Mastitis in Dairy Cows: Causes and Prevention
Mastitis is the leading cause of loss in Delta dairy herds, not because it usually kills the cow but because it quietly steals milk. Subclinical cases show no visible signs, yet they raise the somatic cell count, cut the price paid by the dairy, and over time become chronic and destroy the quarter. The gap between a farm milking 22 litres and one milking 16 from the same breed is usually not feed but milking hygiene and udder health.
Types of mastitis and where infection starts
Mastitis is divided into contagious infection passed from cow to cow at milking, and environmental infection that comes from bedding, soil and water. The contagious form is slower and milder but becomes chronic, led by Staphylococcus aureus and Streptococcus agalactiae, while the environmental form appears suddenly with high fever and a swollen quarter and may progress to sepsis. Knowing the type decides the prevention plan, because each needs different action.
Contributing factors are many: wet contaminated bedding, cracked teats, a milking machine with the wrong vacuum, overlong milking sessions and failure to dry teats after washing. Fat, high-yielding cows are more susceptible, and buffalo need shorter teats and lower vacuum settings. Any teat lesion is an open door for bacteria, which is why treating wounds matters as much as treating the infection.
How to detect subclinical mastitis
Clinical mastitis is easy to spot: clotted or watery milk, a red hot swollen quarter, feed refusal and fever. Subclinical cases are far more numerous and more dangerous because they are invisible in the bucket. The California Mastitis Test is the farmer simple tool: a sample from each quarter is mixed with reagent in a paddle and thickens as cell count rises. Run it monthly and record the quarter number to track progress.
Laboratory milk culture identifies the bacteria and guides antibiotic choice, while bulk tank somatic cell counts give a picture of the whole herd. For farms selling to processors, exceeding the limit means a direct price penalty or a rejected load. Early detection with CMT costs less than treating one clinical case, and far less than losing a whole quarter.
Treatment and withdrawal: what farmers must know
Treatment starts with frequent milking of the affected quarter and complete emptying, then an intramammary antibiotic chosen by the veterinarian from farm culture results, plus an anti-inflammatory to reduce swelling. Severe cases need systemic treatment and fluids, and a teat tube must never be used in a quarter with no infection because that breeds resistance. Preventive antibiotics are not given at random; the veterinary decision is the foundation.
The withdrawal period is a food safety matter, not a formality. Every antibiotic has a defined milk and meat withdrawal time, and milk produced during it is discarded and never added to the bulk tank, because a small volume contaminates the whole load and exposes the farm to penalties. Topical antiseptics such as gentian violet are used on teat wounds only under veterinary supervision, with general support from livestock vitamins.
Daily prevention in the milking parlour
Prevention begins before the machine goes on: wash teats with clean water, dry them with a single-use paper towel, and discard the first streams into a strip cup. After milking, dip teats in an approved antiseptic and leave the cow standing to eat roughage for half an hour so the teat canal closes. Cleaning the machine after every session and checking vacuum and liners every six months prevent many cases.
Clean dry bedding, good ventilation and lower shed humidity protect against the environmental type, and dry cow therapy reduces cases in the next lactation. Cows with repeated infection in the same quarter are gradually culled because they are a permanent source. Apply all of this with your veterinarian, and equip the parlour from medical supplies and our livestock and sheep.
- Wash and dry teats with a single-use paper towel before milking.
- Use a strip cup to discard the first streams of milk.
- Dip teats in antiseptic after milking and keep the cow standing for half an hour.
- Clean the machine after every session and check liners every six months.
- Run a CMT monthly and record which quarter is affected.
- Respect the withdrawal period and never add treated milk to the bulk tank.
Conclusion
Mastitis is managed with hygiene and routine testing, not antibiotics alone. Every pound spent on dry bedding, teat dip and a monthly CMT returns many times over in the milk you sell and protects quarters from permanent damage.
This article is general guidance and is not a substitute for examining your animal by a licensed veterinarian. In emergencies, contact your vet immediately.
