Environmental Mastitis- Causes and Management

• Environmental mastitis has become very common on today’s dairies
• Cows are constantly exposed to contaminants
• Minimizing exposure is critical to controlling environmental mastitis

Mastitis is generally categorized into contagious or environmental mastitis. On most dairy farms today, environmental mastitis cases are quite prevalent. Since environmental mastitis is such a common problem, the following review has been prepared on current ideas about cause, control and treatment of environmental mastitis.

Environmental mastitis-causing bacteria

These bacteria fall into two different groups. Because of their differences, some of what applies to controlling and treating one group may not apply directly to the other.  One group is termed coliforms and the other is the environmental Streps. The term “environmental Streps” is used interchangeably with Strep-non ag.

Certain general considerations apply to both groups. They are both commonly found in the environment of the cow in various bedding materials, manure, dirt, water and other sites as well. These bacteria have adapted to living in these various locations and so have no direct dependency on the cow for survival and propagation. This contrasts with contagious mastitis organisms, such as Staph aureus and Strep ag, which live primarily in and on the cow rather than external sites.

The cow is constantly exposed to environmental bacteria and there is a constant threat of new infections from these environmental sources. The key to controlling them is to manage the cow-environment interaction throughout the productive life of the cow. This means at dry off, during the dry period, at the time of calving and throughout lactation.

The risk of cows developing new infections due to environmental bacteria is heavily linked to the concentration of these bacteria in the locations where cows are housed. New infections result primarily from an environment-to-cow transfer of the bacteria rather than cow-to-cow transfer as with the contagious bacteria. Keeping environmental bacteria numbers as low as possible in the immediate environment of the cow is critical to control of environmental mastitis.

Percentage distribution of clinical mastitis
by pathogen group in four surveys

Bacteriological StatusYear Published	Ontario (1996)	Netherlands (1989)	United Kingdom(1998)	Ohio (1989)
Environmental Streps	14.1	17.6	25.8	25.4
Coliforms	17.2	16.2	18.3	29.7
Staph aureus	6.7	9.6	14.8	1.7
Bacteriologically neg	17.7	23.6	------	27.2

Source: J.S. Hogan and K.L. Smith. 1997. Occurrence of Clinical and subclinical environmental Streptococcal mastitis. Proceedings of a Symposium on Udder Health Management for Environmental Streptococci, Ontario Veterinary College.

Coliforms

This category includes two predominant groups, E. coli and Klebsiella species. They share many similarities, including a Gram negative cell wall. They are commonly called “Gram negatives”. This distinguishes them as a group from the Gram positives, including the various Staph and Strep species.  Because of specific differences in the cell wall of Gram negatives and Gram positives, antibiotic sensitivities differ. Determining this general designation provides direction in terms of management of the disease and treatment of clinical cases.

The coliforms are associated with manure defecated by cows into their surroundings. Coliforms are normal GI tract inhabitants. There is always a supply of new coliforms to replace the ones being removed. Managing their concentration in the environment can be challenging but necessary.

Klebsiella are soil organisms that are commonly found in wood product bedding materials such as sawdust and shavings, especially if the material is green. Other organic bedding materials can also develop Klebsiella buildups, including recycled manure solids.

Hot, humid and wet conditions promote very rapid growth of these organisms in areas where cows are housed or congregate. These conditions may also occur in stockpiled bedding material if it is damp or wet.  Cattle overcrowding creates greater soiling of stalls and alleys and this increases the exposure level. Overcrowding in a dairy places a premium on managing stall and alley cleanliness.

Minimizing exposure is critical in controlling and reducing Coliform mastitis problems.

Many recommendations have been made regarding sand bedding as the bedding of choice for helping reduce buildup of the Coliforms. The reasoning is straightforward. Coliforms use organic material like sawdust and straw as a food source. Using clean sand removes the food supply; therefore, the bacteria cannot grow as well. Even sand bedding can be a concern if not regularly replaced. Manure solids that get into the sand become a food source if not removed, so sand bedded stalls still have to be well managed.

Not all facilities can or want to use sand, so their challenge is to keep stalls as clean and dry as possible using organic bedding. Stall management is critical both in terms of cow cleanliness and bacterial buildup. Bacteria concentrations in stall bedding have been described recently by University of Minnesota researchers.

Bacteria Levels in Free-Stall Bedding**

Farm	Bedding Material	Front  CFU’s/cc*	Middle CFU’s/cc*	Rear CFU’s/cc*
A	Chopped straw & paper	690,000	19 million	41 million
B	Ground Sunflower hulls	3.9 million	919 million	27.3 million
C	Sunflower hulls	1 million	3.6 million	25.3 million
D	Pine sawdust	401,500	Not taken	59.9 million
E	Ground Particle Board	1 million	Not taken	38.3 million
F	Hardwood	738,000	Not taken	13.2 million

  
 ·         CFU’S/cc=colony forming units /cubic  centimeter

** Source: R.F. Bey, J.K. Reneau and R.J Farnsworth. The Role of Bedding Management in Udder Health. Proceedings of the NMC 41st Annual Meeting.2002

As the table indicates, stall bedding materials in the back, middle and front can develop very substantial bacteria concentrations in 24 hours if the moisture, food supply and temperature are favorable to bacterial growth. The need to keep stalls clean is very evident based on these numbers. To date no one has developed a stall additive that will limit bacterial growth for extended periods and not pose a health problem for cows. Lime is effective for about 24 hours and then must be replenished.

The removal of soiled bedding from the back third of the stall and frequent replacement of stall bedding is necessary in order to minimize the bacteria load.

Stalls with high loads of bacteria puts the teats of the cow directly in contact with bacteria and sometimes the bacteria overwhelms the cow’s natural resistance. The following table points out the relationship between cow cleanliness and stall cleanliness:

Cow Cleanliness Scoring
% Cows rated 3 and 4*

Farm Type	Udder	Legs	Upper Leg flank
Free-stall (ave)	20%	61%	19%
Free-stall- best	4%	38%	7%
Stanchion (ave)	20%	25%	30%
Stanchion- best	0%	13%	5%

*1= very clean; 2=slightly soiled; 3= dirty; 4=caked on manure

Source: Dr. Nigel Cook-Bovine Veterinarian March-April 2002

Klebsiella bacteria are known for their potential to grow well in green sawdust material and so this should be avoided at all costs.

Coliform bacteria in relatively small numbers can create very serious mastitis problems if they gain entry to the udder. It does not require massive numbers to invade the gland and create difficulties. Coliforms can cause problems very quickly once they enter. That is why a cow can go from healthy and normal to quite ill in a matter of a few hours.

This where the Gram negative versus Gram positive difference enters the picture. The coliform bacteria are Gram negative and so their cell wall has different characteristics than Gram positive bacteria. It contains components that if broken loose are very toxic to cows and causes fever, swelling etc.  These bacteria, even when dead, release these components into the cow’s body via the milk where they continue to cause problems.

The bacterial wall of Gram negatives also reacts differently to antibiotic treatment. Typically the coliforms do not respond well to antibiotic treatment because of this cell wall difference. Therefore antibiotic therapy is often not part of the treatment used by veterinarians in treating this form of mastitis.

Treatment typically involves frequent milkout to help speed up toxin removal and possible use of anti-inflammatory drugs to reduce the temperature and swelling. In some cases hypertonic saline is used parenterally and in the gland to force movement of fluid into the udder in an effort to dilute and flush out the toxin.

Cows with coliform infections may have strong somatic cell responses in the short term. They are attempting to locate and kill the bacteria and frequently they are successful. However the toxins left behind may still create serious problems.

The SCC response may also be the reason why milk samples from such cows often give NO Growth outcomes when milk samples are cultured. This can be frustrating because while the cow has obvious problems the microbiology, which represents the gold standard for determining causes of infection, suggests no infection.

In recent years vaccines have been developed and introduced that provide protection against the coliforms, at least in terms of minimizing the severity of new infections. These vaccines basically help the body recognize key components of the coliform bacteria and develop an antibody response when they are detected.

These vaccines are considered reasonably effective against Gram negative bacteria in general, including E. coli, Klebsiella and other species sharing similar traits. They should be a part of dairy herd preventive medicine programs.

Minimizing coliform problems extends into the milking center. The objective at milking is to attach a clean liner to a teat that is as free of bacteria as possible. The teat prep routine must leave the teat clean, sanitized and dry. The most effective way of doing that is by applying a pre-dip capable of fast bacterial kill, allowing it up to 30 seconds of skin contact time and then wiping the teat completely clean and dry. This procedure lowers the bacteria counts at the teat end by killing and/or wiping off a high percentage of the bacteria present.

The fewer coliform bacteria on the teat end when the unit is applied the lower the risk of new infections.

Environmental Streps

These are species of streptococcal bacteria that are capable of living and thriving in areas outside the cow, on the cow and occasionally in the udder of the cow. They do not need the cow as a host to survive but they certainly can live in the cow for periods as opportunists. They are commonly found in manure, bedding, soil, on hair, from uterine drainage and other locations as well.

A microbiology lab may describe them in more detail and classify them as non-ag Streps meaning they are Streps but not Strep agalactiae. The lab may go further and speciate them as Strep uberis, Strep dysgalactiae or e-Streps which is a more recent term.

These Strep species may cause mastitis problems and frequently they create clinical mastitis. They are a major problem on many dairies today that have done an effective job of eliminating contagious mastitis.  Another risk with environmental Streps is that they are frequently shed into the milk in large quantity. As a result, infected cows that are not diverted from the tank can be major contributors to bacterial count elevations in raw milk. So Strep non-ag mastitis can also produce a milk quality issue.

The control of this problem is similar to that for coliforms. The objective is to minimize teat end exposure wherever the cow is including the freestalls, in the milking center, the dry cow lot and the fresh cow areas. The more exposure to these bacteria that occurs, the greater the risk of new infections.

There is a tendency for these bacteria to be a problem at dryoff and around the time of calving. The reasons are probably related to both cow and environmental factors. It is well established that at dry off there is a spike in new infections associated with coliforms and environmental Streps. Level of production at dry off, the potential for milk leakage, the lack of twice-daily milking and changes in the housing conditions all create a situation where the risk of new infections occurs. Managing this period so that infections are minimized is critical.

Dry cow therapy of all quarters is still beneficial based on studies recently published. The Streps respond reasonably well at this time and the benefits are seen in the next lactation with more milk being produced.

The key is to help dried-off cows get safely past the first 2-3 weeks of the dry period so that the gland can completely shutdown. It then becomes very resistant to new infections.

As cows approach the next calving, just the opposite happens. The milk producing tissue starts to develop, milk is produced and eventually the udder gets very distended and may leak milk. Cows at this point are under severe stress and have a lowered resistance to all diseases, including mastitis, because of the suppression of the immune system. Just when the challenge is greatest the immune system is at its weakest and cows therefore are most vulnerable to new infections.

To date there are no commercial vaccines available to help combat environmental Strep mastitis. However research is ongoing and some promising results are appearing. Within the next few years it is likely a vaccine to help limit environmental Strep mastitis will be available.

Environmental Strep bacteria are best controlled by limiting their number on the teat end. This is accomplished by maintaining clean dry housing, pre-dipping with a fast acting teat dip, managing dry cow areas to limit bacteria buildups, proper dry cow management including effective dry cow therapy. Application of an external teat sealant provides a 3-4 day seal of the teat end. This helps block bacterial entry into the teat at dry-off and reduces new infections.

Management has always been and will continue to be a significant factor in controlling mastitis as indicated in the following table:

Mastitis Factor cases	Percent of all mastitis
Milking equipment	6 percent
Housing and environment	25 percent
Genetics	20 percent
Management	49 percent

Source: Dr. Nelson Philpot, President: Philpot and Associates International, Homer, La.

Conclusion:

The combination of management, housing and environmental issues accounts for 75% of all mastitis. With environmental mastitis focus on these areas is the key to preventing new cases. Attention to details that reduce the bacterial exposure and improve the immune capability of the cows are critical. This includes maintaining clean dry housing, milking clean, sanitized dry teats, vaccination against the coliforms and using teat sealant to help seal the teat ends when cows are turned dry. 

Research update (article)

Efficacy of a Barrier Teat Dip in the Prevention of New Intra-mammary Infections

Pablo Janowicz 1, Hernan Agüero 2, Chris Foret 1

1 DeLaval, Kansas City, MO, USA • 2 Universidad de Chile, Santiago, Chile

Introduction

Post-milking teat disinfection is an effective procedure for the prevention of mastitis in dairy cows during lactation4. Exposure of teats to environmental mastitis pathogens, which are ubiquitous in the dairy environment, is present throughout the milking and inter-milking periods3. Barrier teat dips are formulated to kill organisms on teat skin immediately after milking and during the inter-milking period4. Only a few studies using the natural exposure protocol recommended by the NMC2 have tested barrier teat dips against a non barrier post milking disinfectant. The objective of this study was to evaluate the efficacy of a barrier teat dip compared to a non barrier teat dip in the prevention of new IMI.

Material and Methods

Results and Conclusion

References