Modelling nutrients flow for outdoor pig farms: effect of stochasticity
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2016-01-01
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This paper first briefly describes a nutrient partitioning model for outdoor pig farms. The model uses input parameters that are commonly available on outdoor pig farms. The mechanistic and dynamic model simulates both animal performances and nutrient losses to the environment based on dietary energy, protein, amino acid, and mineral intake, and digestibility. The model outputs are feed wastage, bird losses, faecal and urinary excretion for Nitrogen, Phosphorus, Potassium, Sulphur, Calcium, Magnesium, Sodium as well as Total Volatile Solids. A simulation study was conducted to compare total farm Nitrogen excretions and losses obtained by a deterministic model (one average sow; N=1) or a stochastic model (a population of sows; N= 400, 900 and 1400). For the stochastic model the coefficients of variation (CV) were set to 0%, 10% and 15%. Each combination n x CV was run 10 times. Variation was applied to litter size at birth and weaning, daily feed intake, and maximum protein deposition rate. The number of litters per sow and year was set to 2.0, 2.2 or 2.4 and the number of sows per ha was kept constant at 13.9. The results from the simulation study shows that overall, less of the N entering the farm as feed is lost to the environment when the number of litters per sow and year increases (79.5%, 77.5%, and 75.5% for 2, 2.2 and 2.4, respectively). The total amount of nitrogen lost to the environment was slightly higher with the deterministic than the stochastic models (+ 0.3 to 2.1 kg N /ha).
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Occasional report no. 29 - Fertilizer and Lime research centre, 2016, pp. ? - ? (7)