Reducing variability in estimating wastewater composition in dairy farms during milking operations

The estimated waste on dairy farms has been studied from a nutrient management perspective in order to handle waste in an environmentally-friendly way. For pasture-based dairy operations, estimating the amount of manure collected in the milking area is critical for designing management systems. With this aim, the “average stay time” concept was developed as a relevant parameter for the cattle on the milking area. It is possible to estimate the average milking time based on individual milking time, number of cows, number of milking units and batches used to divide the cattle. This time varied, from 0.7 to 3.6 h d−1 in the farms studied. The waste under local operating conditions was characterized with experimental data from five farms. An adjusted estimate for solids and nutrients was generated by normalizing the stay time. Mean values per cow per day for 2 h of average stay time were 590 g total solids (TS), 24.6 g total Kjeldahl nitrogen (TKN), 400 g Chemical Oxygen Demand (COD) and 2.6 g total phosphorous (TP). Comparing data obtained using a standard estimate with this developed estimate, a reduction in standard deviation from 41 to 16% in TKN and 46 to 10% TS was obtained. The adjusted variables were tested from over a year on another farm, showing a significant improvement for estimates.