AGA IN ACTION
FAO Technical Session ‘Nutrient use efficiency in animal food chains’
This session was held on 6 December (2 to 6 p.m.) as a special event at the 5th International Nitrogen Conference: Reactive Nitrogen Management for Sustainable Development – Science, Technology and Policy, held in New Delhi (3-7 December 2010) (http://www.n2010.org/).
The objectives of holding this session were:
- a) to discuss and identify strategies for enhancing nutrient use efficiency in animal food chains,
- b) identify future R and D needs, and
- c) sensitize crop scientists to integrate nutrients in the manure in the comprehensive nitrogen management strategy for sustainable intensification of crop production.
Presentations covered basic aspects of feed use efficiency in livestock production, manure excretion and management with examples from dairy in the US, pigs in China and Portugal, poultry and ruminants in India, and ruminants in sub-Saharan Africa.
Conclusions and Recommendations
A substantial amount (60 to 90%) of the N and P fed to livestock is excreted in manure, which can enhance or be detrimental to crop production and the environment. If livestock stocking rates do not exceed land carrying capacities, and if managed properly, manure can have positive impacts on crop production and reduce the need for fertilizer N. Other nutrients (e.g., P, micronutrients) could be recycled by using manure as a fertilizer. Manure is also a good source of carbon, which improves the physical properties of soil and enhances soil water and nutrient retention. A more holistic view is needed in nutrient management for crop production by recognizing and accounting for the nutrients contained in manure.
Synergies exist between strategies for enhancing N and C use in animal food chain and for mitigation of green house gases (GHG). Therefore, increasing food security through improved animal nutrition and manure management and mitigation of climate change are not in conflict.
In developing country situations increasing production and efficiency of the system through improved animal health, fertility, longevity and nutrition hold the most potential for enhancing nutrient use efficiency in animal food chains.
Life cycle analyses (LCA) should be integrated in the development and use of strategies for enhancing nutrient use efficiency and for evaluating impacts on the environment and climate change.
Feeding strategies such as the use of total mixed rations (TMR) and rumen bypass protein in ruminant livestock systems, and the use of phytase in monogastric animals have great potential for enhancing feed nutrient use efficiency. Further R and D work is required to develop other feed processing and use technologies for enhancing nutrient use efficiency.
A number of other dietary approaches are available for enhancing nutrient use efficiency in animal food chains. A document highlighting such approaches could assist in developing animal rations that enhance nutrient use in livestock production system, leading to higher animal production while conserving the environment, natural resources and biodiversity.
Future options for enhancing nutrient use efficiency in animal food chains are: a) understanding the genetics and selecting animals for higher feed conversion efficiency, longevity and fertility, which would maximize feed nutrient conversion into production (e.g., meat, milk) and reduce nutrient excretions in manure, b) breeding forage crops that have optimum energy-to-protein ratios, and c) use of feed additives (e.g., tannins, saponins, probiotics), which seem to have potential to enhance feed conversion efficiencies although longer-term in vivo studies are required to evaluate persistent and consistent effects.
A considerable portion of N (and C) contained in manure from animals fed browses and tree leaves is present in the bound form (due to the presence of polyphenolics), which can be retained in the soil for longer. The addition of low amounts of tannins and other polyphenolic-containing additives to animal diets may therefore enhance feed protein utilization and produce manure that enhances soil N availability and carbon sequestration. Studies on emission of gases from such manures in soil and uptake of nutrients by crops are required.
A substantial part of N in the manure may be lost to the environment as ammonia, or leached through soil as nitrates, which can then denitrify and be emitted as nitrous oxide, a potent GHG. Strategies are required to capture this nitrogen in the manure thereby enhancing the fertilizer N value of manure and decrease negative impacts on the environment.
Guidelines for proper management of manure under tropical conditions should be developed, extended and implemented.
Simple analytical tools are needed for assessing the types, amounts and plant availability of nutrients present in the manure.