Imagine a world without mastitis. It’s easy if you try. No costly treatments or increased risk of mortality, no reduced milk yields, no $2 billion economic loss in the industry. Unfortunately, this is not the world we live in. Mastitis is one of the most significant diseases in the dairy industry. Detected in about one-fourth of all cows across the U.S., every dairy producer has been humbled by the disease. Mastitis has a detrimental effect on both animal health and farm profitability.

Business development manager / AHV USA

For decades, farmers and researchers have been developing treatments and control programs but still mastitis persists. Around half of all mastitis infections can be attributed to recurrent clinical mastitis cases. Simply put, once a cow gets mastitis, she has a much higher chance of encountering the disease a second time. Many of these recurring infections are not actually new but are an initial infection that was never fully resolved. These chronic cases typically do not respond to antibiotic treatment, and the bacteria remains persistent in the mammary gland, negatively impacting the cow time and time again.

In addition to recurring cases, dairy farmers are seeing first-lactation animals enter the milking herd with mastitis. Studies have shown that mastitis pathogens are present in between 29% to 74% of heifers prior to calving, while the prevalence of infection at calving falls between 12% and 57%. Based on what we know about chronic cases, this does not bode well for the heifer in its future lactations. But before we consider the lasting effects, we need to ask how heifers contract this costly disease in the first place.

The answer to how non-lactating heifers develop mastitis is not exactly known. But studies have led to various hypotheses and shown that the teat canals of calves can be colonized by bacteria at a very young age. One way in which this is believed to occur is through the feeding of non-pasteurized milk. Contagious mastitis organisms are most likely spread by calves licking their legs or udders after consuming contaminated milk, and then the bacteria colonize on the teat, eventually leading to infections.

Precautions against mastitis should be taken long before animals enter the milking herd. If initial infection is avoided, the positive impact on future lactations, and the decrease of chronic cases, could be invaluable. First-lactation heifers may also freshen with mastitis because of environmental factors. Herdmates may suck on teats, flies may bite or irritate the teats, or bacteria may be spreading through the bedding or manure.


Antibiotics are the standard for mastitis treatment, but this solution comes with its own issues. Mastitis isn’t caused by a single pathogen, so it can be difficult to treat with traditional methods of antibiotics. Additionally, overuse and the resulting antimicrobial resistance limits the effectiveness of these treatments, and the development of antibiotic-resistant bacteria becomes a critical challenge.

On top of this, bacteria’s resistance to antibiotics can be attributed to its ability to form biofilms. An extracellular polymeric substance, biofilm allows bacteria to hide from threats, increasing its resistance to antibiotics and the host’s immune system. Recent research has shown that a high proportion of microorganisms that cause mastitis can form biofilm, giving them an advantage against the cow and the farmer’s attempts to eradicate mastitis. If biofilm is broken down, the cow’s immune system is given greater opportunity to kill off the bacteria, preventing infection and possibly even reoccurring cases.

By finding ways to remove or prevent biofilm, we may become more successful in our fight against mastitis and those frustrating chronic cases. Quorum sensing is key to the biofilm formation process, and without it, bacteria cannot create or maintain their defenses, leaving them vulnerable. Removing their defense allows the animal’s immune system to respond to the infection more effectively. This alternative to antibiotics is a step in the right direction.

Currently, apart from antibiotics, dairy farmers have very few tools available to treat costly mastitis infections, and while inhibiting quorum sensing supports the cow’s immune system, prevention remains the most important management practice to fight mastitis. Stress events, such as the transition period, heat, overcrowding, spoiled feed and more, can cause animal health to suffer by reducing immunity. Restoring that immunity, and the overall strength of the immune system, is important when combating mastitis and other infections.

Mastitis is not only caused by organisms and bacteria, but by how those bacteria get to the cow to cause infection. Environmental factors such as personnel, milking supplies and equipment, and the milking procedure can all lead to mastitis. Milkers need to follow protocols closely, disinfect milking equipment as needed and monitor the milk from each cow. Additionally, inflations, milking units and vacuum pumps need to be properly functioning.

Calves and heifers may also be affected by mastitis. It is important to treat waste milk as exactly that, waste. Milk from cows with mastitis should be thrown away and not fed to calves, as it may introduce bacteria to a calf’s immune system. Antibiotic resistance can also begin at this stage, if a calf is being fed milk from a cow receiving antibiotic treatment.

When trying to eradicate or reduce mastitis cases on your dairy, remember to go back to the basics:

  • Catch mastitis cases early through stripping or performing a California Mastitis Test (CMT)
  • Identify, separate and milk last chronically infected cows to limit the spread of bacteria throughout the herd
  • Clean and maintain properly working milking equipment
  • Provide clean, dry bedding
  • Train and retrain employees on mastitis protocols and milking procedures

Combating mastitis takes time and attention. Although we may not be able to eradicate mastitis, one misstep, weather event or parlor change may result in taking several steps back in your fight against the disease. The most effective control programs rely on prevention rather than treatment – focus on blocking the initial infection and protect your herd's health throughout all lactations.