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.

본 실험에서는 외인성 효소 첨가제 및 혼합 세균 배양을 통한 고상발효(Solid-state fermentation, SSF)가 채종박(Rapeseed meal, RSM)의 체외건물소화율(In vitro dry matter digestibility, IVDMD) 및 단쇄지방산(Short chain fatty acid) 생성에 미치는 영향을 조사하기 위해 수행되었다. 외인성 효소 칵테일(첨가 및 미첨가) 및 RSM에 대한 SSF(발효 및 비발효)를 나타내는 2 x 2 요인 설계가 적용되었다. 3-step 돼지 소화율 모델을 적용하여 채종박의 건물 소화율을 분석하였으며, 72시간 대장발효 후 상층액을 수집하여 단쇄지방산 생성량을 분석한 후 칼로리 단위로 변환하여 가소화에너지 소화율을 분석하였다. 소장 (IVDMDh) 및 전장 (IVDMDt) 건물소화율에서는 고상발효된 채종박이 더 높게 나타났다 (각각 p < 0.01). 마찬가지로, 외인성 효소 첨가제 처리구에서 채종박의 소장 소화율(IVDMDh)이 증가하는 경향을 나타냈다(p = 0.06). Acetic acid 및 butyric acid의 생산은 대조구에 비해 고상발효 처리 시 유의하게 더 생산되었으며 (각각 p < 0.01), 이는 총 단쇄지방산의 생산 증가 경향을 나타냈다(p = 0.09). 에너지 소화율에서는 채종박의 고상발효 및 외인성 효소제 첨가가 유의적으로 높게 나타났다 ( p < 0.01). 그러므로 채종박의 고상발효 처리는 단백질 이용성을 비롯한 영양적 가치를 향상시키는데 효과적이라고 사료된다.

‘Gwangan’ is a new six-rowed covered barley cultivar developed by the National Institute of Crop Science (NICS), R.D.A in 2004. This cultivar is developed from a cross between “Mirak” and ‘Milyang59’ in 1995. An F6 selection was made at Milyang in 2001 an