatment showed higher serum cortisol level at week 6 (p=0.03). In carcass evaluation, 1 site treatment had shorter days to slaughter 110 kg body weight (p=0.01). Consequently, 1 site system had better performance and economical profits for swine farms.