The Asian-australasian Association of Animal, Asian-Australasian journal of animal sciences, 12(33), p. 2039-2049, 2020
DOI: 10.5713/ajas.20.0089
Full text: Unavailable
Objective: This study was conducted to provide models to accurately predict nitrogen (N) and phosphorus (P) excretion of dairy cows on smallholder farms in Indonesia based on readily available farm data.Methods: The generic model in this study is based on the principles of the Lucas equation, describing the relation between dry matter intake (DMI) and faecal N excretion to predict the quantity of faecal N (Q<sub>FN</sub>). Excretion of urinary N and faecal P were calculated based on National Research Council recommendations for dairy cows. A farm survey was conducted to collect input parameters for the models. The data set was used to calibrate the model to predict Q<sub>FN</sub> for the specific case. The model was validated by comparing the predicted quantity of faecal N with the actual quantity of faecal N (Q<sub>FNACT</sub>) based on measurements, and the calibrated model was compared to the Lucas equation. The models were used to predict N and P excretion of all 144 dairy cows in the data set.Results: Our estimate of true N digestibility equalled the standard value of 92% in the original Lucas equation, whereas our estimate of metabolic faecal N was –0.60 g/100 g DMI, with the standard value being –0.61 g/100 g DMI. Results of the model validation showed that the R<sup>2</sup> was 0.63, the MAE was 15 g/animal/d (17% from Q<sub>FNACT</sub>), and the RMSE was 20 g/animal/d (22% from Q<sub>FNACT</sub>). We predicted that the total N excretion of dairy cows in Indonesia was on average 197 g/animal/d, whereas P excretion was on average 56 g/animal/d.Conclusion: The proposed models can be used with reasonable accuracy to predict N and P excretion of dairy cattle on smallholder farms in Indonesia, which can contribute to improving manure management and reduce environmental issues related to nutrient losses.