Environmental mastitis

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Editor’s note: Fourth in a mastitis series

Environmental mastitis problems can be difficult for veterinarians to deal with if their clients don’t stay on top of management factors to prevent the proliferation of organisms and their subsequent spread to cows’ udders.

And not only can environmental mastitis be difficult to manage on many dairies, it can be expensive, costing between $75 and $115 per case depending on severity, with milk discard and treatment costs. “Any adverse health effect in the fresh cow, which is usually where environmental mastitis problems occur, costs an average of about 2,000 pounds of milk for that lactation,” says Jim Jarrett, DVM, Rome, Ga.

The coliforms, primarily Escherichia coli and Klebsiella spp., are often found to be the main mastitis pathogens in many well-managed herds. On the other hand, better managed herds with more control over environmental conditions (such as dairies with solid-structure housing facilities) often see more problems with environmental Streptococcus species, primarily S. uberis and S. dysgalactiae, followed by coagulase-negative Staphylococcus species, says Greg Goodell, DVM, staff veterinarian at Duo Dairy, Ltd., Loveland, Colo.

“Usually less than five percent of environmental pathogens cultured from clinical cases of mastitis are comprised of Arcanobacter, other coliforms such as Serratia and Enterobacter, Pseudomonas and yeast,” he adds.

“Mastitis in dairy cows is no longer a
mystery,” says Jarrett. “We know how she got it. Bacteria got into her gland and once in, they found conditions that allowed them to reproduce. The best way to prevent infection is to prevent penetration, and we must augment that by keeping the cow’s resistance as high as we can and stop the reproduction once the bacteria is inside the gland.”

Where are they found?

Coliform agents originate from the enteric tract of most mammals. Contamination of the environment, especially bedding, with feces and urine, will allow the bacteria to thrive. Growth of all of the environmental pathogens are enhanced by moisture and warmth so virtually any organic-based media will support these organisms given proper conditions. Organisms such as Pseudomonas are found just about everywhere in nature and have the ability to inhabit water supplies, as well as some teat dips and antibiotic preparations.

“Bacteria must have a combination of three things to be a problem,” says Jarrett. “The right temperature, some moisture and some nourishment to grow. We used to think green hardwood sawdust was contributing to bacterial growth, but now we know the bacteria comes from the logs dragged through the forest that then get contaminated by soil bacteria.”

In the arid western states where dry lot dairies are common, 85 to 90 percent of the mastitis cases during the summer may be due to coliforms because of increased moisture and warmer temperatures, and about 60 percent of cases are attributed to coliforms in the winter, says Goodell. “Dry lot dairies simply do not provide the level of protection from the elements such as rain, sun, wind and snow that enclosed facilities do.”

In more tropical areas, such as the Southeast, bacteria can flourish in the right temperature and humidity. Jarrett says because of that it’s important to impress upon dairy personnel that the fewer bacteria that contaminate bedding, skin and equipment, the fewer bacteria that will contaminate the teat.

Bedding makes a difference

The types of bedding materials your clients choose and the way they manage housing, bedding and manure can have a lot to do with the infection rate of environmental mastitis. Sand makes an ideal bedding choice because of its inorganic nature and inability to support environmental organisms. When used properly, sand seems to provide a higher degree of cow comfort as well as inhibit bacterial growth because of its inorganic nature.

“Inert bedding doesn’t support bacterial growth, so even if you have the right temperature and moisture, there’s nothing for bacteria to use for nourishment,” Jarrett says. “From a biological contamination standpoint, sand just doesn’t offer that nutrition for bacteria to grow.”

Straw packs and chopped straw are most often used in dry lot dairies during periods of wet or cold and can be used with success, but the key is to bed the cows often and regularly in order to keep them dry. Bedding packs must also be removed regularly to keep pathogen loads reduced. This can be an area of high exposure of environmental Streps. for the cow.

Type of bedding is easy to blame on mastitis problems, but that’s not necessarily the root of the problem, says John Ferry, DVM. “Much is made of ‘type’ of bedding,” he says. “When in the vast majority of cases, the problem isn’t type but quantity. Don’t blame that sprinkling of sawdust you put down last week for today’s mastitis.”

Ferry says bedding type is irrelevant if it is contaminated with manure. “Every time the cows are brought to the parlor, the stalls should be raked clean of manure and fresh bedding should be pulled back from the front of the stall.”

Stall design is an important element, too. Ferry says proper stall design minimizes the amount of manure in the stall by properly positioning the cow.

Preventing infections

Bedding and stall management is only part of prevention. Milking procedure is another area where mastitis prevention is critical. “Ensuring that cows are clean and dry prior to attaching milking machines is probably one of the biggest ways to prevent environmental mastitis in the parlor,” says Goodell. “Pre-dipping with disinfectant also helps, however, herds with extremely clean cows coming into the parlor can often eliminate the pre-dip and ‘dry prep’ the cows. Of course, contagious pathogens must be under control for this to work.”

“The amount of teat dip used by employees can be as variable as the amount of bedding they use,” Ferry adds. “You can’t blame your teat dip if two-thirds of the teat never saw any.” Skin integrity is the first natural line of defense, and especially in harsh weather teat dips are needed to prevent drying and chapping.

Teat dips are one area Jarrett says dairies can influence mastitis externally. “Using pre-dips to reduce the number of bacteria that can gain entrance into the gland will help prevent new cases of mastitis.”

Improper milking machine function is another area of concern. Regular maintenance of parlor equipment will help maintain things like proper vacuum levels and automatic take-offs. Ferry says one of the most common causes of Strep. outbreaks is worn inflations. “One of the first questions we should ask in a mastitis outbreak is, ‘What is your schedule for changing inflations,  when was it done last and where is that written down?’” he adds.

Post-dipping with a barrier teat dip during inclement weather will also help ward off increased exposure the herd will experience.

“The more we can educate not only the owner, but everyone on the dairy from the owner down to the milkers, the better chance we have at preventing mastitis,” says Jarrett. “If they understand the biology and how mastitis occurs, they are more likely to milk dry udders, keep bedding clean, give cows excellent nutrition and properly pre-dip.”

Clinical signs

Clinical signs of coliform mastitis can be variable and often depends on if the animal has been vaccinated with an E. coli bacterin. Approximately 85-88 percent of the cows vaccinated with an E. coli bacterin present with little to no systemic signs of disease and have a 5 to 50 percent decrease in milk production, says Goodell. “However, most will have gross signs of inflammation in the infected quarter, which consists of enlargement, increased firmness to the gland, hyperemia and a milk secretion that ranges from off-white in color to serum with varying amounts of clots or flakes.” He adds that cows with systemic disease may also suffer from dehydration, depression, anorexia, fever and agalactia.

Jarrett adds that clinical signs can vary. “They can range from a flake or two to a very acutely or peracute animal that is down with a high fever and dehydration.”

Treatment

Cows with environmental mastitis fall into two different treatment categories: 1) those with coliform mastitis (gram negative organisms) and 2) those with environmental, non-coliform mastitis (gram positive organisms). Treatment and prognosis vary dramatically depending on which type of mastitis is being treated.

Goodell says coliform mastitis therapy may be divided into three groups: mild, moderate and severe. “Mild cases are the majority of cows that are treated,” he says. “They comprise approximately 85 percent of cows treated for coliform mastitis in herds that vaccinate cows with an E. coli bacterin.”

Cows with mild cases may exhibit abnormal milk secretion, a hard and/or swollen gland and a drop of 5 to 50 percent of daily milk production. Goodell treats these cows with phenylbutazone, vitamin E and oxytocin. The cows are hand-stripped after each milking to ensure complete milk removal and if no systemic signs develop in the three day treatment window, the cow is moved from the hospital pen to the mastitis pen for observation.

Moderately infected cows are the most difficult to classify and pose the largest therapeutic dilemma. This category usually accounts for approximately 8 to 10 percent of coliform-infected cows.

Cows with moderate infections may have abnormal milk secretion, hard and swollen glands, 15 to 60 percent drop in production, mild dehydration and sometimes the presence of fever (103.5°F). Goodell treats these cows with phenylbutazone and vitamin E for three days. If dehydrated, they are given oral electrolytes as needed. If febrile, they are given a one-time dose of flunixin meglamine and a broad spectrum antibiotic. They are also given oxytocin and are hand-stripped after each milking .

Severely infected cows are the easiest to identify and have the worst prognosis for return to production (or staying alive), says Goodell. Approximately 5 to 6 percent of cows with coliform mastitis are regarded as severe.

Cows with severe infections have abnormal milk secretion, a hard and swollen gland, 70 to 100 percent drop in milk production, moderate to severe dehydration and depression, and are usually febrile.

Goodell treats these cows with phenylbutazone, vitamin E, oral electrolytes, a broad spectrum antibiotic, flunixin meglamine, one to two liters of hypertonic saline IV at presentation, then as needed. Oxytocin is administered and hand-stripping is also done.

For environmental, non-coliform mastitis, Goodell treats animals on a delayed basis. “Milk samples are collected as they enter the hospital pen, then cows are observed for 72 hours and placed into a mastitis pen,” he says. Frozen samples are cultured once per week. This is done to eliminate unnecessary intramammary antibiotic use. “If the sample comes back with treatable organisms, the cow is pulled back into the hospital pen and treated with intramammary antibiotics. I have used this program for over three years while tracking infection rates by quarter and organism and have concluded that delaying treatment up to seven days does not alter the cure rate significantly.”

Goodell adds that antibiotic susceptibility patterns should be evaluated periodically (quarterly or semi-annually) on all mastitis pathogens present on the farm to ascertain the efficacy of treatment. “This will allow the correct selection of intramammary antibiotic to be used in Gram positive infections as well as the most appropriate parenteral use of antibiotics in moderate or severe cases of coliform infections.”

“Mastitis occurs when bacteria gain entry into the gland and once inside find conditions that allow them to reproduce,” adds Jarrett. “It may be oversimplified, but it comes down to what happens outside the teat and what happens inside. Keeping the bacteria out of the gland depends on management of the environment, the way we milk and reducing the number of bacteria in the vicinity of the teat end. Once the bacteria is inside the cow, we can help the cow fight off an infection by giving her good nutrition including trace minerals, reducing stress and vaccinating her.”

 

Monitoring environmental infections

More important than the few cows clinically infected with environmental mastitis is the number of subclinically infected cows in the herd. Besides monitoring the somatic cell counts on the bulk milk tanks, Goodell uses two methods to evaluate subclinical problems.

1. The first method is composite culturing of three different groups of animals in the herd:

  • The lactating herd: Once a week a sample is collected from the milk tank at the end of the day’s milking and cultured. It will identify the pathogens that typify the subclinical infections in the herd. A change in the type or amount of pathogens that are seen in this sample, environmental or contagious, should trigger a predefined action established by the veterinarian and the dairy.
  • The fresh pen (if in use): There are several methods available that allow collection of composite samples of individual pens. The results from samples obtained from the fresh pen help evaluate the dry period. Changes in this sample often occur before changes in the herd sample and can help identify problems more quickly.
  • The hospital pen: Have the herdsman or some other responsible personnel collect composite milk samples daily from the hospital pen and submit these for culture once per week. This is done as much for contagious pathogens as for the environmental pathogens (one cow shedding Mycoplasma will usually be found in composite samples of 200 cows). However, changes in pathogens from this sample may also help identify a recent change in the population of environmental organisms in clinical cases of mastitis. For example, the predominant organism in the bulk tank samples may be environmental Strep. but the organism causing clinical mastitis may be Klebsiella. Pinpointing the organism will allow more specific actions to be taken, both in terms of preventive actions as well as more specific treatment of the individual cow. In a large herd this should be done weekly.

2. The second method Goodell uses is somatic cell count of individual cows on a monthly or quarterly basis. Herd level monitoring is done by plotting current linear score (LS) of each cow along the X axis and the linear score from previous SCC tests along the Y axis. Most dairy software programs possess the capability to perform this task. Selecting a LS of 4.0 (SCC=200K) for both current and previous tests allows the scatter graph to place cows in one of four quadrants – recovered, chronic, healthy and those with new infections. This is monitored quarterly to detect changes in each population (quadrant) of cows.



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