TCDStransrectal colour Doppler sonographyblood flow velocity (m/s) 1 IntroductionBovine mastitis is still ranked among the main production diseases in dairy herds of developed countries (Miller et al. 1993; Rajala-Schultz & Gröhn 1999; Bradley et al. 2007). Approximately, every third cow in Germany suffers from mastitis once per lactation and a financial impact of about € 0.02 per one litre milk produced is estimated (Fehlings 2008). In 2007 nearly 15% of all animal losses in Germany were based on udder diseases, such as mastitis (ADR 2007). Especially, intramammary infections with Escherichia coli (E. coli) very often lead to anacute mastitis with severe clinical effects (Bannermann et al. 2004). Occuring mainly in the peripartum and the early stage of lactation applied therapies are in many cases insufficient or futile (Olde Riekerink et al. 2008). The consequence of failed therapy can be the total loss of individual animals or enormous economic losses during current and / or subsequent lactations (Seegers et al. 2003). A single case of a total animal loss caused by E. coli mastitis leads to an estimated loss of at least € 1800 (costs in case of successful therapy: about € 180).The identification of the inflammatory event at an early stage is not only a basic demand of milk hygiene and an essential precondition for a successful therapy (Grunert 1990), but also an important factor for the limitation of mammary tissue damages (Burvenich et al. 2003) and economic impacts due to yield losses (De Mol & Ouweltjes 2001).Clinical examination, California Mastitis Test (CMT) (Schalm & Noorlander 1957) and bacteriological examinations (BE) are the most common non-invasive methods for diagnosing mastitis. Beyond that, electrical conductivity (EC) has been investigated for years but is still not sufficiently precise for an early detection of an acute mastitis (Hovinen et al. 2006).2 New methods such as measuring volatile components and potentiometric values of milk (Eriksson et al. 2005; Mottram et al. 2007), as well as a new biosensor system that analyses lactose and EC (Culina et al. 2006) or infrared thermography (Hovinen et al. 2008; Colak et al. 2008) are still under development. The need for a non-invasive early detection method not being related to the act of milking (advantage: before first calving, dry period, clinical signs appear before milk changes) is obvious.From studies with invasive blood flow measurements a close relationship between inflammatory processes of the mammary gland and mammary blood flow rate is known (Dhondt et al. 1977a). Effects of metabolic activities of the mammary gland on mammary blood flow seem to be evident (Lough et al. 1990).In this present study a new non-invasive and quantitative method was used for examining the pudendoepigastric trunk by transrectal colour Doppler sonography (TCDS). The investigated vessel section is the only pre-section of the inguinally running external pudic artery, the major supplier of the mammary gland of cows, which is transrectally accessible (Brag...