Feed efficiency

Can you tell which of the sheep in this photograph eats more or which sheep needs less feed to gain 1kg body weight?

Do you know which of your sheep are more efficient at converting feed to weight gain?

What if you could select for these traits using an Australian Sheep Breeding Value (ASBV) or genomic test before buying your rams?

Agriculture Victoria researchers have been measuring feed efficiency in maternal composite ewes and rams of various breeds to determine the range in feed efficiency within the population.

Feed efficiency is a measure of how efficiently an individual sheep converts feed to product — for example kg gain.

Why are we interested in feed efficiency?

Feed is a significant cost in sheep production systems. Agriculture Victoria researchers have determined that prime lambs can vary substantially in feed conversion efficiency (FCE) ratio or feed consumed/kg gain.

The best lambs tested converted every 2.5kg of feed into 1kg of body weight gain, while others consumed up to 14kg of feed for the same gain.

Farm modelling has estimated that improving FCE can increase farm productivity and profitability by increasing lamb output with lower feed costs.

The same modelling also suggests that improving the FCE of the ewe flock could increase on farm profitability by up to 33 per cent, or up to 38 per cent if lamb feed conversion efficiency was also improved.

Improving feed efficiency (FCE) can increase farm productivity and profitability. 

How do we measure feed efficiency?

Estimating feed efficiency requires a measure of feed intake and the amount of product being produced. In our case we measure liveweight gain.

To measure intake, we use purpose built automated feeders linked with EID technology to record daily meals and feed intake for individual sheep. Sheep spend approximately 42 days in our feed intake facility, with daily recording of feed intake and liveweight measured three times weekly.

We then calculate Residual Feed Intake (RFI), a method for expressing feed efficiency, as the difference between actual and expected feed intake. Expected feed intake is how much feed we would expect the animal to eat given its live weight and weight gain over the measurement period.

Sheep that eat more than expected have a high RFI and are therefore less efficient, while sheep who eat less than expected have low RFI and are more efficient (Figure 5).

How much variation in feed efficiency is there?

To date we have measured RFI in 500 maternal composite ewes at post weaning, hogget and as adults.

For adult ewes, the most efficient ewe consumed 1.09kg of dry matter (DM) per day less than expected, while the least efficient ewe consumed 1.04kg DM per day more than expected.

This means there is more than a 2kg DM difference in feed intake per day between the most and least feed efficient ewes for a given level of production.

Range in Residual Feed Intake in nearly 50% of maternal composite ewes from two years weaning and hogget ages, and as adults.

Heritability of RFI has been estimated at 0.26 for both Merino ewes and growing lambs, however there are currently limited estimates of heritability of RFI for maternal composite sheep. This is a moderate level of heritability (like some fleece and carcase traits) and so is amenable to improvement with selection.

Binge eating sheep are more efficient than nibblers

During this research we observed that some ewes tended to have a high number (up to 30) of small meals each day, while others had fewer (less than five) but larger meals (Figure 7). As hoggets, the average number of meals consumed each day by maternal composite ewes was 10 (range 2–28).

As the daily number of meals increased and meal size decreased, RFI increased (Figure 8). So, sheep who ‘binge eat’ and have a small number of meals each day are more efficient than sheep who ‘nibble’.

The future?

With further measurements of feed efficiency in sheep and appropriate sampling a genomic test for feed efficiency in sheep could be developed. So, while we can’t visually pick the more efficient animals, this technology would make it possible to select rams which will produce more efficient lambs and ewes.

The Australian dairy industry has already introduced an Australian Breeding Value (ABV) for feed efficiency called ‘Feed Saved’. This ABV allows farmers to breed dairy cows which produce the same amount of milk from less feed by selecting bulls that will save at least 100kg DM of feed per cow per year. This ABV makes use of genomic tests to predict ‘feed efficiency’.

Relationships between meal size and meal number in 2014 born maternal composite ewes at post weaning and hogget ages. As meal number increases, meal size tends to decrease.

Relationship between meal number and Residual Feed Intake (RFI) measured in 2014 born maternal composite ewes at post weaning and hogget ages. As number of meals consumed increases, RFI increases (sheep become less efficient).