An Increase in Dietary Net Energy Concentration Affects Nutrient Digestibility and Noxious Gas Emissions and Reveals a Better Growth Rate in Growing–Finishing Pigs

This experiment was performed to evaluate the optimum level of net energy (NE) to improve growth performance and nutrient digestibility, and reduce noxious gas emissions in growing-finishing pigs. A total of 150 pigs ([Yorkshire × Landrace] × Duroc) with an initial average body weight (BW) of 32.64 ± 1.49 kg were randomly assigned to one of five treatments for 112 days (16 weeks: growing stage, initial-week 6; finishing stage, 6-finish/week 16). There were five treatment groups with six replicates and five pigs (three males and two females) per pen. The dietary treatment includes CON, a basal diet (NE 2475 kcal/kg), TRT1, basal diet -5.0% NE (2353 kcal/kg), TRT2, basal diet -2.5% NE (2414 kcal/kg), TRT3, basal diet +2.5% NE (2537 kcal/kg), and TRT4, basal diet +5.0% NE (2599 kcal/kg). Through the experiment, increasing NE by +5.0% increased average daily gain and bodyweight, having the highest value (<i>p</i> < 0.05) and a decreased feed conversion ratio (<i>p</i> < 0.05), whereas decreasing NE by -5% decreased average daily gain (<i>p</i> < 0.05) and increased feed conversion ratio (<i>p</i> < 0.05) at week 6 with no effects on nutrient digestibility and noxious gas emission. Hence, integrating the increasing level of net energy (NE) with +5.0% into the pig diet during the growing-finishing phase can be considered the appropriate approach for enhancing both average daily gain and feed efficiency in pigs. A +5% (2599 kcal/kg) increase in NE has the potential to reduce costs by lowering the amount of feed needed while either sustaining or improving growth, as the use of energy-dense ingredients becomes more cost effective.