Bulk Milk Cell Count Penalty on a Growing Farm
On a 22-cow crossbred farm near Guwahati, bulk milk somatic cell count has risen from 280,000 to 760,000 cells/mL in six weeks, and standard plate count from 80,000 to 250,000 cfu/mL. The farm sends 480 L/day to the cooperative, which pays a base price of Rs 34/L and deducts Rs 2/L when somatic cell count exceeds 500,000. The milker says teat dip ran out three weeks ago and is using plain water; bedding in the loose shed is damp; the water supply is intermittent. Two cows show a California Mastitis Test score of 3 in the left hind quarter, but their milk looks normal in the bulk tank. The farm has a plate cooler but no thermometer record, and the bulk tank is washed only on alternate days.
1. Calculate the immediate daily and monthly penalty, then rank the likely causes of the rise in somatic cell count and plate count. Justify the order of corrective actions.
Read the worked answer
Immediate loss: 480 L/day × Rs 2/L = Rs 960/day; over 30 days = Rs 28,800. This is a direct penalty and does not include possible rejection or lower shelf life.
Likely causes, ranked
- Subclinical mastitis spreading in the herd. The two CMT score 3 quarters show active infection; bulk tank milk dilutes their milk, so visible normality is misleading. Post-milking teat dip stopping three weeks ago is a strong contributor.
- Milking hygiene and water. Plain water is not a disinfectant teat dip; intermittent water makes udder washing and hand hygiene unreliable.
- Damp bedding and environmental contamination. Wet bedding raises teat-end exposure to environmental bacteria and increases plate count.
- Bulk tank cleaning and cooling records. Alternate-day washing and no thermometer record allow bacterial growth and biofilm, raising standard plate count.
Corrective action order
- First, start an approved post-milking teat dip immediately and use single-use paper towels; pre-dip dirty quarters.
- Second, identify and segregate or treat the two high-CMT cows under veterinary advice; milk them last.
- Third, dry the bedding, improve drainage and restore reliable water.
- Fourth, wash and sanitise the bulk tank daily and record wash temperature and milk cooling temperature.
Reasoning: The CMT result and the timing of the dip shortage point to a contagious mastitis problem. Fixing milking routine first reduces new infections; fixing the tank only improves the plate count, not the somatic cell count. Both must be corrected because they affect different tests.
2. Design a four-week monitoring plan with measurable targets and state when the farm should treat, cull or seek veterinary investigation.
Read the worked answer
Week 1 - establish baseline
- Test all 22 cows by CMT; record each quarter.
- Sample bulk milk for somatic cell count and standard plate count.
- Collect composite milk samples from CMT-positive cows for culture and sensitivity before treatment.
- Record teat dip use, tank wash temperature and milk temperature twice daily.
Weeks 2–4 - monitor and act
- Weekly bulk somatic cell count target: below 400,000 cells/mL by week 4; below 250,000 by week 8.
- Weekly standard plate count target: below 100,000 cfu/mL.
- Daily clinical mastitis check; record clots, heat, swelling and milk yield.
- Re-check CMT-positive cows at week 2 and week 4.
Decision rules
- Treat a clinically affected quarter or a CMT-positive cow with a positive culture, using the veterinarian’s sensitivity result. Do not treat all cows blindly.
- Segregate treated cows and discard milk according to the withdrawal period.
- Cull a cow with the same quarter infected in two consecutive lactations, or a chronic high-CMT cow that does not respond and is spreading infection.
- Seek veterinary investigation if somatic cell count is still above 500,000 after four weeks of correct milking hygiene, or if plate count remains above 250,000 despite daily tank washing and cooling records.
Judgement point: The farm should not chase the bulk tank number alone. It must connect cow-level CMT and culture results to the milking routine, then use the four-week targets to decide whether the problem is management, equipment or chronic carrier cows.