Staphylococcus aureus and Escherichia coli prevalence in ovine bulk tank milk

To analyse the effect of bulk tank Staphylococcus aureus and Escherichia coli presence on total bacterial count (BTTBC) and somatic cell count (BTSCC), and to study the factors influencing their prevalence, a total of 752 bulk tank milk samples from 205 dairy sheep flocks belonging to Consortium for Ovine Promotion (CPO) were collected between January and December 2011. Four samplings were carried out in each flock, one per season, throughout one year. Respectively, Staph. aureus and Esch. coli were present in 26.5% and 17.4% of the samples and in 58.5% and 50.7% of the flocks throughout the year. Esch. coli significantly contributed to BTSCC and BTTBC variation, but only a statistical tendency for increased BTSCC was evidenced in the case of Staph. aureus positive samples. Thus, BTSCC and BTTBC were useful variables for monitoring, at least partially, the presence of Esch. coli in bulk tank milk, whereas BTSCC was more useful in the case of Staph. aureus. Some variation factors for specific pathogens, such as season, antibiotic dry therapy, milking type and breed, were also analysed. Season was the most important effect associated with the variation of bulk tank Staph. aureus and Esch. coli prevalence. Staph. aureus had a higher prevalence in winter and spring (i.e., early lactation period), while Esch. coli prevalence was higher in autumn and winter, coinciding with a rainy weather. Lower Staph. aureus prevalence was for dry-treated flocks pointing out this mastitis control practice in the flocks is related with a reduction of contagious mammary pathogens. Finally, hand milking flocks evidenced a higher prevalence for both pathogens than those with machine milking. As a whole, these results are useful for monitoring these pathogens in bulk tank milk and highlight the need for establishing analytical surveillance programmes in dairy sheep flocks.