Mastitis in dairy heifers: prevalence and risk factors.

•The prevalence, risk factors and consequences of mastitis of heifers in early lactation in Switzerland were examined.•The study included 166,518 heifers; 20.6% had a somatic cell count ≥100,000 cells/mL, which indicates subclinical mastitis.•Heifers with subclinical mastitis in early lactation had a higher risk of developing chronic mastitis or leaving the herd prematurely.•The genetic background, morphological traits of the heifers and milk composition had strong associations with subclinical mastitis.