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2.3. Conclusion
The SC methods of counting are validated in dairy sheep. With the Fossomatic method and
good conditions of conservation, it appears possible to perform analysis several days after the
sampling date. For frozen milk, the analysis may be done over 60 days after the sampling date
provided that a suitable analysis temperature is respected.
For these direct methods, representative samples of milk are required. Depending on the
milking routine, the milking throughput, the size of the flock, and the milk recording device, the
collection of milk samples for analysis may be difficult or easy to perform and may require an
increase in the number of technicians in the milking parlour.
With an appropriate subjective interpretation, CMT is well correlated with SCC in dairy
sheep. CMT is less expensive than SCC (no analytical cost) to be performed, but its practical
realisation may be very time consuming in large dairy sheep flocks. Taking into account the
persistence of the subclinical IMI in dairy sheep, it is therefore useful to get several results per
ewe at relevant days in milk (i.e. dynamic of the infections). In that way, CMT results can be
combined with previous SCC results, or vice versa, to confirm the “infected” udders.
3 – Phenotypic Relationships Between SCC and Other Traits
3.1. Relationships between SCC and milk production
The phenotypic correlation between SCC and milk production is negative, about –0.1 to –0.2:
IMI causes a reduction of the milk yield secretion ability of the udder. Some authors report a
reduction of milk production over 20 to 30 %. At the INRA La Fage flock (Lacaune breed), the
estimation of loss of milk production was about 10 % to 15 % for the sheep with SCC over
500,000 to 700,000 cells/ml. C. Gonzalo in 2002 found the same range of loss of production:
between 9 to 10 % for Churra ewe with a pathogen and high SCC (1,000,000 cells/ml).
3.2. Relationship between SCC, milk composition and technological properties of milk
The relationships between SCC and milk composition can be summarized as follows (Pirisi
et al. 2000, Albenzio et al. 2002, Bianchi et al. 2004, Leitner et al. 2003., Vivar-Quintana et al.
2006):
- the pH value of the milk increases with SCC
- the lactose content falls with SCC
- An increase of soluble proteins with SCC. The whey protein content of high SCC milks
may induce an increase in the protein content of the milk, but the casein/protein ratio will
tend to be lower in such high SCC milks. SCC has no significant incidence on nonprotein
nitrogen and urea values.
- SCC seems to have no significant influence on total calcium and phosphorus contents,
while the modification in the filtration system of the infected udder modifies soluble
calcium, soluble phosphorus and potassium.
- SCC does not affect the milk fat content.
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