ME (Metabolisable Energy)
ME — Metabolisable Energy — is the energy in a cattle feed that the animal can actually use for body functions, growth, and milk production. It is calculated as the gross energy of the feed minus losses in faeces, urine, and methane gas. ME is expressed in MJ (megajoules) per kg of dry matter.
Energy losses on the way to ME
Not all the energy in a feed reaches the animal. The energy cascade:
- Gross Energy (GE) — total chemical energy in the feed
- Minus faecal energy loss → Digestible Energy (DE)
- Minus urinary and methane losses → Metabolisable Energy (ME)
- Minus heat loss → Net Energy (NE) — energy actually used for production
ME is the most commonly reported energy metric in modern dairy nutrition because it is more accurate than DE (accounts for methane) and easier to measure than NE.
Typical ME values of common Indian feed ingredients
| Ingredient | ME (MJ/kg DM) |
|---|---|
| Maize | 12.5–13.5 |
| Bypass protein (premium) | 13.6 |
| Soybean meal | 12.5 |
| Groundnut cake | 12.5–13.0 |
| Cotton seed cake | 11.5–12.5 |
| Wheat bran | 10.5–11.5 |
| DORB | 9.0–10.0 |
| Maize silage | 10.0–11.0 |
| Green fodder (mature) | 8.0–9.5 |
| Dry straw | 6.0–7.0 |
ME vs TDN
ME and TDN are two ways of expressing the same general concept — usable energy in a feed:
- TDN is expressed as a percentage of DM (Indian and US standard)
- ME is expressed in MJ/kg DM (European standard)
A working conversion: ME (MJ/kg DM) ≈ 0.15 × TDN (%)
So a feed at 70% TDN delivers approximately 10.5 MJ/kg ME.
ME requirements for a lactating cow
A 450 kg cow yielding 12 L/day of 4.2% fat milk needs approximately:
- Maintenance: ~35 MJ ME/day
- Milk production: 12 L × ~5.1 MJ/L = ~61 MJ/day
- Total: ~96 MJ ME/day
To deliver 96 MJ from a ration with 11 MJ/kg average ME, the cow needs to eat ~8.7 kg DM of concentrate-and-forage mix in addition to maintenance forage.
For higher yields, the ME demand scales:
- 8 L/day cow: ~75 MJ/day
- 15 L/day cow: ~110 MJ/day
- 20 L/day cow: ~135 MJ/day
Practical use
When formulating modern Indian dairy rations, ME is often reported alongside TDN. Compound feed labels typically show TDN; bypass supplements and premium-grade products often show ME (MJ/kg). Both metrics describe the same energy quantity, just in different units.