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Information can be derived from DHIA somatic cell count data.
Dairy Pipeline: May 1997
by
Tom Bailey
Dairy Production Medicine
Virginia-Maryland Regional College of Vet Medicine
Virginia Tech
A tremendous amount of information can be derived from DHIA somatic cell count data if you understand how to use it. DHIA somatic cell counts provide an excellent system to evaluate udder health. This is the first step in developing a mastitis control program. DHIA utilizes linear scores when reporting somatic cell counts. The reasons for this are: (1) linear scores can be directly related to a production loss (1 linear score equals 1.5 pounds per day or about 400 pounds per lactation), (2) linear scores have a high repeatability (less variable) from month to month, (3) the average linear score gives a better picture of a lactation than average raw somatic cell counts, and (4) it is easier to write. As an example see table 1 below. Which is the better situation? Going from a 50,000 SCC to 200,000 SCC or going from 800,000 to 1,600,000? To answer this question, look at the linear score. In the first example there is a change of 2 linear scores or a loss of 3 pounds of milk per day. A change from 800,000 SCC to 1.6 million is a change of 1 linear score or a loss of 1.5 pounds of milk per day. Linear scores can also be used to indicate how many cows have a subclinical infection, or cows that do not have abnormal changes in the milk. A linear score of 5 is used to differentiate infected from noninfected cows. Each month we monitor how many cows are above a 5 linear score. A new infection is a cow that moves from below a 5 linear score last month to above a 5 this month. A chronically infected cow is a cow that is above a 5 for 2 months or more. We can use these linear score changes to culture cows and determine the organism causing the mastitis. The newly infected cows are the ones more likely to yield positive results on culture. Therefore, monitor cows for these changes in linear scores from month to month and rely on your veterinarian to help you formulate a total mastitis program and taylor it to meet your herds needs.
Table 1:
| Somatic cell count | 50,000 | 100,000 | 200,000 | 400,000 | 800,000 | 1,600,000 |
| Lbs Milk loss/day | 0 | 1.5 | 3 | 4.5 | 6 | 7.5 |
| Linear Score | 2 | 3 | 4 | 5 | 6 | 7 |