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Identify mastitis before it spreads

Jerry Olson Published on 19 May 2008

Every dairy producer knows that mastitis can have a substantial impact on milk production and on herd health.

Decreased production and increased chronic health problems can debilitate a dairy operation if mastitis becomes widespread. That’s why identifying mastitis – both clinical and subclinical – is vital to ensure financial health on your operation and the general health of your herd.



Despite current management advancements, mastitis continues to rob the U.S. dairy industry of $1.7 billion per year. As demand for higher milk quality standards increases, dairy producers are urged to improve efforts to control mastitis through prevention and treatment.

Lowered milk production, reduced milk quality, extra labor, increased replacement cow costs, veterinary fees and treatment costs all reinforce the importance of implementing a mastitis control plan on your farm regardless of a co-op’s bonus plan.

Flagging clinical mastitis
A good practice on any dairy is to categorize mastitis events by their level of visual severity.

  1. Mild: Just a few flakes and clots are found when fore-stripping. If herds are not doing fore-stripping, they may not catch this. Subclinical mastitis is rated in this category since there are no physical signs.
  2. Medium: Milk has flakes and clots and the udder has some indication of inflammation. The infected quarter is swollen and may show some redness and disparity in comparison to the matching quarter. The udder has the typical signs of inflammation – pain, heat, redness.
  3. Severe: There are abnormalities in the milk, indications of inflammation in the gland but also systemic signs of the cow being ill. She may be off-feed or lethargic. Sometimes the cow could even appear lame because she doesn’t want to touch the swollen quarter.

Other cows might have subclinical infections
Unlike clinical mastitis, where physical symptoms are evident, subclinical mastitis must be determined through testing and cultures. Depending on the situation, the producer may be testing cows individually through the National Dairy Herd Information Association (DHIA) or monitoring bulk tank SCC scores to identify overall herd SCC changes.

When reviewing SCC counts, if plotted on a graph, the majority of SCC scores would be skewed to the left with lower scores and those fewer animals with high SCC scores would be on the right. When converting the actual SCC number to a logarithm transformation, you can have a normal bell-shaped curve. From that basis, every time we double the SCC, we increase it by a linear score of 1. At 100,000 cells per milliliter, the cows have a score of 3. Animals between 100,000 to 200,000 cows score 4, between 200,000 and 400,000 score a 5 and SCC counts 400,000 to 800,000 are at 6.


There is a strong correlation between the linear score and the amount of milk lost due to mastitis. With first-calf heifers, whenever their score increases by one, you should assume they are losing three-quarters of a pound per day. With cows, it’s even worse. Every time their linear score increases, it can be considered a 1.5-pound loss of milk per day in production.

Producers can also utilize their first-calf heifers as a benchmark of the environmental pressure resulting in subclinical infections at the onset of their first lactation. The numbers suggest that between 20 to 22 percent of first-calf heifers will have SCCs above 200,000. If your first-calf heifers have a higher percentage, that’s a good indication that there may be environmental problems that need to be addressed. If a higher percentage of mature cows have SCC above the first-calf heifers, it is an indication that there may be a severe environmental challenge to cows and/or the dry cow treatment effectiveness needs to be evaluated.

Long-term herd health impact
We’ve talked about the impact mastitis can have on a cow’s milk production, but this infection can also impact an animal’s reproductive performance. Often you can see the impact by reviewing a farm’s record system to see the correlation between animals that have had mastitis and those that are having difficulty breeding back. Typically, the thing that I see when looking at the records of dairies is that it takes 40 days longer to get half of the cows that have had at least one clinical case of mastitis pregnant compared to cows that have not had a case of mastitis.

Furthermore, three studies examined the correlation between clinical mastitis cases and a decrease in reproductive performance in early lactation cows. The results show eight to 15 percent higher conception rates for uninfected animals as compared to those experiencing clinical cases of mastitis. Uninfected animals became pregnant faster with approximately 19 to 25 fewer days open.

Tips to avoid mastitis in the herd
The National Mastitis Council has developed a five-point program that producers should use as standard protocol on all dairies. This includes post-milking teat disinfection, total dry cow therapy, therapy of clinical cases during lactation, proper maintenance of the milking machines and culling chronic problem cows.

These initial five points have been very effective in helping lower clinical and subclinical mastitis in dairy herds.


Develop a protocol
Record keeping and a solid protocol are two tools a producer should utilize in the fight against mastitis. Utilizing computer programs specifically designed to help track events such as mastitis will help producers track which cows have had mastitis and how often. This information is invaluable when it comes to making treatment and culling decisions in consultation with your veterinarian.

Instituting an on-farm protocol will help with the treatment of mastitis, also. A protocol begins with a diagnosis. Once you and your veterinarian have defined how a diagnosis is reached, a treatment protocol should almost automatically kick in. It’s important to have that discussion with your veterinarian before instituting a protocol.

Disease prevention programs are an important part of keeping cows healthy, and they may increase the milk quality premiums you receive. PD

References omitted but are available upon request at

Jerry Olson is a veterinarian withPfizer Animal Health. Email Jerry Olson.