New data expected to change approach to mastitis control - Veterinary Practice
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InFocus

New data expected to change approach to mastitis control

RICHARD GARD reports on the papers at the British Mastitis Conference

WELL over a hundred people attended the 20th British Mastitis Conference and a third were veterinary surgeons.

The event was arranged by the Institute for Animal Health and The Dairy Group, with support from ADAS and an impressive array of sponsors including Boehringer-Ingelheim, Intervet ScheringPlough Animal Health, Pfizer, Dairymaster, Dairy Co, DeLaval, Kilco and Ecolab. The proceedings are available to download at www.iah.bbsrc.ac.uk/bmc.

The overall impression from the papers is of deliberation and accuracy. Another impression is of attention to fine detail in understanding and preventing mastitis. There also appears to be an acceptance that, despite detailed attention, the infections will continue to cause inflammation, disruption and economic loss. Although there were only six presentations, few attendees would have been up to speed on all the content.

It was pointed out by Jamie Leigh (University of Nottingham) that, although the organisms involved have varied little since the five-point plan, knowledge is evolving about specialised sub groups within each species.

New technology is able to identify clusters of bacteria with differing biological properties. It is anticipated that, together with bacterial genomic sequence data, there will be a “massive expansion” in the detailed understanding of the processes underlying mastitis.

Twenty years ago, 137 distinct infectious agents were identified that were linked to mastitis in cattle. The typical outcome results from infection of the mammary gland and associated tissues and is a consequence of successful colonisation, evasion of host defences and induction of marked and overt inflammatory changes. The range of bacterial species present in mastitic samples varies little all over the world.

The application of molecular tools, particularly multi locus sequence typing (MLST), to typing mastitis causing bacteria indicate that Staph. aureus infections arise from a limited restricted reservoir, such as other infected mammary glands. Strep. uberis is more diverse and there could well be populations that not only gain access to the udder from environmental contamination but also can be transmitted from gland to gland. It appears likely that precautions applied to prevent the spread of Staph. aureus may be able to be overcome by the high numbers and long duration of infection recognised with Strep. uberis.

A combination of the advances in biochemistry and computing power, together with a huge reduction in the cost of applying these techniques, will allow mastitis investigations to be carried out at a level of detail never before considered possible. It is expected that the new data will challenge existing knowledge about mastitis control and lead to the development of new interventions to reduce the burden of bovine mastitis.

An understanding that somatic cell count (SCC) is in part a heritable trait allows bulls to have a Predicted Transmitting Ability (PTA), offering a means of reducing the SCC of a herd.

Marco Winters (Dairy Co breeding) indicated the impact on the daughters bred from bulls with a good PTA for SCC. Genetic indices for milk production, fat and protein content have been a cause of bull selection for many years. The acceptance of the role of non production traits in the future performance of herds is becoming commercially important.

Balance needed

Clearly there has to be a balance with the selection of fitness together with production traits and the Profitable Lifetime Index (PLI) has an over 50% emphasis on fitness. This has been developed to overcome the negative genetic trends experienced when selection is based on production traits alone.

The first calves were born in 2006 by applying the new selection tool. The heifers are expected to calve for the first time in 2008. A reduction in SCC can be anticipated from now onwards. Genetic improvements are very cost effective, permanent and accumulate over successive generations. Further research into animal performance data is taking place and an enhancement of genetic evaluations and genetic selection indices will help to provide a sustainable dairy industry.

Those of us working in the dairy industry should “firstly be striving to reduce the number of cases of mastitis that occur and secondly to control the pain caused when cases do arise”, said Jon Huxley, of the School of Veterinary Medicine and Science at the University of Nottingham, who presented a strong case for the use of NSAIDs for mastitis cases.

Mastitis is graded from 1 to 3. It has been recognised for some time that grade 3 (systemic signs) mastitis cases have been associated with discomfort indicators such as an elevated heart and respiratory rate, decreased ruminal activity and food intake and alterations to behaviour and general condition.

Recent research has shown that grade 2 (changes to the quarter such as heat and swelling) cases also have a raised heart and respiration rate. Of particular significance is that the hock to hock distance is higher in both grade 1 and 2 cases indicating that, even when the mastitis is mild, cows alter their stance to reduce pressure on the udder when they walk or stand. Elevated levels of bradykinins and other pain mediators have also been demonstrated with mild cases of mastitis.

Inflammatory mediators and persistent activation of pain fibre pathways in the spinal cord lead to a decrease in pain threshold so that stimuli are perceived as more painful than would normally be the case (hyperalgesia). Chronic pain leads to a perception of normally non-painful stimuli as painful (allodynia) and this has been demonstrated in cows.

Studies with meloxicam have shown a reduction in pain associated with mastitis by inhibition of arachidonate cyclo-oxygenase (COX) enzymes, which lead to a reduction in the synthesis of prostaglandins and thromboxanes that cause pain. A single dose has been shown to be effective.

Flunixin, ketoprofen, meloxicam and tolenamic acid have a licensed indication for use in mastitis. Routine use of NSAIDs in mastitis cases is advised to reduce inflammation and promote rapid recovery of the gland, despite their apparent initial expense. Veterinary surgeons are viewed as the “gatekeepers of knowledge” on this.

Observation of cows in cubicles by someone other than the farmer or herdsman was advised by Martin Yeates from Kingshay consultants. By watching the cows closely during a quiet time, ideally after milking or feeding, the cows will “tell you their problems”.

If more than 10% of resting cows are standing up, then the beds are likely to be uncomfortable. If more than 10% of the cows have damaged hocks and knees, look to poor ventilation causing damp beds and the abrasiveness of the lying surface.

Hair rubbed off, or sores, indicate that the cows find it difficult to lunge when standing up in the cubicle and no more than 5% of cubicles should be dirty. The position of a cow standing in the cubicle will indicate the need for attention to the neck rail, brisket board and cubicle width.

Cubicle design

The importance of the design of cubicles “to keep muck off the teat” was also highlighted by Nigel Cook (University of Wisconsin-Madison). Periods of standing and lying by a dairy cow are called bouts and the average cow has 13.6 bouts per day for a duration of 1.2 hours each bout. Most cows will stand after a lying bout, defaecate and urinate and lie back down again on the lateral side.

Transfer of bacteria to the udder is assessed for direct transfer by lying on contaminated bedding, from legs that are coated in manure and then touch the udder when lying down, splashing of slurry when walking and transfer from contaminated tails.

A view of the milking machine as an influence on mastitis in the modern milking parlour was presented in depth by Norm Schering (GEC WestfaliaSurge Inc). Fundamentally, the machine has to be used within its design parameters and monitored for performance during the whole of the milking cycle.

Milking performance and the system’s cleaning routine combine with interaction between the cow, machine, operator and the environment. Full details of each important aspect of influence of the milking machine on mastitis are in the proceedings.

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