Environmental assessment of digestibility improvement factors applied in animal production

Abstract

Background, Aims and Scope. Many feed ingredients are not fully digested by livestock. However, the addition of digestibilityimproving enzymes to the feed can improve the absorption of e.g. energy and protein and thereby enhance the nutrient value of the feed. Feed production is a major source of environmental impacts in animal production, and it is obvious to assume that enzyme supplementation can help to reduce the environmental impact of animal production. The purpose of the study is, therefore, to assess and compare the environmental burdens of the supplements and compare them with the savings made when enzymes are used in animal production. The properties of enzymes vary considerably and the study takes as its starting point a particular enzyme product, Ronozyme WX CT. Ronozyme WX CT is a xylanase which depolymerises xylans (a group of dietary fibres found in cereal cell walls) into smaller units. The product is a widely accepted means of improving the energy value and the protein digestibility of pig and poultry feed. The study relates to Ronozyme WX CT used for fattening pigs produced in Denmark. Methods. Lifecycle assessment is used as the analytical method, and Ronozyme WX CT production and reductions in feed consumption are modelled using SimaPro 7.0.2. Data on Ronozyme WX CT production are derived from Novozymes' production facilities in Denmark. Other data are derived from the literature and from public databases. Changes in feed consumption are determined by modelling in AgroSoft feed optimisation software. Guidelines from the Intergovernmental Panel on Climate Change (IPCC) are used to estimate reductions in the emission of greenhouse gases resulting from reduced manure generation and changed manure composition. Results. The study shows that the use of Ronozyme WX CT to increase the nutritional value of pig feed is justified by major advantages in terms of reduced potential contribution to global warming, acidification and photochemical ozone formation and reduced use of energy, and in most cases also nutrient enrichment and use of agricultural land. Ronozyme WX CT (xylanase) is often used together with Ronozyme P5000 CT (phytase) and together the two products can contribute considerably to reducing a broad range of environmental impacts from pig production. Discussion. Reduced contribution to acidification and nutrient enrichment is partly driven by reduced feed consumption and partly reduced N-emissions with manure resulting from reduced protein content of the feed. Sensitivity analyses of a range of parameters show that the observed advantages are generally robust although exact magnitudes of environmental advantages are associated with much variation and uncertainty. It should, however be noted that certain changes (e.g. of feed prices) may turn contributions to nutrient enrichment and use of agricultural land into trade-offs. Conclusions. Improvement of energy and protein value of pigfeed by application of Ronozyme xylanase and following feed savings reduces impact on environment per unit of pig-meat produced, and the enzyme product contributes to a sustainable development the Danish pork meat supply. Recommendations. Digestibility-improving enzymes are a promising means of reducing the environmental impact of pig production. The greenhouse gas reducing potential of Ronozyme WX CT in Danish pig production has been estimated at 5% and in the order of 4 million tons of CO2 equivalents if the results are extended to the whole of Europe. Use of Ronozyme WX CT is driven by overall cost savings in animal production, and it is therefore recommended that digestibility-improving enzymes are given more attention as a cost-efficient means of reducing greenhouse gas emissions.