Feed Conversion Ratio in Lamb Fattening: Calculate and Improve It

The feed conversion ratio (FCR) is the number of kilograms of feed an animal eats to gain one kilogram of live weight. You calculate it by dividing the total feed consumed by a group over a period by the total weight it gained in the same period. The lower the ratio, the more efficient the fattening, and the lower your feed cost per kilo produced.

In fattening, feed is by far the largest cost. Two groups of lambs can eat the same ration and finish at the same weight, yet one of them may cost much more to produce because it needed more feed for every kilo of gain. FCR is the number that reveals this difference. Without it, you only see the feed bill, not what you got for it.

How to calculate the feed conversion ratio

You need only three numbers for a group and a period:

1. Feed consumed, in kilograms, over the period (all feeds: concentrate, hay, by-products).
2. Starting weight of the group (sum of individual weights, or average weight times the number of head).
3. Final weight of the same group at the end of the period.

Then:

FCR = total feed consumed (kg) / (final weight - starting weight) (kg)

A simple, illustrative example for a group of 20 lambs over 90 days:

These figures are for illustration only. What matters is the method: keep it the same every time so you can compare groups and seasons fairly.

Two practical notes. First, decide whether you count feed "as fed" or on a dry-matter basis, and stick to it. Most farms use as fed because it matches what they buy. Second, if an animal dies or is sold during the period, remove its feed share and weight from the calculation or note it separately, otherwise the ratio will be distorted.

From FCR to cost per kilo of gain

The ratio becomes really useful when you turn it into money:

Feed cost per kg of gain = FCR x average price of 1 kg of the ration

If your ration costs, for example, 1.2 per kg and your FCR is 7.0, each kilo of gain costs about 8.4 in feed alone. If live weight sells at a price close to that, fattening is barely paying for its feed, before labour, health and other costs. This is why FCR feeds directly into your cost per head.

It also helps you decide when to sell. As lambs get heavier and start laying down fat, they usually need more feed for each extra kilo. At some point, the cost of the next kilo becomes higher than what that kilo will sell for. Following FCR over time shows you when you are getting close to that point.

What affects feed conversion

Many factors influence FCR. The main ones you can act on:

• Age and weight. Young, growing animals generally convert feed better than older, heavier ones.
• Genetics and breed. Some breeds and lines grow faster and more efficiently in feedlots than others. Records per sire help you see which bloodlines perform best.
• Sex. Entire male lambs often grow faster and more efficiently than females, though local market preferences and management also matter.
• Ration balance. Too little energy or protein slows growth; sudden changes upset the rumen. The ration should be built and adjusted with a nutritionist.
• Health. Internal parasites, respiratory problems and digestive troubles waste feed. A health plan agreed with your vet protects FCR.
• Heat. In hot weather animals eat less and use energy to cope with heat. Shade, ventilation and cool water matter.
• Feed waste. Feed spilled on the ground is counted as "eaten" in your records but never turns into meat. Waste makes FCR look worse than the animals really are.

How to improve it in practice

Improving FCR is mostly about steady management rather than one big change:

1. Start with healthy, well-adapted animals. Quarantine and check new arrivals, and follow your vet's vaccination and parasite plan.
2. Adapt them to the ration gradually. A careful transition over about two weeks avoids digestive problems that set animals back.
3. Group by weight and sex. Similar animals compete less at the trough and eat more evenly.
4. Cut waste. Good troughs, enough trough space, and feed that is not left to spoil. Our guide on how to reduce feed costs on a sheep farm covers this in detail.
5. Weigh regularly. Every two to four weeks is a practical rhythm. Animals that are not gaining should be checked and, if needed, removed from the group.
6. Sell at the right time. Do not keep finished animals "just in case"; extra days usually come with a worse ratio.

Tracking FCR with your records

You cannot calculate FCR without two things: the feed each group really eats and regular weights. That is where many farms struggle, because notes are scattered between notebooks, invoices and memory.

In Throf, you record meals per group and they are deducted from your feed stock in kilograms. Weights are entered per animal, so you can see gains for each head and each group. With feed used and weight gained in one place, working out FCR per group becomes a quick calculation rather than an end-of-season guess, and you can compare one batch, ration or season with another. If you are planning a new batch, our 90-day lamb fattening plan shows how to organise weighings from day one.

The short version

FCR tells you how much feed you pay for each kilo you sell. Measure feed and weights for each group, calculate the ratio the same way every time, convert it into cost per kilo of gain, and use it to improve rations, cull poor performers and choose the best time to sell.