The Five-Point Mastitis Control Plan - a Revisory Tutorial!
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The Five-Point Mastitis Control Plan - A Revisory Tutorial! J. Eric Hillerton1, James M. Booth2 1Cambridge, New Zealand 2Worcester, United Kingdom Summary The history, intricacy and some intrigue involved in creating the Five-point Mastitis Control Plan have mostly been discovered some 46 years after its launch. Application of the plan remains essential for good udder health in dairy cows. The story is about great thinking by imaginative scientists, technical innovation by researchers and industry, good applied science to test and trial in the real dairy farming world, and creativity in selling and engaging. All ākonga of mastitis and milk quality need to know their whakapapa to have sufficient mana. Hopefully, most of the story of this upoko is captured here and will help the plan remain tapu. ākonga – disciples or students, whakapapa – genealogy, upoko – chapter, tapu – sacrosanct Early Times The mastitis and milk quality community is (certainly should be) totally familiar with the National Mastitis Council (NMC) 10-point plan, all sorts of newer technologies including internal teat sealants, and now international moves to reduce the quantity, and some types, of antibiotics used in food animals. Entwined in these, and for many farmers, researchers and veterinarians the basis of nearly 50 years of improvement in udder health, has been the teaching and practice of the Five-point mastitis control plan. This has been done to huge effect, some arguing to the point of virtual irrelevance as the etiology and prevalence of intramammary infections have changed so significantly in response to hygienic milk production. It is up to you to judge from this review. This paper will explain where the plan, and name, came from; suggest why it has five points; revise its basis in theory and practice; and describe some of the novel methods used in extension of the plan. If you do not understand the fundamental aspects and drivers you cannot deliver mastitis control effectively. The semi-autobiographical stories of the Yorkshire veterinarian, James Herriot, working pre- World War 2, tell how farmers used to find mastitis (commonly termed felon in older days) by flakes in milk, by the different sound as milk from an infected udder hit the metal pail or by the salty taste of the milk. Intramammary infection was very common then; up to 60% of cows were considered to have one or more quarters infected with, most commonly, Streptococcus agalactiae or Staphylococcus aureus; the herd cell count rarely fell below 1 000 000 cells/mL; and, yet, the severity of clinical mastitis was maybe not too bad. Thankfully, most cows recovered udder health, if never eliminating the pathogen, by response to (very) frequent stripping of the quarter and hosing with cold water. The first effective antibiotics, penicillins, ignoring the sulfa drugs of 15 years earlier, were not available until the mid-1940s. Even then no obvious progress in general herd prevalence of infection or incidence of disease was made NMC Annual Meeting Proceedings (2018) 3 quickly, although ‘blitz’ therapy could eliminate Str. agalactiae, at least for a time (Stableforth et al., 1949). Generally, understanding of the majority of issues around mastitis, except maybe classification of pathogens, was confused, muddled and contradictory. Fortunately, Murphy (1956) developed some key thinking on how to deal with mastitis problems as dairy farming evolved in intensity, with fewer but much larger farms, in major dairying nations. However, mastitis remained a ‘normal’, and mostly uncontrolled, way of life on all dairy farms. Early Thinking Once upon a time, mastitis research workers met very infrequently and were only able to communicate over intervals of about four weeks because no affordable air travel was available on science budgets and that was the time it took for a letter exchange by sea mail. However, good relationships developed from about 1960 onwards between individuals and laboratories, often forged through the International Dairy Federation (IDF) and NMC. It became clear that quite separate approaches to manage mastitis, driven by milk quality issues and the need to grow supply, were developing according to regional philosophies. The US was struggling with contradictory concepts between states and a lack of formal control programs (see Murphy, 1956). The Nordic countries, with a comprehensive state veterinary system, went for strict veterinary control. The key German group in Kiel were the main proponents of managing milk cell count and the recognition of the four states of udder health: clinical mastitis, latent mastitis, sub clinical mastitis and healthy. In the UK, from 1955 the group at the National Institute for Research in Dairying (NIRD) focused on reducing the impact of the infected animals by developing hygienic milking practices. The findings of this group, led by Frank Dodd and Frank Neave, with Roger Kingwill, created the basics of mastitis control that many, including NMC, swiftly adopted, promoted and further improved. The NIRD Philosophy The NIRD work developed from about 15 years of previous research by Dodd and Neave, such that in 1962 they started their series of three Mastitis Field Experiments (MFE). Their thinking began from the point that, after 40 years of international effort and despite the availability of penicillin antibiotics for therapy of clinical mastitis, the incidence of the disease and the prevalence of infection had changed little, with an average of two quarters infected in at least 50% of all cows. This is also captured in the first edition of the NMC Current Concepts of Bovine Mastitis published in 1963. The NIRD group went on to emphasize the Murphy argument that what is needed is good management, if we knew what that was. Dodd et al. (1964) developed the thinking further (when Frank Dodd was on sabbatical at Ithaca) in a presentation to the American Dairy Science Association. That conference paper contains, probably for the first time, their diagram of the possible sequence of events in the development of infection and mastitis (Figure 1, original copied from paper). Epidemiologists will quickly recognize this as a classical Susceptible-Infected-Resistant/Recovered (SIR) model (Kermack & McKendrick, 1927) for infectious diseases. Strangely, no reference to the SIR framework ever appears (apparently) in the writings of the NIRD team. This first diagram was usually simplified in later publications. Various states and stages of infection are described from the model by Dodd et al. (1964). It has to be noted that the philosophy was almost all around new infections and elimination of infections. The studies and the outcomes were focused on I and little on S or R. 4 NMC Annual Meeting Proceedings (2018) 1. The noninfected gland may or may not be susceptible when exposed to pathogens. 2. The infected gland can only be determined with certainty by bacteriology of a milk sample. 3. The infection may be removed by a. Spontaneous recovery or b. Therapy The gland then returns to the uninfected state, with or without a change to susceptibility. 4. The infection may develop to disease which may be resolved by a. Spontaneous recovery or b. Therapy or c. Death From this, they proposed that a control scheme must be based on preventing new infections, the best method, and also on reducing the duration of infections, preferably thru cure rather than leaving a subclinically infected cow. The potential effect of reducing the duration of infections is shown in Figure 2. The discussion is about preventing and removing infections not simply the disease, clinical mastitis. Both herds have 10 infected cows but all infections in herd B are shorter in duration. After MFE1, their first field trial, it was better described as A B C Prevalence = Total cows infected X Average proportion of the of infection during period period that cows are infected For 700 cows in 14 herds, if A was 60% and B 80%, C was 75%. Three-quarters of all cows were infected for 75% of their lactation. Cutting either A or B by 50% would reduce A by 50% but cutting both by 50% would reduce A by 75%. The original philosophy was based on quarters and not the whole udder, but that was over- simplistic because quarters are not independent. In practice, reducing the number of infected quarters by say 50% does not reduce the number of infected cows by 50%. NMC Annual Meeting Proceedings (2018) 5 Figure 2. The effect of the duration of infection on the prevalence. The two herds each have eight cows infected but the average duration is twice as long in herd A; therefore, the prevalence is twice as high (Dodd & Neave, 1970, Figure 5). The methods of control suggested by these models (Dodd et al., 1964) are: Eradication of all forms of infection, possible for Str. agalactiae, but too little was known about most pathogens Prevent infection by immunization (!) Widespread antibiotic therapy – an adjunct but already known to have limited effectiveness against Staphylococcus aureus and possibly cost-benefit prohibited Breeding for resistance None of the four suggestions were possible at that time and some not even now; the one method of practical control was proposed to be appropriate management of cattle, as Murphy (1956) had argued, if only the weak areas could be identified. This was immediately recognized as being limited by the need to train farmers and staff, and ensure that these thousands of people conform to defined work patterns that eliminate greater susceptibility or reduce exposure, by hygienic milking processes. It is assumed in SIR models that in any herd an equilibrium exists for any level or prevalence such that the number of infections removed equals the number of new infections created. For the infection level to be sustained (assuming all individuals are more or less susceptible) R0>1 is required (rate of new cases produced X average period of infection has to exceed 1).