INTRODUCTION

The goal of mastitis control is to prevent new infections; however, new cases will occur, and once established, four ways to eliminate the disease are spontaneous cure, marketing of chronically infected cows, treatment during lactation, and dry cow therapy. Antibiotic treatment is the principle method for eliminating existing infections, and successful therapy involves drugs reaching all sites of infection within the quarter, remaining at appropriate levels for an adequate period of time, and killing all infecting microorganisms. Goals of antimicrobial therapy include returning the cow to normal milk production and composition, preventing mortality in peracute cases, eliminating infectious microorganisms, preventing new infections in the dry period, avoiding drug residues in milk and meat, keeping existing cases from becoming worse, minimizing damage to secretory tissues, reducing spread to other cows, and improving overall herd health.

SPONTANEOUS RECOVERY

Spontaneous recovery occurs in only about 20% of confirmed infections for a variety of mastitis-causing bacteria, and most occur in quarters with mild or recently acquired infections; rarely in the case of chronic Staphylococcus aureus infections (10). Soon after an infection is established, changes in the cow's immune system take place in attempts to eliminate the infecting microorganisms. Spontaneous recovery from specific infections is enhanced in cows that have been vaccinated against the specific bacteria causing the infection. Through future research on this defense mechanism, it is likely that scientists will be able to enhance spontaneous cures using biologic agents such as cytokines, interferons, and colony-stimulating factors.

MARKETING OF REFRACTORY COWS

Culling is often the only practical means to eliminate chronic infections that do not respond to repeated therapy (10). Research has shown that only 7% of cows is responsible for about 40% of all clinical mastitis. Other studies have shown that 50% of all discarded milk was contributed by only 6% of the cows. In addition, 64% of cows that have had two cases of mastitis in a lactation will have another clinical episode before the end of lactation. This figure increases to 70% for cows that have already had three clinical cases. Such chronically infected cows exhibiting periodic flare-ups of clinical mastitis are probably infected with contagious pathogens. These animals constitute a reservoir of microorganisms that ultimately spread to uninfected cows, and should be removed from the herd.

TREATMENT DURING LACTATION

Spontaneous recovery and culling have serious limitations, leaving drug therapy as the principle alternative for eliminating infections. By eliminating infections, it is possible to reduce the level of mastitis in months rather than years. The primary concern of most dairy farmers is how to make the best use of antibiotics and other drugs in treating clinical cases during lactation. Such cases require prompt and appropriate attention, though each must be considered on an individual basis. Treatment in lactation is indicated when cows are infected with Streptococcus agalactiae, when the herd somatic cell count (SCC) is above 400,000/ml, and when clinical mastitis is present. The typical dairy farm can expect to have approximately 45 clinical cases of mastitis per 100 cows per year.

Therapy of Acute Toxic Mastitis: Acute toxic mastitis is most frequently caused by coliform bacteria such as Escherichia coli and Klebsiella pneumoniae. These bacteria produce endotoxin, which results in severe depression, dehydration, inability to stand, diarrhea, and shock; a condition collectively referred to as toxemia. To be successful, therapy must be directed primarily against endotoxin, which eventually reaches the bloodstream and causes the above symptoms. Most management programs involve frequent stripping of affected quarters, use of carefully selected antibiotics, and administration of electrolyte fluids, anti-inflammatory agents, glucose, bicarbonate, and calcium. Though coliform isolates are usually sensitive in laboratory tests to cephalothin, tetracycline, ampicillin, erythromycin, and sulfonamides, the therapeutic value is questionable. Most veterinarians place increased emphasis on supportive therapy to counteract endotoxin-induced shock (3). Severely affected cows may need 40 to 60 liters of fluids intravenously in the first 24 hours after onset of the disease. Selected anti-inflammatory drugs are often used to counteract effects of the endotoxin. Antibiotics are often considered adjunctive to supportive therapies such as fluids, and may be helpful in preventing acute infections from becoming chronic and in cases of septicemia.

Therapy of Subacute Clinical Mastitis: Most cases of clinical mastitis fall into this category. Intramammary infusion with an approved product for a minimum of 3 days, accompanied by frequent hand stripping to remove secretions, bacteria, and cellular debris is often adequate. Treatment should be continued until at least 24 hours after the disappearance of clinical symptoms; otherwise, the infection may only be suppressed to the subclinical level. A true cure, whereby all infecting microorganisms are eliminated from the affected quarter, occurs in less than 50% of cases for most bacterial species. The cure rate is dependent on how long the infection has been present, age of the cow, and type organism involved. Costs associated with treatment of clinical cases include the cost of discarded milk, cost of the drug, and veterinary fees. However, the economic benefits are less easily recognized because the effect on future milk production, reduction in spread of infections within the herd, decreased chronicity of infection, and decreased culling rates are not obvious.

Therapy of Subclinical Mastitis: If antibiotic therapy is to make a significant contribution toward reducing the herd level of mastitis, it is necessary to treat subclinical infections as well as clinical cases. It is not unusual to have 15 to 40 subclinical cases for every clinical case. Generally, treatment of subclinical mastitis during lactation is indicated only when Strep. agalactiae is present, or the dairy producer is in danger of losing his milk market due to a high bulk tank SCC. Cure rates against Strep. agalactiae are usually in the range of 90 to 95%. Cure rates by other microorganisms during lactation will be approximately as follows: environmental streptococci = 40 to 50%; Staph. aureus = 20 to 30%; Staphylococcus species = 50 to 60%; coliforms = 0 to 10%; and Mycoplasma species, yeasts, and Nocardia species = 0%. The organism that is most likely to respond to lactation treatment is Strep. agalactiae. The conventional treatment of other subclinical infections in lactation, such as the environmental streptococci, coliforms, and Staph. aureus is generally not recommended because the cure rate may be as low as 10% and rarely exceeds 50%. Such infections are best treated at drying off or by using the novel treatment strategies discussed below.

THERAPY AT DRYING OFF

When all quarters of all cows are not treated at drying off, 8 to 12% of quarters may develop a new infection during the dry period. The prevention of only 1% of quarters from becoming infected will pay for the entire dry cow treatment program. In herds with a low level of mastitis, preventing new infections during the dry period is more important than curing existing infections. This is because an infected quarter treated at drying off and cured at calving will produce 90% of its potential milk production during the next lactation. However, a quarter that becomes infected during the dry period, or that remains infected from the previous lactation, will produce 30 to 40% less milk.

Treatment at drying off is important because dry cow therapy both cures existing infections caused mainly by contagious pathogens, and prevents the development of new infections caused mainly by environmental pathogens. Effectiveness of dry cow treatment is improved by the use of slow-release products that maintain effective levels of antibiotics for long periods in the nonlactating udder. Other advantages therapy include the following: the cure rate is higher than that during lactation, higher concentrations of long-acting antibiotics can be used, incidence of new infections during the dry period is reduced, damaged tissue is allowed to redevelop before freshening, clinical mastitis at freshening is reduced, salable milk is not contaminated with drug residues, all infected quarters are treated, and laboratory or screening tests are not required.

Improving the cure rate has been attempted by administering additional dry cow treatments 1 to 3 weeks after drying off. However, this procedure has not resulted in a higher cure rate and is not recommended. The teat end of a dry cow is very difficult, if not impossible, to adequately sanitize. Thus, multiple intramammary infusions over the dry period may result in mastitis-causing microorganisms being forced through the teat canal, and then has the potential for doing far more harm than good. Concern has been expressed about the possibility of routine dry cow therapy increasing the resistance of mastitis microorganisms to commonly used drugs. However, despite widespread use of dry cow therapy for three decades, there is no evidence of treatment-associated resistance to drugs.

Selective dry cow therapy may be applicable in herds with a very low level of contagious pathogens. This approach does, however, require knowledge of infection status prior to dry-off, which requires microbial culture and labor. In one study, no differences were found among SCC, clinical mastitis incidence, or time to occurrence of the first clinical episode of lactation between cows receiving total or selective therapy. However, milk yield in the early phase of the subsequent lactation was significantly greater in cows receiving total dry cow therapy.

TREATMENT PROCEDURES

The procedures used to administer intramammary treatments are critical to achieving desired results. For example, the teat end must be sanitized prior to infusion to minimize the number of bacteria present at the teat orifice after milking that could be carried into the teat canal via the infusion cannula. To accomplish this, the teat end must be scrubbed vigorously with a 70% alcohol pledget, usually supplied with commercial mastitis tubes, or with cotton balls soaked in 70% alcohol, and allowed to dry. It is recommended that gloves be worn when treating cows if highly contagious microorganisms, such as Strep. agalactiae or Mycoplasma bovis, are present in the herd. In addition, hands should be dipped in a sanitizing solution between treating animals.

The method of drug infusion can actually cause mastitis by inadvertently introducing microorganisms through the teat canal. Full insertion of the conventional mastitis tube syringe cannula can result in temporary dilation of the teat sphincter muscle. In addition, the keratin plug that normally occludes the teat canal, is either pushed aside or partially removed. Both of these situations create a larger than normal teat canal opening, allowing entry of microorganisms. The syringe cannula may also push microorganisms that are colonized in keratin into the teat cistern. If microorganisms gaining access to the teat cistern by these routes are resistant to the infused antibiotic, then a new infection may result, which may be more severe than the one for which treatment was intended.

Studies designed to compare conventional full insertion with partial insertion of only the first 2 to 3 millimeters of the cannula tip at drying off have demonstrated that mastitis at calving is reduced markedly by using the partial insertion technique (1). Several types of syringe cannulas have since been developed to aid in inserting only the tip of the cannula into the teat canal and to form a seal against the teal opening to provide support during infusion. Use of the partial insertion technique may reduce new infections by major mastitis-causing microorganisms at calving by 50% or more.

Treated animals must be clearly identified in some obvious manner with neck chains or leg bands. In addition, they should be kept separate from untreated animals to aid in preventing their milk from being commingled with milk from untreated animals.

REASONS FOR TREATMENT FAILURES

Treatment failures may be due to delayed treatment, poor selection of drugs or dose levels, stopping treatment too soon, resistance of organisms to drugs, development of bacterial L-forms, protection of bacteria within white blood cells, and presence of deep-seated infections that are walled off by scar tissue, clots, and swelling. A characteristic of inflammation is the formation of inflammatory materials within the mammary gland composed of tissue debris, white blood cells, microorganisms, fibrin, and other blood components that occlude milk ducts draining areas of milk-secreting tissue. Presence of these materials contributes to treatment failures because they impede the diffusion of antibiotics within the treated quarter (7).

NEW TREATMENT STRATEGIES

The purpose of intramammary therapy is to help the cow's natural defenses eliminate the infecting microorganisms. However, most preparations have been designed with little attention to the natural defense mechanisms of the udder and how they influence the effectiveness of antibiotic therapy. The lack of success in curing chronic intramammary infections, particularly those caused by Staph. aureus, has prompted a reevaluation of treatment strategies.

Infections are frequently refractory to intramammary therapy because of the inaccessibility of microorganism due to scar tissue, swelling, and blockage of milk ducts as stated above. Thus, the most effective therapeutic method for treating infections may be systemic administration to reach deep tissue areas of infection because antibiotics can move from the blood into mammary tissue when combined with intramammary infusion. Various treatment methods have been researched in attempts to increase cure rates, and include combination therapy in which cows are treated simultaneously in the udder as well as systemically with compatible drugs, as well as extended therapy in which infected quarters are treated for a longer period of time.

Combination Therapy: A combination of intramuscular injections, together with intramammary infusions has resulted in much higher tissue antibiotic concentrations and a higher cure rate (9). In one study, 49 cows with 78 subclinically infected Staph. aureus quarters were tested. One group of cows received intramammary infusion at each milking for six milkings with a lactating cow product containing 62.5 mg amoxicillin. Another group of cows received the same intramammary infusion regimen plus intramuscular injections of 6 million units of procaine penicillin G after each milking for 3 days.

The combination of intramammary and intramuscular treatment cured 51% of quarters compared with 25% of quarters for intramammary infusion alone. Thus, combination therapy was twice as effective as conventional infusion alone, and allowed more antibiotic to penetrate deep areas of infection, increasing the cure rate. The SCC taken prior to initiation of therapy from milk of cured quarters averaged 2,500,000/ml and was lower than from failed quarters (4,000,000/ml). By 8 days after treatment, SCC for cured quarters was 340,000/ml compared with 1,900,000/ml for failed quarters, and at 21 days, SCC were 224,000/ml for cured and 1,975,000/ml for failed quarters.

Extended Therapy: Another alternative for enhancing cure rates when treating chronic infections involves the use of pirlimycin hydrochloride and is called extended therapy. Pirlimycin has excellent activity against Staph. aureus and it penetrates scar tissue quite well; 50% of the drug is absorbed from the udder into the bloodstream and 50% of that amount is then reexcreted back into the udder, thus aiding the drug in reaching infected tissues.

A treatment protocol using three series of on-label treatments, separated by 36-hour milk discard periods, was developed (8). Milk was saleable for human consumption 36 hours following the third series of treatments. In one investigation using the three-treatment regimen, the drug was administered to quarters that had failed repeated therapy attempts. Results showed that 41% of quarters were cured. In a second study using a commercial dairy herd in which extensive treatment of subclinical Staph. aureus infections had not been practiced during lactation, 86% of quarters were cured. The SCC were monitored in the infected quarters in both experiments and a decrease from 3,400,000 to 280,000/ml was observed. Whether or not the use of other drugs in such a treatment regimen will also yield higher cure rates has not been determined.

Combining Antibiotic Therapy with Vaccination: More recently, vaccination has been employed to amplify the cow's immune system against Staph. aureus antigens and augment the effectiveness of antibiotic therapy. In one study (11), vaccination in combination with intramammary therapy was evaluated over a 1-year period in 48-cow herd with a Staph. aureus prevalence of 58.3% of cows. After selected Staph. aureus cows were dried off or culled, 20 animals were vaccinated at 2 and at 14 days prior to antibiotic therapy. Vaccinations were subcutaneous in the area of the supramammary lymph node with a bacterin containing an encapsulated strain of Staph. aureus plus an autogenous strain isolated from the herd. Each cow was then treated using extended therapy with pirlimycin and vaccinated again 7 days later. All but 3 quarters responded to this vaccine/treatment program, and by 5 months after trial initiation, Staph. aureus was eliminated from the herd. The herd SCC was reduced from 492 x 10³/ml 1 year later. All herds would not be expected to exhibit this degree of success, but this strategy may be extremely useful to certain Staph. aureus herds.

No matter what treatment strategy is used, the probability of curing existing infections is reduced under the following conditions: older cows, high SCC, rear quarters are infected, cows in early to mid-lactation, and presence of multiple quarter infections. Because of the low probability of cure, it is important for dairy producers and veterinarians to use great care in selecting Staph. aureus-infected cows for treatment in lactation.

PERMANENT DRY-OFF OF QUARTERS WITH REFRACTORY INFECTIONS

A procedure for salvaging genetically superior animals with refractory infections (Nocardia, Arcanabacterium, and Pseudomonas species) for future production is to treat infected quarters with 2% chlorhexidine diacetate (2). The method involves infusing 60 ml of chlorhexidine into the quarter, milking the quarter out at the next milking, and reinfusing the quarter a second time at 24 hours. All milking of the infused quarter should be discontinued for the life of the cow. Secretory activity of the treated quarter will cease within 14 to 63 days, and it will become nonfunctional; adjacent quarters are not affected. In addition, such quarters no longer constitute a reservoir for mastitis-causing organisms. Treated quarters must be identified in a manner to insure that they are not milked to avoid the presence of chemical residues in herd milk. Three other procedures that have reported to be effective include 20 ml of tincture of iodine infused one time, 60 ml of 3% silver nitrate infused twice at 48-hour intervals, and 80 ml of 3% phenolic acid infused one time.

SUPPORTIVE THERAPY AND NURSING CARE

The provision of fresh drinking water, high quality hay, and a comfortable environment is important in hastening recovery from clinical mastitis. Also, frequent hand stripping of affected quarters aids in removing toxic substances resulting from infection. Use of the milk letdown hormone, oxytocin, facilitates complete removal of milk, debris, and toxins. In instances where gangrene develops, surgical removal of the teat may facilitate drainage of toxic materials and increase the chances of salvaging the cow.

Clean, dry, bedding in an environment that is well ventilated is desirable. If corticosteroids are used as adjunct therapy, the chances of a subsequent bacteremia are increased; therefore, extreme caution in the use of these compounds should be exercised. Some cows may become hypocalcemic during the course of the disease. Careful administration of calcium solutions may be undertaken if serum biochemistry values warrant such therapeutic measures. These cows are very susceptible to cardiac arrhythmias, cardiac failure, and death if calcium is administered too rapidly or when not indicated.

Daily production, appearance of milk, and water and feed intake should be monitored and recorded to assess the cow's progress. Cows with severe clinical cases will experience additional undesirable stress, if for example, temperature extremes exist in the hospital environment. Thus, cow comfort is of utmost importance.

AVOIDING DRUG RESIDUES

Antibiotics are an essential tool for disease management in food animals; healthier animals means safer food, which translates to healthier consumers. Because milk is universally produced and widely used in a variety of food products, it is targeted for special monitoring. Every effort must be made to ensure that milk products and meat are free of drug residues because some humans are very sensitive to certain drugs.

Most dairy farmers are very conscientious about taking all possible precautions to avoid drug residues, especially from cows treated for mastitis. It must be remembered, however, that intramuscular injections, uterine boluses, and antibiotics in feed may also produce antibiotic residues in milk. This is further compounded by the fact that the withdrawal time for such products is often longer than that for intramammary infusions. To avoid detectable residues in milk, it is imperative that label instructions be followed exactly.

Treated cows should be kept separate, and should be clearly marked in an appropriate manner. Written records should also be kept of all treated cows, and can help in making culling decisions for problem cows with chronic mastitis. Farmers should also give serious consideration to obtaining the necessary materials for conducting drug residue tests on their own farm. It also is important that treated animals not be sold for slaughter until the drug withdrawal time for meat has elapsed.

ANTIBIOTIC RESISTANCE TESTING

The primary concern about antibiotic resistance is based on the fear that resistant strains of bacteria will be transferred to humans as a result of improper handling. However, no conclusive data have been forthcoming to link antibiotic use in animals with a documented treatment failure in humans. It may also be argued that limiting drug usage on farms may actually contribute to an increase in drug resistance. In fact, drug resistance is more prevalent in less-developed countries than in developed countries where drug use is more common. The annual culling rate on traditional dairy farms that use antibiotics as part of their animal health program is 30% compared with 50 to 60% on organic dairy farms that do not use antibiotics.

If cure rates appear particularly low when treating clinical or subclinical mastitis, it is possible that the infecting microorganisms are resistant to the antibiotic being infused. For example, Staph. aureus is often resistant to penicillin; thus, other antibiotics need to be considered. In such instances, it is advisable to collect milk samples from infected quarters or the bulk milk tank for culture. The diagnostic laboratory or herd veterinarian will then isolate specific microorganisms and test them against a spectrum of antibiotics to determine the ones to which the microorganisms are susceptible or resistant. The most widely used technique is the plate-disc method developed by Kirby-Bauer. Microorganisms resistant in the laboratory can be assumed to be unresponsive to treatment with that antibiotic.

Microorganisms susceptible to an antibiotic in the laboratory may resist the drug in the udder for the following reasons: bacteria may be protected from the antibiotic by the inflammatory process, antibiotic concentrations at the sites of the infection may be too low or too transient, the acidity of the mammary secretion may be such that it renders the antibiotic ineffective, the antibiotic may be bound by proteins in the quarter, the antibiotic may have been combined with another antibiotic rendering it inactive, bacterial growth may be slowed by conditions existing in secretions and the antibiotic may require rapid bacterial growth to be effective, and certain elements such as physiologic concentrations of calcium can antagonize the activity of some antibiotics.

USE OF CORTICOSTEROIDS

Use of anti-inflammatory products can be helpful in management of toxemia, udder edema, tissue inflammation, and mediator-induced shock. Unfortunately, some anti-inflammatory products cause suppression of the immune system and other undesired side effects. In most acute inflammatory disease conditions, such as acute coliform mastitis, the short- and intermediate-acting corticosteroids can be administered for no longer than 2 or 3 days to show positive results. This group includes cortisone, prednisone, prednisolone, methylprednisolone, and isofluprednone.

There are some situations, such as late gestation, when corticosteroid use is not indicated, regardless of how short-acting the product may be. Administration to animals during the last 3 months of pregnancy may also induce premature calving, followed by retained placenta and infection of the uterus. Such drugs do, however, aid in reducing swelling and pain and enhance the removal of toxic secretions as well as promote better diffusion of intramammary infusions. In bacteria-induced conditions accompanied by edema, inflammation, and/or shock, short-acting corticosteroids can provide safe and effective therapy. It must be noted, however, that overdosing with even a short-acting product can produce the same undesirable side effects as long-acting products.

OXYTOCIN THERAPY

Oxytocin is naturally released from the brain into the bloodstream in response to the stimuli associated with milking. This milk letdown hormone causes contraction of the milk-producing alveoli within the mammary gland, resulting in the expulsion of milk. It is believed that administrating exogenous oxytocin further flushes residual bacteria-laden fluid after milking, which may aid in eliminating the infection. In addition, inflammatory by-products and bacterial toxins are removed. Similarly, evacuation of milk actually stimulates the production of more milk, enhances leukocyte movement into the quarter, and activates other antimicrobial components.

Commonly, veterinarians recommend frequent stripping of affected quarters (six times a day) following oxytocin administration (40 to 50 units intramuscularly). This may be accompanied by supportive therapy using aspirin or banamine. Cows usually recover from clinical symptoms within 24 to 48 hours. In one study, oxytocin was injected intramuscularly at 100 units every 12 hours for two or three milkings in attempts to treat clinical mastitis cases. The clinical cure rate (return of the quarter and the milk to normal by 20 days) was about 70%, but the bacteriologic cure rate (absence of the infecting microorganism by day 20) was 49%. This cure rate is similar to that observed after treatment with most antibiotics; however, use of oxytocin does not result in the potential contamination of milk with antibiotic residues, has no withdrawal time, and is less costly. However, as discussed below, relapses can occur.

Veterinarians in California compared the economic benefits of three different treatment regimens (5). Cows with mild clinical mastitis were assigned to one of three treatment groups: 1) treatment with 62.5 mg of intramammary amoxicillin every 12 hours for three milkings, 2) treatment with 200 mg of intramammary cephapirin every 12 hours for two milkings, and 3) treatment intramuscularly with 100 units of oxytocin every 12 hours for three milkings. Clinical and bacteriologic cure rates were similar among the three groups of animals. However, there was not an economic advantage to oxytocin treatment due to the longer time required for milk from animals in this group to return to normal. This problem was further compounded by the fact that there was a higher relapse rate among the oxytocin-treated cows (41%). Moreover, 65% of cows treated with oxytocin experienced at least one additional case of clinical mastitis during the remainder of lactation. Many of the relapses (38%) and additional clinical cases (69%) were caused by environmental streptococci. Oxytocin treatment may be cost effective for herds in which coliforms cause a majority of clinical cases and in which environmental streptococci are a minor problem.

Another study was conducted in England to compare effectiveness of treating Streptococcus uberis mastitis with oxytocin versus antibiotics (6). The comparison was made following detection of clinical mastitis by 1) changes in electrical conductivity, or 2) detection after appearance of clinical symptoms. When the developing disease was treated with antibiotics based on changes in electrical conductivity, clinical mastitis was prevented and all infections were eliminated. Treatment included intramammary administration of antibiotic at each milking for 3 days. Treatment of cows with 20 IU of oxytocin for six successive milkings that were predicted to develop disease eliminated 25% of infections, but 75% of the cows developed clinical mastitis.

OTHER NONANTIBIOTIC APPROACHES TO TREATMENT

Use of hypertonic (7.2%) saline has been used to alleviate clinical symptoms. Practitioners recommend that 2 ml/45 kg of body weight be injected intravenously. In addition, 500 to 1000 ml can be infused intramammarily. This is performed one time after each milking for 2 to 3 days. A 50 to 60% clearing of clinical symptoms is observed in some cases; however, it is likely that the spontaneous cure rate will be very similar. This saline solution draws water into the mammary gland and dilutes bacteria and their toxins, helping to facilitate their removal during milking. In addition, use of saline creates profuse thirst in animals, thereby promoting even greater water intake.

Another trial studied the effects of treating clinical mastitis with intramammary infusions of either a Lactobacillus (probiotic) or an antibiotic (cephapirin) preparation (4). The majority of pathogens isolated were Gram-negative bacilli and environmental streptococci. Treatment of quarters with Lactobacillus cured 21.7% of infected quarters compared with a 73.7% cure rate after infusion with cephapirin.

HOMEOPATHIC TREATMENT OF MASTITIS

Homeopathy can be defined as a specific stimulating therapy that activates the host defense mechanisms. In theory, a toxic dose of any substance that causes clinical symptoms in a healthy animal can be used to prepare a homeopathic remedy to cure diseased animals that show similar symptoms. The precise method of action of homeopathics has not been determined, but they are prepared from a variety of plant, animal, and mineral sources. Homeopathics are prepared by a series of dilutions that renders toxic substances safe to use. A review of literature on use of homeopathic medicine indicates that there are no conclusive data to justify its use for treatment of mastitis. When homeopathic remedies were routinely applied to dairy cows on an individual basis during both lactating and nonlactating periods, there was no effect on either the SCC or level of intramammary infection.

SUMMARY

Drug therapy is usually recommended for the elimination of existing intramammary infections as spontaneous recovery and culling have limited application. Treatment during lactation is recommended when cows are infected with Strep. agalactiae, when the herd SCC is greater than 400,000/ ml, and when clinical mastitis is present. Most cases of subacute clinical mastitis can be treated with an approved intramammary infusion product for a minimum of 3 days accompanied by frequent stripping to remove secretions, bacteria, and cellular debris. However, a true cure, whereby all infecting microorganisms are eliminated occurs in less than 50% of cases for most bacterial species. Treatment of subclinical infections using conventional intramammary infusion during lactation is quite successful against Strep. agalactiae. Chronic Staph. aureus infections are best treated using a combination of intramammary infusion with parenteral drug administration, with extended therapy, or by combining antibiotic therapy with vaccination. Infected quarters are best treated with antibiotics at drying off, at which time the cure rate is much greater than that found during lactation. Whether cows are treated during lactation or at dry-off, proper teat end sanitization and infusion procedures must be followed. Alternatives to antibiotics have been attempted to eliminate infections; however, any success using oxytocin, probiotics, or homeopathics has not been documented.

REFERENCES

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3. Erskine, R. J., J. H. Kirk, J. W. Tyler, and F. J. DeGraves. 1993. Advances in the therapy for mastitis. Vet. Clin. North Am. Food Anim. Pract. 9:499-517.

4. Greene, W. A., A. M. Gano, K. L. Smith, J. S. Hogan, and D. A. Todhunter. 1991. Comparison of probiotic and antibiotic intramammary therapy of cattle with elevated somatic cell counts. J. Dairy Sci. 74:2976-2981.

5. Guterbock, W. M., A. L. Van Eenennaam, R. J. Anderson, I. A. Gardner, J. S. Cullor, and C. A. Holmberg. 1993. Efficacy of intramammary antibiotic therapy for treatment of clinical mastitis caused by environmental pathogens. J. Dairy Sci. 76:3437-3444.

6. Hillerton, J. E., and J. E. Semmens. 1999. Comparison of treatment of mastitis by oxytocin or antibiotics following detection according to changes in milk electrical conductivity prior to visible signs. J. Dairy Sci. 82:93-98.

7. Nickerson, S. C. 1996. Clinical mastitis: to treat or not to treat. Pages 355-377 in Proc. Western Canadian Dairy Seminar. Volume 8. Red Deer, Alberta.

8. Owens, W. E., C. H. Ray, R. L. Boddie, N. T. Boddie, C. A. Pratt, S. C. Nickerson, J. W. Hallberg, and A. P. Belchner. 1995. Efficacy of sequential pirlimycin intramammary treatment against chronic Staph. aureus intramammary infection. Pages 144-145 in Proc. 34th Annu. Meet. Natl. Mastitis Counc., Fort Worth, TX. Natl. Mastitis Counc., Inc. Madison, WI.

9. Owens, W. E., J. L. Watts, R. L. Boddie, and S. C. Nickerson. 1988. Antibiotic treatment of mastitis: comparison of intramammary and intramammary plus intramuscular therapies. J. Dairy Sci. 71:3143-3147.

10. Philpot, W. N., and S. C. Nickerson. 1992. Mastitis: Counter Attack. Babson Bros. Co., Naperville, IL. 150 pp.

11. Sears, P. M., and A. P. Belschner. 1999. Alternative management and economic consideration in Staphylococcus aureus elimination programs. Pages 86-95 in Proc 38th Annu. Meet. Natl. Mastitis Counc., Arlington, VA. Natl. Mastitis Counc., Inc. Madison, WI.