Highlights from the 2001 National Mastitis Council Proceedings

• Key points from the 2001 National Mastitis Council Proceedings are presented

Setting SCC Cutpoints for Cow and Herd Interpretation

Ian Dohoo, University of Prince Edward Island

High speed cell counters has made SCC data readily available. Having SCC numbers and making the best use of it are two different issues, however. Dairymen may see SCC data from individual cows using DHIA or from bulk tank tests conducted by their milk handler. Dr. Dohoo discusses how to correctly use SCC numbers for mastitis management purposes.

1. Somatic cell counts from individual cows or groups of cows have normal variation. Infection status is a significant factor influencing somatic cell count but it is not perfectly related to the somatic cell count.
2. Intra-mammary infections increase cell counts. However, using a specific threshold value to determine a cow's infection status will lead to errors simply because of the normal variation in SCC numbers. For individual cows, the higher the SCC threshold value, the more likely the possibility of false negatives (cows that are really infected being classified as not infected). The lower the threshold value, the greater the risk of false positives (cows that are not infected being classified as infected).
3. Choosing a threshold value is a management decision that may differ by farm or purpose. To evaluate dry cows for
   treatment at dry off, a low threshold may be best  even though some uninfected cows will be treated. The risk associated with this decision is low, whereas the risk of not treating an infected cow at dry off is relatively high. Any threshold value chosen must meet the objectives of the individual dairy.
4. For example, producers who want to maintain a particular bulk tank SCC, may need to set a much lower threshold value to initiate additional mastitis control procedures in order to meet their target.

Factors Affecting the Success of Antibiotic Treatment at Dry Off

Ynte Schukken, Cornell University

The following key points are made in this article:

1. Concern about widespread use of antibiotics in dairying has lead to reevaluation of  antibiotic programs in many countries. Antibiotics should be used where most needed and most effective.
2. In some countries, comprehensive mastitis control programs have produced very low cell count herds. In these programs, dry cow antibiotic treatment occurs only in infected quarters of mastitic cows.
3. Success of dry cow antibiotic treatment is determined by the age of cow, the number of quarters infected, the SCC at dry off and the presence of clinical mastitis during the current lactation. These factors may be used to predict success of dry cow antibiotic treatment for individual cows.
4. Effectively curing Staph aureus infected cows is difficult because of antibiotic resistance and physical factors such as scar tissue protection of infection sites.
5. An accurate diagnosis of the infectious agent allows the correct drug to be selected. This offers the best chance for successful treatment.
6. Currently, most US dairies with average milk quality will still benefit from dry cow treatment of all quarters of all cows at dry off.

Can Somatic Cell Counts Get Too Low?

Ynte Schukken, Cornell University

Can somatic cell counts get too low? The concern is whether cows with very low cell counts has a higher risk for clinical mastitis.  Dr. Schukken makes several interesting points:

1. Research shows that the somatic cell count in cows that have never had mastitis is generally below 100,000/ml. except in the last month of lactation.
2. The presence of a small number of resident somatic cells plays a crucial role in the immune response to invading bacteria. If there were no somatic cells present, bacteria could invade unchallenged and cause disease unhindered.
3. Individual cows with extremely low cell counts (less than 100,000) may be at greater risk for clinical infections or more more severe infections.However, much of this research used cows innoculated with mastitis organisms.
4. For bulk milk SCC, no clear relationship has been observed between low cell counts and mastitis incidence.  However, there is some evidence that herds with low bulk milk SCC have more severe systemic symptoms when mastitis does occur.
5. Generally most dairies will benefit from lower somatic cell counts in terms of more production and better quality milk. The key is to maintain cows in a healthy state so their system can respond quickly and effectively when the udder is challenged by invading bacteria.

Strategies for Protecting the Teat at Dry Off

John Williamson, Hamilton, New Zealand

Key points:

1. The formation of a solid keratin plug at dry-off is key to preventing new udder infections, especially by environmental bacteria such as Strep uberis. Unfortunately a high percentage of cows take longer than 7 days to produce this plug and some never produce an effective keratin seal. Such cows are very susceptible to new infections in the first three weeks post dry-off.
2. Sealing the streak canal with a sealant plug has produced improved new infection resistance at dry-off based on New Zealand conditions.
3. Sealing the teat canal at dry-off by a natural keratin plug and either an internal or an external teat sealant will improve resistance to new infections by forming a physical barrier to invading bacteria.

Enhancing Immunity During the Dry Period: Pitfalls and Opportunities

Ron Erskine, Michigan State University

1. The periods immediately after dry off and prior to calving are times when cows are very susceptible to new infections.
2. Dry cow antibiotic treatment improves early dry period udder defense but is not very effective during the pre-partum.
   The fully involuted udder is very resistant to all potential new bacterial infections.
3. Vaccines are now available that help boost the immune defenses. Coliform bacterins are widely used.
4. In the future, compounds that stimulate the immune system may be available but are currently in the experimental stages.
5. The immune system is heavily suppressed during the period around calving. Elevated cortisol levels at this time reduce activity of the immune system. As a result, minimizing exposure to mastitis organisms is critical at this time.
6. Implementing and Monitoring Mastitis Control Programs for the Dry Period

John Day, Jerome, Idaho

1. Mastitis control requires a well thought out plan with standard operating procedures for all key activities.
2. An effective standard operating procedure requires:
   a.  Potential hazard areas to be identified. For example, dry period management.
   b.  Critical control points to be set for each hazard. For example, bedding cleanliness during the dry period.
   c. Limits for critical control points. For example, cell count of fresh cows on day 3-4 post calving.
   d.  Monitoring programs for critical control points.
   e.  Established action plans for use when limits are exceeded.
   f.Verification of results

Automatic Milking and Milk Quality: A European Perspective

Henk Hogeveen, Lelystad, The Netherlands

1. Milking rules and regulations require milk be inspected prior to milking. If a problem is detected it is diverted away from the tank. Today humans do that inspecting,  but with automatic milkers how is it accomplished successfully?
2. Data from automatic systems in Europe suggests that milk bacteria content, somatic cells and acid degree values appear to rise in comparison to milking done with conventional systems.
3. Better sensing and milk evaluation devices are needed to monitor and divert problem milk from cows milked with robotic systems.

Automatic Milking Systems in North America: Issues and Challenges Unique to Ontario

Jack Rodenburg, Ontario Ministry of Agriculture, Food and Rural Affairs

1. Robotic milking systems appear to be an option for the typical Ontario dairy with less than 200 cows.
2. Concerns in terms of the physical installation include freezing conditions, stray voltage, feeding systems which typically is not done in the milking center in North America, water quality from farm well water used to clean systems and milk quality in general.
3. To date there has been an increase in the bacteria counts and more cases of freezing point violations due to added water on farms where robot systems have been installed

Related Links:

British Mastitis Council

This link will direct you to the proceedings from previous British Mastitis Council meetings as well as information about the 2002 program.