Global prevalence of subclinical ketosis in dairy cows: A systematic review and meta-analysis.

The objectives of this study were to estimate the global prevalence of SCK in dairy cows, to identify optimum thresholds for BHB determining, to explore heterogeneity for some particular characteristics (continents, diagnosis techniques, cut-off, sample type, parity, breed, and housing), and to determine the SCK prevalence trend. SCK prevalence levels in dairy cows from various countries were calculated using bibliographic databases up until May 17, 2021 to screen titles and abstracts for possible eligibility. Thirty-eight studies from six continents were then included using a random-effects model to calculate the pooled SCK prevalence. Subgroup meta-analyses were performed to assess the heterogeneity of the prevalence for the above characteristics. Meta-regression and cumulative meta-analysis were used to assess the SCK prevalence trends. The results showed that the global prevalence of SCK in dairy cows was 22.7% [95% CI 21.2-24.3%]. No significant differences in SCK prevalence were observed among continents, diagnostic techniques, cut-off values-≥1.0, ≥1.2 and ≥1.4 mmol/L, sample types-milk and blood, and parities. However, the prevalence in Holsteins (19.8%) was significantly lower than other mixed breeds (23.7%). The SCK prevalence was significantly higher in indoor barns (27.8%) than in pasture and unspecified housing. In meta-regression, the SCK prevalence was not associated with study years or days in milk. The cumulative evidence suggested that the prevalence of SCK in dairy cows was associated with a wide range of risk factors. This study illustrates that the global prevalence of SCK in dairy cows is quite high; therefore, there is an urgent need to globally reduce the SCK prevalence in dairy farms.