great lakes dairy sheep symposium - the Department of Animal ...

At each test, the color changes were observed by two different persons in order to detect
possible different color perception. The reading with the hand held device was also done twice at
a few second intervals to measure the repeatability of the reader. All milk samples used in the
trial were sent to a certified laboratory were the somatic cell count in the milk was detected
through a Fossomatic 360. The laboratory machine is not especially calibrated for sheep milk.
Its accuracy, however, has been tested by comparing the results of a microscopic count
(DMSCC) with the electronic count (ESCC). Results of the PortaSCC® were tested against the
results from the Fossomatic count.
On 8/22/06 each sample of milk was tested twice at a few minute intervals on two different
PortaSCC® strips in order to detect the repeatability.
At each test we looked at:
- the repeatability of the reading of color by two different persons
- the accuracy of the color compared to the laboratory results using the same range
- the accuracy of the hand held reader compared to the color
- the accuracy of the hand held device compared to the laboratory results
- the repeatability of the PortaSCC® on the same sample (last test only).
The accuracy is simply a percentage of identical results between the Fossomatic and the
PortaSCC®. Repeatability is a percentage of identical results for 2 identical milk samples
measured by PortaSCC®
Results
The 18 tests done on 4/17 and the 7 tests done on 4/20 were discarded from the results
because the strips used on those dates were past the expiration date. All other results are shown
in Table 1.
Colors. The colors were generally perceived to be the same by two different people. The
percentage of time that the two people had the same reading varied from 75% to 96%. The
differences between the two technicians came mostly from hesitation between a no color change
and a slight coloration meaning that the accuracy of the test is affected mostly in the low range of
SCC up to 200,000. This is quite an acceptable result knowing that an animal with a somatic cell
count of 200,000 or less is considered as having a healthy udder (Bergonnier et al., 1997).
Correlation between laboratory results and colors. All laboratory results that were less
than 200,000 SC were considered 0 and corresponding to a no color change in the PortaSCC®
test. The percentage of identical results between the laboratory and the colors shown in the
PortaSCC® varies between 81% and 94%. Most of the discrepancies occur in the middle ranges.
Therefore, a no color change is definitively an indication of low SCC (less than 200,000) and a
deep color change an indication of a high somatic cell count (more than 1 million). However the
PortaSCC® does not seem to give quite as accurate results for intermediary ranges (between
200,000 and 1 million), meaning that it is less reliable to distinguish a count of 250,000 from a
count of 750,000 just looking at the color on the strip. Also, the repeatability of the color change
on the same sample of milk was high at 93%.
94