Subclinical Mastitis and Antibiotic Residue in a Freshly Calved Cow
A crossbred cow (HF x Sahiwal, 4th lactation) calved 18 days ago and yields 14 L/day. The milk appears normal, but the California Mastitis Test on the left hind quarter gives a 2+ reaction (thick gel), somatic cell count is 6.0 lakh/mL, and the quarter feels firm with a small clot on the strip cup. Rectal temperature is 38.8 C, appetite is normal, and rumen motility is 3 contractions per 2 minutes. She is fed 6 kg wheat straw, 4 kg concentrate (18% CP) and about 5 kg green fodder daily; body condition score is 2.5 and she has lost 25 kg since calving. The milk buyer tests every can for antibiotic residue and rejects the whole 200 L can, paying nothing, if it is positive. The farmer has oxytetracycline intramammary tubes and wants to treat for 3 days, then sell milk from day 2 because 'the cow is eating well and the milk looks fine'. Milking is by hand, teat dipping is not practised, and the shed floor stays wet.
1. Classify the mastitis, advise on treatment and milk withholding, and calculate the cost of discarding milk compared with a rejected can. Assume milk at Rs 35/L and a 4-day withdrawal after a 3-day treatment.
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Classification: CMT 2+, SCC 6.0 lakh/mL and a visible clot on the strip cup mean this is clinical mastitis of the left hind quarter, even though the milk looks normal in the bucket. Normal temperature and appetite indicate a mild, localised case with no systemic illness.
Treatment: Use the intramammary tube in the affected quarter after milking for the label course, and milk the quarter out frequently (3 times daily). A mild case may need an anti-inflammatory, but no systemic antibiotic is indicated while she is afebrile. Ideally take a sample for culture before the first tube; if the organism is resistant to oxytetracycline, change the product.
Withholding: Milk from all four quarters must be discarded during treatment and for the label withdrawal period, 4 days here. Selling on day 2 would leave residues and fail the buyer's test.
Cost: Discard 3 + 4 = 7 days x 14 L = 98 L x Rs 35 = Rs 3,430. A rejected 200 L can = 200 x 35 = Rs 7,000, plus loss of the buyer. Withholding is the cheaper and legal option. Record the dates and recheck CMT after 7 days.
2. Using the thumb rule of 2 kg concentrate for maintenance plus 1 kg for every 2.5 L of milk, assess the ration and explain how the negative energy balance affects udder health and milk yield.
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Requirement: Maintenance 2 kg + (14/2.5) = 5.6 kg, total about 7.6 kg concentrate/day. She receives 4 kg, a deficit of about 3.6 kg, while also eating 6 kg wheat straw, which is low in energy and protein and bulky.
Consequences: She has lost 25 kg in 18 days and is at BCS 2.5, clear evidence of negative energy balance. The cow mobilises body fat, milk yield peaks lower, and immune function declines, which raises the risk of mastitis and metritis. Protein supply is also short for 14 L, so milk protein and persistency suffer.
Correction: Increase concentrate gradually, by 0.5 kg every 2-3 days, to 7-8 kg; do not jump suddenly or rumen acidosis follows. Add 15-20 kg good green fodder, 200 g mineral mixture and 50 g salt daily, and 100-150 g bypass fat if she continues to lose weight. Feed 3-4 times a day and offer straw alongside, not alone.
Monitoring: Weigh or condition-score monthly; a cow losing weight after calving needs the ration corrected before production drops further.
3. Design a mastitis control plan for this shed. Which practices would you change first, and how would you handle the chronic quarter?
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The first changes are the ones that break the infection chain at milking and keep the environment dry.
Milking routine: Wash hands and use a clean, individual towel per cow; discard foremilk into a strip cup; use full-hand milking without overmilking; dip all teats in an approved iodine dip immediately after milking, when the teat canal is open. Milk healthy cows first and this cow last.
Environment: Concrete floor kept dry and sloped, clean bedding, no slurry around the standing area, and fly control, because flies carry mastitis organisms and the wet floor keeps teats contaminated.
Dry period and records: Treat all quarters at drying off after the last milking (dry cow therapy), and record CMT monthly to detect subclinical cases early. Cull or stop breeding from a quarter that stays CMT-positive after two treatments.
This cow: Recheck CMT 7 days after treatment. If the left hind quarter remains 2+ with clots and low yield in that quarter, it is becoming chronic; she can stay in the herd if the other quarters are clean, but she should not be kept for breeding. Do not use her milk until withdrawal is complete.