The main motivation so far for using protease in broiler production has been to reduce feed costs without any loss of animal performance. The reduction of soy in the diet leads to a reduction for all of the environmental impact categories associated with broiler production.
Although livestock production has generally been considered to have various negative environmental impacts, broiler production has often been found to be relatively friendly to the environment. This does not mean, however, that broiler production systems do not have features that require special attention in terms of their environmental consequences. A better control of nitrogen emissions, such as ammonia and nitrous oxide that contribute to global warming and nitrate leaching is one area of concern. Such emissions can occur at many stages of the poultry production chain, including the growing of crops for feed, bird housing and during manure management (Figure 1). Some emissions can have repercussions that are relatively local, for example ammonia can have harmful effects in and close to poultry buildings, while others, such as nitrous oxide, have a global impact.
Popularity of poultry meat growing steadily
The popularity of poultry meat is growing steadily across the globe, with increases in world population, urbanisation and disposable income thought to be the primary contributors. These days it is often the meat of choice for health-conscious consumers looking to reduce the animal fat in their diet. In addition, it does not pose an issue on religious or cultural grounds, unlike some other types of meat. Consequently, in order to keep up with demand and successfully increase output without damaging the environment, the broiler industry will need some operational changes. The emission of nitrogen is recognised especially as a major environmental problem and its impact is seen in three major areas; global warming potential, eutrophication potential and acidification potential.
Global Warming Potential
Global Warming Potential (GWP) is a measure of the greenhouse gas emissions to the atmosphere. Man-made greenhouse gas emissions are thought to be primarily responsible for global warming, causing the atmosphere to trap higher than usual amounts of outgoing long wavelength (thermal) radiation, translating into higher temperatures. The main sources of GWP are carbon dioxide (CO2) from fossil fuel and land use changes, nitrous oxide (N2O) and methane (CH4). The sum of GWP per functional unit is more commonly known as the ‘carbon footprint’. N2O is generated from oxidation/reduction of nitrogen compounds in poultry litter during drying, storage and composting and is proportional to the amount of nitrogen excreted in animal waste.
Eutrophication Potential (EP) is used to assess the over-supply of nutrients reaching water systems through leaching, run-off or atmospheric deposition. Eutrophication can occur in both aquatic and terrestrial ecosystems. In terrestrial ecosystems, the nutrient enrichment of soils through agriculture can eventually lead to drinking water contamination and soil acidification. The main sources are nitrate (NO3-) and phosphate (PO43-) leaching into water and ammonia (NH3) emissions to the air. Both NO3- and NH3 emissions are associated with broiler production. NO3- from the application of nitrogen to crops and NH3 is released from litter in the poultry house and when spread on fields.
The Acidification Potential (AP) is predominantly an indicator of potential reduction of soil pH. The main source is ammonia emissions, together with sulphur dioxide (SO2) from fossil fuel combustion. When SOx and NOx are released into the atmosphere, they can mix with rainwater, forming the acids H2SO4 and HNO3. Agricultural NH3 emissions also cause acidification, due to conversion of NH3 into nitric acid in the atmosphere. Acid rain is a threat to plants, animals, humans, general soil, water biology and even buildings. The release of NH3 from litter in both the poultry house and when spread on fields once again plays an important role.
The use of an in-feed mono-component protease, such as Ronozyme ProAct, has proven to be very successful in the fight against nitrogen emissions due to their ability to improve the amino acid digestibility of commonly used feed ingredients. Ultimately, a more efficient use of protein in feed ingredients translates into less nitrogen excretion in manure, as diets lower in protein can be followed without any loss in the economic performance of the broiler. An additional benefit of re-formulating feeds with a protease is that the amount of soybean in a broiler diet also tends to fall. This has positive consequences for GWP as normally it means the resulting diets have a lower content of ingredients grown in areas of recent land-use change, which in turn means less CO2 emissions.
Life cycle assessment
A systematic quantitative approach is essential to effectively evaluate the environmental impact of complex livestock systems such as broiler production. A methodology called Life Cycle Assessment (LCA) is often used to assess holistically the environmental impact of changes in such systems. It takes into account all the processes in a production chain, starting from the production of the raw materials and ending with waste disposal. For each process, specific data relating to the consumption of resources and the production of potentially harmful emissions are collected. It can be used as an effective tool to compare the environmental implications of enzyme-assisted processes compared to conventional ones. A recent LCA study has quantified the overall environmental impact when Ronozyme ProAct is added to the feed used in standard indoor broiler production.
Everything is taken into account
This LCA assessment was undertaken for typical soya-based diets without protease, containing standard protein content (control), and compared with a diet that was supplemented with protease. In the protease supplemented diets, the protein and amino acid content was also reduced, in line with the digestibility improvements seen with the enzyme. Seven separate trials were evaluated in all and two scenarios were assessed – the feed production chain and the broiler production chain. Data used for the feed production chain included feed crop production, additive production, ingredient and feed processing, ingredient transport and fertiliser production. Whereas data for the broiler production chain took into account everything related to feed production plus energy use in housing the broilers, broiler house emissions, storage and land spreading of the manure, broiler breeder production and hatching. Information for the analysis was sourced from the broiler industry, wherever possible, and it was assumed that all manure was used as a fertiliser.
The results of the analysis of the feed production chain showed that, with protease supplementation, a reduction was seen for all of the environmental impact categories evaluated (Figure 2). The reduction was particularly significant for GWP, reaching a 12% reduction in some cases, with an average of 5%. The main reason for this improvement was a reduced level of soya in the diet when feeding a protease. This was associated with a decrease in CO2 emissions, stemming from land-use changes relating to soya production and its subsequent transport. Small but significant improvements were also seen in EP and larger ones in AP.
When the whole production chain was taken into account (Figure 3), there was a large reduction in both EP and AP. The largest improvement was seen for the AP, with a maximum reduction of 9% and an average of 5%. This was linked to lower housing and manure emissions, with a particular reduction in NH3. By improving the digestibility of amino acids in protein ingredients, proteases can lead to a reduction of nitrogen in manure, resulting in reduced ammonia emission, which in turn affects both the AP and EP.
Effective and practical
The main difference between a normal diet and a protease supplemented diet is a reduction in the amount of soya used. The reduction of environmental impact through this approach is often higher compared with other nutritional studies aiming to reduce soya in broiler diets. For example, the use of realistic inclusions of peas to replace soya reduced the GWP of broiler production by about 4%, but with other European protein sources (beans/sunflower) the reduction was smaller or non-existent. The performance of the birds in these studies was also assumed to have remained unchanged. If, as may be expected with the use of such alternative crops, growth was reduced, the environmental benefits would be even smaller. This indicates that when aiming to improve the environmental performance of broilers, the use of a protease in feed is one of the more promising nutritional strategies, either used alone or combined with other dietary alterations or changes in animal husbandry. Compared with non-nutritional methods aimed at reducing the ammonia emissions arising from poultry, use of a protease can also be considered more practical, as it requires no change in building design or need for capital investment.
Combined environmental and economic benefits
The main motivation for using protease in broiler production has been to reduce feed costs without any loss of animal performance. It now seems clear that such economic benefits are associated with a significant reduction in environmental impact. In certain regions of the world, where regulation determines the amount of nitrogen which can be applied to land, the economic advantages may be further enhanced by the environmental benefits. Protease will not only influence the profitability of an operation, it will also allow an increase in birds reared per unit of land while complying with environmental legislation requirements. Together with improved air quality for both birds and workers through reduced ammonia emissions, the use of a protease becomes an important nutritional strategy.