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. 2023 Oct 22;13(20):3295.
doi: 10.3390/ani13203295.

Longitudinal Study of Subclinical Mastitis in Sheep in Greece: An Investigation into Incidence Risk, Associations with Milk Quality and Risk Factors of the Infection

Charalambia K Michael  1 , Daphne T Lianou  1 , Natalia G C Vasileiou  2 , Vasia S Mavrogianni  1 , Efthymia Petinaki  3 , George C Fthenakis  1
Affiliations

Longitudinal Study of Subclinical Mastitis in Sheep in Greece: An Investigation into Incidence Risk, Associations with Milk Quality and Risk Factors of the Infection

Charalambia K Michael et al. Animals (Basel). .

Abstract

The objectives of this work were (a) to describe the incidence risk of subclinical mastitis in dairy flocks throughout the milking period, (b) to present potential associations of subclinical mastitis with the quality of milk and (c) to identify risk factors for high-incidence risk of the infection. A longitudinal study was performed in 12 dairy sheep flocks in Greece. Mammary secretion samples from 240 ewes and bulk-tank milk samples were collected in four repeated visits over a period of six months for bacteriological, chemical and cytological examinations. Overall, the incidence risk of subclinical mastitis throughout the study period was 51.7%, and it varied among farms from 25.0% to 75.0%. The respective figure for staphylococcal subclinical mastitis was 48.8%. The incidence risk of recurrence of subclinical mastitis among ewes in the flocks was 35.4%. The most frequently identified bacteria from cases of subclinical mastitis were S. aureus and S. simulans; of the mastitis-causing staphylococcal isolates, 65.4% were biofilm-forming. Somatic cell counts in bulk-tank milk progressively increased as the lactation period advanced, with significant increases seen on the third and fourth visits to the farms. Somatic cell counts in bulk-tank milk correlated well with prevalence of subclinical mastitis in flocks. A significant inverse correlation and a significant positive correlation were seen for prevalence of subclinical mastitis versus total protein content or added water in bulk-tank milk. During multivariable analysis, younger age of newborns when taken away from the dam and consequently delayed start of milking of ewes, omission of anti-mastitis vaccination of ewes and lack of employed staff on the farms emerged to be significantly associated (positively) with increased incidence risk of subclinical mastitis.

Keywords: Staphylococcus; farmer demography; goat; mastitis; milk; predictor; prevalence; sheep; somatic cell counts; subclinical mastitis; vaccination.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Scatterplot of prevalence of subclinical mastitis and somatic cell counts in bulk-tank milk in 12 sheep flocks in Greece monitored throughout a milking period (dashed line is trendline).
Figure 2
Figure 2
Progressive changes in prevalence of subclinical mastitis and in somatic cell counts in bulk-tank milk in 12 sheep flocks in Greece monitored throughout a milking period (four sampling occasions on each flock).
Figure 3
Figure 3
Scatterplot of prevalence of subclinical mastitis and protein content in bulk-tank milk in 12 sheep flocks in Greece monitored throughout a milking period (dashed line is trendline).
Figure 4
Figure 4
Scatterplot of prevalence of subclinical mastitis and added water in bulk-tank milk in 12 sheep flocks in Greece monitored throughout a milking period (dashed line is trendline).
Figure 5
Figure 5
Scatterplot of incidence risk of subclinical mastitis and age when lambs were taken away from their dams in 12 sheep flocks in Greece monitored throughout a milking period (dashed line is trendline).
Figure 6
Figure 6
Incidence risk of subclinical mastitis (solid bars) or staphylococcal subclinical mastitis (motif bars) in sheep flocks in Greece monitored throughout a milking period, vaccinated (green bars) or not vaccinated (violet bars) against staphylococcal mastitis (bars indicate 95% confidence intervals).
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