Making a Difference
The experiences of the farmers involved in the trial were varied depending on the prevalence of Gram positive infections. However, all the farms found the technique enabled them to make more confident and targeted decisions about their antibiotic requirements.
Reducing the unnecessary administering of antibiotics has financial and ethical benefits to dairy farmers and further advances in the practicalities of such diagnosis techniques would have significant benefits for the industry.
The team are keen to see more trials in mastitis typing as the dataset collected was insufficient in this field lab to make confident statistical conclusions. There are plans to start a new field lab continuing the investigations and more information will be available as this develops.
Results from trial
In total for the trial there were 176 eligible cases. 78 of these were culture cases and 98 were treatment cases.
Of the 78 culture cases 19 (24 %) were left untreated after showing a Gram negative culture result or no growth and 59 (76 %) were treated, showing a Gram positive or mixed culture result.
a) Clinical cure rates:
Clinical cure, defined as the milk appearing normal again, was achieved in 91 out of 93 treatment cases (98 %) and 72 out of 75 culture cases (96 %). Of the culture cases which required treatment the clinical cure rate was 96 % (55 of 57 cases), of the culture cases which were left untreated the clinical cure rate was 94 % (17 out of 18 cases).
b) Days to clinical cure
Of those cows with usable data (56) the average number of days from detecting a case to clinical cure was 4.3 days for treatment cows and 4.6 days for culture cows. Of those culture cows treated the average days to clinical cure was 4.7 days, of those untreated 4.3 days.
c) Days to return to the bulk tank
The average days to return to the bulk tank, considering clinical cure and organic milk withdrawal periods for treated cows was 13.7 days for treatment cases and 13.2 days for culture cases. Of those culture cases which were left untreated the average was 4.4 days.
d) Recurrence rates:
Of the 92 treatment cases with usable data 23 % (21) of cows had a subsequent case of mastitis in the same lactation (not necessarily in the same quarter). Of the 66 culture cases with data 26 % (17) had a recurrent case. The recurrence rate of culture untreated cows was 39 % (7 out of 18), of the culture and treated cows was 21 % (10 out of 48).
e) Subsequent somatic cell count:
Greater somatic cells counts indicate a greater level of infection in the animal. The treatment cases gave an average subsequent linear score of 4.19, the culture cases of 3.99. Of those culture cases treated the subsequent score was 3.87, of those untreated it was 4.38.
(...)The expected saving in antibiotic treatments using the culture kit was about 24% across the eight farms. The percentage of culture cases which did not require treatments varied considerably between farms and ranged from 0 to 60%. The numbers are too small to evaluate whether any differences in outcomes are significant. Clinical cure rates are very good in all groups.
The differences in somatic cell counts and recurrence rates have to be monitored in a larger study in the future, and their statistical and clinical significance evaluated.
However, these preliminary results may encourage more interest among farmers (organic and non-organic) to be included in a wider trial.
Cost effectiveness of methods short review
There is a wide range of costs depending on the percentage of Gram negative cases and bacteriological cure rates, but in a simulation of 5000 non-organic mastitis cases by Down et al. (2016), on farm culture was not cost-effective in most circumstances. The situation, however, may be different for organic farms: due to the higher milk price and the required extended withdrawal periods the potential cost saving per case not treated are considerably higher.
Based on the small (but real) numbers in this trial, the potential cost benefit analysis for organic farmers could be as follows:
Assumed milk yield: 20 litres per day
Assumed milk price: 35 ppl
Saving for every mastitis case not treated: 9 days of milk - £63
Saving in mastitis tubes (4 tubes @ £2.50) - £10
Total saving for every untreated case - £73
Assumed cost per culture (plates, consumables, labour, incubator) - £8
If 25% of cultured cases remain untreated, the cost saving per cultured case is:
(£73 – (4 x £8))/4
Average net benefit for every case cultured - £10.50
This simple calculation is based on the assumption that there is no difference in mastitis outcomes due to wrongly allocating cases or delaying treatments. Higher case numbers are needed to verify whether or not there are statistically and/or clinically significant differences in outcomes under UK conditions (...)
Milestone: Cost effectiveness of methods reviewed
Cost effectiveness review continued
Comparing with the average total cost of a mastitis case of about £250 the figure appears to be modest. This shows again that preventing mastitis should be a main priority on every dairy farm, which will reduce pain in the cows, costs to the farmer and antibiotic usage. It would be wrong to allocate resources (money and labour) into culturing and selective treatment before taking up preventive measures as outlined in industry initiatives like the AHDB Dairy Mastitis Control Plan.
However, where this is in place, culturing has the potential benefit of further reducing the use of antibiotics on many farms. Cost-effectiveness on farm level is only one aspect of it. Avoiding antibiotic resistance is a public good. O’Neill in his 2016 report highlights the use of rapid diagnostic tests as one main recommendation to avoid resistance. “High-income countries should make it mandatory that by 2020 the prescription of antibiotics will need to be informed by data and testing technology wherever it is available”. Where this is not cost effective in the short term the public should pay for a public good. In a dairy situation milk buyers could subsidise the introduction of on farm testing in a similar way they have subsidised measures to reduce Johne’s disease.
Milestone: Cost effectiveness of methods reviewed
Ethical issues short review
No test is 100 % sensitive and specific. Wherever a treatment is based on a test result there will always be some cases which should be treated and don’t and others which get treated but don’t require it. The farmer and practitioner are in a potential dilemma between maximising the chance of a positive short term outcome and minimising the long term risk of drug resistance.
Other areas in veterinary medicine where selective treatments based on test results have become recognised best practice are:
- SCOPS (Sustainable control of parasites in sheep): To avoid wormer resistance it is recommended amongst other measures to treat only after a high worm egg count and to leave a proportion of a group untreated, based on body condition, number of lambs etc.
- Selective dry cow therapy: Based on somatic cell count and mastitis history only selected animals receive long-acting antibiotic tubes at drying off. This replaces the decade old recommendation for non organic dairies to blanket treat every cow with an antibiotic at drying off.
Both areas are backed by an increasing body of scientific evidence, but on an individual basis there is the risk of wrongly allocating groups or animals with potential negative consequences, and in spite of this potential for failure scientific and industry bodies recommend these approaches due to their long term benefits.
The evidence for selective treatment of clinical mastitis under UK conditions is still incomplete due to the small number of cases so far, but this trial provides the first real figures on its practical use. It is hoped that the results may encourage more farmers to take part and test the method for themselves and disclose high quality data for further analysis.
Milestone: Ethical issues reviewed
Protocol usage progress
At a progress monitoring meeting, minor difficulties with following the protocol were discussed with remedial actions agreed. Mostly this was around removing condensation on the agar plates prior to plating up and encouraging trial members to send in all records, not just those where gram negative organisms were found.
Milestone: Progress monitoring
Second training session - all hosts trained
This training session at Neston Park Farm was for farmers who could not make the first session. In total there are now 11 herds and over 2,200 dairy cows on the trial. The aim is to capture information on 400 mastitis cases over the next 6 - 8 months which will give reliable results on the effectiveness of mastitis typing for dairy herds.
Milestone: Second training session
An introduction was given to health and safety aspects of on-farm culture and on the definition and grading of mastitis – only mild and moderate degree cases of mastitis are to be included in the trial. The allocation to trial or control group is done by odd or even cow number (Odd – grOw, Even – trEat) , which turned out to be the most practical way. It was also agreed that regular milking staff (including relief) can be trained, but cows getting mastitis during an, untrained milking must be excluded from the trial. A folder with instructions, record sheets, and agreement forms was given to all participants. The recording sheet and the information required was explained. This was followed by a training session on taking aseptic milk samples, applying sample to culture medium and reading cultured sample after 24 hours.
Milestone: Training meeting
White Hart, Mere: The group introduced themselves and discussed their interest in looking at the potential for mastitis typing. Peter Plate (coordinator and vet) detailed the theory of this new approach to mastitis treatment which stems from the fact that mastitis is sometimes caused by gram negative bacteria. These have a high spontaneous cure rate which makes treatment with antimicrobials sometimes unnecessary. On farm typing is now available which would reduce the delay for starting treatment to 24 hours. Following a group discussion, it was agreed that at 10 group members were prepared to host farm trials.
Milestone: First meeting