Friesians have also been disadvantaged through the comparison of their type to a Holstein base. A separate "index" be composed to greater has been suggested to reflect the aspects of maintenance for bodyweight, protein percentage, longevity, and calf value. National Milk Records figures suggest highest yields are achieved between the fifth and seventh lactations; if so, this is particularly so for Friesians, with a greater lift for mature cows, and sustained over more lactations. However, production index only takes the first five lactations into account.