Abstract:
BACKGROUND : Subclinical mastitis (SCM) is one of the most economically important diseases affecting the dairy
industry. The SCM does not cause visible changes in the udder or physical changes of the milk as compared to clinical
mastitis, and a clear overview of the prevalence and risk factors in the different regions of Africa is still lacking. The
objective of this study was to investigate the prevalence of SCM and assess the associated risk factors and dominant
bacterial pathogens among cattle in Africa.
MATERIALS AND METHODS : We gathered and systematically reviewed literature concerning SCM, published in English
from January 2010 through December 2020 in two databases (PubMed and Web of Science), and meta-analysis was
conducted using the ‘meta’ and ‘metafor’ packages in the R statistical software.
RESULTS : A total of 258 studies were retrieved and at the end of the screening, 82 full-texts were eligible for inclusion
in the meta-analysis. The prevalence of SCM was reported in 11 countries in five regions of Africa, and the randomeffects
model showed that the weighted pooled prevalence estimate (PPE) was 48.2% (95% CI: 43.6–52.8%).
Heterogeneity was high and statistically significant as I2 (proportion of observed variation) was 98.1% (95% CI:
98.0-98.3%), τ2 (true between-study variance) was 0.0433 (95% CI: 0.0322–0.0611), and the Cochran Q statistic was
4362.8 (p < 0.0001). Subgroup and meta-regression analyses showed that East Africa had significantly (p = 0.0092) the
highest PPE of SCM (67.7%, 95% CI: 55.7–78.7) followed by West Africa (50.5%, 95%CI: 31.4–69.5), and the lowest was
in North Africa (40.3%, 95%: 32.2–48.6). Other significant moderators for SCM were age (p < 0.0001), breed (p = 0.0002),
lactation stage (p = 0.019) and parity (p = 0.0008) of cattle. Staphylococcus species (prevalence 43.7%) were the most
predominant pathogens, followed by Streptococcus (18.2%) and Escherichia species (9.5%).
CONCLUSION : The present study showed a high variation of SCM prevalence in various parts of Africa, although there is
a need for more data in some regions. The reported prevalence is a clear sign of inappropriate management practices among cattle herds and an indicator of the threat that SCM poses to the dairy industry. The information about the
predisposing factors may guide effective management and control strategies to reduce transmission of the disease.
