The Dairy Antibiogram test is the result of a joint venture between Bayer and Morrinsville-based production animal research company, Cognosco.
Cognosco director Dr Scott McDougall said that vets and farmers will be able to collate the results of the test to paint a picture of where resistance lies in dairy herds nationally, ensuring a more targeted use of appropriate antibiotics against bacteria.
The test has been developed from a Dutch concept, but modified to the New Zealand situation. It targets the two most important mastitis bacteria, S. aureus and Strep. Uberis, through a bulk-milk sampling technique that cultures bacterial growth, and then assesses the amount of a number of different antibiotics required to kill those bugs.
The Antibiogram partners have developed a novel screening process where the S. aureus and Strep. uberis can be recovered from among the other bacteria present in bulk tank milk.
Bayer dairy veterinarian Dr Ray Castle said clinical mastitis occurred in 10-20% of NZ’s dairy cows every year. Each case of clinical mastitis cost the farmer about $250 per cow, with additional losses attributable to chronic and sub-clinical infections.
The test involves a consultation between vet and farmer, with bulk-milk sample results providing a report on the level of resistance, if any, detected in a particular herd.
McDougall said the test was a herd-screening test, and wouldn’t identify an individual cow’s resistance to a particular antibiotic, but it would give a broad-brush indicator of that herd’s bacteria-resistance status.
“Then, if it proves there is resistance in the herd, the next step down is to identify individual cows, and their individual quarters if necessary, within the herd.”
He said his support for Antibiogram came from the “herd” overview it gave, which was sufficiently accurate as a first indicator and well-suited to NZ’s larger herd sizes.
“Historically, we have struggled to get samples from individual cows for culture and resistance testing due to logistics, particularly in spring when farmers are really busy.
“So this system is really easy for farmers, as they don’t need to identify and culture individual cows.”
The Antibiogram test is also providing a means of starting the conversation about antibiotic resistance between vets and their farmer clients.
“Colleagues are saying it is relatively easy to demonstrate the value to herd owners,” McDougall said.
With greater public awareness of antibiotic resistance, NZ’s farm sector wasn’t immune from pressure to dial-back antibiotic use, even if evidence so far didn’t support any significant shifts in antibiotic resistance among the national herd.
The test promises to provide another means of helping the industry demonstrate to consumers and regulators that the sector is using antibiotics in a prudent way, and that resistance isn’t increasing.
Earlier research by McDougall and his colleagues on farmer antibiotic use had helped vets develop an antibiotic plan they can take to farmers to develop a more effective treatment regime.
“We found that farmers who engaged with their vet on a plan actually held or even reduced the amount of antibiotics they used,” McDougall said.
“We have since had a roadshow to 220 dairy vets nationally around the whole resistance story and encouraged them to discuss with farmers how we need to do, and be seen to be doing, the right thing.”
With vets supporting the Antibiogram test, a significant amount of data will also be generated.
Bayer’s Ray Castle said ideally he would like to see all dairy farms nationally have their milk undergo the Dairy Antibiogram test.
“The test will give us this clarity, and go a long way to ensuring effective treatment of mastitis in our dairy herds,” he said.
McDougall said, from a researcher’s perspective, the test promised to offer a treasure trove of data to better understand how bacteria populations and resistance patterns changed through lactation.
“We have vets planning to test this spring, and then again around drying-off time. Over time, and with sufficient samples, this will help identify any seasonal changes in bug populations, or in resistance profiles.
“The data will also eventually enable us to benchmark nationally for herds’ resistance status, and when we identify any herds that are outliers, this can be the start of a constructive conversation between vet and farmer on how to manage that.
“The next step may be to identify individual cows infected with resistant bacteria and treat appropriately, or in some cases culling may be the best option,” McDougall said.
