ME vs NE in Pig Diets: Comparing Energy on the Right Basis

Metabolizable energy, or ME, accounts for fecal, urinary, and gaseous energy losses. Net energy, or NE, additionally accounts for the heat associated with utilizing feed. They are different energy systems, not interchangeable labels for the same ingredient value.

When formulating pig diets, the important starting point is consistency: use an appropriate energy system across ingredients, nutrient relationships, requirements, and any performance model. A mix of ME and NE coefficients can make a diet appear adequate without representing a coherent calculation.

Follow the energy accounting pathway

System	Conceptual accounting
Gross energy, GE	Total combustible energy measured in the feed
Digestible energy, DE	GE minus fecal energy losses
Metabolizable energy, ME	DE minus urinary and gaseous energy losses
Net energy, NE	ME minus heat increment

These are accounting definitions; assigning practical ingredient values requires an appropriate measurement or prediction method. Kansas State’s ingredient evaluation fact sheet describes energy systems, prediction approaches, and why the same system should be used consistently within a formulation.

Why ingredient rankings can change

Different feed components do not all have the same efficiency of energy utilization. Accounting for heat increment can therefore change the relative value of ingredients compared with an ME-only evaluation. This matters when replacing starch-rich ingredients with higher-protein or higher-fiber alternatives.

That does not make a feed ingredient inherently good or bad. Its value depends on the complete formulation, price, animal category, digestibility, and other constraints. Use the energy system that matches the intended specification and evaluation method, not whichever number makes an ingredient appear cheapest.

Do not convert every ingredient using one constant

Consider two hypothetical ingredients. A is assigned 3,200 kcal ME/kg and 2,450 kcal NE/kg; B is assigned 2,900 kcal ME/kg and 1,900 kcal NE/kg. Their NE:ME ratios are approximately 0.766 and 0.655. These are teaching values, not feed-table entries.

Multiplying both ME values by 0.75 would assign NE values of 2,400 and 2,175 kcal/kg. The second estimate differs substantially from its assigned value. A single factor hides ingredient-specific differences. Use a supported equation with its required inputs or a compatible reference value, and retain the method used.

Also separate conversion of units from prediction of energy systems. One Mcal equals 1,000 kcal, and one Mcal equals 4.184 MJ. Those conversions are exact unit relationships. Predicting NE from other data is a nutritional modeling step with assumptions.

Link amino acids to the correct denominator

A label such as “lysine:energy” is incomplete unless it identifies total or SID lysine, the energy system, and the units. Four grams of SID lysine per Mcal NE is not numerically equivalent to four grams per Mcal ME.

For a hypothetical diet containing 10 g SID lysine/kg, 2.5 Mcal NE/kg gives 4.0 g/Mcal NE. If that diet contains 3.3 Mcal ME/kg, it gives about 3.03 g/Mcal ME. Both describe the same feed using different denominators. Neither number alone establishes that the diet meets a particular animal’s requirement.

Read the SID amino acid guide for the numerator. Kansas State’s diet formulation framework connects energy selection with amino acid specification and economic evaluation.

Compare daily supply as well as concentration

At 2.5 Mcal NE/kg and 2.4 kg feed intake/day, daily NE supply is 6.0 Mcal. A second diet at 2.6 Mcal/kg and 2.2 kg/day supplies 5.72 Mcal. Higher concentration does not guarantee higher daily energy intake.

Those intake values are hypothetical. A performance model must estimate or receive intake; it cannot assume that every animal consumes the same amount regardless of diet and conditions. Document whether reported performance is measured, predicted, or simply a scenario assumption.

Audit an energy-driven economic comparison

1. Confirm each ingredient’s energy system, units, moisture basis, and source.
2. Check that the diet specification uses a compatible system.
3. Recheck amino acid-to-energy relationships.
4. Identify the model’s intake and growth assumptions and applicable population.
5. Compare feed cost per gain or margin using consistent time and weight boundaries.
6. Check sensitivity to prices and uncertain biological responses.

A lower price per tonne does not by itself establish lower production cost. Our swine economics guide works through that comparison.

Key takeaways

• ME and NE describe different stages of energy accounting.
• Do not mix their ingredient values or requirement denominators.
• Separate exact unit conversions from nutritional prediction equations.
• Evaluate energy concentration alongside intake, amino acids, and economics.

Frequently asked questions

Is the highest-NE diet always the best?

No. Its price, nutrient balance, expected intake and growth, and commercial objective all matter.

Can I compare kcal/kg with kcal/lb directly?

No. Convert the mass denominator first. Also check energy system and moisture basis; changing only the unit label is insufficient.

Does DietForge’s energy economics cover every species?

No. Its built-in growth, cost-per-gain, and income-over-feed-cost models currently cover swine. Other livestock species can be formulated, with their economics models planned for the future.

Explore the economic effect

DietForge Pro includes swine economics tools for evaluating scenarios. Review model assumptions and ingredient values before acting on predicted performance.