Mastitis Control Program for

Staph-InfectedDairy Cows

Staphylococcus is a general namefor a class of small, round bacteriacapable of causing mastitis(inflammation of the udder) indairy cows.

There are a number of primaryspecies of staphylococci. Amongthese is Staphylococcus aureus, alsoreferred to as Staph. aureus or"staph." Staph. aureus is the majorcause of chronic or recurring clini-cal mastitis in dairy cows. Otherspecies of staphylococci can be iso-lated from the cow's mammarygland, but their role in causing mas-titis is not as well understood.

This bulletin will focus on thesources of Staph. aureus infectionswithin a dairy herd, and suggestcontrol and prevention tips for thedairy farmer.

Where can Staph. aureus befound on the farm?

The main sources are teat skin,teat sores and milk from infectedcows. Chemical irritation, chappingand other physical damage to teatsmay increase the probability thatstaph infections will develop on theteats.

Purchased cows can be anothermajor source of new staph infectionswithin a herd.

Roger MellenbergerDepartment of Animal Science

John KirkDepartment of Large Animal Clinical Sciences

How does the infection movefrom cow to cow once itdevelops?

Staph infections are usually trans-ferred from infected cows to non-infected cows during milking viacontaminated teat cup liners,milkers' hands, and common washsponges or rags.

What kind of mastitis problemscan Staph. aureus cause?

Because of its toxin (poison) pro-duction, Staph. aureus can causemastitis problems ranging from non-clinical infections to clinical or gan-grenous infections that may kill thecow. Once Staph. aureus gets intothe mammary gland, it will invadedeep into secretory cells and ductaltissue. Staph infections produce scartissue and can cause small abscessesto form in the udder. Both may per-manently limit an infected quarter'sability to produce milk.

How widespread can a staphproblem be within a herd?

It is not unusual to find dairyherds in which 30 percent or moreof lactating cows have two or morequarters infected with Staph. aureus.Cows that have been infected at leastonce have a greater chance ofbecoming reinfected, and the prob-

ability that staph infections willoccur increases with cowage.

What signs might tip me off thata Staph. aureus problem ispresent in my herd?

These clues can indicate that aproblem exists:• Several cows in the herd havechronic clinical mastitis.

You should be aware that clinicalcases caused by Staph. aureus canoccur in any age cow and at anytimeduring lactation. Infected quarterswill "flare up" at regular intervals(about every two weeks to onemonth). Milk produced frominfected quarters will be watery oroff-colored and will contain flakesand clots. Most infected cows willnot run a fever. Udders will probablyswell, and infections will respondvery poorly to lactational antibiotictherapy.

Even with the use of good drycow treatment products, you canexpect that at least 30 to 50 percentof the cows infected during a lacta-tion will still be infected, and possi-bly develop into chronic cases, dur-ing the next lactation.• A herd somatic cell count or aDHIAweighted somatic cell count

ranging from 400,000 to 800,000(linear score of 5 to 6) during theyear.

If the bulk count rises highenough, it may result in a warningfrom your milk cooperative.

Usually, less than 10 percent ofstaph-infected cows within a dailyherd will have counts higher than1,500,000. This is one way that staphinfections differ from other mastitisinfections. A dairy herd that containsthe same percentage of Streptococ-cus agalactiae- infected cows, forexample, will generally show muchhigher bulk tank somatic cell counts.

• Presence of pockets of scar tissuein infected quarters that can bedetected by palpating (touching).• An increase in the rate of chronicclinical mastitis within the herd fol-lowing the purchase of lactatingcows.• Appearance of gangrenous mastitisin first -lactation fresh cows, espe-cially during colder weather.

What should I do if one or moreof the situations describedabove applies to my herd?

First, confirm the existence of theinfection in your herd. Collect sterilemilk samples for culture tests from15 percent of your herd (or at least10 to 20 lactating cows selected atrandom), or from a minimum of 20cows with somatic cell counts of400,000 or higher (linear score of 5).Have the samples cultured by a qual-ified microbiological laboratory.Your veterinarian may have theproper lab facilities, or you cansubmit samples to your state animalhealth diagnostic lab or your milkproducers' association. Costs for thecultures may range from $1 per cowto about $10 per culture, dependingon the organism responsible for theinfection and the laboratoryinvolved.

What kind of results from theculture tests would indicate aproblem?

Positive results from 50 percent ormore of the milk samples you hadcultured for Staph. aureus would

indicate a significant problem withinyour herd. If less than. 50 percent of

. the results are positive, but you havenoticed some of the other above-mentioned symptoms, resamplewithin two months the cows thatproduced positive cultures.

Assuming that I have confirmedthe existence of mastitis prob-lem caused by Staph. aureus,what management steps shouldI take to solve the problem?

Of course, the more severe yourproblem, the more quickly you needto put a control progra-m into action.It is very important, however, tobegin a long-term prevention pro-gram at the same time. A combina-tion control/prevention program willkeep the problem from recurring.

The urgency of your control pro-gram will depend on several things,including:

• Your bulk tank somatic cell count.• The severity- and rate of clinicalmastitis within your herd.• Your present cash flow situation.

You should begin a control pro-gram at once: If you are discardingmore than 5 percent of your milkdaily; if more than 5 percent of yourherd is being treated for staph infec-tions at a given time; and/or if yourbulk tank somatic cell count is400';000 or greater. Failure to act onthe problem could result in a sub-stantial financial loss.

STAPH CONTROLPROGRAM• Cull chronically infected cows.

But which cows should I cull?First priority for culling should be

made for older cows that have thesecharacteristics:

• Chronic clinical mastitis.• Monthly somatic cell counts thatremain higher than 400,000 (linearscore of 5) over two lactations.• More than three treatments duringthe present lactation.

The number of cows culled willdepend on the availability ofreplacements and your- cash flowsituation.

• Segregate infected cows from non-infected cows during milking.

Which cows should be includedin the segregated group?

The segregated infection groupshould include all cows that havebeen treated for mastitis during thepresent lactation, cows cultured pos-itive for Staph. aureus, and cows thathave a somatic cell count consist-ently above 400,000 or a linear scoreof 5.

What method should I use toseparate the infected cows?

There are three options of free-stall housing you can use to segre-gate the infected and questionablecows from the non-infected cowsduring milking time:

OPTION I-Establish a separate lotfor staph-infected cows. Milk thesecows last. Culture fresh cows beforeassigning them to either the infectedlot or the non-infected lot. Treatedcows should be included in theinfected group.

Cows should leave the infected lotonly through death or culling, or byproducing a negative culture resultfollowing dry treatment. Becauseinfected cows are more likely thanthe rest of the herd to becomeinfected again, many farmers chooseto keep the infected group separatedon a permanent basis.

A cow would move from the non-infected lot to the infected lot eitherwhen a case of clinical mastitisoccurs or when a milk culture is pos-itive for Staph. aureus. Remember, asomatic cell count greater than400,000 or a linear score of 5 from acow that was previously considerednon-infected indicates a need to cul-ture a milk sample from that cow.

OPTION 2 - Use separate milkingequipment for treated and infectedcows, if the number of infectedcows is relatively low. The clawunits used for infected cows shouldnot be used to milk any non-infectedcows. With this option, the infectedcows would not have to be physi-cally separated from non-infectedcows, but they would need to beclearly identified at milking time.

Table 1Bacld1ush Routine

• Maintenance of a closed herd.• Good calf management so ade-quate numbers of replacement heif-ers are available.• Periodic bulk tank sampling tomonitor somatic cell counts oncethe infection problem is undercontrol.• Cooperating with your local veteri-narian to establish Staph. aureuscontrol and prevention programs.

STEP1. Running-water rinse2. 25 ppm iodine flush3. Running-water rinse4. Water removal from claw

APPROXIMATE TIME ALLOWED10-15 sec.45 sec.-1 minute10-15 sec.

OPTION 3-Backflush all milkingunits between cows. Table 1 out-lines a true backflush routine.

Some dairy farmers backflush clawunits manually between cows, butthis is time consuming (2 to 3 min-utes per unit). Commercial auto-matic backflush units are availableand are very effective at removingstaph organisms from teat cup liners.Most backflush units are installed incombination with automatic-removalmilking units.

Though backflushing can elimi-nate the need to segregate cows, youshould realize that the cost of install-ing backflush units can range from$1,000 to $2,000 per unit, plus costsfor automatic takeoffs. Therefore,each farmer should determine thecost:benefit ratio of backflush unitsfor his or her farm.

What other management stepsshould I take?• Dry off infected, pregnant cowsimmediately if they are within 80 to90 days of calving, and dry treatthem.• Postpone further purchases ofcows.• Perform a total evaluation of milk-ing equipment functions, especiallypump capacity, controller function,line sizes, vacuum level, pulsatorfunction and inflation condition.• Evaluate milking procedures.• If you have not already done so,establish a teat dipping program,using a germicidal teat dip, and a drycow treatment program, using acommercially available antibioticdesigned specifically for dry cows;• Provide adequate balanced rationsfor your herd, with special emphasison vitamins and selenium.• Evaluate housing conditions forbred heifers, dry cows, cows at calv-ing and lactating cows, checking forpotential sources of teat injury.

• Consider having your milkers weardisposable plastic gloves duringdaily milking routines. Culture testscan indicate the presence of Staph.aureus on the hands, but the bacte-ria are often hard to eliminate.

Would vaccinating myherd help?

A good general vaccination pro-gram is recommended for any dairyherd to combat diseases, but thevaccinations that are currently avail-able will not prevent staphinfections.

Is there anything I can do toprevent or reduce the chancesof my herd becoming infectedby Staph. aureus?

Yes. Naturally, a good preventionprogram begins with a dairy farmeror herdsperson who is truly inter-ested in milking cows. The state-ment that mastitis is a man-madedisease is true for many farms.

Important measures you can takeinclude:

• Proper nutrition and soundgeneral vaccination programs forheifers and cows.• Good sanitation in housing areas.• Properly designed and maintainedmilking equipment, and properusage of the equipment.• Teat dipping.• Dry treatment of all cows.• Enrollment in the DHIA somaticcell count program.• Culling of chronically infectedcows.• limited, managed use ofveterinarian-recommended antibio-tics for treatment of mastitis duringlactation. Treatment of staph infec-tions during lactation will cure only10 to 20 percent of infections; there-fore, lactation therapy should belimited to severe clinical cases.

This is one in a series of bulletinson mastitis control in dairy herds.Contact your county CooperativeExtension Service office for infor-mation on other forms of mastitisand how to control them.

Dip teats regularly after milking toreduce the risk of a Staph. aureusinfection developing.

SOMATIC CEll COUNfS ANDEQUIVALENTDHIA UNEAR SCORES

DHIAlinearAverage SomaticCell Count

12,50025,00050,000

100,000200,000400,000800,000

1,600,0003,200,0006,400,000

Score

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