A Simulation Model to Evaluate the Impact of Grass Management on Milk Yield, Milk Per Area and Feed Efficiency

Harvest time of grass is a critical management decision on dairy farms. This study evaluated which maturity stage harvest would be ideal for three scenarios using the target variables energy‐corrected milk (ECM) yield, milk yield per area and feed efficiency. These scenarios were model based for farms where either barn capacity, land availability or quota regulations were the most limiting factors. From 15 different fields on six farms, 429 samples were taken over the course of 3 years. Samples and test plots were analysed for their constituents and yields. The grass represented permanent grassland and temporary ryegrass fields. Out of these grass samples, potential dry matter intake (DMI), estimated ECM yield, estimated milk yield per area and estimated feed efficiency were predicted with estimated milk yield per area derived from the MILK2016 model and DMI and ECM estimated based on organic matter digestibility (OMD). Predictions showed that harvest at heading was not ideal for all scenarios. Outcomes varied between farms, fields, cuttings, maturity stages, years and types of grassland as well as interactions between those. Effects of maturity stage were strongest in first cuttings and not different in third cuttings. First cuttings showed higher values for all target variables than regrowth. The effect of maturity varied between years, showing differences above 15% for all three target variables. The type of grassland only showed an interaction with the sampling year for estimated milk per area. The ideal harvest time varies depending on the scenario and its most limiting factor. Furthermore, cutting, year and type affect the respective target variables significantly. Especially, the ideal amount of milk per area can be achieved at later maturity stages compared to estimated ECM yield and feed efficiency. Precision farming technologies can help in decision making on harvest timing.