The animal Article of the Month for May is entitled ‘Visceral organ weights, digestion and carcass characteristics of beef bulls differing in residual feed intake offered a high concentrate diet’

Selection for feed efficient cattle is a way of improving profitability and also decreasing negative environmental effects of beef production.  As feed represents the single largest variable cost in beef production, a 10% improvement in feed efficiency generates more profit for beef producers than an equivalent improvement in rate of gain. Residual feed intake (RFI), defined as the difference between actual and expected feed intake is a measure of feed efficiency that is independent of growth rate and mature body size. Negative or lower values are more desirable as animals that eat less than expected are deemed feed efficient.  RFI is becoming the concept of choice for studying physiological mechanisms underlying variation in feed efficiency in beef cattle.

Our article in the June edition of animal proposed that the size of the visceral organs associated with the gastrointestinal tract (GIT) and liver, may influence energy requirements for basal metabolism and hence RFI, owing to the disproportionate amount of energy consumed by these organs relative to their weight.

The results of our study found that the empty reticulo-rumen was lighter in feed efficient beef bulls compared to their inefficient counterparts suggesting that the size of this organ contributes to variation in RFI. Additionally, RFI was negatively correlated with economically relevant traits such as kill-out proportion, carcass conformation and predicted meat proportion suggesting that low RFI (feed efficient) bulls not only reduced input costs but may also have a greater carcass output value for producers.

Although this study identified a source of variation in RFI, there are still many other unknown processes underlying variation in feed efficiency in beef cattle. For example, biological processes within the tissues of the splanchnic bed have been shown to have differing efficiencies and we suggested that further research on the efficiency of these metabolic processes between cattle of high and low RFI is warranted.

Production system economics found that by using low RFI bulls (and current concentrate prices), the producer may save €35/bull over a 105 day finishing period. This further confirms the feed cost savings that may be obtained by using low RFI cattle in beef production systems.

A significant obstacle to the wide spread adoption of RFI as a measure of feed efficiency and incorporation of this trait (or its component traits) into selection indices is the enormous cost of acquiring individual feed intake in beef cattle. Therefore, developing biomarkers for the rapid and early identification of low RFI (feed efficient) cattle has become the focus of many research groups.

This paper is freely available for one month

Authors: C. Fitzsimons, D. A. Kenny and M. McGee

The animal Article of the Month is selected by the Editor-in-Chief and is freely available for one month