An Illustration of lactation curves stratified by lactation yields within herd

Abstract. Based on the lactation curves ofa total of 817 cows from three herds the Variation of the shape of lactation curves is illustrated stratified by herd, lactation number and total lactation produetion. The data was collected from on-farm Computers connected to recording of yields on a daily basis. The results from this ongoing project show that a differentiation of cows according 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 ofthe lactation. The results also illustrate that it is still debatable what kind of criterion for the persistency of lactation produetion should be used. This question should be answered in relation to the desired length of lactation. Today, random regression models for the 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 impaet ofthe data structure can be analysed by mimicking different recording scenarios.