Excretion calculations of cattle in Finland : Amount and composition of faeces and urine

Abstract

Information of the faeces and urine excreted by different livestock groups is needed in several different functions, including monitoring emissions to air and waters from livestock production and manure management, calculating agricultural nutrient balances, and estimating annual amounts of manure and its nutrients to promote their efficient use. In Finland, Natural Resources Institute Finland (Luke) is responsible for the national excretion calculations. The official Finnish excretion calculations provide national annual amounts of several components of faeces and urine. The most important ones are N, P and amounts of fresh faeces and urine. Several additional components such as dry matter, organic matter and K are also provided. The input data needed in the calculations is updated annually to match the volume of livestock production of each year while the calculation procedures are updated less frequently and only when the methodology can be clearly improved. The calculations are performed annually giving results for each year separately and thus building a time series of excretion per year. As cattle is the main livestock sector in Finland, they produce approximately 75% of all manure in Finland, which is 9 750 000 tons annually (Luostarinen et al. 2023). Thus, it is also essential that their excretion is estimated as precisely as possible. The excretion calculations of cattle are conducted separately for different animal categories based on their gender, age and type of production (dairy and beef). The result for each animal category represents an average animal in Finland, and results from individual farms can deviate significantly from it. The components included in the calculations are nitrogen (N), phosphorus (P), potassium (K), dry matter and organic matter for faeces and urine separately. The annual amounts of all these components are calculated as the difference between nutrient intake and the nutrients retained in the animals and their products, i.e. "nutrient input – nutrient retention = nutrient excretion". While this may sound simple, the actual calculations are complex. A critical factor of excretion calculations is to accurately estimate the amount and composition of feeds consumed on average by the animals in different cattle categories. These data were obtained by calculating the energy requirement of the animals based on their maintenance requirements and the level of production (milk yield and/or growth rate). The diet composition was based on field data and expert assessments. There is much less uncertainty in estimating the amounts of nutrients retained in the animals themselves (growth including foetus) and in the milk excreted than in the intake of nutrients. The detailed steps in the calculations are described in the report. Based on the results for year 2021 as an example, the annual N, P and K excretion of one dairy cow were 145, 22.9 and 125 kg, respectively. For a beef bull aged over 12 months, the annual N, P and K excretions were 69.3, 8.22 and 73.1 kg, respectively.