First, you should become familiar with the milk quality scores that are printed on the DHI Herd Total Report. These reports use the linear score system to grade milk quality. All DHI centers are now using this linear scoring system. For each increase in linear score, there is a doubling of the number of somatic cells. Linear scores have a higher heritability than the somatic cell count.
Linear score has a normal frequency distribution.
This means about half the cows in a herd will be above average and half below. The linear score is easy to use between herds for udder health comparison. That's because the somatic cell count can be badly distorted by a few cows with very high counts. Table 1 associates the linear score with average somatic cell count and average milk loss. A high linear score means udder damage and reduced milk production.