Optimized for all browsers and Internet Explorer 8
Search   
Canadian Bovine Mastitis Research Network
 

All about Mastitis I Management / Prevention

Detecting High Bulk Tank SCC Problems I Defining the Problem  

Do I Have A High Somatic Cell Count Problem?

Since the introduction of the standard mastitis prevention program in the late 1960s, enormous progress has been made in decreasing the average bulk tank somatic cell count (SCC).

Most European countries and Canada have experienced a decrease in bulk tank SCC as result of widespread adoption of the standard mastitis prevention program consisting of 1) Proper milking technique and maintenance of the milking machine, 2) Teat ‘dipping’ after milking, 3) Treatment at dry-off of all cows with antibiotics, 4) Proper treatment of cows with clinical mastitis, and 5) Culling mastitis problem cows. Adoption of this program was partly the result of the introduction of penalty limits for bulk tank SCC, such as the current Canadian limit of 500,000 cells/mL, and premiums for low bulk tank SCC.

In other countries, such as the USA, where the regulatory limit for bulk tank SCC is 750,000 cells/ml, average bulk tank SCC has remained at a higher level, particularly in the southern states. In every region of the world, however, high bulk tank SCC problem herds can be found. In Canada, where the average bulk tank SCC was 230,000 cells/ml in 2005, 5% of the herds has an average SCC over 400,000 cells/ml, while in 32% of the herds at least once a year average SCC is higher than 400,000 cells/ml.

You just received a report warning you that your bulk tank SCC is getting too high. How will you react and respond to this situation? Of course, you want the number to go down. Before thinking of solving a high bulk tank SCC problem in a herd, it is important to define the problem using primary udder health parameters and to detect cows causing the problem. Here are some tips to put you on the right track.

Detecting High Bulk Tank SCC Problems
 
A problem can only be addressed if it is recognized. The sooner a problem is detected, the easier it will be to solve it. The veterinarian is the obvious person to work with when dealing with a high bulk tank SCC problem. Every high bulk tank SCC problem, and most clinical mastitis problems, can be solved if the farmer is sufficiently motivated, advisors have sufficient knowledge for solving the problem, information can be obtained from farm records or laboratory tests, and farmer and advisor work together to formulate and implement a jointly determined plan.
 
Defining the Problem

Using the data that are available and possibly data that still need to be collected (e.g. culture results) the following questions should be answered:

  1. When did the increase in bulk tank SCC occur and is this a significant increase? The significance of the increase depends on the size of the herd and the bulk tank SCC goals that the herd has had before (Table 1). Because normal variation will be smaller in larger herds, alarm values will be closer to target values than in small herds.

    The association between bulk tank SCC and the percentage of high SCC cows is not linear. The percentage of high SCC cows in the herd based on the farm’s bulk tank SCC is, however, often higher than you think. For example, on farms with a bulk tank SCC >350,000 cells/ml, on average 40% of the lactating cows will have a high SCC (>200,000 cells/ml). In herds with high milk production, the percentage will be higher (dilution effect), because of lower SCC in high producing cows, regardless of infection status.

    An udder health problem can be masked through frequent culling of cows with clinical mastitis or a high SCC. On average, 5% of cows are culled because of udder health (high SCC or clinical mastitis). If the percentage is higher than 5%, this should be considered a problem and needs to be looked at. 
     
  2. Did an increase occur around the same time last year? High bulk tank SCC problems are often seasonal. Most often they start in the beginning of the summer, peak in August/September, after which bulk tank SCC decreases again. With the decreasing bulk tank SCC in the fall often the motivation to implement management changes also decreases and the same problem occurs again the next year. 
     
  3. What is the parity and stage of lactation of high SCC (and clinical mastitis) cows? For example, does the distribution point at a problem in heifers, in high producing cows, or around the dry-period? Control of high bulk tank SCC problems is impossible without individual cow SCC data. Therefore, problem herds that do not participate in a milk quality recording program should start sampling all cows individually for SCC, preferably with a monthly interval. To prevent reoccurrence of the problem, monitoring of individual cow SCC, and bulk tank SCC, should be continued after the peak in bulk tank SCC is over.

    On average, in herds with a monthly DHI test and a bulk tank SCC around 200,000 cells/ml, 10% of the low SCC cows will have a high SCC at the following DHI test. If more than 10% of cows change from low to high SCC, the rate of new infections is too high and prevention needs attention. If more than 10% of animals have high SCC at multiple subsequent tests, the proportion of chronic infections is too high. In that situation, treatment and culling strategies need to be reviewed.

    The distribution of parity and days in milk of cows with high SCC and/or clinical mastitis needs to be compared with the distribution in the herd to see whether the cows with mastitis are a specific subset of the total herd. The following situations or combinations thereof are most common:
    • Increase in the proportion of cows with a high SCC with increasing parity;
    • Increase in the proportion of cows with a high SCC with days in milk;
    • Peak in high SCC prevalence and clinical mastitis incidence in heifers in the 1st month of lactation. The percentage of heifers calving with a high SCC varies considerably among herds. A herd is considered to have a heifer mastitis problem if > 15% of the heifers have an SCC > 200,000 cells/ml after 10 days in milk.
     
  4. What are the most important bacteria involved? Average SCC differs among the bacteria that cause the infection: SCC of a Staph. aureus infection is, on average, lower than of a Strep. agalactiae or Strep. uberis infection. SCC of a cow with Staph. aureus infection is also more likely to fluctuate. Without culture, however, it is impossible to know for certain which bacteria cause the problem.

    Recent milk culture results are often not available. As a start, a bulk tank sample can be submitted for bacteriological culture to determine whether one of the contagious bacteria, Staph. aureus, Strep. agalactiae, or Mycoplasma spp., plays a role in the problem. To determine what bacteria cause the high SCC cases, quarter milk samples of all high SCC cows should be cultured. Composite samples of the 4 quarters can be used for this purpose, especially when the bulk tank sample yields Strep. agalactiae, but quarter samples are preferred, particularly for Staph. aureus. Screening of quarter level SCCs can help select quarters that should be sampled. Tools such as the California Mastitis Test may help screening which quarters need to be sampled. Quarter level information on infection status can be important for treatment or culling decisions. Thorough instruction on aseptic sampling technique is needed to prevent contamination of samples during collection.

    Once you have identified and defined the problem of high SCC in your herd, you will need to formulate and implement a herd management plan. The elements of this plan will be discussed in a second article to be published shortly. Until then, pull out those SCC reports from the pile and evaluate them from a new perspective.
Table 1 - Tables to determine whether an increase of bulk tank somatic cell count (cells/ml) should prompt intervention. Action is needed if the average of the bulk tank somatic cell count over the period is higher than the action value. A. Farm with 50 cows and an average production of 9000 milk kg/cow/year.
 
A. Farm with 50 cows and an average production of 9000 milk kg/cow/year.

Action Value (average)
Goal
1 month
3 months
6 months
12 months
150,000
195,000
175,000
170,000
160,000
200,000
275,000
245,000
230,000
220,000
250,000
355,000
310,000
290,000
280,000
300,000
435,000
380,000
355,000
340,000

B. Farms with 70 cows and an average production of 9000 milk kg/cow/year.

Action Value (average)
Goal
1 month
3 months
6 months
12 months
150,000
180,000
165,000
160,000
160,000
200,000
260,000
235,000
220,000
220,000
250,000
340,000
300,000
285,000
275,000
300,000
420,000
370,000
350,000
335,000

Herman W. Barkema1, Sarne De Vliegher2, Julie Baillargeon3, and Ruth N. Zadoks4.

1Veterinarian, Department of Production Animal Health, Faculty of Veterinary Medicine, University of Calgary.
2Veterinarian, Department of Reproduction, Obstetrics and Herd Health, Faculty of Veterinary Medicine, Ghent University, Belgium.
3Agronome, Agente de transfert, Réseau canadien de recherche sur la mammite bovine.
4Veterinarian, Division of Veterinary Clinical Studies, Royal (Dick) School of Veterinary Studies, University of Edinburgh, Easter Bush Veterinary Centre, Roslin, and Moredun Research Institute, Pentlands Science Park, Bush Loan, Penicuik, Scotland, UK.




Member Access
Cohort data bank