Subclinical Mastitis is an Ongoing Battle

Published on Wed, 07/15/2020 - 10:36am

Subclinical Mastitis is an Ongoing Battle

By Jaclyn Krymowski

Mastitis is an enemy on the frontlines in the battle against dairy health, quality and productivity. The industry has invested millions of dollars’ worth of research into this issue, and we’ve amassed a wealth of information on how to prevent and treat it. Yet, every year mastitis still causes the industry countless financial and production losses both directly and indirectly. A good chunk of these can be contributed to the unchecked incidences of subclinical cases proliferating within the herd.

Udder health survelliance and action are key in maintaining lactating herd wellness. This is only accomplished in a team effort. When you think about it, your milkers are really your first line of defense for milk quality and safety. By developing a strategic plan to identify and manage subclinical mastitis cases, you incorporate your staff and teach them to use the right tools.

The importance of the subclinical
Simply put, subclinical infections those an animal is not symptomatic of. These cows won’t have hot and swollen udders, clots or bloody milk but still are maintain a SCC above the “healthy” threshold. The rule of thumb says that any seemingly healthy animal with 200,000 or more somatic cells/ml is subclinically mastitic. The higher your rate of clinical cases, the higher your subclinical rate. Data says for every clinically diagnosed case of mastitis there are anywhere from 15 to 40 others you’ll never see unless you test.

This can and should be monitored and managed on individual and herd levels. One of the easiest ways you can diagnosis a chronic subclinical issue is a high bulk tank somatic cell count. The same 200,000 SCC threshold also applies to the bulk tank – however even this isn’t sure fire. There are cases where only a few animals are severely infected and function as “shedders” putting out millions of somatic cells.

Cows who develop clinical cases are subject to becoming chronic cases themselves. With each freshening, these animals will always have an above average cell score. Chronic cases are also less likely to respond to antibiotic treatment. Not to mention these animals are very inefficient producers. Even if an animal falls within a “reasonable” range of somatic cells, say 200,000-300,000, these chronic cases do maintain a sort of infectious reservoir within the herd and are very capable of transmitting bacteria and viruses to their healthy herdmates, especially if managed improperly.

Successful testing
Successfully handling subclinical and chronic cases involves several tools. In fact, without the right technologies, it would be virtually impossible to even diagnosis, let alone treat, these animals.

Cow side testing is the first step in implementing a herd-wide management program. Routine DHIA testing is perhaps one of the most ideal ways to know exactly what the cell counts of invidiuals are. Newer systems and robotic setups already have electronic tools to measure scores with the same accuracy.

And of course, there’s always the old faithful California Mastitis Test (CMT).  Extremely cheap, simple and easy to train just about any milker to perform, it is also subject to being done hastily and improperly. Unfortunately, this test will not give you a direct SCC measurement and is also not as reliable at detecting fresh cows within the first four days of calving. But certainly having earned its home in every parlor, the CMT is a great way to identify subclinical animals at a glance and to do quick follow ups to see if treatments were successful.

The next diagnostic tool is lab culturing. A good place to start might be to do a bacteriological culture on all animals who test with a SCC of 200,000 and above. Not only does this give you details on how to specifically treat these animals, you can also identify trends and be able to prevent further transmission of certain pathogens to the rest of the herd.

Treatment and management
Success for subclinical mastitis treatment depends on a lot of factors. Staph. aureus and Strep. ag are two very common offenders but other pathogens such as streptococci and various gram-negative organisms are also possible.
Knowing what you are dealing with is very important in subclinical cases; a lot of experts will advise not treating certain animals depending on the pathogen. Not to mention, it is certainly not cost effective or necessary in the majority of these cases. For example, Staph. aureus is typically not worth pursuing because the cure rate in the lactation period is low whereas Strep. ag tends to be pretty successful.

“The cost effectiveness of treatment during lactation is driven by the interaction between the value of discarded milk and the potential benefits of treatment,” says Dr. Pamela L. Ruegg, DVM, MPVM, of the University of Wisconsin in her article Improving Treatments of Subclinical Mastitis. “If there is a positive production response to treatment then potential benefits of treatment are more evident.  Except for Strep. ag, very little data that documents significant production responses after lactational therapy of subclinical mastitis is available.”

Chronic and acute subclinical animals can still be managed within the milking herd instead of automatically getting shipped with the culls. Once you’ve identified said animals, it is a good idea to look at their treatment history. See if there’s any cycle to days in milk when SCC spiked up or production decreased. If your bulk tank score is satisfactory, it may not hurt you to let some chronic animals slip by and go into the tank without it dragging the score down too much.

If you can afford it, separating chronic animals from the rest of the herd is very beneficial, especially if you are struggling with a pathogen such as Staph. aureus or mycoplasma. You can also do things like having an increased dry period for these cows and keeping them on a dry cow treatment program.

Mastitis has been with us as long as we’ve been milking cows, and it’s certainly here to stay. Subclinical cases can be tricky and frustrating, especially when you try to pin a dollar value to them or develop a prevention program. But if you keep your herd well managed and keep your parlor staff engaged and informed, you can make a difference in your herd and bulk tank.