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

From: An investigative framework to facilitate epidemiological thinking during herd problem-solving

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