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

Regarding the dynamics of the infection, the decision can be taken using several possible
criteria, as for instance :
- ewes with several iSCC over 1,000,000 or 1,500,000 cells/ml during the lactation;
- ewes who experienced acute or severe chronic IMI : strong udder asymmetry, diffuse
hardness, abscesses… (caution : abscesses must be differentiated from cysts)
- a combination of iSCC results and udder indicators.
2. antibiotic treatment at drying-off
The implementation of a dry therapy significantly reduced the bulk tank milk SCC (Gonzalo
et al. 2005 and 2006). In dairy sheep, the cure rate of drying-off intramammary antibiotherapy
ranged from 65 to 96 %. Considering the length of the dry period in dairy sheep, the preventative
interest of the drying off treatment can be discussed. Without drying-off treatment, the dynamic
of infection during the dry period would be (Bergonnier et al 2003):
For infected udders:
- cure rate: 45 %
- rate of new infection (substitution): 23 %
- persistence of the IMI: 32 %
For uninfected udders:
- rate of new infection: 10 to 25 %
Taking into account all the above parameters, a selective drying-off antibiotic treatment
(devoted to infected and doubtful udders only) may be preferred to a systematic one. Limiting
the number of treatments may cover the cost of iSCC or CMT which are needed to select the
candidate ewes for such a selective treatment.
In dairy sheep, the use of drying-off intramammary antibiotherapy may be associated, in a
few cases, to acute mastitis caused by opportunistic pathogens (P. aeruginosa or A. fumigatus).
Hygienic precautions may reduce this risk: before the treatment (for example P. aeruginosa in
the water), during the treatment but also at lambing (contact with moldy forage).
At last, but not least, considering the dry period duration, it can be assumed that the risk of
residues in the milk after lambing is very low. If the drying-off treatment is made by waves, the
treated ewes must be clearly marked to avoid the risk of milking them (i.e. antibiotic in the milk).
4.3.3. Genetic control
Contrary to cattle, no genetic antagonism between milk yield and clinical mastitis has been
demonstrated for sheep (Barillet et al., 2001a). Thus in practice, improving udder health in dairy
sheep could be limited, in a first approach, to selection against subclinical mastitis using milk
somatic cell count (SCC). Estimates of heritability of the lactation somatic cell score (LSCS)
computed as in Wiggans and Shook (1987) ranged for sheep between 0.10 to 0.18 (El Saied et
al., 1999, Mavrogenis et al., 1999, Barillet et al., 2001a, Othmane et al., 2002, Rupp et al., 2003,
Serrano et al., 2003, Legarra and Ugarte, 2005). Relationships between milk yield and LSCS
were close to zero, from slightly favourable (-0.29) to slightly antagonistic (0.20). It can be
pointed out that several estimates in the Lacaune breed always showed a moderate antagonism;
confirmed in addition by a selection experiment with divergent selection for milk yield (Barillet
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