Silsoe Research Institute,
Silsoe, Bedford,
UK
Sustainable livestock production requires producers to meet product quality specifications and achieve profitability. Equally, however, improved welfare standards need to be attained and compliance be achieved with environmental legislation (e.g. Integrated Pollution Prevention and Control, IPPC) that limits the environmental impact of the production process. This leads to dilemmas for the stockman who traditionally bases his livestock management decisions on judgement and experience. The introduction of integrated management systems (IMS), designed to control simultaneously more than one, and ideally all, inter-related processes, could reconcile these dilemmas.
The first stage of an IMS for broiler production has been developed at Silsoe, based directly on principles taken from control theory. It encompasses a closed-loop, model based control system for calculating the correct diet to be fed to broilers to enable a target weight to be achieved on a target date. The model, a genetic algorithm developed to predict growth rate from nutrients consumed on a daily basis, performed well in full-scale, commercial validation trials.
To quantify the relationships between nutrient uptake, growth, and emissions, simultaneous measurements have been made of diet, bird performance, and emissions of ammonia, dust and odour. A 1% reduction in protein intake corresponded to a little less than a 1% reduction in ammonia emission in a trial involving only cockerels. Direct causal relationships were confounded, however, by other factors, such as gender and disease. Limited litter sampling did not show any single litter characteristic to be a reliable indicator of ammonia emission. Multi-parametric relationships appear to be more promising, but more rigorous litter sampling is required to pursue this. Relationships were found between diet and emissions of dust and odour. Highest dust and odour emissions occurred with the most extreme diets (lowest protein and highest energy), as a consequence of unusually unsettled bird behaviour.
This project has demonstrated the ability to quantify many of the factors involved in pollutant emissions. Integrating environmental parameters into an automated management system is not straightforward, and further work is required to achieve an IMS that can control both production matters and pollutant emissions.
Introduction
Two projects concerning an Integrated Management System (IMS) for broiler production have been completed at Silsoe Research Institute. One sought to develop a genetic algorithm model of bird growth according to nutrient intake; the other sought to measure the emissions of ammonia, dust, and odour according to nutrient intake. Features of the research were the integral role of 3 commercial partners, and that both projects utilised the same full-scale trials on flocks of approximately 35,000 birds reared in 8 identical, modern houses comprising a commercial site. This paper focuses on the second, environmental project.
Approaches and methods
Four of the 8 houses were instrumented to monitor aerial emissions of ammonia, dust and odour. Air was drawn into sampling lines located adjacent to four of the fan ducts in each of the four building. Ammonia concentration in the air was measured by converting the ammonia into nitric oxide, which was fed to a chemiluminescence nitrogen oxide analyser, which was calibrated regularly. These measurements were made continuously throughout each trial. Continuous measurements of ventilation rate were made using impeller sensors installed in six fans (one for each ventilation stage) in each house. Gravimetric dust samples were collected at two locations in each house, at an average interval of about 10 days to enable the inhalable and respirable fractions of the dust during the day and night time to be quantified. At similar intervals, samples of air for odour concentration measurement were collected from a ridge extraction duct. The analysis was carried out according to prEN 13725 (CEN, 1999) using a forced-choice olfactometer and odour panel of six assessors. A litter sample was also collected from each house on these occasions. This was analysed for moisture content, pH, nitrogen content and ammoniacal nitrogen content. Temperature and relative humidity were monitored at two locations in each house. A meteorological mast was erected on the site to monitor temperature, relative humidity, wind speed and wind direction at 10 m height.
Results
The trial diets were generally fed only between crop days 15 and 35 of the (typically) 42 ¬day rearing period. A standard introductory 'starter' diet was fed to establish the flocks, and a standard 'withdrawal' diet was fed over the final week. The birds were fed ad libitum. The extremes to which the role of diet could be tested were restricted by bird welfare considerations, and by compensatory feeding practices adopted by the birds. The most extreme protein intake trial had target intake values of 70%, 80%, 90%, and 100% of the normal commercial practice level, based on the lysine content, which is recognised as being the limiting amino acid. This trial was abandoned for bird welfare reasons because the flocks receiving the lowest protein diets exhibited disturbed, flighty, aggressive behaviour towards each other that reached unacceptable levels. This clearly limited the diet blends that could be tested. The highest dust concentrations (of up to 15 mg/m3 for a 24 hour average) and odour concentrations occurred in this abandoned trial.
One protein trial has been published (Robertson et al, 2000, Robertson et al, 2002). Full experimental descriptions, and detailed results for this specific trial are contained therein. All four houses contained approximately 34,000 cockerels. The target protein intakes were 85%, 90%, 100% and 110% protein (in Houses 1, 2, 3, and 4 respectively). The ammonia concentrations in all 4 houses were consistently below 15 ppm, and so were comfortably below the 20 ppm maximum continuous exposure limit recommended for livestock by the Commission Internationale du Génie Rural (CIGR, 1992).
Mean ammonia emission rates over the crop life were in the range 1.8-2.2 g/hr/500 kg (based on a mean bird weight of 1 kg over the crop duration). These rates are one-quarter to one-fifth of the rate reported previously for broilers in the UK (Wathes, 1998, Misselbrook et al, 2000). These results reveal that modern practices are capable of achieving production at lower concentrations and emissions of ammonia than were indicated by similar, relatively recent measurements in older houses (Wathes et al, 1997). The cumulative ammonia emissions from the four houses in this trial are shown in Figure 1.
An analysis of the actual protein intake in each house showed that the ammonia emission profiles exhibited similarities to the protein intake profiles. The intakes for Houses 2 and 3 were almost identical to each other, and were lower than that in House 4 and higher than that in House 1. The highest protein intake house produced the largest ammonia emission, and the lowest protein intake house produced the lowest emission. A 1% reduction in protein intake corresponded to a little under a 1% reduction in ammonia emitted. A further complicating factor that played a role in this, and in other trials, was an outbreak of Coccidiosis. This appeared to have the effect of reducing ammonia concentrations and hence emissions (due, it is hypothesised, to crusting of the litter), but to different extents depending on the severity of the outbreak in each house. However, other trials revealed other findings that it is important to consider before drawing conclusions.
The cumulative ammonia emissions from another trial are shown in Figure 2. Pullets were reared in Houses 1 and 3 (approximately 39,000 in each), and cockerels in Houses 2 and 4 (approximately 33,500 in each). In Houses 1 and 2, the target diet was changed from low protein to high protein; whilst in Houses 3 and 4 the flocks were retained on a low protein target diet throughout. Compensatory feeding again occurred in the target low-protein houses. Coccidiosis also occurred and was most pronounced in House 2. A particularly interesting indication from this trial is that pullets emit more ammonia than do cockerels (final weights of birds were similar across the four houses), which is consistent with them being less efficient protein converters. The other interesting indication is the further evidence of Coccidiosis corresponding to a reduced ammonia emission (House 2 compared with House 3).
Total ammonia emissions were generally in the range 150-200 kg per house, which is of the order of 5g per bird reared. Non-utilised protein is the primary driver of ammonia emissions. The ability of the bird-growth model to predict this is a valuable tool towards managing ammonia emissions. There is evidence from these trials of the need to model cockerels and pullets separately in this respect, and to model the role of Coccidiosis, which is not an uncommon occurrence in broiler production. The other key parameter influencing ammonia emissions is the litter. Limited litter sampling showed that no single parameter served as a reliable measure of ammonia emissions, but multi-parametric relationships look more promising. However, it was recognised in this study that litter conditions vary markedly across a house floor, and that more detailed sampling is needed to pursue this further.
Inhalable dust concentrations averaged over 24 hours were typically around 5-7 mg/m3 towards the end of the crop (when they tended to be greatest). The respirable dust sub¬-fraction, was found to be approximately one order of magnitude smaller than the inhalable fraction. Generally, concentrations and emissions were a little higher in the day than in the night; emissions were generally higher during the summer than during the winter. Overall, dust emissions were at a maximum towards the end of the crop and were in the range 0.5-1 kg/hr per house of inhalable dust. This corresponds to an emission of the order of 10 g per bird reared. Odour concentrations peaked at 4,000-5,000 odour units (ouE)/m3, but were generally in the range 1,000-3,000 ouE /m3 beyond day 30. Odour emissions peaked at 100,000-150,000 ouE /s but were more generally in the range 20,000-40,000 ouE /s beyond day 30. The most unusually high dust and odour levels corresponded with the most extreme diets (the lowest protein diets in the protein trial, and the highest energy diets in the energy trial) because of the associated unsettled behaviour of the birds.
Conclusions
Unique, commercial-scale trials, each involving some 140,000 broilers in four identical, modern houses, have produced new data and appreciations of the role of diet on aerial pollutant emissions.
Evidence has been obtained of a lower protein intake corresponding to a lower ammonia emission. A 1% reduction in protein intake corresponded to a little less than a 1% reduction in ammonia emission in a trial involving only cockerels. Direct causal relationships are confounded, however, by other factors that were found to be strongly impacting. These included the observations that ammonia emissions were higher for pullets than for cockerels, and that Coccidiosis outbreaks tended to reduce ammonia emissions. The limited litter sampling and analysis that was undertaken did not show any single litter characteristic to be a reliable indicator of ammonia emission. Multi-parametric relationships were found to be more promising, although more detailed litter sampling is required to pursue this. Relationships were also found between diet and emissions of dust and odour. Highest dust and odour emissions occurred with the most extreme diets (lowest protein and highest energy), as a consequence of unusually unsettled bird behaviour.
The bird-growth model developed in the partner project can predict the non-utilised protein consumed by the birds and so provides a prediction of the principal driver of ammonia emissions. If the roles of the outstanding factors described above could be resolved and modelled, then an IMS capable of controlling bird growth and pollutant emissions simultaneously would be achievable.
References
CEN (1999) Air quality - Determination of odour concentration measurement by dynamic olfactometry. Draft prEN 13725, European Committee for Standardisation (CEN), Brussels
CIGR (1992) 2nd Report of Working Group on Climatization of Animal Houses. 2nd Edition. Commission Internationale du GJnie Rural, Faculty of Agricultural Sciences, State University of Gent, Belgium
Misselbrook, T.H., Van Der Weerden, T.J., Pain, B.F., Jarvis, S.C., Chambers, B.J., Smith, K.A., Phillips, V.R., Demmers, T.G.M. (2000) Ammonia emission factors for UK agriculture. Atmospheric Environment, 34,
Phillips, V.R., Cowell, D.A., Sneath, R.W., Cumby, T.R., Williams, A.G., Demmers, T.G.M., Sanders, D. (1998) A review of ways to abate ammonia emissions from UK livestock buildings and waste stores. Final report to MAFF on project WA 0640, Silsoe Research Institute
Robertson, A.P., Hoxey, R.P., Demmers, T.G.M., Welch, S.K., Sneath, R.W., Short, J.L., Richards, A. F., Cook, P.A., Fothergill, A., Filmer, D., Hudson, N.A.J., Fisher, C. (2000) Commercial-scale studies of the effect of broiler protein intake on ammonia emissions. AgEng 2000, Warwick, UK, 2-7 July 2000 (Silsoe Research Institute)
Robertson, A.P., Hoxey, R.P., Demmers, T.G.M., Welch, S.K., Sneath, R.W., Stacey K.F., Fothergill, A., Filmer, D., Fisher, C. (2002) Commercial-scale studies of the effect of broiler protein intake on aerial pollutant emissions. Accepted, Biosystems Engineering
Wathes, C.M., Holden, M.R., Sneath, R.W., White, R.P., Phillips, V.R. (1997) Concentrations and emission rates of aerial ammonia, nitrous oxide, methane, carbon dioxide, dust and endotoxin in UK broiler and layer houses. British Poultry Science, 38, 14-28
Wathes, C.M. (1998) Aerial emissions from poultry production. World's Poultry Science Journal, 54, 241-251
From Proceedings of 11th European Poultry Conference, Bremen, Germany)
