Validation of PigBal model predictions for pig manure production

PigBal is a mass balance model that uses pig diet, digestibility and production data to predict the manure solids and nutrients produced by pig herds. It has been widely used for designing piggery effluent treatment systems and sustainable reuse areas at Australian piggeries. More recently, PigBal has also been used to estimate piggery volatile solids production for assessing greenhouse gas emissions for statutory reporting purposes by government, and for evaluating the energy potential from anaerobic digestion of pig effluent. This paper has compared PigBal predictions of manure total, volatile, and fixed solids, and nitrogen (N), phosphorus (P) and potassium (K), with manure production data generated in a replicated trial, which involved collecting manure from pigs housed in metabolic pens. Predictions of total, volatile, and fixed solids and K in the excreted manure were relatively good (combined diet R2 ≥ 0.79, modelling efficiency (EF) ≥ 0.70) whereas predictions of N and P, were generally less accurate (combined diet R2 0.56 and 0.66, EF 0.19 and -0.22, respectively). PigBal generally under-predicted lower N values while over-predicting higher values, and generally over-predicted manure P production for all diets. The most likely causes for this less accurate performance were ammonium-N volatilisation losses between manure excretion and sample analysis, and the inability of PigBal to account for higher rates of P uptake by pigs fed diets containing phytase. The outcomes of this research suggest that there is a need for further investigation and model development to enhance PigBal's capabilities for more accurately assessing nutrient loads. However, PigBal's satisfactory performance in predicting solids excretion demonstrates that it is suitable for assessing the methane component of greenhouse gas emission and the energy potential from anaerobic digestion of volatile solids in piggery effluent. The apparent overestimation of N and P excretion may result in conservative nutrient application rates to land and the over-prediction of the nitrous oxide component of greenhouse gas emissions. © CSIRO 2016

Predicting long-term solid accumulation in waste stabilisation lagoons through a combined CFD-process model approach

Sludge accumulation in anaerobic lagoons is one of the major issues determining long-term operating costs. However, very little mechanistic analysis has been done on long-term sludge behaviour. A coupled hydrodynamic-biochemical model was developed using computational fluid dynamics (CFD), and results from this applied to a compartmental based model (CBM) for long-term simulation. The CFD model incorporates a mixture method for the spatial-and temporal evolution of fluid and solids with a non-Newtonian rheology. CFD was used to evaluate short term hydrodynamics, and a common CBM used to understand the fluid movement and sludge behaviour of full-scale anaerobic lagoons (with varying depths, sidewall slopes, and loading rates), operating in commercial piggeries located in Southern Queensland and Southern New South Wales, Australia. The results found that the lagoons had varying hydrodynamics, and sludge accumulates rapidly in sloped sidewall lagoons, forming a variable depth bed which occupied a substantial fraction of the lagoons. Shallow lagoons were dominated by significant surface recirculation dynamics, and were susceptible to solids accumulation, while deep lagoons allowed the formation of a well developed settled fraction. Predicted lagoon lifetimes varied substantially, but predicted long-term accumulation rates were approximately double that observed, due to long-term degradation of slowly degradable material

Predicting long-term solid accumulation in waste stabilisation lagoons through a combined CFD-process model approach

Sludge accumulation in anaerobic lagoons is one of the major issues determining long-term operating costs. However, very little mechanistic analysis has been done on long-term sludge behaviour. A coupled hydrodynamic-biochemical model was developed using computational fluid dynamics (CFD), and results from this applied to a compartmental based model (CBM) for long-term simulation. The CFD model incorporates a mixture method for the spatial-and temporal evolution of fluid and solids with a non-Newtonian rheology. CFD was used to evaluate short term hydrodynamics, and a common CBM used to understand the fluid movement and sludge behaviour of full-scale anaerobic lagoons (with varying depths, sidewall slopes, and loading rates), operating in commercial piggeries located in Southern Queensland and Southern New South Wales, Australia. The results found that the lagoons had varying hydrodynamics, and sludge accumulates rapidly in sloped sidewall lagoons, forming a variable depth bed which occupied a substantial fraction of the lagoons. Shallow lagoons were dominated by significant surface recirculation dynamics, and were susceptible to solids accumulation, while deep lagoons allowed the formation of a well developed settled fraction. Predicted lagoon lifetimes varied substantially, but predicted long-term accumulation rates were approximately double that observed, due to long-term degradation of slowly degradable material

Demographics and practices of semi-intensive free-range farming systems in Australia with an outdoor stocking density of ≤1500 hens/hectare

Baseline information on demographics and practices on semi-intensive free-range egg farms with an outdoor stocking density of ≤1500 hens/hectare in Australia is presented. Free-range egg production is changing the structure of the egg industry in Australia and a broad variety and tiers of free-range systems have emerged due to lack of concrete legislative standards on outdoor stocking densities in the past. Information was extracted from a pre-existing online free-range poultry survey dataset, consisting of a total of 79 questions related to nutrition, pasture management, welfare and health, animal housing, environmental impact and economics. Forty-one free-range egg farms, with an outdoor stocking density of ≤1500 hens/hectare, were identified in the dataset from all major Australian states. Two types of semi-intensive free-range housing systems were documented: mobile (modified caravan/trailer) housing (56%), and fixed sheds (44%). Seventy-two percent of respondents reported >75% of the hens in the flock used the outdoor range. All respondents reported ingestion of range components by hens in the form of vegetation, insects, stones and grit. Up to 10% mortality was reported by 40% respondents with predation (34%), cannibalism (29%), heat stress (24%) and grass impaction (19.5%) as major causes. Biosecurity on farms was sub-optimal with 8 of the 10 actions implemented by <50% respondents. Customer demand, consumer sentiment and welfare were the major factors for farmers moving into free-range egg production. This study resulted in identification of current practices and key challenges on semi-intensive free-range egg farms. Applied research and communication of results to farmers is highly recommended to ensure optimum health and welfare of free-range laying hens and sustained egg production

Demographics and practices of semi-intensive free-range farming systems in Australia with an outdoor stocking density of ≤1500 hens/hectare

Baseline information on demographics and practices on semi-intensive free-range egg farms with an outdoor stocking density of ≤1500 hens/hectare in Australia is presented. Free-range egg production is changing the structure of the egg industry in Australia and a broad variety and tiers of free-range systems have emerged due to lack of concrete legislative standards on outdoor stocking densities in the past. Information was extracted from a pre-existing online free-range poultry survey dataset, consisting of a total of 79 questions related to nutrition, pasture management, welfare and health, animal housing, environmental impact and economics. Forty-one free-range egg farms, with an outdoor stocking density of ≤1500 hens/hectare, were identified in the dataset from all major Australian states. Two types of semi-intensive free-range housing systems were documented: mobile (modified caravan/trailer) housing (56%), and fixed sheds (44%). Seventy-two percent of respondents reported >75% of the hens in the flock used the outdoor range. All respondents reported ingestion of range components by hens in the form of vegetation, insects, stones and grit. Up to 10% mortality was reported by 40% respondents with predation (34%), cannibalism (29%), heat stress (24%) and grass impaction (19.5%) as major causes. Biosecurity on farms was sub-optimal with 8 of the 10 actions implemented by <50% respondents. Customer demand, consumer sentiment and welfare were the major factors for farmers moving into free-range egg production. This study resulted in identification of current practices and key challenges on semi-intensive free-range egg farms. Applied research and communication of results to farmers is highly recommended to ensure optimum health and welfare of free-range laying hens and sustained egg production

Temporal and spatial trends in adult nuisance fly populations at Australian cattle feedlots

A comprehensive trapping program to determine the species composition, seasonality and distribution of adult nuisance fly populations at a southern Queensland feedlot was conducted from 2001 to 2003. Short-term information on nuisance fly populations was also collected from two feedlots located in other climatic regions. Twenty-five species of Diptera were identified. The more commonly trapped species were the house fly, Musca domestica L. (Muscidae) (38%), the hairy maggot blowfly, Chrysomya rufifacies (Macquart) (Calliphoridae) (27%) and the bush fly, Musca vetustissima Walker (Muscidae) (15%). Seasonal effects were the major determinant of fly populations. All commonly trapped fly species had low abundance during the coldest winter months, July and August. Musca domestica had one annual, broad peak in abundance starting in spring and extending over about 8 or 9 months. Musca vetustissima had a major abundance peak in October/November and a smaller peak around April. Stomoxys calcitrans (L.) (stable fly) (Muscidae) showed two annual peaks in abundance, with the major peak in May. Chrysomya spp. were most abundant during spring, summer and autumn, whereas the highest numbers of Calliphora augur (F.) (blue-bodied blowfly) (Calliphoridae) were trapped in winter. The sites within the feedlot with the highest catches of M. domestica were the feed mill, cattle pens and the hospital area and of S. calcitrans the manure piles, silage pits and the feed mill. The lowest catches of M. domestica and S. calcitrans were obtained in the traps situated a few kilometres outside the feedlot. In contrast, M. vetustissima and blowfly catches were higher in outside traps and traps near the manure piles than any other feedlot site. There was a correlation between the animals' number of fly avoidance movements and M. domestica catches and between the number of leg stomps and stable fly catches, respectively

Demographics and practices of semi-intensive free-range farming systems in Australia with an outdoor stocking density of ≤1500 hens/hectare

<div><p>Baseline information on demographics and practices on semi-intensive free-range egg farms with an outdoor stocking density of ≤1500 hens/hectare in Australia is presented. Free-range egg production is changing the structure of the egg industry in Australia and a broad variety and tiers of free-range systems have emerged due to lack of concrete legislative standards on outdoor stocking densities in the past. Information was extracted from a pre-existing online free-range poultry survey dataset, consisting of a total of 79 questions related to nutrition, pasture management, welfare and health, animal housing, environmental impact and economics. Forty-one free-range egg farms, with an outdoor stocking density of ≤1500 hens/hectare, were identified in the dataset from all major Australian states. Two types of semi-intensive free-range housing systems were documented: mobile (modified caravan/trailer) housing (56%), and fixed sheds (44%). Seventy-two percent of respondents reported >75% of the hens in the flock used the outdoor range. All respondents reported ingestion of range components by hens in the form of vegetation, insects, stones and grit. Up to 10% mortality was reported by 40% respondents with predation (34%), cannibalism (29%), heat stress (24%) and grass impaction (19.5%) as major causes. Biosecurity on farms was sub-optimal with 8 of the 10 actions implemented by <50% respondents. Customer demand, consumer sentiment and welfare were the major factors for farmers moving into free-range egg production. This study resulted in identification of current practices and key challenges on semi-intensive free-range egg farms. Applied research and communication of results to farmers is highly recommended to ensure optimum health and welfare of free-range laying hens and sustained egg production.</p></div

Main categories and information within each category recorded in the survey questionnaire.

<p>Main categories and information within each category recorded in the survey questionnaire.</p

Feed characteristics and management as reported by respondent farms.

<p>Feed characteristics and management as reported by respondent farms.</p

Range access on respondent free-range farms with a stocking density of 1500 hens/hectare.

<p>(a) Percentage of barn wall covered by pop-holes (b) Percentage of range used by hens (c) Percentage of flock using the range area (d) Hours/day birds access the range.</p