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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