How it works
The science behind the numbers
Feedwise is a deterministic engine built on published animal-nutrition science. Every number — energy, protein, minerals, intake — traces to a named source, listed below. The maths is fixed equations from the published standards, run the same way every time.
AFRC energy & protein system
Requirements are built with the AFRC (1993) metabolisable-energy and metabolisable-protein framework — the same system professional nutritionists use — with New Zealand calibration from Beef+Lamb NZ and DairyNZ.
Law of the minimum
Achievable production is the smallest of what energy, protein and physical intake each allow — and capped at the animal’s realistic genetic potential. We tell you which one is holding things back.
The rumen-fill ceiling
Our point of difference: the rumen can only hold so much fibre. We cap intake by NDF rumen-fill, not just appetite, so a bulky diet shows its true limit instead of an optimistic number.
Checked against the experts
We cross-check the engine against professional formulation tools and real laboratory reports. On our reference cases its requirements land within a few percent of the expert figures across energy, protein and the key minerals.
The coefficients below are calibrated to the published science and are under review by our nutrition advisor. A few are marked under review while we confirm them — the engine always runs on sensible, sourced defaults.
Every number, and where it comes from
Nothing here is a black box. Open any group to see the values the engine uses and the source behind each. Some are exact published constants; others are calibrated to NZ conditions.
Energy12 values
| Coefficient | Value | Source | Status |
|---|---|---|---|
| Gross energy of dry matter | 18.4MJ/kg DM | AFRC 1993 | Established |
| Efficiency of ME for maintenance (k_m) | 0.35·q + 0.503 | AFRC 1993 / ARC 1980 | Established |
| Efficiency of ME for lactation (k_l) | 0.35·q + 0.420 | AFRC 1993 | Established |
| Efficiency of ME for growth (k_g) | 0.78·q + 0.006 | AFRC 1993 | Established |
| Fasting metabolism (sheep)(sheep) | 0.25MJ/kg^0.75 | AFRC 1993 (young sheep 0.25; adults 0.23) | Established |
| Fasting metabolism (cattle)(cattle) | 0.38MJ/kg^0.75 | Calibrated to Beef+Lamb NZ / Nicol & Brookes 2007 (500 kg cow ~60 MJ/d) | Under review |
| Grazing/activity allowance (sheep)(sheep) | 0.011MJ/kg LW | AFRC 1993 (range 0.0067–0.024) | Established |
| Grazing/activity allowance (cattle)(cattle) | 0.01MJ/kg LW | AFRC 1993 (0.0071–0.0095) | Calibrated |
| Ewe milk energy(sheep) | 5.2MJ/L | Pulina; Brett et al. (ewe milk GE ~5.0–6.0 at 6.5% fat) | Calibrated |
| Cow milk energy (default)(cattle) | 3.1MJ/L (net) | AFRC; refined by the entered fat/protein (Tyrrell-Reid lineage) | Calibrated |
| Energy value of liveweight gain (lamb)(sheep) | 12 + 0.12·(LW−20)MJ/kg net | AFRC 1993; measured EBW-gain energy | Calibrated |
| Energy value of liveweight gain (cattle)(cattle) | 14 + 0.012·(LW−150)MJ/kg net | Beef+Lamb NZ / Nicol & Brookes 2007 (~35–50 MJ ME/kg) | Calibrated |
Protein8 values
| Coefficient | Value | Source | Status |
|---|---|---|---|
| MP from microbial crude protein | 0.6375 | AFRC 1993 (0.75 true protein × 0.85 digestibility) | Established |
| Fermentable ME fraction of ME | 0.92 | AFRC 1993 (forage default; excludes fat/acids) | Calibrated |
| MP maintenance (sheep)(sheep) | 2.5g/kg^0.75 | AFRC (basal endogenous + scurf/dermal ~2.3–2.9) | Calibrated |
| MP maintenance (cattle)(cattle) | 2.5g/kg^0.75 | AFRC/NRC (range ~2.3–3.8) | Under review |
| Milk true protein (ewe)(sheep) | 52g/L | Measured ewe milk (48–58) | Calibrated |
| Milk true protein (cow)(cattle) | 33g/L | Standard dairy 3.3% | Established |
| Efficiency of MP for milk | 0.68 | AFRC 1993 (0.68; revised 0.67) | Established |
| ERDP / DUP (default fallback) | 0.70 / 0.10 of CPfraction | AFRC 1993 — now FEED-SPECIFIC (see Feed library) | Established |
Minerals11 values
| Coefficient | Value | Source | Status |
|---|---|---|---|
| Calcium true absorption (sheep)(sheep) | 0.38 | NZ forage (NASEM grass 0.30–0.40) | Calibrated |
| Phosphorus true absorption (sheep)(sheep) | 0.5 | Forage ~0.50–0.58 (AFRC/INRA) | Calibrated |
| Magnesium true absorption (sheep)(sheep) | 0.17 | ARC 0.17 (conservative); NASEM base 0.31 | Calibrated |
| Sodium true absorption (sheep)(sheep) | 0.9 | ARC/NASEM 0.90–0.91 | Established |
| Calcium maintenance (sheep)(sheep) | 0.623·DMI + 0.228g/d | AFRC 1991 (per kg DM intake) | Established |
| Phosphorus maintenance (sheep)(sheep) | 0.693·DMI − 0.06g/d | AFRC 1991 (per kg DM intake) | Established |
| Sodium maintenance (sheep)(sheep) | 22mg/kg LW | ARC sheep net endogenous ~26 (obligatory salivary recycling) | Established |
| Sodium maintenance (cattle)(cattle) | 6mg/kg LW | ARC cattle ~6 (NOT the higher sheep figure) | Calibrated |
| Milk calcium (ewe)(sheep) | 1.9g/L | Measured ewe milk 1.6–1.9 | Established |
| Mg–K antagonism: K threshold | 2.5% DM K | NRC/CSIRO/NZ (Mg uptake falls above ~2.5–3% K) | Calibrated |
| Mg–K antagonism: max reduction | 0.4fraction | Literature ~20–40%+ | Calibrated |
Intake6 values
| Coefficient | Value | Source | Status |
|---|---|---|---|
| NDF-fill ceiling (lamb)(sheep) | 0.021fraction of LW | Cannas et al. (sheep NDF intake 5.4442·BW^-0.25) | Established |
| NDF-fill ceiling (ewe, non-lactating base)(sheep) | 0.017fraction of LW | Cannas et al. (×1.1 lactation uplift = lactating value) | Established |
| NDF-fill ceiling (cow, non-lactating base)(cattle) | 0.011fraction of LW | Mertens 1987/1994 (×1.1 = the 1.2% dairy benchmark) | Established |
| Lactation NDF-capacity uplift | 1.1× | Physiology (larger functional rumen, faster passage) | Under review |
| Late-pregnancy intake depression | 0.15max fraction | Literature 10–30% (worse for multiples) | Calibrated |
| Appetite ceiling (ewe)(sheep) | 0.045fraction of LW | Lactating ewes 4.0–5.5% BW | Established |
Pregnancy3 values
| Coefficient | Value | Source | Status |
|---|---|---|---|
| Pregnancy ME per foetus (ewe, at term)(sheep) | 9.5MJ/d | Beef+Lamb NZ FS83 (single ~9.6, twin ~7.3/foetus) | Established |
| Pregnancy ME per foetus (cow, at term)(cattle) | 42MJ/d | Beef+Lamb NZ FS90 / Nicol & Brookes (~40–45) | Established |
| Pregnancy MP per foetus (ewe, at term)(sheep) | 45g/d | AFRC 1993 Table 9 (increment ~39–57) | Calibrated |
Genetic ceiling4 values
| Coefficient | Value | Source | Status |
|---|---|---|---|
| Genetic ceiling — lamb gain(sheep) | 400g/day | NZGA / Beef+Lamb NZ (best NZ mobs ~409; finishing ~350) | Calibrated |
| Genetic ceiling — cattle gain(cattle) | 1600g/day | Beef+Lamb NZ (observed max ~1.48–1.55 kg/d) | Calibrated |
| Genetic ceiling — ewe milk(sheep) | 6L/day | East Friesian peak ~5–6 L | Under review |
| Genetic ceiling — cow milk(cattle) | 50L/day | NZ pasture peaks ~30–40; 50 = generous ceiling | Under review |
Rumen health2 values
| Coefficient | Value | Source | Status |
|---|---|---|---|
| Rumen NDF minimum (ewe)(sheep) | 30% DM | Extrapolated (NRC defines no sheep NDF requirement) | Under review |
| Rumen NDF minimum (dairy cow)(cattle) | 27% DM | NRC (min total NDF ~25%, 19% forage) | Calibrated |
Risk indices3 values
| Coefficient | Value | Source | Status |
|---|---|---|---|
| Grass-staggers danger ratio | 2.2K/(Ca+Mg) meq | Kemp & 't Hart 1957 | Established |
| DCAD milk-fever threshold (dry/transition) | 300meq/kg | NRC/NASEM; DAIReXNET (lactating optimum is +250–340) | Established |
| Equivalent weights (DCAD/staggers) | Na 435, K 256…meq/% DM | Standard atomic equivalent weights | Established |
Primary sources
- AFRC (1993) — Energy and Protein Requirements of Ruminants
- CSIRO (2007) — Nutrient Requirements of Domesticated Ruminants
- NRC / NASEM — Nutrient Requirements of Sheep, Beef Cattle, and Dairy Cattle
- Beef + Lamb New Zealand — FeedSmart fact sheets (Nicol & Brookes 2007)
- DairyNZ — Facts & Figures; feed and pasture guidance
- Grace & Knowles — mineral & trace-element nutrition of NZ grazing livestock
- Feedipedia (INRAE / CIRAD / FAO) — feed composition & protein degradability
Feedwise gives indicative models for decision support. It is not a substitute for a nutritionist or veterinarian — for animal-health decisions, talk to your vet.