The International Standards Organization (ISO) produces international standards for milking equipment. These describe the minimum specifications of design, installation, maintenance and testing of milking machines (BS ISO, 1996). Often these standards are adopted and exceeded by national standards. Standards are rarely mandatory and in some countries variations in interpretation and even disagreement can lead to differences in operating conditions of the milking machine.

A survey of plant test results in the UK (Berry & Scrivens, 1997) showed that, on annual or biannual testing, more than 75% of plants failed to meet the then existing standard (BS5545, 1988). In the UK, most types of plant installed since 1994 meet the newest ISO standard (BS ISO, 1996). However, one type of plant has many features different from all other types. This is a type of plant whose major variations include a smaller claw bowl volume (150 ml), a narrower long milk tube diameter (13·5 mm), 8 mm milk pulse tube, greater cluster weight (approximately 3·5 kg) and simultaneous pulsation used on a plant with milk lift and milking at an installed system vacuum of 47–48 kPa. The majority of parlours installed with this equipment at the time of this study had no form of indexing (see below).

A study has been undertaken to assess 20 new installations for compliance with the ISO requirements (BS ISO, 1996), performance in a static test, milking performance, cow behaviour and the effects on teat condition. Compliance to standards and static test results have been reported elsewhere (Ohnstad, 1997), with no plant proving entirely satisfactory. Some plants had major problems with vacuum level, pulsation characteristics and large air leaks. The physical operation of the milking plant has important implications for cow behaviour and welfare and also ergonomics of the milking operation. The effects on teat condition have already been reported (Hillerton et al. 2000). Here the effects on cow behaviour and milking performance are assessed. Comparisons have been made in line with the International Dairy Federation recommendations (IDF, 1997) to examine the performance and interactions of the cow, the machine and the operator in evaluating the milking process.