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:

1. Gross Energy (GE) — total chemical energy in the feed
2. Minus faecal energy loss → Digestible Energy (DE)
3. Minus urinary and methane losses → Metabolisable Energy (ME)
4. 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

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

What an ME deficiency actually looks like

Many Indian dairy animals run on chronically low-ME rations. Symptoms are gradual and often blamed on other factors:

• Milk yield plateau below genetic potential — the cow's body cannot fund higher production without enough ME, even when protein and minerals are adequate
• Body condition score drops below 2.5 during peak lactation — the cow is mobilising body fat to make up the ME deficit
• Delayed return to heat after calving — energy-starved cows postpone reproduction. A cow that doesn't show heat by day 90 post-calving is often ME-deficient, not "shy"
• Low milk fat percentage in mid-late lactation — ME deficit triggers metabolic shifts that suppress milk fat synthesis
• Pica (eating soil, chewing wood) — sometimes a sign of phosphorus or sodium deficiency, but also seen in chronically energy-starved animals

The standard fix is to add a concentrated energy source to the ration: more maize grain in the concentrate mix, bypass fat at 200-300 g/day for high-yielders, or better-quality maize silage replacing low-energy mature green fodder.

Why ME is rising as a metric in India

Historically, Indian dairy nutrition used TDN exclusively. ME is becoming more common because:

1. It accounts for methane loss — important as Indian dairy increasingly tracks greenhouse-gas footprint
2. It works better for bypass fat — high-energy supplements show their value more clearly in MJ than in TDN%
3. International nutrition software (NRC, INRA) uses ME, so consulting nutritionists trained in those systems prefer the metric
4. Better for high-yield calculations — a 25 L/day cow's ME demand is easier to verify (~165 MJ/day) than its TDN demand (~75%)

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.