Environmental Mastitis -- Source and Causes
by Winston Ingalls, Ph.D.
West Agro, Inc., Kansas City, MO
Mastitis, as has been stated many times, is an infection of the mammary gland and may be caused by any one of a large number of different bacterial species. Certain bacteria live primarily in the gland of the cow and on the teat skin and are spread primarily cow to cow by the milking cluster or the hands of milkers. These organisms are generally referred to as contagious mastitis pathogens.
Another large group of bacteria is also present in the environment of the cow at all times and under various circumstances may cause a significant mastitis problem. These bacteria often are the cause of serious mastitis problems on dairies where contagious pathogens are well controlled and not the cause of many new infections.
What species of environmental bacteria are likely to be involved? Two different groups generally are responsible for many of the new infections caused by environmental bacteria. One group is termed coliforms and includes E. coli and a somewhat similar bacteria group termed Klebsiella.
The other group is the environmental Streptococci, which includes Streptococcus uberis, Streptococci dysgalactiae plus several other species that may on occasion may be involved. In the U.S., Strep uberis is the most frequently identified environmental Strep species in new infections caused by this group. Often this group is referred to simply as Strep non-ags.
This group of organisms is present at all times on all dairy farms. They are fecal bacteria so each time the cow defecates they are placed in the environment. Coliforms are capable of living in bedding, especially wood product bedding materials such as sawdust and shavings. When bedding materials are mixed with ample quantities of manure, leaked milk, urine and then warmed up with body heat or warm weather, rapid and explosive growth of these bacteria can occur in this material.
The concentration of coliforms in the environment of the cow is a significant factor in the incident rate of new infections. When the concentration builds up the risk is increased and when the concentration is reduced the threat is reduced. Routine cleaning and replacement of soiled bedding is a simple practice that reduces risk by lowering the bacterial concentration. When cows are moved out of housing areas to be milked, stall maintenance should be performed. Remove soiled bedding from the back of stalls and replace it with fresher, clean material. This helps lower the bacteria count but recognize that as soon as it is soiled again the pattern of bacterial buildup begins anew so stall maintenance has to be done routinely.
Monitor the alleys where cows walk to and from the milking area. If they are sloppy and wet there is a risk that some of this may be splashed onto legs, tail switches and teats and this again produces risk through increased bacterial exposure. These alleys should be clean when cattle are moving to and from the milking center.
What is the Best Bedding Material?
Bacteria that live in the environment generally have developed an ability to use organic materials such as wood products and straw as foodstuffs. For this reason organic bedding material is not the best to help control environmental bacteria growth. Sand, free of dirt and organic material, is frequently recommended because it is inorganic and offers no nutrient value for bacteria that may be deposited in it. Also, while it not an absorbent material, it drains well and the moisture content of upper layers tends to stay relatively low.
For optimum performance the sand has to be replenished routinely and manure needs to be removed from the rear of the stalls frequently to minimize buildup. Sand poses a challenge for waste handling systems but it can be managed so problems are minimized. Sand handling equipment is available that allows it to be uniformly placed into stalls with little manual labor. In new dairies, with freestall construction, sand needs to be considered the bedding material of choice. When sand is not an option, sawdust, straw or recycled manure solids are frequently used. The key to limiting problems is frequent replacement of bedding as it becomes soiled to prevent bacteria counts from becoming excessive.
Importance of Milking Clean Cows
When cows are prepared for milking, the dirtier the teats the greater the risk of mastitis problems. The risk is greatest when dirt on the teats is wet due either to rain or excessive amounts of water being sprayed on cows prior to milking. Water allows bacteria to become mobile and they may end up at the teat end. The key at milking time is to attach a unit to a very well cleaned, sanitized, dry teat. When a milking unit is attached to a wet dirty teat, coated with bacteria, it is possible while milking that some may gain entry to the udder and start new infections.
Properly cleaned teats reduces the amount of dirt present on the teats and teat ends but it also reduces the bacteria load. Sanitizing the teat will also reduce the bacteria load in proportion to the effectiveness of the sanitizer used. The more effective the sanitizer the greater the bacteria reduction.
Finally, thoroughly wiping dry the teat and teat end, also removes soil load and the accompanying bacteria through mechanical action. Therefore if the teat skin is first wetted with a sanitizing material such as pre-dip sanitizers for 30-45 seconds and then thoroughly wiped dry, the wiping action helps remove many of the bacteria loosened by the wetting action of the sanitizer.
The keys are to attach a milking unit to a clean, sanitized, dry teat and during milking be certain that dirty water is not allowed to locate and accumulate at the liner mouthpiece. When this occurs the threat of mastitis due to teat end exposure to coliforms as well as environmental Streptococci is reduced.
Another tool, helpful in reducing coliform mastitis problems, is the use of coliform bacterins to vaccinate cows. These products provide cows with increased immunity against the coliform bacterial species. The vaccines, based on published research results, help reduce the severity of infections that may occur and this means fewer severely ill cows and less milk loss.
This group of organisms has become a major issue on many well-managed dairies where contagious mastitis is not an issue. They often are referred to collectively as Strep non-ags. They are in the Streptococci family, but are not Streptococcus agalactiae, which is a true contagious mastitis pathogen.
They pose a tough challenge. They are capable of living in the environment of the cow, on the cow and in the udder of the cow. Body sites including the vulva area, hair coat, skin and muzzle of the cow may all harbor these bacteria species. When they do enter the gland they may develop infections that last for short or extended periods and may behave somewhat as contagious bacteria. A major concern is that a high percentage of these udder infections become clinical requiring some type of treatment.
Bedding materials may play a role in determining the numbers present in housing areas. They appear to thrive well on straw bedding materials so this may assist their buildup in areas such as bedded packs where dry cows are often housed.
They can and will survive through the dry period if the dry cow treatment program is ineffective or non-existent. Take a close look at late lactation cows going dry and when they come fresh. If they are not effectively treated at dry-off the odds increase that in the first 30-60 days post freshening cows will encounter new Strep non-ag infections that may have originated during the latter part of the dry period. Make sure, using antibiotic sensitivity testing, that the dry cow antibiotic chosen is effective against environmental Strep species present.
Environmental Streps can produce confusing symptoms. It is possible for them to seriously elevate the somatic cell count in infected cows and yet the milk from such cows may appear near normal based on visual inspection.
Infected cows may release large numbers of bacteria into the raw milk and can significantly elevate the SPC of raw milk. Generally, at some point, a high percentage of these infections become clinical and cows then have to pulled out and treated. Treatment during lactation is not 100% effective and depending on the species, antibiotic resistance may be an issue.
Minimizing problems with environmental Streps requires action similar to that associated with coliforms with a few exceptions. Since these organisms can be found growing on the hair coat and skin it is essential to remove udder hair and to milk a very clean, dry teat. If water drains off from the hair coat it can carry these bacteria with it into the liner mouthpiece and once in the cluster it is possible they may be able to enter the teat during milking if there are liner slips and squawks.
Pre-dipping has been demonstrated effective in reducing the development of new infections. The bactericidal action of a teat dip, applied pre-milking, allows it to do a superior job of sanitizing the teats. Therefore when units are applied after the pre-dip has been wiped off, the teat skin has a low concentration of bacteria on it.
Be aware of the importance of cleanliness in the calving area and work at making it clean and sanitary. Cows that calve and have uterine discharges may shed these Streptococcal species, contaminating the bedding material. This exposes the next cow that enters the calving area to potential risk. It is critical these areas be frequently cleaned and kept clean.
Controlling environmental Strep mastitis problems involves several considerations. First is verifying, by sampling and culturing milk from clinical cases, that the dominant organism present is a Strep non-ag species. If this pattern is repeated in a number of clinical cases it is a strong indication this is the problem and the source has to be determined.
Examine the milking routine. Look for wet, dirty cows entering the parlor, too much water being used to clean cows, long hair on the udders, ineffective pre-milking teat sanitation program, wet cows being milked, frequent liner squawks and slips poor teat dipping practices resulting in poor coverage. Failure in any of these areas can lead to problems.
Review dry cow treatment products, housing conditions, freshening area cleanliness and calving area sanitation procedures between cows.
Review the diet of the dry cows especially being certain the levels of selenium and vitamin E are in line with current recommendations. These compounds are known to assist the body in fighting off infection so deficiencies may play a role in increased new infections.
Resolving the problem generally occurs over time as each possible cause is evaluated and improvements made. It is a never-ending battle and if slipups occur, the problem will return with the same consequences, elevated cell counts, clinical symptoms and lost milk.