Can feed efficient progeny be bred from feed efficient sires?
EFFICIENCY is a term that is now being used widely within the agricultural industry, whether that be from whole-farm e ciency to fuel e ciency.
As well as weaning e ciency, feed e ciency is a metric that is starting to gain interest in the UK beef industry, but what does feed e ciency truly mean?
Essentially, e ciency is a measure of how well inputs are converted into outputs. Therefore, feed e ciency of beef cattle is a measure of how well the feed the cattle consume is converted into the production of beef. With feed accounting for around 70% of the cost of production of beef cattle, the aim is to produce an animal that can utilise the feed better and maintain productivity levels.
A traditional measure of feed e ciency in cattle has been feed conversion ratio (FCR). This is a ratio of feed intake to bodyweight gain. In other words, how many kg of feed is needed for the animal to gain 1kg of bodyweight.
FCR for beef cattle is 6-10:1, so between 6-10kg of feed is needed to increase liveweight by 1kg. In comparison, the FCR for poultry is 1.7-2:1, so only between 1.7-2kg of feed is needed to gain 1kg of bodyweight. A slight issue with FCR is that it does not distinguish between the amount of feed that is required simply for maintenance of the animal and the amount needed for growth of the animal.
Nowadays, Residual Feed Intake (RFI) is regarded as a much better measure of feed e ciency especially in beef cattle.
RFI is a measure of the dierence between the actual feed intake of the animal and its predicted feed intake. The animal’s predicted feed intake is a result of statistical modelling of dry matter intake (DMI) on sources of expendable energy such as maintenance, growth and fat levels.
Cattle with a high negative RFI value would indicate those that were the most feed e cient. A negative RFI value signifies that these cattle would need less ‘inputs’ (i.e. feed) to achieve a desired ‘output’ target.
RFI is being examined more closely by beef breed societies and individual breeders as it is thought to be a moderately heritable trait in the range of 28-44% heritability. Through genetic selection it should therefore be possible to have more feed e cient cattle.
The possibility of breeding feed e cient progeny from feed e cient sires was examined in a small-scale study, funded through the Scottish Government’s Farming For A Better Climate project.
Data for this particular study was supplied by The Stabiliser Cattle Company from a batch of cattle that were under-going some feed e ciency trial work between January and March 2024. The study cattle were sired by five dierent bulls (Average No. progeny per sire = 5; range 2-13).
They were fed through a GrowSafe System® which allowed the daily feed intake for each individual animal to be recorded.
Cattle were fed a diet comprising of 75% grass silage (30%DM), 5% straw, 7% protein and 13% barley. Samples of the diet components were taken on a regular basis for analysis throughout the recording period.
The cattle were weighed weekly on the same day every week for consistence. A few days a£er the end of the data collection period, they were ultrasound scanned to take measurements for rump fat depth, rib fat depth, eye muscle area and intramuscular fat depth.
To ensure that the cattle did not have access to another potential feed source, they were bedded on a sand/sawdust combination rather than straw.
Liveweight gain (LWG) was calculated for each individual animal using Regression analysis. This method was used as it takes all the recorded weights across the study period into consideration, not just the start and end weight and therefore gives a better reflection of the growth of the animal.
Residual feed intake was calculated by subtracting the actual DMI from the expected DMI for each of the study cattle. Expected DMI was modelled using the data for LWG, mid test metabolic LW (i.e. metabolic liveweight (LW0.75) of each animal at day 28 of the
56-day study period) and the ultrasound scanning data (rump fat depth, rib fat depth, eye muscle area, intramuscular fat).
Study animals ranked by feed e ciency
(residual feed intake) and dierentiated between sires – Sire 1 (gold), Sire 2 (green), Sire 3 (lilac), Sire 4 (light blue), Sire 5 (dark blue) can be shown in the table below.
The Stabiliser Cattle Company has an EBV (Estimated Breeding Value), feed to gain, which has been calculated from individual daily feed intake and weight records. It indicates the conversion of feed with negative values being more favourable as that would indicate those cattle require less feed per kg of gain. Of the five sires of the cattle in this study, two of the sires had a negative value for the Feed to Gain trait (range
-0.4 to -0.18) and three had
a positive value (range: 0.04 to 0.4).
The majority of progeny by Sire 2 (green) had a negative calculated RFI from this particular study. Sire 2 was one of the sires that were negative for the feed to gain trait. Sire 5 (dark blue) had a spread of progeny in terms of feed e ciency (RFI) despite being a sire with a negative value for this trait.
However, the accuracy level for many EBV traits is o£en low. Also, maternal genetics will play their part as well. Nonetheless, what this small-scale study has shown is that it can be possible to breed feed e cient progeny from feed e cient sires.
Feed e ciency will be one of the topics being highlighted as part of SAC Consulting’s ‘Big Beef Roadshow’ events in May and June at various locations throughout Scotland.