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

SOMATIC CELL COUNTS IN DAIRY SHEEP MILK
G. Lagriffoul 1 , F. Barillet 2 , R. Rupp 2 , X. Berthelot 3 , D. Bergonier 3
1 Institut de l’Elevage - Comité National Brebis Laitières
Campus INRA de Toulouse, France
2 INRA-SAGA, Toulouse, France
3 ENVT, Toulouse, France
Special attention is given to intramammary infections (IMI) of dairy sheep due to economic
consequences (loss of milk production, price penalties for milk, costs of involuntary culling…),
decreases of hygienic quality of milk (contaminants in milk as S. aureus, salmonella…) and legal
control (as established for instance in Europe by EU directives defining the bacteriological
quality of milk). In dairy sheep, IMI are characterised by a low percentage of clinical IMI,
generally lower than 5 %, and a greater percentage of subclinical IMI in the range of 10 to 50 %
or more. 80 % of the subclinical IMI are due to Coagulase Negative Staphylococci (CNS) which
cannot be considered as minor pathogens in dairy sheep as it is the case in dairy cattle. Some of
them cause a high increase of somatic cell counts (SCC) and there is accumulative evidence
showing that IMI constitute the major cause of SCC. It is well established that SCC are the best
indirect test of bacterial status of a gland. As a consequence, the control of udder health (in
particular subclinical IMI) may focus on the control of SCC. But such plans of SCC control have
to take into account specificities of dairy sheep production, as the size of the flocks, the milking
routine and throughput, the costs of the analysis and the control measures… Recent advances
make it possible to control the somatic cells of dairy sheep milk. However, knowledge for some
critical points needs to be improved in order to make the plans more efficient and less expensive.
The aim of this article is to make a rapid review of the knowledge of somatic cells in dairy
sheep milk. After some general background regarding the origin and the counting methods of
somatic cells in sheep milk, we will focus on the consequences of high somatic cell counts on the
cheese making properties and finally conclude with mammary gland disease control.
1 – Origin of Somatic Cells in the Milk
1.1. Somatic cells composition for normal milk
For sheep as for the other dairy species, somatic cells are a natural component of the milk.
Ewe’s milk contains the same types of cells as cow’s milk. For normal milk (from an udder
without any intra mammary infection), the range of the percentage of the different types of
somatic cells are the following (Bergonier et al, 2003) :
- epithelial cells, less than 5%,
- polymorphonuclear neutrophil leukocytes (PMNL), 10-35 %,
- macrophages, 45-85 %,
- lympocytes, 10-17 %.
38