TROUBLESHOOTING MASTITIS PROBLEMS
Joe Hogan and Larry Smith
Ohio Agricultural Research and Development
Center
Wooster, Ohio
Introduction
The initial process to effectively troubleshoot mastitis problems in dairy herds is to determine the specific pathogens causing the concern. Secondly, the series of prior and current events that have culminated in an unacceptable amount of disease in the herd must be determined. The final step is implementing corrective measures that are needed to improve mammary health to the appeasement of the producer, regulatory agency, or milk marketing organization. While the role of the troubleshooter does include presenting a clear and concise plan that can economically eliminate or reduce the source of pathogens creating the mastitis problem, the emphasis of this paper will be on the first two steps of the process. These are the analytical "detective" procedures that involve a thorough understanding of the epidemiology of mastitis and the primary sources of mastitis pathogens in a herd. Ultimately the responsibility of implementing change to improve mammary health in a problem herd rests with the producer.
Identifying the Problem
Most mastitis problems are defined as either a series of undesirable bulk tank milk SCC or an unacceptable incidence of clinical mastitis. Both of these are consequences of the cows’ responses to intramammary infections. The magnitude and duration of these responses are largely a function of the microorganisms infecting the glands. Therefore, to make permanent desired corrections in a herd, the infection rates and duration of infections must be controlled and not merely introduce procedures that eliminate the signs and symptoms manifested by the disease. The key to the process is to correctly identify the prevalent pathogens causing intramammary infections in the problem cows.
The most reliable procedure for identifying etiological agents of mastitis remains the bacteriological culturing of milk from individual mammary quarters. The sampling scheme most prudent when troubleshooting herds is simply to sample the quarters causing the problem. In high SCC herds, the quarters or cows to sample can be chosen from a recent DHI report or by measuring individual cow SCC on the herd. Herds that are not routinely measuring individual cow SCC and are hesitant to spend the time and money for such testing may use a CMT to determine the high SCC quarters. A concern with this approach is the number of cows or quarters that should be sampled to assure a true representation of the herd problem. A host of epidemiological models is available to calculate statistical probabilities and confidence limits, but a more pragmatic approach is to predetermine the lower SCC (or CMT) considered a problem and sample all cows greater than that limit.
Problem herds experiencing an unacceptable rate of clinical mastitis are more problematic than high SCC herds because clinical signs are often transitory and the affected quarters or cows treated with an antimicrobial drug. Sampling quarters that had clinical mastitis within the past week to a month will generally provide little useful information because most pathogens will have been eliminated by therapy or spontaneous cure. A sampling scheme should be implemented to secure milk samples from clinically mastitic quarters prior to any therapy. These milk samples can be frozen for up to a month or until enough of the clinical cases have sampled to ascribe a source of pathogens.
The primary reason for sampling problem cows when troubleshooting is to help determine the source of pathogens. A general idea of what pathogens are causing infections will allow for an educated deduction of what farm management practices may be responsible for the mastitis problem. Sampling schemes other than that described above tend not to be as efficient in securing the data needed to make the proper decisions. For example, taking random samples to find out which cows are infected can have some benefit in screening a herd, but a tremendous amount of error is associated with sampling a specific cow one time to determine her true intramammary infection status. Whole herd sampling schemes generally are expensive and sampling a cow that is not a problem will almost always tell you what you already know..... she is not a problem! Instituting a monitoring system such as sampling all fresh cows can have future long term reward in early detection of a problem. However, most herds in need of troubleshooting have shuffled resources to other endeavors and require more immediate response to stay legal or profitable.
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 lead 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.
Conclusions
Troubleshooting herds incorporates various mixtures of science and art. The reliance on intuition (and possible liability) can be minimized by analytically evaluating factual data. The single most important aspect of competently troubleshooting a mastitis herd is to correctly identify the causative microbial agents. Many logical recommendations can be made to most herds without the aid of microbial culturing, but the risk of error is much greater to cause the problem to persist or even exacerbate. Incorporating culture results, the current knowledge of microbial ecology and epidemiology of mastitis pathogens, and with the history of management changes will enable those troubleshooting a herd to provide more useful information to the producer to correct management deficiencies.