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• Bulk tank milk cultures are a valuable management tool for any size dairy.
• A consistent mastitis control program is the best defense against all mastitis.
• Bulk tank milk bacteria counts can not be used to predict the number of infected quarters in a herd

The primary purpose of Bulk Tank Milk (BTM) culturing is to determine if a herd has contagious mastitis caused by Staphylococcus aureus, Streptococcus agalactiae, or Mycoplasma . The presence of these pathogens in BTM almost always indicates the presence of infected quarters in the herd. Characteristics of some common BTM isolates are summarized below.

CONTAGIOUS MASTITIS

Streptococcus agalactiae

The only reported reservoir for Strep. Ag. is infected udders. Strep. Ag. in BTM is due exclusively to the shedding of bacteria in milk from infected quarters. Strep. Ag. infected quarters significantly contribute to both elevated BTM standard plate counts (SPC) and somatic cell counts (SCC). An effective mastitis control program (see next page) will eradicate this microbe from a herd within 2 to 3 years, if the herd remains closed. Strep. Ag. eradication is an attainable goal. Blitz treatment (treating all animals infected with Strep Ag) is beneficial if animals are in early to mid lactation. There is a 98% cure rate and a return of $200-$400 per cow. Late lactation cows should be treated at dry-off only because they can’t produce enough milk in the remainder of their lactation to cover the cost of blitz treatment.

Mycoplasma species

The source of Mycoplasma is infected animals. Depending upon the species it may be found in the udder as well as the reproductive tract, eyes, respiratory tract, and joints. Mycoplasma is extremely contagious and is spread at milking. If less than 5% of the herd is infected, culling is recommended. If greater than 5% is affected, separate positive animals, milk them last, and do not feed their milk to calves. Calves that are infected may show lameness, ear infections, or respiratory signs. Eventually calves will recover, but the stress of calving may cause them to break with mastitis. There is no treatment for Mycoplasma. Prevention is the key. Test and quarantine all new purchases before allowing them to join the herd.

taphylococcus aureus

Presence of Staph. aureus in BTM results from the same management inadequacies as those responsible for Strep. Ag.Implementing and maintaining an effective mastitis control program will generally reduce the level of Staph. aureus infected quarters to <1% within a herd. Infected cows should be separated from healthy animals and milked last. Do not feed colostrum from infected animals because heifer calves can harbor the bacteria and calve with mastitis. An effective mastitis control program can reduce the incidence of Staph. aureus infected quarters to <1% within a herd. An attainable goal is < 50 CFU/ml in BTM. Dry treatment is the best time to cure infections with a cure rate of 50%.

ENVIRONMENTAL MASTITIS

Staphylococcus species

These include staphylococcal species other than Staph. aureus and are also reported as coagulase negative staph (CNS). CNS are normal teat skin flora and often are the bacterial group most frequently isolated from infected glands. High CNS counts in BTM may indicate poor udder preparation and teat sanitation. Mastitis caused by this group of organisms usually results in only a slight elevation of quarter SCC (<300,000/ml). Isolated instances have been noted where high standard plate counts were due to growth of CNS in improperly cleaned milking equipment. Treat clinical infections (obviously abnormal milk) with an antibiotic approved for the treatment of mastitis. An attainable goal for CNS counts in BTM is <1,000 CFU/ml.

Environmental streptococci and coliforms

Isolating large numbers of environmental streptococci and coliforms from BTM indicates poor hygiene either during equipment cleaning and sanitation, during milking, or between milkings. These two microbial groups share common sources of contamination such as bedding, soil, manure, and water. Milking wet udders, organic soil buildup in milklines, cracked gaskets and inflations, inadequately heated wash water, inadequate cooling of milk, and mastitis can all contribute to high environmental streptococcal and coliform counts in BTM. Lowering BTM counts of these bacteria usually involves evaluation of environmental situations. Treat clinical infections (obviously abnormal milk) with an antibiotic approved for the treatment of mastitis. Realistic goals for BTM counts of environmental streptococci and coliforms are <1,000 CFU/ml and < 500 CFU/ml, respectively.

MASTITIS CONTROL PROGRAM

• Forestrip to check for abnormal milk or clots indicating mastitis.
• Wash teats with a sanitizing predip and allow at least 30 seconds of contact time.
• Remove predip with a clean dry towel, leaving the teat clean and dry for milker attachment
• Attach milker 1½ to 2 minutes after forestripping for optimal milk letdown and faster milkout.
• Adjust unit as necessary. Milker squawks are a primary means of spreading contagious mastitis.
• Shut off vacuum before removing unit.
• Postdip with a 1% iodine teat dip containing glycerin. 1% iodine is the most effective teat dip for Staph. aureus.
• Dry treat every cow at dry-off.

References:

www.NMConline.org
The economic benefit of treating subclinical Strep. Ag. Mastitis in lactation cows. 1987. JAVMA 191:1556-1561.