Nutritional approaches to reducing the environmental impact of outdoor pigs
Published: October 3, 2007
By: S A Edwards
Our thanks to the author and Conference Organisers, a Committee consisting of both University and Industry colleagues.
The full paper will appear in the Conference Proceedings ('Recent Advances in Animal Nutrition - 2007', edited by Phil Garnsworthy and Julian Wiseman) published by Nottingham University Press in the autumn of 2007 www.nup.com
Courtesy of the 41st Annual University of Nottingham Feed Conference www.nottingham.ac.uk/biosciences/ah/research/conferences.php
The challenges of outdoor pigs
The growth of outdoor pig production in the UK has been driven by economic, marketing and agronomic advantages. Outdoor pigs offer the producer a cost effective production system, with favourable consumer perception of animal welfare which has resulted in niche marketing opportunities. They also offer the landowner a good “break crop” in an arable rotation, giving effective land clearance of volunteers and a significant manurial residue for the subsequent crop, allowing savings in inorganic fertiliser.
However, management of their environmental impact poses challenges under conditions of year round land occupation and nutrient deposition. At current commercial stocking rates, the level of deposition of excreted nutrients onto land can be high. With the historic approach of using a single diet for dry and lactating sows for simplicity of management, inputs could total as much as 600 kg N and 150 kg P per hectare per annum.
Because the free-draining soils best suited to pig production are also those giving greatest risk of nutrient leaching to groundwater, plant capture and utilisation of these deposited nutrients is highly desirable. However, the nature of rotation management and land rental arrangements often results in pigs moving onto autumn stubbles, where vegetation cover has little opportunity to establish.
Even when pigs go on to established vegetation, their rooting and foraging activities can quickly remove ground cover. This leaves bare soils giving higher risk of gaseous nitrogen loss by volatilisation in warm dry conditions, and nitrogen and phosphorus run-off and leaching during periods of high rainfall. Whilst nose-ringing of pigs can preserve vegetation, and reduce these risks, animal welfare considerations make this approach contentious.
Meeting the challenges
There is no single, or simple, solution to preventing environmental impact of outdoor pigs. Producers must therefore combine nutritional, management and agronomic approaches to target key risk factors.
Reducing levels of excreted nutrients
Modern nutritional expertise makes it possible to match dietary inputs more closely to requirements, and hence reduce excess nutrients excreted onto land. Historically, diet formulation for outdoor pigs has focussed more on simplicity of management and physical quality of feed than on minimising nutrient excretion, and these objectives may sometimes be in conflict. Limitations are imposed by raw material costs, lack of a wider range of commercially available synthetic amino acids and uncertainties about the safety margins needed to avoid detrimental effects on performance. However, significant reductions can be made by raw material selection, enzyme utilisation and dietary specification adjustment for season, stage of the reproductive cycle and, in the case of batch stocked sites, for sow parity.
Reducing nutrient loss from feed wastage
Outdoor systems require significantly higher feed inputs than indoor systems (typically by 10-15%), arising from climatic penalties and wastage through ground feeding losses and wildlife scavenging. The relative contribution of these sources of poorer feed utilisation is still uncertain. In order to target nutrient inputs more accurately, it is important to know and maximise actual intake, and minimise wastage of feed provided. Evidence from the spatial distribution of soil nutrients after pig occupation suggests significant wastage might be occurring around feeding areas. Management strategies to reduce this by trough feeding have resulted in better feed efficiency, but require care in implementation.
Managing pig excretory behaviour
Even when nutrient excretion is minimised by good diet formulation, the excretory behaviour of pigs can still result in localised areas of high soil nutrient loading and hence pollution risk. Understanding and modifying the natural behaviour of the animals is key to achieving better spatial distribution of excreta, and hence more even manuring of following crops.
Promoting and utilising vegetation cover
Capture of excreted inorganic nutrients by vegetation and their fixation in slow release organic forms offers the greatest potential for minimising short term nutrient losses and maximising long term nutrient utilisation in rotations incorporating pigs. Dietary modifications to reduce foraging motivation of dry sows by increasing fibre content may slow vegetation destruction, and strategic use of root crops might also play a role. Predicting and adjusting for nutrient intake from pasture and forages will then become important in refining dietary inputs. Data on this subject are currently limited, but indicate that significant contributions to overall nutrition could be achieved.
Conclusions
Managing the nutrition of outdoor pigs for reduced environmental impact, in addition to maximal reproductive performance, requires more closely targeted nutrient inputs than in the past, in combination with skilled system management and careful rotation planning. By achieving this, outdoor pigs can continue to be regarded as a valuable rotation option rather than an environmental hazard.
Acknowledgements
Work described in this paper has been funded by SEERAD and by the Defra “Ecopig” project (IS0215). I gratefully acknowledge the input of many collaborators and students at Newcastle University, SAC, CEH and BQP, and the co-operation of commercial producers in carrying out trial work.
Author: S A Edwards
Newcastle University, School of Agriculture, Food and Rural Development, Agriculture Building, Newcastle upon Tyne NE1 7RU
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