Prediction of manure nitrogen and carbon output from grower-finisher pigs

Abstract

Intensive pig production may be a hazard to the environment due to plant nutrient leakage and losses. To facilitate efficient and sustainable manure management and reduce oversupplying of crops with nutrients, there is a need for precise assessment of nutrient content in manure and manure excretion. This study has developed algorithms for predicting the amount of excreta and manure content of nitrogen (N) and carbon (C). Data compiled from 285 digestibility and N balance experiments with growing-finishing pigs diets fed diets varying widely in chemical composition were used to establish algorithms. The main input variables were analysed nutrients contents together with intake of dry matter and digestibility of organic matter (diOM). The accuracy and prediction power of the obtained prediction equations were tested with another dataset consisting of 116 digestibility and N balance experiments with varying chemical compositions. Prediction equations related to C was tested using 26 digestibility experiments. The dietary fibre (DF) fractions like crude fibre, non-starch polysaccharides (NSP), analysed DF and calculated dietary fibre (cDF) were all highly negatively correlated to digestibility and positively to manure output. Including more than one or two predictors only marginally improved predicting the C and N content in excreta as well as the daily excretion rates. The best predictor for estimating the daily amount of faeces and daily faecal N and C excretion was diOM, and the second best predictor was cDF. However, the equations became more precise when dry matter intake or animal body weight was added as independent variable. For urine N equations, the dietary protein intake was the best predictor. The partitioning of N between faeces and urine was related to the concentration of cDF with a shift in N excretion in urine to N excreted in faeces as more carbohydrate was fermented. The ratio of C/N in faeces was depending on cDF in the diet. The wide variation in the diets included in the predictions ensures that the equations also are relevant and applicable in developing as well as developed countries as a useful tool for efficient handling and use of manure nutrients in practice.