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Managing mastitis

The British Mastitis Conference 2020 discussed new developments in tackling mastitis, from the value of selective dry cow therapy at quarter level to the impact of automatic milking systems

07 December 2020, at 8:10am

The 32nd British Mastitis Conference was the first to be held online, organised by The Dairy Group, the British Cattle Veterinary Association (BCVA), Quality Milk Management Services (QMMS) and the University of Nottingham. The meeting was well supported with over 100 delegates, a third of which were members of veterinary practices. Ian Ohnstad of The Dairy Group acted as chairman and facilitator of the presentations from speakers located in the UK, the Netherlands, USA, France and Belgium. Poster presentations and discussions with authors have been an important part of this conference in the past, and this was no different in the new online format; questions from delegates were available to all and put to speakers at the end of each session. The best poster award was voted on remotely and congratulations given to Huw McConochie and Alturo Gomez for a review entitled “High somatic cell counts are not always a consequence of intramammary infections“.

Andrew Bradley, of QMMS, outlined the findings from a trial (807 cows from six herds) to investigate the worth of selective dry cow therapy at the quarter level. A basic point was emphasised that it is no longer acceptable to administer antibiotics to prevent new infections. This is a major change from the original mastitis control understanding, where dry cow therapy was targeted to prevent Gram-positive infections developing within the udder during the dry cow period, as well as eliminating existing infections. The herds selected had 12-month rolling mean somatic cell counts of 122 to 313 cells per ml. This reflects the modern dairy herd, where infections are predominately of environmental origin. Historically, with higher levels of infection it has been identified that infections transfer from one quarter to another, as each quarter is not structurally independent. However, current on-farm infection indicates that a quarter approach can now be considered.

In the trial, teat sealant was administered to all quarters with cows allocated to an uninfected group (last three cell count readings less than 200,000 and no clinical mastitis) or infected (any of last three cell count readings of over 200,000 or having clinical mastitis). Quarters received teat sealant alone or sealant plus dry cow antibiotic, and California Milk Test scores indicated quarter infection. Bacteriology and somatic cell count readings were also carried out with samples taken at drying off, calving and post-calving, and of any clinical cases. The findings indicate that selecting quarters for treatment had little effect on major pathogens and there appears to be little justification in applying antibiotics as well as teat sealant to low cell count cows, or to low (CMT score 0) cell count quarters of high cell count cows. It was emphasized that a herd-specific approach is essential if quarter selection therapy is to be adopted.

The president of the National Mastitis Council, Sarne De Vliegher of Ghent University, leads a mastitis research team that has been recording and investigating minor (typically non clinical cases with moderate increase in cell count) and major pathogens (potentially severe clinical mastitis and distinctly elevated cell counts). He presented an update of mastitis pathogens which deserves to be read in full. He indicated that placing bacteria into major, minor, environmental and contagious categories is no longer sufficient.

Streptococcus agalactiae is now recognised as able to survive in the environment as well as in the mammary gland and S. uberis can be contagious as well as environmental. Lactococcus lactis has been utilised as a cheese starter, is considered to be non-pathogenic and has been used as a mastitis therapy and a teat dip. A clinical outbreak, with high cell count and chronic cases in the USA, found the organ-ism in sand bedding. It seems likely that the presence of Lactococcus species on dairy farms, as a potential cause of clinical and subclinical mastitis, has been under-reported. A single case of a new species, Streptococcus bovimastitidis, has been identified in New Zealand through gene sequencing. Another new pathogen is Streptococcus lutetiensis, formerly recognised as a strain of S. bovis.

Ongoing studies of non-aureus staphylococci (NAS) have confirmed faecal shedding, with the same strains on the teat end, in milk and in faeces. NAS-infected heifers have shown a mildly elevated cell count but an increase in milk production. The inhibitory capability of 26 species of NAS isolates against S. aureus yielded 25 novel bacteriocin precursors that might have clinical applications. The awareness of gene clusters and their interpretation for disease control introduces unfamiliar language as well as unfamiliar organisms.

The majority of teat tissue stress seems to occur during the low flow period at the end of milking with conventional vacuum control. Doug Reinemann from the University of Wisconsin-Madison, outlined the benefits of a new technology that adjusts milking vacuum level according to milk flow rate, developed by DeLaval. Flow Control Vacuum provides the highest milking vacuum during the peak flow period of milking and challenges the current ISO guidelines. It is proposed that over-milking could be eliminated with the new system.

The University of Liverpool posed the question whether full or partial insertion of the teat sealant syringe nozzle into the teat is related to udder infection. George Oikonomou presented the findings from a trial involving three pedigree Holstein herds in the UK. No difference was recorded for post-calving somatic cell count, new infection rates, cure rates or mastitis incidence between the two application methods, but it was emphasised that the correct aseptic technique was applied. A study involving 150 clinical mastitis cases in Italy was discussed by Erik Grandemange. Cows were treated with intramuscular injections of penethamate alone or combined with intramammary antibiotic, with 80 percent of the cows receiving four intramuscular injections and 20 percent receiving three. There were no significant differences between the recorded outcomes. The authors conclude that intramuscular injection of penethamate is safe and efficacious.

In discussing some causes of high cell counts unrelated to intramammary infection, Huw McConochie of Zinpro Animal Nutrition put forward the proposition that a leaky gut puts toxins into circulation, leading to inflammation and higher cell counts. Challenge studies have shown that the administration of a lipopolysaccharide binding protein as a trace element supplement incorporating a zinc amino acid chelate is beneficial. Maintaining epithelial integrity reduces the severity of inflammation and reduces the risk of raised cell counts.

A study conducted at the University of Bristol involved 30 dairy farmers working in collaboration to reduce antimicrobial use. Lisa Morgan, Innovation for Agriculture, enthusiastically outlined the benefits of the farmer action groups where the farmers meet on-farm in groups of six. There were no lectures, presentations or external speakers. The group approach differs from traditional advisory and extension services by prioritising and promoting farmer expertise in identifying and solving farm-specific challenges. The farmers developed 30 practical action plans with high levels of implementation within a year. There were many questions from delegates and general support for this “social stuff” and veterinary practice involvement with individual farmers will assist the positive outcomes. It has been announced that the BCVA has taken on the task of managing the MilkSure programme, which has trained staff from over 3,000 herds utilising veterinary practices to work with clients to reduce and target antimicrobial use.

When herds are changed to an automatic milking system, lower health performance can take place, sometimes for years. Tom Greenham of Advanced Milking broke down the areas where increased awareness of likely problems allows bespoke interventions to maintain performance well within acceptable levels for cow health and welfare, and business profitability. Robotic milking means irregular milking intervals, which challenges the interpretation of cell count readings. Practical considerations include: lame cows make fewer visits to the milking box; lame cows stand around for longer with splashing of faeces onto teats and are bullied by other cows; cows need to be clean before entering the box; buildings are never empty of cows so effective floor cleaning can be an issue; post-milking spraying or teat dipping can be variable and udder hair needs trimming, with teat location devices in good order; each milking machine has a high number of cow passes with increased risk of infection transfer; detection of clinical mastitis can be variable. A lack of data on withdrawal periods of intramammaries with variable milking intervals has led to an increase in injectable antibiotic use. The need to prevent mastitis is increasingly important in automatically milked herds.

James Breen of the University of Nottingham and Evidence Group gave examples of use of the QuarterPRO scheme, launched in February 2020. Farmers, vets and advisors are able to use novel and bespoke software to convert and present a dairy herd’s milk recording and clinical mastitis data such that the predominant pattern of new infections are identified as contagious or environmental, lactating or dry period origin. The pattern analysis tool and resource material indicate areas to be discussed and the process repeated every quarter with pattern, resource material and ongoing application. The tool and other materials are freely available online. Eighteen months of data is accessed, but for herds without individual cow cell count data, or that do not report clinical mastitis events, automatic conversion of data is not an option, but available data can be entered manually.

QuarterPRO is an entry-level scheme for farmers who have not engaged with the AHDB Dairy Mastitis Control Plan, possibly because engagement with plan deliverers was considered too onerous or the herd is considered not to have a serious mastitis problem. Discussions between herdsmen and vets on the predominant infection patterns and ways of preventing disease have been shown to be a beneficial approach. It is important to target areas identified for new infections for the relevant season, to be aware of findings each quarter and to target interventions that will be most beneficial to the herd. The scheme also provides a structure and framework for a more detailed investigation if required.