Understanding Mastitis: From Perspective of Inflammation

Inflammation and infection are among the commonest buzzwords in veterinary practice. The fact that inflammation appears to play a major role in many diseases makes it the fieriest topic of discussion nonetheless inflammation protects and heals the body after an injury or infection. Inflammation is an amazing process that, from the surface appears swelling and can hurt, but it’s all part of making things better. Mastitis, the most devastating inflammation of dairy animals causes huge economic loss to the dairy industry worldwide. An inflammation based understanding of mastitis opens the door for novel strategies in limiting the duration as well as cost of treatment.

The term inflammation comes from the Latin word, ‘Inflammatio’ which means to set on fire. The very purpose of inflammation is to burn away the harmful stimuli such as pathogens, allergens, injuries or any other irritants thereby initiate the healing response. However, just like fire, if inflammation is not extinguished then it can rapidly spread and beget more inflammation.

Acute and chronic forms of inflammation can be seen as inflammatory response based on the severity, duration, immune response and therapeutic intervention. Acute inflammation typically reveals all five cardinal signs of inflammation.

Mastitis is recorded as the most costly disease which affects dairy cattle throughout the world resulting in huge losses. In India it ranks second only to FMD in terms of economic loss to the country. Mastitis, inflammation of the mammary glands is the body response to defend against the invading microorganisms/physical agents into the mammary gland. Thus, the inflammatory reaction is something good but it may, unfortunately, also cause damage to the udder tissue. It is often affecting not only the mammary gland, but the whole organism systemically manifested by decreased appetite, depression, increased body temperature, and alteration of the whole metabolism. The economic consequences of bovine mastitis are colossal which include cost of treatment, production losses, reduced milk quality, reduced milk yield, increased culling rates and overall public health.

Mastitis is considered to be a multifactorial disease. Whilst over 200 microbial species have been identified as causative agents of mastitis. The major causes of mastitis are as follows;

Bacteria (~70%)
Yeast & Molds (~2%)
Unknown (~28%) e.g. Physical trauma & Weather extremes

Understanding Mastitis: From Perspective of Inflammation - Image 2

Risk factors for Mastitis

Mastitis is complex; there is no simple solution to its control. To simplify understanding of the mastitis complexity, it is useful to consider the three major factors involved in this disease:-

Microorganisms (as causative agent)
Cow (as host)
Environment (which can influence both the cow and the microorganisms)

Development of Mastitis

Microorganisms penetrate the teat canal and multiply in the mammary gland leading to development of mastitis. It involves breaching of 3 lines of mammary defense mechanisms by the microorganisms to develop the disease.

First line of defense: Invasion of teat by microbes

Second line of defense: Microbial encounter by mammary localized leukocytes

Third line of defense: Destruction of alveolar tissue

Economic implications of Mastitis in dairy animals

Mastitis has been and continues to be recognized as one of the major disease problems concerning the dairy industry. The economic damage of mastitis, either clinical or sub-clinical can be brought down to a few categories:-

Milk production losses: In both clinical and sub-clinical mastitis, there is a loss in milk production. Milk production loss in sub-clinical mastitis is not obvious to the producer, because this is milk never produced, and therefore never seen. It is a hidden cost or lost income opportunity.
Drugs: This is a straightforward economic damage. Drugs, necessary to treat a cow with mastitis, cost money. The duration of treatment in clinical mastitis may vary from days to weeks to months.
Discarded milk: Economic damage due to discarded milk is comparable with the damage of a decreased milk production. However, there is one difference; the discarded milk is actually produced by the cows, which means that feeding costs for that amount of milk has to be taken into account with the calculations. The economic damage of 100 kg discarded milk is therefore larger than for 100 kg decreased production.
Veterinarian:Besides delivering drugs, the veterinarian might have to spend time on diagnosis of a (clinical) mastitis case or supportive therapy.
Labour: Treating mastitic cows, while other cows are waiting in the milking parlour, is work that a farmer does not like to do. So (s)he is willing to spend money to prevent that.
Milk quality:Mastitis influences the quality of milk. Some of these changes cause a less efficient processing of milk and might result in products with less favourable properties. Examples are an unstable and rancid taste of milk, a lower cheese yield and a decreased shelf life.
Culling:Cows with mastitis have a higher risk of being culled. The cost due to premature replacement of animals due to mastitis is probably one of the largest areas of economic loss. However, it is also a hidden cost.

Potential Interventions

An inflammation-based understanding of mastitis opens the door for novel strategies in limiting the duration as well as cost of treatment. The complex interactions of stress, inflammatory cascades, and metabolic pathways allows for a broad array of potential treatments to prevent mastitis.

Knowledge of the causative agents, the milk production environment and the mammary gland as a reservoir, should be understood as a whole. These are the driving forces of the persistence and spread of the disease in the herd. Three pronged approach to mastitis including prevention of the disease by focusing on the reduction of new infection risk, the control of mammary gland state & the management of the existing clinical cases. All control tools should be developed to deal with the disease and finally to manipulate the immunity and to reduce the carrier state.

Despite world-wide efforts, mastitis has remained economically the most important disease in dairy cattle regardless of numerous mastitis control programmes in place it is still a major challenge for the dairy industry.