American Association of Bovine Practitioners
Guidelines for Therapy of Clinical Mastitis in Lactating Dairy CowsThe immediate goal of the producer to return the quarter and the milk to clinically normal. Secondary goals are to eliminate mastitis-causing organisms from the quarter, to prevent further damage to the milk-secreting tissue, to help sustain future milk production by the cow and to lower the somatic cell count (SCC). This must be done in a cost-effective manner, without causing drug residues in milk or meat. The role of the veterinarian is to design rational treatment protocols that help cows recover, improve the owners net profit and protect the consumer from violative drug residues.
Most clinical mastitis is treated by dairy producers or their employees. Treatment protocols for use by non-veterinarians must be based on products labeled for therapy of mastitis. Treatments using extra-label drugs should be recommended only when no on-label alternatives exist, or when the veterinarian can document that the available on-label drugs are ineffective.
Mastitis management must focus on prevention. Therapy of CM should be part of an udder health program that includes milking hygiene, management of the cows’ environment, milking equipment evaluation and maintenance, evaluation of milking technique, appropriate immunizations and a culling protocol.
The veterinarian’s recommendations for therapy must be based on knowledge of the likely etiology for each herd, based on recent culture results. Severity of clinical signs and the appearance of the milk are not reliable evidence of etiology. Coliform mastitis, for example, can be mild and chronic or peracute and severe. Therapy of a given cow often begins before her culture results can be known. However, a treatment protocol can be designed based on the known pattern of pathogens involved in the etiology of CM on the farm. This may be done by culturing pretreatment milk samples from cows with CM or a high SCC. Bulk tank milk microbiology is of value when Streptococcus agalactiae, Staphylococcus aureus or Myco plasma sp. are present, but not for the diagnosis of CM caused by environmental pathogens. Antibiotic susceptibility testing should not be done on bulk tank or pooled milk samples. The relationship between antibiotic susceptibility testing of isolates from CM cases and outcome of therapy has not been established.
Good records are a prerequisite for an effective therapy program and are needed to document residue prevention efforts. It is especially useful to know the cow’s past history of mastitis problems. The AABP Mastitis Committee has designed a set of forms for on-farm use, suitable for copying and distribution by veterinarians. These are available from the Milk and Dairy Beef Quality Assurance Program and Pharmacia & Upjohn Animal Health.
Treatment should be undertaken only if it is likely to be profitable. The profitability of therapy depends on the likely etiologic agent, the cow’s age, past mastitis history, past production history, past success of available treatments, stage of lactation, state of pregnancy, value of the cow as a cull, price and availability of replacement animals, other medical problems and goals of the owner. Clearly, there is no point in treating an old open cow with a poor production record and an extensive history of udder problems. Treatment of a healthy, young cow in early lactation with no prior mastitis history is more likely to have a profitable outcome.
Hopeless cases should not be treated. Mastitis caused by NAycoplasvna sp., Serratia sp., Pseudomonas sp., Arcanobacterium sp. (formerly Actinomyces sp.), Nocardia sp., Prototheca sp., Mycobacterium sp., yeasts, fungi and most other unusual pathogens is refractory to all known therapy. Mastitis caused by Staphylococcus aureus is refractory to treatment in most cows.
A protocol is needed for cows that repeatedly get CM. Treatments that have been shown to be ineffective need not be repeated. After three or four episodes, these cows either should be allowed to recover without treatment, sold or the affected quarter dried off. In many herds a large proportion of the discarded milk results from mastitis in a few repeat offenders.
Untested combinations of extra-label products should not be formulated. There is no scientific evidence for their efficacy and safety, withdrawal times generally are unknown and their formulation for sale is illegal. Multidose containers should never be used because of the risk of contamination with resistant organisms such as Mycoplasma and yeast.
Antibiotics are unlikely to be of benefit in CM caused by gram-negative organisms. Thorough milkout with supportive therapy, possibly including anti-inflammatory drugs, should be the basis of treatment. Severely ill cows may benefit from systemic antibiotics.
Clinical mastitis should be classified according to severity. Severe mastitis, where the cow is depressed and off feed, should be treated with supportive therapy aimed at counteracting the effects of endotoxin through the use of treatments such as fluids, calcium, hypertonic saline, anti-inflammatory drugs and complete and frequent milkout of the affected quarter(s). Studies have shown that antibiotics make little difference in the outcome of severe coliform mastitis. Intramammary antibiotics are poorly distributed in a severely swollen gland. Successful treatment of these cows may require veterinary intervention and should at least follow a protocol established in consultation with the herd veterinarian.
Clinical mastitis caused by Streptococcus agalactiae should be treated with approved intramammary antibiotics. Clinical mastitis caused by Staphylococcus aureus can be treated with intramammary antibiotics to reduce clinical signs, but few cows will be cured during lactation.
Mild CM in herds with no history of mastitis caused by S. agalactiae may be allowed to recover with no antibiotic therapy, relying only on complete milkout, perhaps with the aid of oxytocin injections.
Intermediate cases caused by gram-positive organisms may benefit from intramammary antibiotics or a combination of intramammary and systemic antibiotics. Antibiotics approved for systemic use in lactating cows may not cross the blood-milk barrier in therapeutic concentrations. Anti-inflammatory therapy may be used to reduce udder swelling and to help cows feel better.
Even in the absence of definitive data regarding the efficacy of therapy
for clinical mastitis, veterinarians can help their clients design rational
treatment protocols that limit antibiotic use to the cases most likely
to benefit from them.