FOR two days, 90 veterinary surgeons and others listened to, considered and discussed the latest international understanding about mastitis.
The occasion was a joint undertaking by Cornell University and the University of Nottingham to present a course for the UK, sponsored by Hipra. The emphasis was very much on preventing problems and there were discussions on cows, infection and immunology.
The International Mastitis Course is being run in nine countries with the Cornell Quality Milk Production Services linking with other specialists in each country. For this course Ynte Shukken and Frank Welcome shared the honours with Andrew Bradley, Martin Green and James Breen.
Professor Shukken presented information from many studies and showed that cows exhibit different inflammatory response patterns to different bacteria.
The pattern for E. coli is a rapid rise in cell count and a rapid fall, whereas Strep. uberis has a rapid rise and then a maintained inflammatory response and Staph. aureus typically a lower level of response, but then a fluctuating cell count that persists.
However, the cell count is not the only indicator and 10% of E. coli infections are known to persist even though the cell count is low. All three of the principal pathogens of concern for UK herds can be acute, chronic and sub-clinical infections. Intramammary infection is referred to as a bacteria-specific event with important differences between pathogens and persistent infections occurring in all bacterial species.
This understanding challenges the view that “the primary source of environmental pathogens is the surroundings in which a cow lives”. Also challenged is the classical definition that “the infected gland is the main source of Staph. aureus”.
Cow to cow transfer of infection is contagious and environmental infections come from outside the cow. And so there are environmental organisms that become intramammary infections and then the organism transfers to another cow and that cow enables transfer to a third.
With contagious pathogens the persistence of the organism in the gland is relevant but also the transmission from quarter to quarter and cow to cow.
Great importance is placed on collecting data from the farm and contagious mastitis is characterised by long-duration intramammary infection (IMI), high cell count cows, high cell count prior to clinical cases.
Prevalence increases with days in milk and the incidence is related to prevalence, whereas environmental mastitis has short duration IMI, low cell count cows, low cell count prior to clinical cases, high clinical incidence post-partum, incidence not related to prevalence.
This all leads into an on-farm analysis of new infections, chronic infections, healthy cows and cured cows.
To reduce the duration of infection, and reduce the risk to other cows, the approaches are: treating the cow, drying off or culling.
Preventing new infections requires a herd reduction in the number of cows shedding pathogens by isolation of individuals, or treatment, reducing environmental sources of infection and reducing contact between infection-free animals and shedding animals.
The cows most likely to be cured by treatment are in their first lactation. Treated cows are more likely to become re-infected. Cows with persistent infections may have a low likelihood of being cured but treatment has a direct effect on the cow as well as an indirect effect by reducing the risk of a pathogen transmitting to other cows.
Neutrophils are very important to combat infection but it is the active neutrophil response of a cow that determines how effective the cells are in fighting infection. The speed of influx of white blood cells into the mammary gland influences the severity of the infection. Slow influx, high severity.
Bacteria that are intracellular are protected from phagocytosis. Macrophages and neutrophils have bacteria-specific receptors. Inflammatory response is often reduced in late lactation making the cows extremely susceptible to infection.
Frank Welcome methodically went through the on-farm application of mastitis control programmes and how data are utilised, particularly for large herds. A book Udder Health Large Herd Edition is part of the Cow Signals (www.cowsignals.com) range of publications and covers the full range of management issues with many charts and graphics.
There is emphasis on the team approach with the veterinary surgeon an integral team member. Each delegate received a copy and as Hipra is also a supporter of the publication, further copies may be available from the company.
Martin Green and James Breen reviewed the UK situation with discussion about the barriers to effective herd health plans and the ongoing work with the DairyCo Mastitis Control Plan involving over 1,000 herds to date and building.
On-farm monitoring to identify the source of infection with clinical mastitis, cure rates and recurrence, with indications of management and therapy issues, were explained.
New tools to predict the effect on particular farms of specific management changes and predictive genetic models for pathogen behaviour and cow susceptibility are likely to be discussed at future meetings. Emphasis is again placed on data collection and interpretation.
One of the major differences between the UK and other countries is that UK herds have not been routinely vaccinated. The vaccine now available (Startvac) inhibits the development of the cell wall with E. coli and hinders the formation of exoplysaccharides (biofilm/slime) that surrounds Staph. aureus. Biofilm/slime enhances growth of the bacteria and confers resistance to antibiotics.
The international experience is that use of the vaccine is in addition to the “five point plan” and other applications and management to reduce pathogen transmission and infection. Whether the DairyCo Plan will now include vaccination is a point for further discussion.
The speakers emphasised that the efficacy of the vaccine wanes with days in milk and that the aim is to reduce mastitis over the calving and early lactation period. Various trials have shown that cases of clinical mastitis resolve more quickly rather than seeing a major reduction in clinical incidence.
Considerable emphasis is placed on reducing shedding with Staph, which reduces the days of risk to other cows and the volume of infection. The beneficial effects are therefore an addition of individual cow duration of infection plus a reduced pool of bacteria available to infect the herd.
Andrew Bradley described the situation with coliform mastitis and the results of UK vaccination field trials. The coliform group of organisms are of increasing importance in low cell count herds that have good control of contagious pathogens. Clinical cases are usually mild but low cell count herds experience more severe cases.
New intramammary coliform infections are known to increase before calving and decline as the lactation progresses, with 75% recorded as originating in the dry period. Somatic cell count patterns are of limited diagnostic use with coliform infections but interrogation of clinical incidence indicates the likely origin of infections and allows targeting of control measures.
The traditional view is that a combination of antibiotic dry cow therapy and teat sealant is more likely to result in a cow being pathogen-free post calving and less likely to suffer a case of clinical mastitis in the first 100 days of lactation. However, there is concern about administration of antibiotic to uninfected cows and so a “more thoughtful approach” is needed for low cell count herds.
The UK study involved over 3,000 cows in seven herds with over 5,000 lactations. The study design was for unvaccinated and two vaccination regimes to be compared within each herd.
A full analysis is due for publication but the “label” regime for injections of 45 and 10 days before calving and 52 days post-calving appears to be the more successful application.
A reduction was recorded in mastitis severity, fewer cows were culled for mastitis and a significant improvement in milk production of 1.5 litres plus per cow per day was recorded during the first 120 days in milk. Both vaccination regimes showed an increase in milk production.
There were over 12 hours of presentations covering a wide range of understanding and experience. It was confirmed that the current UK attitude to control is effective for many herds, but recognising the at-risk periods and the infections involved indicates that some herds will benefit from targeted control around the calving period.