A new mastitis test to reduce antibiotic use on dairy farms is being trialled through an on-farm ‘field lab’ with Innovative Farmers.
Mastitis remains one of the main reasons for using antibiotics on dairy farms and the industry continues to work hard to reduce usage.
Significant progress has already been made in reducing preventative use in dairy cows during the dry period, but reducing the use for treatment of clinical mastitis during the milking period remains a challenge.
To help counter this it is important that possible solutions are tested on farms.
Vet, Peter Plate, from the Royal Veterinary College, is involved in an on-farm trial looking at the effectiveness of a new farm bacteria test kit in establishing the cause of infection and the need for antibiotics.
He explains that there is a growing body of evidence which suggests that cases of mild mastitis can be cured without antibiotic treatment where it is caused by certain organisms known as gram-negative bacteria. This is much less common when the causative bacteria is from gram-positive bactaria.
Mr Plate says: “This means there is an increasing interest from farmers to identify mastitis causative organisms via on-farm tests, which may negate the need for using antibiotics when gram-negative bacteria are responsible.”
He adds this has the potential to reduce antibiotic use, as well as saving farmers the cost of medication and treatment and the cost of discarded milk.
In a bid to investigate this further, Innovative Farmers have brought dairy farmers and researchers together to set up some on-farm trials. This ‘field lab’ is investigating whether one of the latest bacteria test kits on the market, MastDecide, can be practically used to identify the bacteria and reduce antibiotic use without affecting animal welfare and milk quality.
The trial has now been running for about 10 months and has involved eight farms, ranging from 100- to 600-cow herds, on conventional and organic systems, mainly based in the south of England.
Half of the cows in each of the herds is treated for mastitis in line with pre-trial protocols. The other half is tested using MastDecide. If the results of this test show gram-negative bacteria the farmer does not treat that particular cow with antibiotics. Cows with gram-positive bacteria are treated with antibiotics.
Mr Plate say initial findings are positive and the test could be a useful additional tool in the armoury of some farms to help reduce antibiotic use, but he would like to follow results through for longer.
He says: “The test is fairly simple to use and interpret. The test kit comes with two small tubes containing a pink liquid. A small sterile milk sample is added and then the test vessels are placed in an incubator for 12-14 hours.
“There are three possible outcomes. If both tubes stay pink in colour there is no bacteria detected in the milk sample, so no antibiotics are needed.
“If there is one white tube and one pink tube it suggests there is gram-negative bacteria, so no antibiotics are needed, but if both tubes turn white then this indicates there is gram-positive bacteria present and antibiotic treatment is needed.”
Mr Plate says the test leads to easy decisions about treatments and because the tubes are sealed there is no risk of cross-contamination.
As part of the field lab the samples are also sent to Quality Milk Management Services for additional laboratory testing to see how reliable the on-farm test results are.
Mr Plate says: “The laboratory testing shows the on-farm testing is correct about 85-90 per cent of the time. This means there will be 10-15 per cent which we may treat the wrong way.
“So while the testing means we will get some treatments wrong, that is the price we have to pay for not treating with a blanket approach.
However, Mr Plate says initial estimates suggest using the MastDecide test to help make treatment decisions has reduced antibiotic use by about 40 per cent on the participating farms. However, he adds this this can vary widely between farms, depending on the ratio of gram positive and gram negative cases. So before embarking it makes sense to know which the predominant bacteria are.
He adds: “Farmer feedback to the test has been positive, with cows that have shown gram-negative bacteria and therefore not receiving treatment recovering well. We have some farmers who plan to use it across their whole herd.”
In terms of the cost savings of not using antibiotics, he says modest calculations suggest there could be an economic benefit of about 25 per cent. this is highly dependent on the predominant mastitis bacteria and the accuracy to identify cases correctly – a cost calculation will be part of the analysis.
The field labs are ongoing and Mr Plate says the impact on long-term somatic cell counts will be analysed once cows have completed a full lactation.
Mr Plate says the on-farm test will not be useful to all dairy producers.
“Not all farmers are geared up to take a sterile milk sample, and it also depends on the ratio of gram positive and gram negative bacteria on the farm.
“For those farmers who have more cases of gram positive bacteria it is probably not the best option.
“But for those farmers who have the right spectrum of bacteria, and have the ability to collect these samples then it could be a useful additional tool.”
Mr Plate adds that these sort of tests should not take away from the emphasis on prevention.
He says: “This is not the solution for farms who have a high rate of mastitis and high use of antimicrobials. In these cases the first thing to do would be to work with the vet to prevent or reduce cases.
“For many farms there is more scope for reducing antibiotic use by reducing the number of cases in the first place.”
Dairy farmer John Shiles is one of the dairy farmers involved with the Innovative Farmers field lab, and says he has found the testing to be ‘worthwhile’ with antibiotic treatments reduced.
Mr Shiles, who worked as a vet until seven years ago, farms with his parents Henry and Jenny. The herd of 450 Holstein cows are milked three times a day, yielding an average of 12,000 litres.
Housed all year round, the cubicles sheds are a combination of sand bedded and straw and mattress bedded.
He says: “Overall the health of our herd is pretty good, but we do try to keep a close eye on the number of mastitis cases we have, as we want to reduce treatment with antibiotics.”
He estimates he normally sees about 40 cases of mastitis per 100 cows a year and before embarking on the trial, all cows showing signs of mastitis received a non-steroidal anti-inflammatory drug (NSAID) and antibiotic treatment.
He says: “Now cows showing signs of mastitis are treated with a NSAID and antibiotic if they have an even cow number.
“For odd number cows we will treat with a NSAID and run the MastDecide test on them.
“It is an easy test to use and because there is a quick turnaround of the result we are not losing too much time.”
Mr Shiles says about half of the cows that are tested need antibiotic treatment. He adds that while it is frustrating the test is not 100 per cent accurate, he says they are still treating less cows than they would have done before.
He says: “It has definitely been worthwhile as it has helped us to reduce antibiotic usage.”
Looking ahead, Mr Shiles says he would like to be able to use the test across all cows, and at the same time is planning on making changes to cow housing to help minimise the risk of environmental mastitis.
“Now we are only treating the cows that need treatment, but overall our aim is to reduce the number of cases in the first place.
“We are planning on moving all the herd onto sand bedded cubicles in the future, and want to make improvements to shed ventilation. Our aim needs to be for a cow not to get mastitis in the first place.”