Mastitis is inflammation of the mammary gland, in the vast majority of cases caused by bacteria entering through the teat canal. It is the most widespread and economically damaging disease of dairy cattle, because it strikes on three fronts at once: milk quantity, milk quality, and the rate at which cows are culled prematurely.
Two forms, one of them invisible
The clinical form is visible: the milk changes (clots, discolouration, watery appearance), the affected quarter may be hot, swollen, and painful, and in severe cases the cow becomes febrile and off feed. In the subclinical form the milk looks normal and the udder feels normal, yet inflammation is present and yield falls silently. This hidden form is the more prevalent one and the source of the greatest losses in most herds.
Why does the distinction matter?
A clinical case is noticed and treated. A subclinical case is not, so the cow remains a source of infection for the rest of the herd during milking for months. Treating what you can see is therefore not enough; a routine screening programme is needed to reveal what you cannot.
Where does the infection come from?
Mastitis pathogens are practically classified into two groups, each demanding an entirely different prevention strategy:
- Contagious pathogens spread from cow to cow during milking via hands, clusters, and shared towels — chiefly Staphylococcus aureus and Streptococcus agalactiae. Control rests on milking hygiene, teat dipping, milking order, and segregating infected cows.
- Environmental pathogens live in bedding, manure, mud, and standing water — chiefly Escherichia coli and other streptococci. Control rests on dry, clean, well-ventilated lying areas, not on antibiotics.
Diagnosis before treatment
The first step at every milking is to strip the first squirts from each teat into a dark strip cup; clots and flakes show up clearly there long before the bulk tank's appearance changes. Subclinical cases are detected with a cow-side test that estimates somatic cell count, and by tracking somatic cell counts in bulk-tank reports and individual cow records.
But a clinical examination does not tell you which organism is involved. Culturing a milk sample from the affected quarter with susceptibility testing is what determines whether an antibiotic is useful at all and which one to choose. Without culture, drug selection is guesswork — a leading cause of both treatment failure and emerging resistance.
How to take a valid sample
Clean the teat end, swab it with alcohol and let it dry, discard the first two squirts, then fill the tube from the affected quarter alone, cap it immediately, and chill it. A contaminated sample yields a misleading culture that leads to the wrong treatment.
Treatment: when it helps and how it is given
The approved treatment for bacterial cases is intramammary antibiotics licensed for the purpose, given through the teat canal at the dose and duration stated on the label. In severe cases with systemic signs, the veterinarian adds systemic therapy, fluids, and non-steroidal anti-inflammatory drugs at their discretion.
Yet not every case of mastitis responds to antibiotics. Some — particularly chronic Staphylococcus aureus infections — cure at low rates no matter how long treatment continues, because the organism walls itself off inside udder tissue away from the drug. Some mild environmental cases resolve on their own. Hence the treatment decision is now built on culture results, cow age, and history rather than on habit.
Dry-period therapy
Dry-cow products are given at dry-off after the last milking; their aim is to clear infections accumulated during lactation and stop them carrying over to the next one. Modern practice has moved toward selective dry-cow therapy: antibiotics only for cows confirmed or suspected to be infected, with an internal teat sealant alone for the rest — which substantially reduces on-farm antibiotic consumption.
Milk withdrawal: the rule that is not bent
Every licensed udder product carries a milk withdrawal period and a meat withdrawal period on its label. The milk withdrawal is counted from the last dose given, not the first, and is measured in milkings or hours exactly as the label states. Milk from that period is separated and discarded; it does not enter the bulk tank and is not fed to calves destined for sale.
Four situations that extend withdrawal beyond the label
Increasing the dose, using extra tubes, extending the course, or using a product not licensed for dairy cows — each is extralabel use that voids the printed withdrawal. In these cases an extended withdrawal interval is set by the veterinarian by consulting specialist residue sources, never estimated from personal experience.
Remember that the treated quarter is not isolated from the rest of the udder as far as the laboratory is concerned: milk from all four quarters mixes in the tank, and a small amount from one cow is enough to contaminate the whole herd's tank and get the load rejected. The real loss is not one cow's milk but a farm's.
Prevention comes before all of this
- Clean and dry the teats with a separate towel for each cow before attaching the cluster; a shared towel is an excellent infection vehicle.
- Dip teats in an approved disinfectant immediately after every milking; the teat canal stays open for roughly half an hour afterwards.
- Keep cows standing after milking by offering feed, so the teat canal closes before it touches bedding.
- Maintain the milking machine, its vacuum level, and its pulsation; a faulty machine damages the teat end and opens the door to infection.
- Milk infected cows last, or dedicate a separate unit to them.
- Keep bedding dry, clean, and refreshed; this is the most effective measure against environmental pathogens.
Check the milk and meat withdrawal periods for the active substance you used before returning milk to the tank.
Calculate the withdrawal period