Late-summer feed deficit on a Waikato dairy platform
On a 110 ha effective Waikato dairy platform, 320 spring-calving Friesian-cross cows are averaging 1.7 kg MS/cow/day in late January. Pasture growth has fallen to 24 kg DM/ha/day and average pasture cover is 1,850 kg DM/ha, below the 2,000 kg DM/ha target. Herd demand is about 42 kg DM/ha/day. Cows are averaging body condition score 4.0 and dropping. Palm kernel expeller costs $380/t delivered and is 90% DM. The expected pasture response to nitrogen fertiliser is 8 kg DM/kg N at $1.10/kg N, but soil moisture is below 10% volumetric and no rain is forecast for 10 days. The bank has asked for a cashflow forecast, and the vet has warned that BCS below 3.5 will affect next season's reproduction.
1. Calculate the daily pasture DM deficit and the 30-day shortfall. Then evaluate two options-buying palm kernel expeller or drying off 40 cows-showing the feed and cost calculations. Assume a dry cow eats 10 kg DM/day and PKE is fed at 4 kg DM/cow/day.
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Daily deficit = (42 − 24) kg DM/ha/day × 110 ha = 1,980 kg DM/day. Over 30 days the shortfall is 1,980 × 30 = 59,400 kg DM.
PKE at 4 kg DM/cow/day supplies 4 × 320 = 1,280 kg DM/day. That leaves 700 kg DM/day. Fresh PKE needed = 700 ÷ 0.90 = 778 kg/day, costing 0.778 × $380 = $296/day, or $8,880 over 30 days. It closes only about two-thirds of the deficit, so pasture cover would still decline.
Drying off 40 cows: lactation demand per cow is 42 × 110 ÷ 320 = 14.4 kg DM/day. A dry cow eats 10 kg DM/day, so the saving is 4.4 × 40 = 176 kg DM/day-only 9% of the deficit. The milk sacrificed is 40 × 1.7 = 68 kg MS/day; at $6.50/kg MS that is $442/day, or $13,260 over 30 days. Drying off 40 cows is therefore expensive and does not solve the feed gap.
2. Recommend a 30-day plan and justify it using body condition, pasture cover, reproduction and cashflow.
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The plan should reduce demand and buy supplement together, because neither option alone closes a 1,980 kg DM/day gap. Priority is to dry off or cull the thinnest cows first-those below BCS 3.5-rather than a random 40. This protects reproduction and reduces risk of metabolic disease. Feed PKE at about 4 kg DM/cow/day to the milking herd and monitor pasture cover weekly; if cover falls below 1,800 kg DM/ha, increase PKE or dry off more cows. Do not graze below 1,700 kg DM/ha, because pasture recovery after rain depends on residual leaf area. The cashflow cost of PKE is about $8,900 for 30 days, which is cheaper than losing 68 kg MS/day from 40 cows. Present the bank with a feed budget showing the deficit narrowing as cows are dried off and rain arrives.
3. Explain why applying nitrogen fertiliser now is unlikely to be economic, using the response rate and soil moisture.
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The quoted response is 8 kg DM/kg N, so the fertiliser cost per kg DM is $1.10 ÷ 8 = $0.1375/kg DM-cheaper than PKE at $380 ÷ (1,000 × 0.90) = $0.422/kg DM. However, that response assumes adequate soil moisture. At below 10% volumetric moisture, urea cannot dissolve and roots cannot take up nitrogen, so the response approaches zero. Applying N now would add cost without feed and could increase nitrate loss when rain eventually arrives. The correct decision is to defer N until soil moisture and pasture growth indicate a likely response, and use PKE or reduced demand to manage the immediate deficit.