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 |