What mastitis bugs grow on your farm?

Mastitis is one of the biggest concerns for milk producers; and the most expensive - it costs farmers $200 per cow, per year; which totals over US$130 million in losses to the industry annually.

Once you consider costs of treatments, loss of milk and increased farm labour, it all adds up to a substantial amount. On top of that, there are also issues that are difficult to put a dollar value on — such as animal welfare and consumer awareness.

Consumers are more conscious of how food products are made; becoming increasingly aware of the environmental impact of food production and how medicines are being used in the food they eat. By better understanding the causes and treatments of mastitis, producers are in a better position to meet consumer needs and maintain market share.

The European Union is applying pressure to the dairy industry globally to regulate antibiotic usage. In order for Australia to begin developing guidelines for our producers, we first need to understand how we use antibiotics in our milking herds.

Resistance of mastitis-causing bacteria is becoming a greater problem for milk producers. Increasing levels of antibiotic resistance means that it takes longer to treat a cow, more courses of antibiotics are needed, the cow spends more time off the vat, and recovery is slower. Farmers may see this when they have to re-treat cows multiple times and they don’t seem to recover from the infection.

Understanding what bacteria is causing the infection allows producers to choose the most appropriate antibiotic, allowing targeted and more effective treatment. Targeted treatment improves animal welfare, reduces treatment costs and reduces time milk gets diverted from the vat, leading to increased income for producers.

Researchers and students from Murdoch University, supported by Western Dairy, have begun investigating what bacteria cause mastitis on WA dairy farms by sampling, culturing and identifying bacteria using state-of-the-art technology.

A study performed in the Macalister region in Victoria demonstrated that the types of bacteria that grow on farms can vary greatly, not only from farm-to-farm, but also between regions. This means that nation-wide studies identifying bacterial types and levels of resistance will have to be performed to gain a clear picture of where the Australian dairy industry currently stands.

A total of 266 samples from 10 farms in South-West WA have been tested and bacterial identification performed using the MALDI-TOF at Murdoch’s premiere Antimicrobial Resistance Laboratory.

Farmers volunteered to participate in the study, which involved collecting some demographic data and information on mastitis management. Veterinary researchers and students then visit the farm during milking to collect milk samples from consistently high somatic cell count cows.

Finding so far show that the most commonly identified group of bacteria are an opportunistic bacteria known as Coagulase Negative Staphylococci or CNS. The most commonly isolated bacteria are Staphylococcus haemolyticus. This is a significant finding because studies have shown S. haemolyticus to be an important pathogen in human hospitals and commonly carries high levels of antimicrobial resistance.

Staphylococcus chromogenes was the second most common CNS bacteria to be cultured. S. chromogenes is interesting because it has been shown to be ‘host-adapted’ – meaning its specialised for survival in the udder and on the cow. Interestingly, there has been no publications yet indicating it has been identified in Australia herds.

These bacteria have been shown to colonise the udder and can live within the mammary tissue for long periods of time without causing disease until the conditions are right. This can be after the cow has calved (lowered immune system), during times of heat stress (summer) and poorer quality diet (just prior to break of season).

The second most common group of bacteria identified was infectious bacteria such as Staphylococcus aureus and Corynebacterium bovis.

Contagious mastitic infections can be managed through milking management factors such as changing gloves between cows, milking infected cows on a separate cluster, and washing clusters between cows.

Previous studies performed in Australia have shown that S. aureus was the most common bacteria-causing mastitis. However, our study shows that CNS are the most common bacteria-causing mastitis.

As a producer, this information is important because it shows that management factors such as washing clusters between cows, wearing gloves and milking infected cows last has significantly impacted the amount of contagious mastitis in WA herds.

It also means that producers may have to begin using alternative methods to control opportunistic pathogens, such as reducing heat stress and managing transition cows more effectively.

Further research is being performed by researchers at Murdoch University, with funding, support and collaboration with Western Dairy, to determine the levels of resistance among the bacteria found on WA dairy farms.