A dataset of 1,846,990 completed lactation records was created using milk recording data from 8,967 commercial dairy farms in the United Kingdom over a five year period. Herd-specific lactation curves describing levels of milk, fat and protein by lactation number and month of calving were generated for each farm. The actual yield of milk and protein proportion at the first milk recording of individual cow lactations were compared with the levels taken from the lactation curves. Logistic regression analysis showed that cows producing milk with a lower percentage of protein than average had a significantly lower probability of being in-calf at 100 days post calving and a significantly higher probability of being culled at the end of lactation. The culling rates derived from the studied database demonstrate the current high wastage rate of commercial dairy cows. Much of this wastage is due to involuntary culling as a result of reproductive failure.