An illustration of lactation curves stratified by lactation yields within herd

Based on the lactation curves of a total of 817 cows from three herds the v ariation of the shape of lactation curves is illustrated stratified by herd , lactation number and total lactation production. The data was collected f rom on-farm computers connected to recording of yields on a daily basis. Th e results from this ongoing project show that a differentiation of cows acc ording to total yield per lactation or 305-day yield based on records from early lactations is difficult and thus highly questions the set-up of yield groups in the beginning of the lactation. The results also illustrate that it is still debatable what kind of criterion for the persistency of lactat ion production should be used. This question should be answered in relation to the desired length of lactation. Today, random regression models for th e genetic evaluation of dairy animals seem to be a promising alternative to more traditional methods. Future research in this field should make use of data from daily recordings since by this the impact of the data structure can be analysed by mimicking different recording scenarios.