NEL (Net Energy for Lactation)
NEL — Net Energy for Lactation — is the most refined energy measure used in dairy nutrition. It represents the energy in a feed that is actually available for milk production after all metabolic losses are subtracted. NEL is expressed in MJ (or Mcal) per kg of dry matter.
The energy cascade
NEL is the last step in the dietary energy cascade:
- Gross Energy (GE) — total chemical energy
- Minus faecal loss → Digestible Energy (DE)
- Minus urinary and methane loss → Metabolisable Energy (ME)
- Minus heat increment (heat from digestion and metabolism) → Net Energy (NE)
- Split into:
- NEL — Net Energy for Lactation
- NEM — Net Energy for Maintenance
- NEG — Net Energy for Growth
The conversion from ME to NEL accounts for the heat the animal produces simply by digesting and metabolising the feed.
NEL vs ME vs TDN
NEL, ME, and TDN are three ways of measuring usable energy, with different levels of refinement:
- TDN is the simplest (Indian standard) — total digestible nutrients as % of DM
- ME subtracts methane and urinary losses (European standard)
- NEL further subtracts heat increment — the most accurate measure of energy available for milk
Approximate conversions:
- ME (MJ/kg DM) ≈ 0.15 × TDN (%)
- NEL (MJ/kg DM) ≈ 0.6 × ME (MJ/kg DM)
- NEL (MJ/kg DM) ≈ 0.09 × TDN (%)
A feed at 70% TDN delivers approximately 10.5 MJ/kg ME and 6.3 MJ/kg NEL.
Typical NEL values
| Ingredient | NEL (MJ/kg DM) |
|---|---|
| Maize | 7.5–8.5 |
| Soybean meal | 7.5–8.0 |
| Bypass fat | 25–30 (very high) |
| Cotton seed cake (premium) | 7.0–7.5 |
| Wheat bran | 6.3–7.0 |
| DORB | 5.5–6.0 |
| Maize silage | 6.0–6.6 |
| Green fodder (mature) | 4.8–5.8 |
| Dry straw | 3.5–4.2 |
NEL requirements
A working approximation for a lactating cow:
- Maintenance: ~21 MJ NEL/day for a 450 kg cow
- Per litre of milk (4% fat): ~3.1 MJ NEL/L
So a 450 kg cow producing 12 L/day at 4% fat needs: 21 + (12 × 3.1) = 58 MJ NEL/day
To deliver 58 MJ from a ration with 6.5 MJ/kg average NEL, the cow needs to eat ~9 kg DM. Add maintenance forage and the total ration is ~14–16 kg DM.
Practical use
NEL is the standard energy metric for modern Indian commercial dairy ration formulation, used by professional nutritionists and computer-based ration formulation software. For smallholder dairy, TDN remains the more commonly cited number on feed bags and in routine practice, but NEL is increasingly used in premium feed product specifications.