Table 3 An epidemiological approach to herd problem-solving, using mastitis as an example

1. Initially focusing on performance

 [Individual milk recording data are generally needed]

  a. Building the framework

   i. Defining the problem, in terms of performance

    An increase in somatic cell count (SCC)

   ii. Developing a case definition

    For example:

     • A cow with SCC >200,000 cells/mL at the current milk recording, or

     • A cow with SCC>200,000 cells/mL at three or more tests during the current lactation

   iii. Calculating simple measures of case frequency and of epidemiological association

     • Case frequency

      • by parity

      • by stage of lactation

     • Epidemiological association

      • Odds ratio, relative risk

  b. Looking for patterns

   • In time

   • In space

   • Among different animal groupings

  c. Critically evaluating patterns and clues

   • Generate plausible hypotheses, given:

    • The patterns observed, and

    • A sound understanding of relevant biological processes (such as the source and spread of infectious agents, see Figure 1)

2. Then focusing on relevant farm activities

 [Conducted through on-farm investigation, observation, interview etc.]

 A focused investigation of relevant farm activities, consistent with all plausible hypotheses. This could include some or all of the following:

  i. The milking parlour

   The milking machine

    • Dry test

     • Capacity

     • Vacuum, airflows

     • Pulsators

     • Liners and other rubberware

    • Performance testing

   The milking routine

    • Prior to cups-on

     • Teat cleanliness

     • Let-down

    • During milking

     • Milking time per cow

     • Cow behaviour, milking time per cow, overmilking

     • Completeness of milking, cluster alignment

     • Teat cup slips

    • After cups-off

     • Teat condition

     • Teat disinfection

   Detection of clinical cases

    ii. The environment

   Around calving

   During housing

   At pasture

    • The walkways

    • The grazing areas

3. Conducting focused diagnostic testing and other examinations

 [Focusing on the problem animals]

  • Milk cultures

4. Developing recommendations, and communicating these to farmers

 • Facilitating understanding

 • With the farmer

  • Prioritising actions

  • Developing recommendations