Feed Conversion Ratio Calculator NZ

Feed conversion ratio is how many kilograms of dry matter it takes to put on a kilogram of liveweight, and this works it out from your mob, your feeding rate and your weights, then prices it so you also know what that gain is costing. Everything is on a dry matter basis rather than as fed, which matters more than it sounds: baleage might be 45 percent dry matter and hay 85, so a tonne of each delivers quite different amounts of actual feed, and a ratio calculated as fed compares moisture as much as it compares performance. Two cautions worth having up front. The ratio only means something if the feed and the gain cover exactly the same animals over exactly the same days, and the most common way to get it wrong is to count supplement while ignoring the pasture eaten alongside it, which flatters the answer enormously. And a good ratio is not automatically the cheaper option, because a poorer conversion on cheap feed regularly beats a better one on expensive feed. The cost of gain per kilogram is usually the number that decides things, which is why it sits beside the ratio here rather than underneath it.

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kg DM
$
/kg DM
kg
kg
10.3
kilograms of dry matter per kilogram of liveweight gain
Cost per kg of gain$3.29
Feed cost per head$230.40
Dry matter fed36,000 kg DM
Gain per head70 kg

Count every kilogram the mob ate, pasture included. Counting only the supplement is the most common way this figure comes out flattering and wrong.

How it works

Total dry matter is the mob size multiplied by the daily feeding rate and the number of days. Total gain is the weight each animal put on multiplied by the mob size. The ratio is the first divided by the second. Cost of gain takes the same total dry matter, prices it, and divides by the total gain, which gives dollars per kilogram of liveweight added. Feed cost per head is the whole feed bill spread back across the mob.

Maintenance is inside the ratio

A large share of what any animal eats goes to staying alive rather than to gaining, and that share does not disappear when growth slows. So the ratio worsens whenever gain falls away even if the feeding has not changed at all, which is why a mob on a poor run of weather can show a badly deteriorating conversion while eating exactly what it always did. It is also why the same feed converts better in a fast growing young animal than in one near mature weight: the maintenance cost is being spread over more gain in the first case and less in the second.

Worked example

Fifty cattle fed 12 kilograms of dry matter a head each day for 60 days eat 36,000 kilograms of dry matter between them. Over the same 60 days they went from 250 to 320 kilograms, which is 70 kilograms each and 3,500 kilograms of gain across the mob. That is a feed conversion ratio of 10.3 kilograms of dry matter per kilogram of gain. At 32 cents a kilogram of dry matter the feed bill is $11,520, which puts the cost of gain at $3.29 a kilogram and $230.40 a head. Whether that is worth doing depends on what a kilogram of liveweight is worth when they are sold, not on the ratio itself.

Related calculators

Data sources: no benchmark ratio is supplied, because a good ratio depends on species, class, feed and how much intake goes to maintenance. Every figure is one you enter. Dry matter percentages for common feeds are handled in the winter feed calculator rather than assumed here.

Frequently asked questions

How do you calculate feed conversion ratio?

Divide the feed eaten by the liveweight gained over the same period. On pasture systems both sides are usually in kilograms, with feed measured as dry matter rather than as fed, so the answer is kilograms of dry matter per kilogram of gain. A lower number means the feed is being converted more efficiently. Feed and gain must cover exactly the same animals over exactly the same days or the ratio means nothing.

Why is feed measured as dry matter?

Because feeds carry wildly different amounts of water, and comparing them as fed compares moisture as much as feed. Baleage might be 45 percent dry matter and hay 85 percent, so a tonne of each delivers quite different amounts of actual feed. Converting everything to a dry matter basis is what makes a ratio calculated on one feed comparable with one calculated on another.

What is a good feed conversion ratio?

It depends entirely on the species, the class of stock, the feed and how much of the intake is going to maintenance rather than gain, so no single benchmark is offered here. A useful comparison is against your own figure from a previous mob on similar feed, because that holds most of the variables still. The cost of gain per kilogram is often the more decisive number anyway, since a poorer ratio on cheap feed can beat a better one on expensive feed.