A systems approach to evaluate nitrogen utilization efficiency and environmental impacts of swine growing-finishing feeding programs in U.S. pork production systems

Abstract

Traditionally, swine diets have been formulated to meet nutrient requirements at the lowest cost with little regard toward minimizing environmental impacts. The overall objective of this study was to evaluate the relative differences among four grower-finisher feeding programs, using precision diet formulation practices, on growth performance, carcass composition, nitrogen utilization efficiency, and environmental impacts. In Exp. 1, four 4-phase growing-finishing feeding programs consisting of diets containing corn and soybean meal (CSBM), low protein CSBM supplemented with crystalline amino acids (LP), CSBM with 30% distillers dried grains with solubles (DDGS), and DDGS supplemented with crystalline Ile, Val, and Trp (DDGS+IVT) were fed to 288 mixed sex pigs (initial BW = 36.9 ± 4.2 kg) for 12-wk to determine effects on growth performance and carcass characteristics. Pigs fed CSBM had greater (P < 0.05) final BW than those fed LP and DDGS, and greater gain efficiency than pigs fed LP. Pigs fed DDGS+IVT tended to have greater (P = 0.06) backfat depth than pigs fed DDGS, and less (P < 0.05) loin muscle area than pigs fed CSBM. In Exp. 2, nitrogen (N) and phosphorus (P) balance of barrows (n = 32; initial BW = 59.9 ± 5.1 kg) fed each of the phase-2 diets from Exp. 1 was determined in a 12-d metabolism study (7-d adaptation and 5-d collection). Pigs fed CSBM had a greater (P < 0.05) amount of N retained than pigs fed other diets, but also had a greater (P < 0.05) amount of urinary N excretion and blood urea N than pigs fed LP and DDGS+IVT diets. Pigs fed LP tended (P = 0.07) to have the greatest N utilization efficiency but the least (P < 0.05) P retained as a percentage of P intake among dietary treatments. Diet composition and data collected from Exp. 1 and 2 were used to calculate life cycle assessment environmental impacts using Opteinics™ software (BASF, Lampertheim, Germany). The CSBM feeding program had the least impact on climate change, marine and freshwater eutrophication, and fossil resource use. The LP feeding program had the least impact on acidification, terrestrial eutrophication, and water use, while the DDGS feeding programs had the least impact on land use. These results indicate that feeding corn-soybean meal diets optimized growth performance and carcass composition while simultaneously reducing impacts on climate change, marine and freshwater eutrophication, and fossil resource use compared with the other feeding programs evaluated.