NE + MP ADG Calculator

NASEM 2016 — Full Reference

This calculator predicts ADG from two independent nutritional constraints and reports whichever is lower as the predicted ADG. Both approaches follow the Nutrient Requirements of Beef Cattle, 8th revised edition (NASEM, 2016).

Overview of the two constraints

NE-allowable ADG — the gain the ration's net energy will support after satisfying maintenance. Comes from the California Net Energy System framework, updated in NASEM 2016 to use empty body fat (EBF) as the compositional endpoint.

MP-allowable ADG — the gain the ration's metabolizable protein will support after satisfying maintenance protein needs. Ties directly to net protein deposition in the gain.

Both constraints must be met. If protein supply exceeds requirement at the NE-driven gain, energy is limiting. If protein supply falls short, protein is limiting and predicted ADG drops to whatever the MP supply supports.

Net Energy Side — equations

Avg BW = (in-weight + out-weight) / 2, in lb.
NEm requirement (Mcal/d) = (BW/2.205)^0.75 × 0.077.
NEm intake (lb DM/d) = NEmr / (diet NEm / 100).
× Maintenance = DMI / NEm intake (rough intake benchmark; ~2.5–3.5× is typical for feedlots).
NEg intake (lb DM/d) = DMI − NEm intake.
Retained energy (RE, Mcal/d) = NEg intake × (diet NEg / 100).
Shrunk weight gain (kg/d) = 13.91 × RE^0.9116 × EQSBW^−0.6837.
NE-allowable ADG (lb/d) = SWG × 2.205.

EQSBW — the 28% EBF scaling

NASEM 2016 replaces the 1996 frame-size buckets (LF steer, MF steer, etc.) with a continuous scale based on where each animal will finish compositionally. The reference animal is a medium-frame steer at 478 kg (1054 lb) SBW at 28% empty body fat.

Auto mode (default):
  EQSBW (kg) = avg SBW (kg) × (1054 / AFSBW)
  Where AFSBW = the shrunk body weight at which the animal will be at 28% EBF (its compositional finish point). Use this when predicting whole-feeding-period average performance.

Manual mode:
  Enter EQSBW (lb) directly. Use this when predicting gain at a specific single body weight (a point-in-time calculation, like the NASEM 2016 worksheet example). Typically EQSBW equals SBW when the animal being evaluated is the reference animal — no scaling needed.

Class defaults for auto mode (adjustable): MF Steer 1054 lb · LF Steer 1250 lb · MF Heifer 1000 lb · LF Heifer 1150 lb · Holstein 1400 lb. Heifers finish lighter (fatten earlier); Holsteins finish heavier; large-frame types finish heavier than medium-frame.

Metabolizable Protein Side — equations

MP supply and requirement are computed in grams per day and compared. The gain that just uses up available MP is the MP-allowable ADG.

Diet ME (Mcal/kg DM) is back-calculated from your diet NEm by inverting the NRC cubic:
  NEm = 1.37·ME − 0.138·ME² + 0.0105·ME³ − 1.12.
Diet TDN (% DM) = ME / 3.6154 × 100  (from DE = 4.409·TDN, ME = 0.82·DE).
TDN intake (lb/d) = DMI × TDN%/100.
MCP predicted (g/d) = 0.13 × TDN intake (converted to grams). This is the microbial CP synthesis the rumen could support if RDP is not limiting.

Protein partitioning: user enters RDP as % of CP. RUP = 100 − RDP (they're complements). RDP supply (g/d) = CP intake × RDP%/100; RUP supply (g/d) = CP intake × RUP%/100.

RDP adequacy check (NASEM 2016): the rumen microbes need RDP-derived N to synthesize protein. Required RDP ≈ MCP × 1.18 (accounts for N recycling losses).
  If RDP supply ≥ RDP required: MCP actual = MCP predicted (energy-limited synthesis).
  If RDP supply < RDP required: MCP actual = RDP supply / 1.18 (RDP-limited synthesis).
This is exactly why feedlot rations get urea supplementation — high-grain diets can easily be RDP-short even at reasonable total CP levels.

MP supply (g/d) = 0.64 × MCP actual + 0.80 × RUP. The 0.64 is microbial true-protein fraction × intestinal digestibility; the 0.80 is RUP intestinal digestibility.
MP maintenance (g/d) = 3.8 × SBW^0.75 (kg). NASEM 2016 combined coefficient for scurf, endogenous urinary N, and metabolic fecal protein.
MP for gain (g/d) = MP supply − MP maintenance.
NPg required (g/d) = SWG × {268 − 29.4 × (RE/SWG)}, where SWG is in kg/d, RE in Mcal/d. As RE/SWG rises (fattier gain near finish), NPg falls — the equation captures that finishing cattle deposit less protein per unit of gain.
MPg required (g/d) = NPg / 0.492. The 0.492 is the NP:MP efficiency NASEM 2016 uses for most growing cattle.
MP-allowable ADG is solved iteratively: find the SWG at which required MPg equals available MP for gain.

Assumptions and simplifications

• SBW is assumed equal to the weights you enter (i.e. inputs are already shrunk; typical convention).
• RUP intestinal digestibility fixed at 0.80. NASEM 2016 allows feed-specific values; this calculator uses the population average.
• RDP requirement multiplier fixed at 1.18. NASEM 2016 uses close to this value across most diet types.
• The MCP predictor is the classical 0.13 × TDN, then capped by the RDP-adequacy check.
• No adjustments for implants, ionophores, breed-specific NEm requirements, environmental stress, or acidosis. All of these are documented in NASEM 2016 chapters if you need to layer them on.

Interpreting results

• Energy limiting — protein is in excess; excess protein is deaminated and excreted (economic loss + environmental N). Consider reducing CP or shifting some RDP toward RUP.
• Protein limiting — energy is unused. If RDP balance is negative, the ration is RDP-short — the microbes can't make full MCP. Add urea, DDGS with more soluble N, or another RDP source. If RDP is adequate but MP is still short, RUP source (bypass protein) is the fix.
• Well balanced — the diet's NE and MP are close to matched at this stage of growth. This is the target for a properly formulated finishing ration.

Citations

NASEM. 2016. Nutrient Requirements of Beef Cattle, 8th rev. ed. National Academies Press, Washington, DC.
Garrett, W.N. 1980. Energy utilization by growing cattle. Energy Metab. EAAP Publ. 26:3.
Galyean, M.L., and L.O. Tedeschi. 2014. Predicting microbial protein synthesis in beef cattle. J. Anim. Sci. 92:5099–5111.