Mastitis is a bacterial infection, costing an estimated £120M/annum to the UK sheep industry. Mastitis can lead to the death of the ewe, decreased milk yield and premature culling. An intervention study was conducted on one flock in England to test the impact of raising hygiene in the perinatal period on occurrence of mastitis. Ewes were allocated to control (n = 422) or intervention (n = 315) groups at lambing. Researchers managed the intervention ewes; antibacterial hand gel was used before handling ewes and overalls and boots disinfected daily. Intervention ewes were put in pens post-lambing which had antibacterial bedding powder beneath straw bedding and were cleaned daily. Data on the presence of intramammary mass (IMM) an indicator of chronic mastitis, were collected on five occasions: during pregnancy, at lambing, early and late lactation, and pre-tupping. Occurrence of acute mastitis (AM), lambing assistance and ewe death were recorded. The period prevalence of ewes with an IMM was 37.5% and incidence rate of AM was 5.5%. Ewe death was associated with lambing assistance (OR = 7.22). Control ewes (30.9%) were more likely to receive lambing assistance than intervention ewes (27.6%); researchers would wait at least 30 minutes before assisting whereas farm staff would intervene before this. IMMs were associated with AM (OR = 17.10) and a previously detected IMM (OR = 3.25). AM was more likely to occur in ewes where an IMM was detected at a previous examination (OR = 15.49). While raised hygiene did not appear to affect mastitis, ewes were mixed post-housing which may have confounded results and the study may have needed longer to detect any effect. The link between assistance and death is an important finding for welfare and cost to farmers and needs further investigation to determine whether down to hygiene or other factors.