Mastitis. Just saying the word can cause blood pressure to rise within the dairy industry. For some, it is an everyday battle, using all one’s power to combat. For others, the approach to mastitis is to live with it in hopes of it not causing too much damage.
In 1996, the USDA National Animal Health Monitoring System (NAHMS) survey estimated that mastitis affected 13% of dairy cows in the U.S. By 2014, that number had climbed to 25%, a number consistent with university data published over the past few years. But with all the technological advances, one must ask: Why haven’t we been able to get better control of this issue?
Disease transmission
As long as living organisms have been on Earth, they have been getting sick. And for nearly as long, humans have been trying to grasp what causes disease. Modern medicine accepts that infectious disease occurs when there becomes an imbalance between the host, the environment and the pathogen. This triad of disease balances the interactions between these three legs of the stool with the organism’s ability to stay healthy. If any of the three gets out of balance, the risk of disease is increased.
Modern dairy farming has implemented this triad of disease extensively into management to prevent mastitis in cattle. Emphasis on bedding choice in freestalls, manure handling, inflations and vacuum line pressure for the milking units, towels and disinfectants are all decisions that impact the environment and can increase or decrease the risk of mastitis. Studies have been done to better understand the virulence and transmission mechanisms of known udder pathogens. Growth media and culture techniques to isolate and identify these pathogens have been developed. Vaccines that target these pathogens are given to the cow. When it comes to the third aspect – the cow – less has been done.
Part of the reason the cow portion of the disease triad hasn’t been emphasized as much is the difficulty in changing her in support of what we are trying to accomplish. Cows have been selected for more milk production, which has inadvertently increased the risk of mastitis. Udder conformation, age and stage of lactation all are factors that affect a cow’s susceptibility to infection. While environmental changes can be made quickly, changing the size and shape of a cow’s teats in a herd can take years of selective breeding. The cow may be the most difficult factor to deal with in the triad of disease, so maximizing what we can do with her in the moment becomes more important.
The immune system
Typically, when discussing the immune system, vaccines and antibodies lead the discussion. With milk quality, somatic cells get mentioned more frequently. In biology, somatic cells are any cells that aren’t germ cells or those that can produce offspring. In milk, most somatic cells are cells from the immune system known as neutrophils and macrophages. These cells circulate through the bloodstream and migrate into tissues in which pathogens have passed. Unlike antibodies, these cell lines are not specific and respond very quickly to infection.
Fueling the immune system with trace minerals
While changing the udder conformation of a cow or her age may not be a possibility in improving her resistance to disease, it is possible to strengthen her immune system. Ample scientific evidence supports the role of trace minerals in supporting the immune system. What is often overlooked with trace minerals is the fluctuations in demand during lactation.
At freshening, a cow may lose up to 30% of the trace mineral reserves in her liver. Over the next few months, those levels will return to pre-freshening levels, typically peaking in late lactation. Through the dry period, liver levels will decrease as the cow transfers minerals to her fetus. At freshening, with milk production and the risk of mastitis, the cow finds herself with the lowest levels of trace minerals to support her immune system. Even with properly balanced trace minerals going into the ration, the cow is unable to absorb them quickly enough to return her mineral stores to the levels needed to support immune function in her system and in the udder.
Recent research has indicated that the most efficient way of restoring a cow’s trace mineral status is via injection. Data presented from a study at the Spanish International Buiatrics Congress with over 400 cows demonstrated that cows injected with trace minerals (ITM) during the dry period had a 74% reduction in clinical mastitis during the first 30 days of lactation compared with nontreated controls. As this study was done on a farm undergoing selective dry-cow therapy, the effect of injectable trace minerals was separated by dry-off treatment. Lactating cows without mastitis received only teat sealant, while the rest were also treated with an intramammary antibiotic. Trace mineral treatment led to a similar clinical mastitis reduction regardless of the dry-cow therapy.
While mastitis continues to be a costly disease for the dairy industry, focusing on all three aspects of disease susceptibility – including the cow – may give us our best chance at controlling it.
