Current and Previous Conditions
Collect as much information as possible about past and current management of the herd. Having a thorough record of milk quality parameters, mastitis cases, and dates that management practices were changed over the three-year period would be ideal. However, the resources on most problem herds tend to fall considerably short of ideal. A couple of approaches are helpful in interpreting the data regardless of the volume of information available. First, arranging herd data in chronological order is helpful in documenting if the problem is acute, a result of a long-term chronic increase in infections, or if cyclic patterns are apparent. Secondly, individual cow data such as SCC should be stratified and graphed by days in milk and lactation number. This can give valuable insight to specific management practices that are deficient in the herd. The deficiencies in management that leads to mastitis problems tend to be either 1) acute management deficiencies — the almost immediate response to the change in a specific management condition, 2) additive or cyclic management deficiencies — the additive affects of several factors that may be influenced by season, lactation status, etc., or 3) chronic management deficiencies -- the effect of a single change that takes a long time to accumulate enough infections to be recognized.
Immediate and disastrous changes in the mammary health status of a herd can result from a single change in management. Acute management deficiencies include a contaminated source of bedding, purchased animals, or a milking machine wreck. These scenarios are usually easy to recognize, can be equated with culture results, and corrected. Unfortunately, immediate increases in mastitis due to a single obvious factor tend to be the exception rather than the rule.
Often a suspect management practice has little negative impact until another external factor is superimposed. An example of additive or cyclic management deficiencies is the use of sawdust bedding. Most accept that the use of sawdust as bedding is significant risk factor for coliform mastitis. However, the mammary health of a herd may not suffer due to the use of sawdust bedding during cooler weather periods of the winter, spring and fall months. During summer months bacterial populations in sawdust increase, thus the source of coliform pathogens at the teat end increases and the rate of clinical mastitis increases with the rise in temperature. The management practice did not change in this example, but coupled with an external factor the previously harmless husbandry practice can lead to a mastitis problem in a herd.
Possibly the most problematic scenario is when the management change happened far enough in the past that most will not associate the change with the current mastitis problem. A classical example of chronic management deficiencies is when a post milking teat dip management strategy is changed whereby the efficacy of the practice is reduced, but not eliminated. Poor application of teat dips with sprayers and the use of products with marginal efficacy may take many months or years to result in accumulative infections yielding a high bulk milk SCC. The level of contagious mastitis in a herd spraying teat dip will follow a sigmoid curve from the time that the practice is changed until it reaches a level of concern. The lag time from the management change until a linear increase in intramammary infections gives a false sense of security that the change was not harmful. This is common in herds with a low prevalence of Staphylococcus aureus infections that change to spraying teat dip as the post-milking hygiene. Producers are often reluctant to associate the mastitis problem with teat spraying as the practice may have been in place for a year or more before the accumulative effect is realized in bulk tank SCC.