Solving mastitis [3/5] the battle against pathogens

In the last two articles, we talked about udder health. When the first line of defence is breached, in this case the teat and udder skin, there is the possibility for pathogens to invade the udder and cause subclinical, clinical and chronic mastitis. To eradicate the pathogen efficiently, you have to:

Cow health, Milking


(1)    develop an appreciation of the process of analysing the records of a herd with a high bulk tank SCC in order to identify areas of opportunity;
(2)    understand the steps necessary for digging deeper into the areas of opportunity for herds with high bulk tank SCCs in order to come up with a prioritised list of solutions; 
(3)    work through the ways to communicate these solutions to the dairy management team and know how to monitor the progress of changes that are implemented. 

Where to start trouble shooting?

In order to know where to start, you need data obtained from farm records on the following subjects with regards to clinical mastitis: how many cases, parity, stage of lactation (DIM), season, designation of repeat cases and which quarter affected.  With regards to subclinical mastitis, we look at how many cases, parity, stage of lactation/dry period and new vs chronic.  The bulk tank SCC gives an indication of udder health on the farm. Please note that this is done on composite bulk tank samples multiple times per month. Individual SCC is tested monthly. A lot can happen with the cell count of an individual cow between test days. You can even miss cows, and therefore the MQC-C is valuable. 

In order to troubleshoot high somatic cell counts and clinical mastitis, you need to define the major problem for the herd. Is it primarily a subclinical mastitis problem in a low bulk tank SCC herd, a subclinical mastitis problem with a high bulk tank SCC, or is it a combination of a clinical and a subclinical mastitis problem? In figure 1 you see a plot of the incidence rate of clinical mastitis on the y-axis and bulk tank milk SCC on the x-axis. You will notice that there is very little correlation between the two parameters. You can have herds that are low-cell-count herds with a lot of clinical mastitis cases. You can also have high-cell-count herds that have a significant amount of clinical mastitis and high-cell-count herds that have very little clinical mastitis. What we really need to know next is what is/are the predominant organism(s) causing either subclinical or clinical mastitis. If you encounter a herd where they do not have any culture data, you need: 
(1)    for at least every 2 weeks to 3 weeks, individual cow cultures from clinical mastitis cases;
(2)    samples from high SCC cows (depending on the herd, ten to twenty samples); 
(3)    samples from fresh cows (3 days to 5 days after calving, because you want to know if cows calving have something at the start of their lactation). 

pathogens 1.png
Figure 1: scatter plot of bulk milk SCC and incidence rate of clinical mastitis. Cornell University (Animal Health Diagnostic Center, Webinar 2020, on troubleshooting high somatic cell counts). 

Environmental and contagious mastitis 

Once we know which pathogen we are dealing with, we can split into two different situations, and this really determines our management in terms of how we are going to approach the problem. Is this predominantly a contagious or an environmental problem based on the individual cow culture results? There are very different patterns of pathogens from farm to farm. Knowledge about this can be of great help to the farm in terms of preventing mastitis and therefore lowering the clinical or even the subclinical rate and lowering the bulk tank SCC over time. 
When it is contagious mastitis, then the source of the pathogen is the infected cows. Major organisms are:
-    Streptococcus agalactiae
-    Staphylococcus aureus
-    Mycoplasma spp.
-    Other pathogens in certain situations, such as prototheca
In environmental mastitis, the source of pathogen is the environment, or any surface with which the cow or her manure comes into contact. 
-    Streptococcus spp. (uberis, dysgalactiae)
-    E. coli
-    Klebsiella spp.
-    CNS staphylococcus spp.
-    Other pathogens in certain situations 

The next question is, when does the initial mastitis happen?

During the dry period: with regards to environmental and contagious mastitis, it is with the dry cows that we can help the farm fix their primary problem. Is mastitis caused during the dry period or is it something that happened during lactation? 

pathogens 2.png
Figure 2. Major spike right after dry-off and another major spike right after calving. We really cannot ignore the dry period when we look at mastitis. Is there a major problem during the dry period, or are we doing reasonably well during the dry period? Cornell University (Animal Health Diagnostic Center, Webinar 2020, on troubleshooting high somatic cell counts). 

The following parameters can be used in analysis focusing on the dry period:
- Percentage of fresh cows on first test day with SCC >200,000 cells/ml. More than 15% of fresh cows with a high test is not desirable (figure 3). 
- Percentage of clinical mastitis cases that are less than 30 days in milk (DIM).
- Clinical mastitis cases per month, to have a sense of the overall picture. 

Parameters to analyse focusing on the lactation period (figure 3)
- Percentage of cows with new subclinical infections this test day (current test day SSC >200,000 cells/ml and previous test day SCC <200,000 cells/ml).
- Percentage of cows with chronic subclinical infections (last two test days SCC >200,000 cells/ml).

pathogens 3.png
Figure 3. When does the initial mastitis happen? This table can be helpful for indicating the greatest opportunity period: lactation or dry period. After gathering all the data, you are able to distinguish between periods. Cornell University (Animal Health Diagnostic Center, Webinar 2020, on troubleshooting high somatic cell counts). 

Where is the greatest area of opportunity?

Our overall goal is to prevent mastitis. If we reduce the incidence, then we have fewer cows with a high cell count, fewer cows to treat and fewer cows with the opportunity to become chronic. Find a way to reduce the incidence of mastitis, clinical and subclinical. 

Based on culture and analysis we now know:
- the predominant organism;
- lactating cows vs dry cows, or both.

Now do a targeted risk assessment on the farm in the area of concern. If the main pathogen is the contagious organism, the focus is on preventing new lactating cows from getting infected during milking (post-dipping teat spray/skin and teat health) and eliminating existing infections (culling and culture milk of purchased animals). However, if it is an environmental pathogen, prevention of new infections during the dry period and in springing heifers is needed. Think about dry-off procedure, stall and/or pack cleanliness, etc. Also prevent new lactating cow infections: milking time, pre-dipping, clean and healthy teats, etc. When we are looking at bulk tank SCC, the overall solution is to prevent new mastitis cases. Short-term solutions for reducing the number of high SCC cows are the treatment of lactating and dry cows, removal from the tank and culling.

Strategy for improvement of udder health in your herds 

Identify the key players in your milk quality team. 
-    Make use of each one in their area of expertise (veterinarian, consumables, nutritionists, etc.) 
-    Encourage communication and data sharing between parties.
-    Hold farm meetings with all parties to interpret all the data together.
-    Identify specific areas of opportunity for the farm.

For each individual herd and its milk quality team, provide a robust set of data that can be used to identify areas of opportunity for improving milk quality. Clarify whether these areas of opportunity are at:
-    whole system level;
-    individual personnel management level;
-    a combination of both.

After a change is made, reassess all the relevant areas in order to document the effects of the change. 

Repeat this data collection every 3 months in order to:
-    develop a trend line of the data;
-    prevent disasters from happening;
-    promote continuous improvement;
-    assess changes that have been made;
-    reduce the tendency to look for the ‘silver bullet’.