A summary of the information presented at the 2004 National Mastitis Council's annual meeting.
Topics included: mastitis detection and treatment options, dry period length, factors affecting the development of mastitis infections and consequences of mastitis infections.
The 2004 NMC meeting was held in Charlotte , NC . The format was similar to past years but the attendance continues to become more international. The meeting has become the meeting of choice for those interested in issues related to mastitis and milk quality.
A Sunday pre-meeting program involved presentations on key issues related to mastitis.
Dr. Ruegg of the University of Wisconsin made it clear that treatment is an important part of managing mastitis, including sub-clinical mastitis. Treatment requires knowledge of the pathogens involved and identifying antibiotics and treatment strategies that are most likely to provide a cure. Not treating infections is a decision that can lead to unintended negative consequences so dairymen need to work closely with their veterinarian to define a strategy to manage infections.
Dr. Erskine of Michigan State pointed out the key factors in successful mastitis treatment with antibiotics. Identifying the bacteria causing the infection, knowing the physiological status of the cow and attacking the infection with appropriate doses of antibiotics most appropriate for the bacteria in question gives the best likelihood of a positive outcome. Many mastitis treatment “failures” are the result of failing to adhere to these principles.
Dr. Morin of the University of Illinois discussed non antibiotic treatment for mastitis. There is a need, on occasion, for providing supplemental fluids in animals with insufficient hydration due to mastitis. Fluid loss assessment should be done to determine the fluid status. In mild cases, intra-ruminal dosing with hypotonic fluids is acceptable while in severe cases intravenous infusion with iso-osmotic fluid is best.
Nonsteroidal anti-inflammatory drugs (NSAIDS) often are administered. There may be benefits but there is still no clear answer regarding under what conditions these drugs should be used and what the appropriate doses are.
Oxytocin injections and frequent milkout of quarters are often recommended as the sole treatment for certain clinical mastitis cases. Dr. Morin found no solid evidence of this being effective, and in many situations (ie. clinical Strep mastitis) it is likely to increase the risk of problems, so the approach needs to be carefully reviewed. Because of the concern of using too many antibiotics and the poor response to antibiotics in many cases, alternative approaches are of interest. The data supporting these non-antibiotic treatment approaches is lacking in many cases, so dairymen need to carefully assess how such methods are used.
According to Dr. Herman Barkema of Canada , Staph aureus remains a very tough pathogen to eliminate and many of the recommendations for treatment are based on research protocols that were improperly designed to answer the question of treatment efficacy. Improved protocols for assessing treatment strategies are needed in his estimation.
Dr. Ynte Schukken of Cornell provided evidence that, in some cows, coliform infections can be chronic and be responsible for recurring clinical episodes of mastitis. This is contrary to traditional thinking about coliform mastitis- which is generally considered a hard hitting short term problem.
Finally Dr. Wenz of Colorado State pointed out that good documentation is essential for managing mastitis. Deciding on key basic mastitis indicators to be monitored, establishing a base line for each and using a data logging and analyzing system should allow trends to be noted and better decisions to be made sooner. Without such information, mastitis management is likely to be unsuccessful.
The keynote address for the NMC meeting was delivered by Dr. David Barbano of Cornell University , and he made several key points. First, research has clearly established that elevated bacteria counts and somatic cells in raw milk leads to reduced quality of milk and reduced shelf life. The enzymes in milk from cows with elevated SCC cannot be eliminated by heat treatment. The key is to produce milk that has initial low bacteria and cell counts and low levels of enzymes known to be detrimental to milk quality. This relationship has been known for some time but now it has additional implications because of how milk and milk products are and will be handled by major retailers.
Milk and milk products in the future are more likely to be subject to more time in distribution systems as large scale wholesalers and retailers such as Wal-Mart handle products through their distribution network. They will require products that can last longer with no negatives such as off-flavors or loss of product quality. This will also apply to countries that export products long distances to markets. The initial quality must be very good otherwise the wholesaler, retailer and end consumer will be dissatisfied. Those who can provide the highest quality products will gain market share.
Bottom line: produce the highest quality milk or face a risk of market loss.
Dr. Hamann of Kiel , Germany provided information on the relationship between somatic cell counts and milk quality. His data indicated a pattern of reduced quality starting at 100,000 cells/ml. Above this level; milk is abnormal even though it may not be visibly abnormal. It is his view that “normal milk” contains less than 100,000 cells/ml. This will be a challenge for many US dairymen. We currently have a national limit of 750,000/ml, a rolling average of approximately 315,000/ml and we tend to accept 200,000/ml as a reasonable benchmark for herd somatic cell counts.
Dr. Allen Britten re-emphasized the significance of fresh cow new infection rates. Generally, dairymen have reasonable success eliminating existing infections and preventing new infections during the early dry period with dry cow treatment therapies at dry off. Near calving however these products are no longer present, the immune system is suppressed so during this period cows are vulnerable to new infections.
These new infections must be identified and treated as soon as possible after calving to minimize overall problems. Identification may be made on early colostrum with the CMT so long as the users are well trained and only focus on finding CMT 3 cows. The new direct cell counter (DCC) from DeLaval will provide a farm based cell counting option that allows accurate counts to be determined on milk from cows fresh 3 or more days. The keys are to accurately determine new infections immediately after freshening and treat them promptly.
Dr. Steve Oliver of Tennessee discussed another significant mastitis problem for many dairymen- heifer mastitis. Researchers indicate that a significant percentage of first calf heifers have mastitis infections at calving. The prevalence is related to overall herd infection status, housing conditions and especially fly control programs. Staph aureus is one of the primary concerns but there are also a lot of new heifer infections caused by the coagulase negative Staphs or CNS. Flies can contribute to spread of the problem so an effective fly control program is essential. Treating heifers in each quarter with a lactating cow tube prior to calving has been demonstrated by researchers to eliminate a high percentage of these infections. The downside is that the risk of antibiotic residues has to be dealt with by more testing etc. The further in advance of calving these treatments are administered the less risk there is with residues. Also this use of lactating tubes constitutes an off-label use of a drug and veterinarians must be involved in any such program.
The key point is to recognize that this group of cattle (first calf heifers), are vulnerable to new infections so be on the lookout, implement prevention procedures and test and act early to minimize problems.
Dr. Leo Timms of Iowa State provided a comprehensive overview of teat end problems associated with winter conditions. The key point made was that winter cold and wind accelerates problems including teat end cracking and hyperkeratosis. Under such conditions it becomes a real challenge to maintain good teat end condition. Implementing practices known to help reduce problems is necessary to minimize winter teat condition issues. These include shelter from wind, eliminating water to wash teats, using high emollient post milking teat dips and blotting off the teat dip droplet on the teat end before cows are released.
Over-milking and the impact on teat end condition is probably one of the most frequently discussed topics amongst dairymen and people involved with machine milking. Dr. Morton Dam Rasmussen of Denmark provided information on how the roles of the milking unit and end-of-milking settings for take-offs should be considered.
Over-milking is defined by Rasmussen as occurring when the removal rate of milk from the teat cistern exceeds the entry rate of milk into the teat cistern. Some can occur at the very beginning of milking but most of it tends to occur at the end. Once this occurs, the conditions allow negative consequences. These may include teat end hyperkeratosis with prolonged overmilking and liner crawl and eventually ring development around the teat base.
End-of-milking flow rate settings for automatic takeoffs need to be adjusted for each farm to minimize this problem. Ideally the machine settings should allow complete milk out followed by prompt unit removal. This may be accomplished at higher end-of-milking flow rates than originally considered acceptable. Doing so allows more parlor throughput, since total machine in-time is reduced, and there is less teat end stress. Leaving a bit more milk in the udder does not appear to increase mastitis problems. Establishing acceptable settings for unit removal requires evaluating the production level of the herd, milking frequency and what the dairyman is willing to accept in terms of milk left in the udder.
Dr.Graeme Mein of Australia described the issue of the milking machine and its potential role in mastitis. If the machine influences new infection rates, it would have to involve one or more of the following mechanisms:
1) changing the number of bacteria on the teat ends
2) changing the ability of the teat canal to prevent bacteria entry
3) providing forces that permit bacteria to enter the teat canal
4) dispersing bacteria within the udder
5) it could be related to the frequency and degree of udder evacuation.
While each of these may be possible the best estimate is that only 6-20% of new infections are related to direct or indirect milking machine effects and 10% might be related to direct effects. This suggests that other farm factors such as housing conditions, dry period management, teat dipping, etc. account for the vast majority of new infections. It is important that milking systems perform according to established norms, as when they do the milking system is a very minor factor influencing new infection rates.
New Zealand dairy farms have developed some unique concepts of managing dairy cows and milking that allows them to be very low-cost producers of milk. The labor situation in New Zealand requires owner operators to milk large numbers of cows rapidly with minimal hired labor. Therefore, pre-milking routines are minimal compared to what is used in many other countries. It is likely that the cows in the national herd have been naturally selected to perform under these circumstances. Also, pasture conditions produce relatively clean cows as they enter the milking center. Teat cups are attached to “visibly clean teats”. Only obviously dirty cows are rinsed as needed. The typical dairy farm has a Bactoscan value less than 10,000 and coliform counts less than 500/ml so their approach allows them to produce milk with acceptable bacteria levels.
Dr. Kermit Bachman of Florida discussed a topic that has received much attention recently. What is the appropriate length for a dry period. Traditionally a 60 day dry period has been considered optimum but the scientific basis for this may be questionable. Bachman and others have experimented with 45 day, 30 day and 0 day dry periods to determine the impact on the cow. Their interest stems from the fact that shutting down the milk production system and then restarting it appears to produce a lot of difficulties in terms of metabolic diseases, mastitis, feed intakes etc. There are also economic questions using a 60 day dry period. Therefore do we need to have a dry period and if so how long is long enough?
The work to date has several outcomes. For first calf heifers it appears that a 60 day period is appropriate otherwise they suffer poor performance in the second lactation. For multiparous cows the research suggests that a 30 day period is adequate though to become familiar with managing a shorter dry period it is recommended that dairymen start with a 40 day period and work slowly toward a 30 day period.
Short dry periods mean challenges for dry cow therapies and potential residue risks so this has to be closely monitored. Shorter dry periods should minimize diet and group changes which in turn should be a benefit for the cows.
A paper by Dr. Mike Brouk of Kansas State dealt with cooling dairy cattle and the various options. Dairy cows produce lots of body heat and often they are housed in environments where the ambient conditions during summer are hot and often humid. When cows cannot dissipate sufficient body heat they develop elevated body temperatures and reduced milk production and their immune system starts to function less effectively. Typically there is a production drop, increased incidence of disease and a significant impact on reproductive performance. All these factors pose serious economic penalties. Can heat stress be managed in a way that makes economic sense?
Housing and management options to handle heat stress must consider ambient conditions. In very hot climates with very low relative humidity, evaporating water (evaporative cooling) removes heat from the air as the water is turned to water vapor. The air also increases in percent relative humidity. The net result can be significant temperature drops within local zones where evaporative cooling is applied. Cattle can then transfer body heat to the air around them so long as the ambient temperatures are less than their body temperature.
In situations with high temperature and humidity, evaporative cooling is less effective. In this case, wetting cows directly and then evaporating the water from the body using fans facilitates body heat removal, thus lowering the average body temperature.
It is possible to modify the body temperature of dairy cows through various means. The method chosen is dictated by the typical ambient conditions for the area. Selecting the best approach means working with professionals familiar with dairy cow physiology and techniques that facilitate temperature modification.