Cell color key:   Good surplus — forage exceeds need by >1 Mcal/day   Slight surplus   Minor deficit — within BCS buffer, no supplement   Moderate deficit — BCS draws down   Supplement needed — BCS floor reached
BCS color key:   ≥5.5 Good condition   5.2–5.5 Adequate   5.0–5.2 Watch closely   <5.0 Supplement floor — rebreeding risk

Zero supplement required. BCS draws down through early gestation (Jan-Feb), recovers strongly on spring flush (Apr-May), and returns to 5.58 just before next calving in October. Peak lactation hits fall when forage is still adequate. Best alignment of the four scenarios.

104 Mcal supplement needed Jan-Mar during mid/late gestation — a lower demand phase, making deficits more manageable. Peak lactation hits summer slump which is a challenge, but the cow is not at peak demand. Late gestation aligns with spring flush (Apr-May) which is a significant advantage. Rebreeds in September when BCS is recovering. Third best overall.

208 Mcal supplement needed — highest of all four scenarios. The critical problem: late gestation (highest non-lactation demand) falls in January and February, the two worst forage months of the year. This double penalty of high demand against lowest forage quality drives the large supplement requirement. Traditional and common but the worst energy alignment of any calving date examined.

116 Mcal supplement needed — second highest. Peak lactation hits January and February, the coldest months on the worst forage, causing rapid BCS decline. However total supplement is considerably less than March (116 vs 208 Mcal) because late gestation falls in October and November when forage is still moderate. Rebreeds in March coming off the winter lactation drain — timing is not ideal for conception.

Model basis: NRC Beef Cattle 2016 adjusted 5% for forage-efficient moderate-frame beef cow (NEm = 16.29 Mcal/day for 1,350 lb). Forage calibrated so October calving requires zero supplementation with BCS cycling naturally between 5.0–5.8. Spring forage 0.67–0.68, summer 0.52–0.57, fall 0.60–0.61, winter hay 0.51–0.53 Mcal/lb DM. 1 BCS unit = 440 Mcal stored energy. BCS gain capped at 0.20 units/month (realistic pasture rate). Milk pullback: cow reduces milk production when BCS drops below 5.0, protecting her own condition at the calf's expense. Cycle-end BCS is measured in the month immediately before next calving — the correct endpoint for comparing annual recovery across different calving dates. Known limitations of this first-pass model: heat stress penalty not included (disadvantages June calving further), breed variation not modeled, direct calf nutrition cost of early weaning not included, BCS buffer assumes linear energy mobilization.