THE USE OF LACTATION PERSISTENCE AS AN INDICATOR IN THE SELECTION OF THE MATERNAL LINES OF HF COWS

The research material for this study consisted of a group of 163 Polish Holstein Friesian cows (PHF). For the study, the cows were assigned to 14 maternal lineages covering three genera- tions. The aim of this study was to indicate possibilities for selecting cows with the goal of maintaining lineages on the farm which are characterised high productive qualities based on lactation persistency index. Basic milk parameters were analysed over a 305-day lactation cycle and information on somatic cell content was also gathered based on sample milkings. A characterisation of lactation persistency for a given lactation was generated as a percent difference between milk yield in the 2nd and 10th month of lactation, and a lactation persistency curve was developed for particular lineages in succes- sive lactations, representing changes in the productivity of the cows. It was determined that together with increasing numbers of lactations among the cows studied, the average lactation persistency index also increased. For younger cows, this index did not exceed 30%, while in the older group this index amounted to 70%. Cows with the highest lactation persistency values 70.1–80% were also char- acterised by the highest milk production in average daily milk yields during peak lactation, amount- ing to 56.14 kg at values of for the index. Cows which began their milk production stage with a high persistency index in the 1st and 2nd lactations, in successive lactations saw a significant decrease in this index. Breeding cattle within maternal lines characterized by a high and stable level of lactation persistence index can ensure a high level of milk production in this line of cows.