RAW MILK QUALITY ASSESSMENT:
THE RISK OF MULTIPLE OCCURENCES OF EXCESSIVE SOMATIC CELL COUNTS IS MORE THAN JUST PURE CHANCE
G. Bühlmann
Agroscope Liebefeld-Posieux, Swiss Federal Research Station for Animal Production and Dairy Products (ALP), CH-3003 Berne georges.buehlmann@alp.admin.ch, www.alp.admin.ch
INTRODUCTION
A raw milk sample with more than 350,000 somatic cells per millilitre (SCC/ml) is considered to be substandard in Switzerland.
In every case of excess an investigation is carried out into how often the milk producer in question exceeded the tolerance limits over the previous five months. This acts as the criterion under private law for any price deductions and, in case of five incidences of
excess in a row, for the imposition of a ban on milk delivery.
MULTIPLE OCCURENCES OF EXCESSIVE SOMATIC CELL COUNTS OBSERVED AND EXPECTED
The expected values for single and multiple excesses, calculated according to the „same risk for all“ principle, differ markedly from the actual counts recorded. Excesses are therefore not chance events.
The relatively small number of single excesses and the high number of multiples are an indication of the causal link with supplier-dependent factors.
In Switzerland in 2001, 13,015 suppliers instead of the expected 16,134 were detected with a single excess after a previous period free of
excesses and after at least five inspections. This is only 81 % of the expected value. In contrast there were 65 % more suppliers than expected with two or more excesses, specifically 7,873 instead of 4,753.
The quality statistics for the years 1997 to 2004 show similar conditions.
The occurrences of excesses also depend on the season and geographical region. Increased somatic cell counts are recorded especially
in late summer. Excesses are generally less common in the Central Plateau and more frequent in some rather more remote regions.
If these variable factors are included in the calculation of the expected frequencies, then several modifications arise.
CONCLUSIONS
The risk of one excess is dynamic and contains at least three significant components:
a) the season b) the region
c) especially the medium-term history of sample quality of the holding in question.
Whilst with a) and b) improvements of a general nature are possible (general hygiene, animal husbandry, logistics), as far as c) is concerned, specific weak points must be looked for in the effected holdings.
The quality control of commercial milk, which takes account of previous history, is a successful tool for objective assessment and for identifying unfavourable situations; the graduated weighting is selective, informative and effective.
PROBABILITY OF EXCESS observed (red) and expected (blue) YEARS
EXCESS SINGLE Pobserved = 0.03121 Pexpected = 0.03849
ALP 2006
0.0000 0.0125 0.0250 0.0375 0.0500
P
EXCESS TWICE Pobserved = 0.01277 Pexpected = 0.01001
ALP 2006
0.000 0.005 0.010 0.015
P
EXCESS TRIPLE Pobserved = 0.00438 Pexpected = 0.00105
ALP 2006
1997 1998 1999 2000 2001 2002 2003 2004 YEAR
0.000 0.001 0.002 0.003 0.004 0.005
P
MONTHS
EXCESS SINGLE Pobserved = 0.03121 Pexpected = 0.03849
ALP 2006
0.00 0.01 0.02 0.03 0.04 0.05 0.06
P
EXCESS TWICE Pobserved = 0.01277 Pexpected = 0.01001
ALP 2006
0.00 0.01 0.02 0.03
P
EXCESS TRIPLE Pobserved = 0.00438 Pexpected = 0.00105
ALP 2006
01 02 03 04 05 06 07 08 09 10 11 12
MONTH 0.000
0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008
P
REGIONS
SINGLE
ALP 2006
0.00 0.01 0.02 0.03 0.04 0.05 0.06
P
TWICE
ALP 2006
0.00 0.01 0.02 0.03
P
TRIPLE
ALP 2006
IR BESGA ZSNOS
FR+NE SO TGNWS AG VS VD+GE TI REGION
0.000 0.002 0.004 0.006 0.008 0.010 0.012
P
PERIODICITY
SINGLE
ALP 2006
0.00 0.01 0.02 0.03 0.04 0.05 0.06
P
TWICE
ALP 2006
0.00 0.01 0.02 0.03
P
TRIPLE
ALP 2006
1997 1998 1999 2000 2001 2002 2003 2004 2005 TIME
0.000 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.010
P
65th ANNUAL ASSEMBLY OF THE SSM - Lausanne 2006
