Herd-level milk drop, a CMT-positive quarter and an antibiotic notice
A dairy farmer in Nadia milks eight crossbred cows (HF × Jersey) twice a day and sells to the village cooperative, which pays on fat and SNF. Average yield has fallen from 12.0 to 9.0 litres/day over the past three weeks; herd fat has slipped from 4.1% to 3.4%. Two cows calved 50 and 55 days ago. One of them has a hard right hind quarter, milk that looks normal on stripping, and a CMT score of 2 (++). Feed is 10 kg paddy straw, 1 kg rice bran and free grazing on a dry stubble field; there is no green fodder because the berseem field failed, and no mineral mixture has been fed for four months. Ambient temperature has been 38-40°C. The cooperative has just issued a notice that milk from any animal treated with intramammary antibiotic must be withheld for 96 hours. A private buyer offers a flat ₹36 per litre, collects from the gate, and does not ask questions.
1. Rank the likely causes of the fall in yield and fat, and name the one measurement that will separate the infectious from the nutritional explanation fastest.
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Ranked causes
- Energy deficit - the largest single factor. Rough TDN intake: 10 kg straw × 0.90 DM × 0.40 = 3.6 kg; 1 kg rice bran ≈ 0.6 kg; dry stubble grazing ≈ negligible. Total ≈ 4.2 kg TDN. A 400 kg cow giving 10 L needs about 3.0 + (0.32 × 10) ≈ 6.2 kg TDN, so she is roughly 2 kg TDN short - enough to cut yield by 2–3 L and to depress fat synthesis.
- Heat stress. At 38–40°C the THI is well above 80; intake falls, rumination time falls and the cow diverts energy to dissipating heat.
- Subclinical mastitis in at least one quarter (hard quarter, CMT 2). This explains part of the yield loss in that cow and a local fall in fat and casein, but not the herd-wide 3 L drop.
- Mineral deficiency after four months without a mineral mixture - low Zn, Cu, Se and P depress intake, fertility and udder defence.
Fastest separator: quarter-level CMT plus somatic cell count on all eight cows. If only one or two cows are positive, the herd drop is nutritional and thermal; if most are positive, udder health and milking hygiene become the lead explanation.
2. Rebuild the ration for a 400 kg cow yielding 10 litres using feeds he can buy locally, and show that it meets TDN and CP.
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Target: about 6.2 kg TDN and 0.95–1.1 kg CP per day, plus 50 g mineral mixture and 40 g salt; green fodder restored to 20 kg.
| Feed | Quantity | TDN (kg) | CP (kg) |
|---|---|---|---|
| Green fodder (maize/hybrid napier) | 20 kg | 2.40 | 0.40 |
| Paddy straw | 4 kg | 1.44 | 0.14 |
| Maize grain | 3 kg | 2.10 | 0.27 |
| Mustard cake | 1 kg | 0.60 | 0.30 |
| Mineral mixture + salt | 50 g + 40 g | - | - |
| Total | ≈ 6.54 | ≈ 1.11 |
Reasoning
- Straw is cut from 10 kg to 4 kg because it fills the rumen at 40% TDN and caps intake; the space is given to green fodder, which is cheap energy and supplies carotene.
- Maize supplies the fermentable energy the herd is short of; mustard cake covers protein and is cheaper per kg CP than extra rice bran.
- Rice bran is dropped to avoid a high-fat, poor-quality concentrate that goes rancid in summer.
- Feed the concentrate in three or four small meals, and offer the major meal after milking and in the cooler part of the day to limit heat-stress depression of intake.
- Recheck body condition after 21 days; if yield crosses 12 L, add 1 kg concentrate per 2.5 L of extra milk.
3. How should he handle the antibiotic treatment, the 96-hour withholding and the private buyer's flat ₹36 offer?
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Treatment and withholding
- Get a veterinarian to confirm the quarter and select the intramammary preparation; strip the affected quarter before treatment and milk the cow last, or with a separate cluster.
- Withhold all milk from the treated cow for at least 96 hours from the last dose - longer if the product label says so. Mark the cow with coloured leg tape and write the treatment and release date on a board, because the commonest residue failure is a forgotten release date.
- Discard the withheld milk - do not feed it to calves without veterinary clearance, and never pool it with saleable milk.
The private buyer offer
- The cooperative price is fat-linked; at 3.4% fat his current cooperative realization is roughly ₹30–31/L, so ₹36 looks about ₹5/L better. But selling withheld milk into an unmonitored channel is a food-safety violation with residue risk to consumers and would cost him cooperative membership and reputation.
- Over 96 hours, one cow at about 8 L/day means roughly 32 L withheld, an immediate loss of about ₹1,000. That is small against the penalty risk and against losing the cooperative's SNF bonus and veterinary support.
- Use the private offer only for legitimately saleable milk and only if the price, after accounting for the fat-based cooperative premium, genuinely stays higher; keep the cooperative as the base buyer.