How much methane do lambs produce?
A 42 kg lamb growing at 300 g/day belches about 35 g of methane a day — because it eats about 2.1 kg of dry matter, and every kilogram carries 16.8 g of CH₄.
Also asked about as finishing lambs, weaned lambs.
How the number is worked out
- 1. What it needs to eat. The engine works out the energy the animal needs, then divides by the quality of the feed to get kilograms of dry matter — 22.6 MJ ÷ 11 MJ/kg = 2.1 kg DM a day.
- 2. Methane per kilogram eaten. 16.8 g of CH₄ for every kilogram of dry matter, from the New Zealand national greenhouse-gas inventory (IPCC 2019 Eq 10.21a).
- The yield does not change with the feed. In this model — and in the national inventory it comes from — a kilogram of dry matter carries the same methane whether it is grass, silage or grain. Feed changes the answer by changing how many kilograms it takes, not the methane in each one.
- Enteric methane only. Belched methane. Not dung, not urine, not nitrous oxide, not the fuel in the tractor.
- The tables assume 11 MJ ME/kg DM feed. That is good ryegrass/clover pasture. Poorer feed means more kilograms for the same job and more methane with them — the calculator lets you change it.
- Some of the top rows are more than it could eat. A table steps through a production range without asking whether the animal can physically hold that much feed. Whether a diet fits is a separate question, and the feed calculator answers it — it knows the feed, so it knows the gut fill.
Every coefficient behind this, with its source, is on how it works.
Methane by liveweight — holding weight
An animal doing nothing but staying alive still eats, so it still belches. This is the floor every other figure on the page sits on top of.
| Liveweight | Dry matter eaten | Methane | CO₂-equivalent |
|---|---|---|---|
| 20 kg | 0.4 kg DM | 7 g/day | 0.2 kg/day |
| 31 kg | 0.5 kg DM | 9 g/day | 0.3 kg/day |
| 42 kg | 0.7 kg DM | 12 g/day | 0.3 kg/day |
| 53 kg | 0.8 kg DM | 14 g/day | 0.4 kg/day |
| 64 kg | 1.0 kg DM | 16 g/day | 0.5 kg/day |
| 75 kg | 1.1 kg DM | 18 g/day | 0.5 kg/day |
The bit that matters — methane per kilogram of gain
Total methane goes up as production rises — the animal eats more. But methane per unit of product goes down, because maintenance is a fixed overhead spread across more meat. This is the one lever on this page that cuts emissions and makes the farm money at the same time.
| Growth rate | Dry matter eaten | Methane total | Per kg gain |
|---|---|---|---|
| 50 g/day | 0.9 kg DM | 15 g/day | 306 g |
| 150 g/day | 1.4 kg DM | 23 g/day | 153 g |
| 300 g/day | 2.1 kg DM | 35 g/day | 115 g |
| 400 g/day | 2.5 kg DM | 42 g/day | 106 g |
| 500 g/day | 3.0 kg DM | 50 g/day | 101 g |
At a 42 kg liveweight on 11 MJ ME/kg DM feed. The same effect is why a slow-finishing lamb carries more methane per kilogram of gain than a fast one — it spends longer on maintenance for the same carcass.
Work it out for your own stock
Same engine as the tables above. Change a lever and it tells you what it cost you.
From 2.1 kg DM eaten a day (22.6 MJ ME ÷ 11.0 MJ/kg), at 16.8 g CH₄ per kg of dry matter.
- Per kg of gain
- 115 g CH₄
- 6.8 kg DM per kg
- Per head per day, as CO₂e
- 1.0 kg CO₂e
- GWP100 = 28
And for a whole finishing run — start weight to finish weight
Growing faster costs more methane a day and less per kilogram of carcass, because the lamb spends fewer days on maintenance. This is the trade-off in full.
Starts as a worked example — the class defaults, on 11.0 MJ ME/kg DM feed. Put your own weights and growth rate in.
- Days to finish
- 110 days
- 33 kg of gain
- Methane for the run
- 4.39 kg CH₄
- 261 kg DM eaten, at 11.0 MJ/kg
- Per kg of gain
- 133 g CH₄
- over 110 days
Enteric (belched) methane only — it excludes dung, urine and nitrous oxide, so it is not a farm emissions return.
The two things that actually move it
- Feed quality. Methane rides on kilograms of dry matter, and better feed delivers the same energy in fewer kilograms. Swapping lambs from 9 to 11 MJ ME/kg DM feed cuts what they have to eat for the same job — and cuts the methane with it. The yield per kilogram never changes; the kilograms do.
- Production per head. Maintenance is a fixed cost in both feed and methane. Anything that gets more liveweight out of the same animal — better genetics, better feeding, fewer empty days — spreads that overhead further.
Feedwise gives indicative models for decision support. These are modelled figures, not a measurement of your animals and not an emissions return — for reporting, use the tool your processor or council requires.