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Don’t forget the basics when troubleshooting milk quality

Contributed by Leo Timms Published on 29 February 2016

Our overall goal is to have the highest-quality milk with the lowest SCC (and the least number of cows with SCC problems). When SCC becomes elevated or clinical mastitis escalates, we are often called upon to troubleshoot and evaluate on-farm milk quality practices and areas.

We have developed many checklists and systematic approaches to evaluate these practices. Often when the evaluation or investigation is finished, we create a list of good or properly conducted procedures and others that need attention. Sometimes we get too focused on the “needs attention” list (like wearing gloves).



This may be an important practice (and I fully support the use of gloves), but if the data show there is a fresh cow problem, wearing gloves is not the immediate issue or concern.

Worse yet is that forcing glove use may decrease milker attitude and result in poorer milking and higher SCC. While checklists are important, often troubleshooting is jumped into without examining the basics:

  • What problem am I addressing: new or old?

  • What data do I have to help me ascertain the number of animals involved as well as new versus chronic cases?

  • What organisms are involved and does this new problem have similar or different organisms compared to past?

Also, SCC can go up with no new cases, can go down with new cases, and will never go down unless existing infections or problem cows are dealt with. Too often, we jump to items on the checklist and make changes without clearly laying out the whole problem and addressing cow and organism dynamics. This article will help us remember the basics when troubleshooting milk quality issues.

Highest milk quality = lowest SCC = lowest number of problem animals

$$$ = Prevent new cases and decrease duration of existing cases


1. Bulk tank or DHI weighted-average SCC

Bulk tank SCC is an electronic measurement of less than 1 ml of milk that represents all of the cells and milk from all cows (and is hopefully then agitated properly). DHI weighted-average SCC is really an overall weight or scale reading where every individual cow is weighted (SCC per ml milk x volume of milk) and total cells / total volume.

While this is an important number, this small fraction of milk does not inform us of how many problem cows (high-SCC or clinical) we have and whether they are old or new cases. Since individual cows are crucial to this overall measurement, the average SCC can also go up without any new cases (problem cows gain weight: higher SCC or more volume), go down and yet there are new cases, and will never go down unless problem cows are dealt with.

2. Individual-cow SCC

It is imperative that herds have individual SCC data. This allows a look at the size, scope and dynamics of the problem. It is best to have monthly DHI data, but even some individual electronic tests or individual-cow California Mastitis Tests (CMTs) can work.

There is no excuse for not having individual SCC. Individual-cow data also allows for categorizing cows (problem or not) as well as evaluating cow and herd dynamics (chronic versus new cases; cured cases).

3. Defining a ‘problem’ cow

A key step is defining what a problem SCC cow is (what SCC level triggers attention). Research would support that an individual-cow SCC of 200,000 cells per ml (linear score 4) is the proper threshold, and most DHI use this to put cows on the good or bad side of the scale.

Some producers believe this is too low. It must be remembered that an individual-cow SCC is a weighted average of four separate quarters, and an SCC of 200,000 with three uninfected quarters (less than 100,000) means the last infected quarter is greater than 500,000 cells per ml. This is a problem cow.


4. Cow impact on tank SCC

Remember that the cow’s overall impact on tank SCC is her SCC (concentration) x her milk volume. Oftentimes, people try to lower SCC by manipulating high-SCC cows with low milk volume from the tank (dry-off, etc.) This often results in no change and occasionally an increase in SCC.

5. Monitoring individual cows (herd) with scatterplots

Visual scatterplots are often used to assess cow SCC dynamics. By plotting previous versus current SCC, four distinct populations arise: uninfected (low for two months), chronic (high for two months), cured (high SCC but now low) and new high-SCC cows. Individual lactation groups can be represented differently, and individual cows can often be identified by highlighting on the sign.

One major problem with this is it misses one of the highest-risk groups, fresh cows (only have one SCC).

6. Monitoring fresh cows

Monitoring first test-day SCC on fresh cows is excellent but may still be far from calving date. Utilizing a CMT on fresh cows offers a better and more timely observation. The key is to get the secretion (colostrum or thick milk) and CMT reagent to mix (so get your fingers dirty) before swirling and reading.

No gel has a negative predictive value (uninfected) of greater than 95 percent. Presence of gelling only has a 25 to 50 percent positive predictive value for infection. SCC can be high due to IMI or high in a protective role, especially on teats that are open prior to calving (heifers also).

7. Germ warfare: Know your organisms

High SCC means irritation and inflammation with greater than 99 percent due to infection. Routine bulk tank cultures can help, but presence of contagious organisms does not define number of problem cows.

Also, low bulk tank environmentals can mean excellent milker pre-milking sanitation even in the face of environmental mastitis problems. Individual culturing of “problem cows” is the most definitive in contagious and environmental but also areas for prevention and therapy.

  • Staph. aureus: Contagious, infected cows, milking practices, teat health since S. aureus is wound-invader – especially critical for heifers, fresh cows and winter.

  • Environmental streps: Bedding and environment – look for teat-end problems with S. dysgalactiae.

  • Coliforms: Fecal material and H2O. These are poor skin-colonizers but great swimmers and grow fast in milk.

  • Prototheca: Infected cows, but where’s the water?

8. Mastitis: Pathogen-host interactions

Mastitis occurs when a pathogen gets in the host and the host reacts. The number one goal should always be to minimize the bacterial numbers, no matter what pathogen, and this should happen all day in all areas where animals are (not just at milking and not just milking cows).

These pathogens interact or invade most times at a very specific spot (teat end or orifice), so evaluation of and attention to teat health is critical. Finally, a healthy host is critical, and clean cows and environment can still result in problem cows when the host’s immune system is compromised.

9. Dealing with problem cows: Prevention is number one

This should be monitored and proven, and may help SCC eventually go down (limit new infections) but often keeps it from going up (SCC stays the same). This often frustrates farmers who make many changes and their SCC remains stagnant.

That is because they neglect to address problem cows (heavyweights) and make decisions to move them. This can be achieved by a variety of means, including spontaneous cure, treatment, dry-off, selling or segregating milk, but decisions must be executed. Sometimes even praying helps.

10. Dealing with people as well as cows

While most of this article focuses on cows, it is ultimately the procedures and practices we implement and have in place consistently that make quality milk achievable. And people are the key. So make sure to look at the cows and the people, pay proper attention and training to both, and make sure the attitudes of both excel.  PD

—Published in the 2015 National Mastitis Council Annual Meeting Proceedings.

Leo Timms
  • Leo Timms

  • Associate Professor
  • Iowa State University
  • Email Leo Timms