During a dynamic cohort study performed in 5 selected organic farms of Lower Saxony between January 2004 and May 2005, udder health data and therapeutic measures were collected. The aim of the study was to compare the usually practiced medical treatments of mastitic udders in organic farms with the scientific realizations. The farms in particular distinguish through a good compliance in previous studies. In the entire year 2004 the study farms removed 5.8% +/- 2.8% (min. 2.9 - max. 9.0) of the animals due to mastitis problems. Only little differences regarding the prevalence of mastitis between the five farms were found while the udder health situation in all examined herds improved from summer to winter. Dominating mastitis pathogens were CNS und Streptococcus uberis. The incidence of clinical mastitis was 50 cases per 100-cow-years at risk and pathogens could be detected in 48% of all mastitis cases (CNS 45%, Sc. uberis 27%, Entero-bacteriaceae 17%, Enterococci 9%, Sc. dysgalactiae 2%). Mastitis therapeutic treatments were accomplished on the average 0.9 +/- 0.6 (min. 0.06 - max. 1.44) times per animal of the herds while mastitis thera-peutic treatments had a portion of 54% +/- 24% of all treatments (min. 21% - max. 88%). Contrary to earlier studies more than 70% of all clinical cases were treated allopathically. Homoeopathic remedies were used in 26% of all cases. Contrary to evidence-based requirements 35% of all mastitis treatments were done with animals, which exhibited no more considerable probability of healing due to their mastitis history. At drying off 24.6% of the animals were treated with antibiotics. The new infection rate in the dry period was 35% +/- 18% (min. 22% - max. 65%) and the healing rate amounted to 46% +/- 12% (min. 33% - max. 59%). Large differences in the treatment intensity between the enterprises with comparable mastitis prevalence and incidence indicates possibilities to improve the use of therapeutics. In particular regarding the selection of therapy-resistant animals substantial differences were found
