Repeatability in ranking of dairy farms on technical and economic performance over years.

Repeatability of farm average 305-day milk production and gross margin per 100 kg of milk was evaluated for 39 farms. Ranking of gross margin, its underlying factors (i.e. milk price, returns from cull cows and calves, costs of concentrates, and costs of roughage purchases per 100 kg of milk), and 305-day milk production was not completely random over the four years of the study. The coefficient of concordance ranged between 0.55 and 0.82. The costs of roughage purchased had the lowest concordance over time, and 305-day milk production had the highest concordance. For each year and each farm, the difference between average gross margin and farm-specific gross margin was calculated. The standard deviations (SD) of these values was calculated for each farm, and showed differences between farms in variability in gross margin over years (the farm-year-specific SD varied between farms from 0.56 to 5.73). All the underlying factors showed a deviation over years. So, variability of gross margin can be due to changes in all underlying factors. The impact on gross margin of purchased roughage was not of major importance because its absolute impact on the gross margin is small. We concluded that milk-production data over one year is a reliable indicator for the typical farm milk production. Because gross margin fluctuates considerably over time, however it is preferred to base economic research on data from more than one year.

An approach to nutrient management on dairy farms.

In the European Union, groundwater should contain less than 50 mg of nitrate/L. Individual countries have developed alternative strategies for phosphorus (P). In The Netherlands, regulations based on P limited the amount of manure applied per hectare. A more balanced P supply to the land has been achieved by transport of manure from surplus to deficit regions. Costs of processing of manure to pellets appeared to be (too) high. In animal production experiments, lowering the P content of concentrates and mineral supplements reduced P losses without an adverse effect on production. In addition to the European guideline for nitrate, ammonia volatilization should be reduced by 50 to 70%. Management practices for reducing nitrogen (N) losses were studied with a farm model, developed at PR. A combination of a more efficient use of fertilizer N, restricted grazing, and a more balanced diet, and, to a lesser extent, higher milk production per cow resulted in considerable reductions in nitrate leaching. The application of slurry by injection diminishes the ammonia volatilization at farm level by almost 50%. This technique has become obligatory, and is only allowed during the growing season. Other techniques, like low emission housing and covering of slurry storage have relatively high costs. Starting in 1998, farmers have to keep a record of nutrients on a balance sheet. A tax will be imposed on surpluses of N and P. This new instrument replaces the regulations based on P. To further improve efficiency of use of N and P, farmers have the nutrient balance sheet available as an integrated management tool. Urea content in bulk milk has been introduced as a new indicator for the utilization of N in the diet. Also, fertilizer applications are improved. Furthermore, an experimental farm was set up to integrate all available expertise and analyze the resulting nutrient flows and farm performance.