The overall aim of beef cattle breeding is to improve profitability through genetic progress. Feed costs are arguably the largest, most variable input costs and any reductions made herein will increase profit. This, among other reasons, is why feed efficiency has become so important in cattle breeding. It is important to note that feed efficiency is a broad term and there are several different measures of feed efficiency (Archer et al. 1999), the term you are likely most familiar with is Net Feed Intake (NFI) which is also often referred to as residual feed intake, they are, however, the same thing.
Why do we use Net Feed Intake as the preferred measure of feed efficiency? Koch et al. 1963 suggested that feed intake could be adjusted for body weight and weight gain, effectively partitioning feed intake into two components (1) the feed intake expected for a given level of production (referring to the expected requirements for an animal of a certain age, breed and stage of reproduction or growth); and (2) the residual portion. This meant that we would be able to identify animals that deviated from their expected level of feed intake, where more efficient animals have lower (negative) residual feed intakes. Still not following. Net Feed Intake is the difference, negative (better) or positive (worse), between the actual amount of feed the animal consumed to gain weight and the expected amount of feed consumed by the animal, given the animals weight at the time of consumption. Net Feed Intake, as all other traits, is measured within a contemporary group to ensure comparability of data and to eliminate all environmental conditions during measurement.
Most of the confusion that arises around Net Feed Intake generally stems from not properly understanding the trait definition. The Breedplan definition of Net Feed Intake EBVs is that they are estimates of the genetic differences between animals in feed intake at a standard weight and rate of gain for a given feeding phase (post-wean or finishing respectively). This implies that Net Feed Intake is independent of weight and growth rate. It is also important to understand the relationship between Feed Conversion Ratio and Net Feed Intake, although they are positively correlated there is one distinct difference between them. Net Feed Intake is uncorrelated with body weight and growth rate, whereas Feed Conversion ratio is NOT independent of weight and growth rate, if selection is placed on Feed Conversion Ratio alone it could potentially result in larger cattle with a higher maintenance requirement. Always apply a balanced approach to when choosing which traits to include in your breeding objective, do not single trait select.
Misconception #1
- Feed Efficiency only makes sense if you have a terminal production system where all the calves are sent to the feedlot, and not maternal systems wherein heifers are kept as replacements.
The truth in this statement comes down to the measure of feed efficiency that is being referred to (remember there are a few). Since Net Feed Intake is a trait that is independent of weight and growth rate it can be used to measure feed efficiency in either system. Archer et al. 1999 found that Net Feed Intake during the post-wean period and at maturity had high positive genetic correlations suggesting that selection decisions based on Net Feed Intake measured during the post-weaning period has the potential to translate to genetic improvements in Net Feed Intake of the cow herd (i.e., maternal systems). Heritability estimates of Net Feed Intake have ranged from 0.26 to 0.58, and generally fall within the moderate heritability range and tend to be similar to estimates for growth traits. Therefore, it can be expected that with sufficient data, selection for Net Feed Intake would be effective.
Misconception #2
- It takes 2.5 times more energy to create a pound (0.4545kg) of fat than it does to create a pound of muscle, therefore by selecting for feed efficiency you are inadvertently selecting for taller, leaner, later maturing animals that do not have the propensity to put on fat.
Depending on age, sex and level of production approximately 65-70% of the total energy required for meat production is used for maintenance, leaving approximately 30% of energy intake for growth and reproduction (Cabezas-Garcia et al. 2021). Differences in efficiency of growth may be due to differences in composition of gain. For example, Ferrel and Jenkins (1998) showed that differences in rate of water, protein and fat deposition influence efficiency and rate of body weight gain primarily because fat has higher energy density than either protein or water. Although more energy expenditure is required for fat versus protein deposition, maintenance of protein requires more energy than maintenance of fat (Crews 2005). Therefore, although it indeed takes more energy to create a pound of fat compared to muscle, this is not affected by selecting for Net Feed Intake which focuses on selecting animals with a lower maintenance requirement (Lisa Rumsfeld (Vytelle) – Personal Communication).
Misconception #3
- Daughters of feed-efficient bulls will be tall, late maturing, and difficult to get bred.
Once again, since NFI is a measure independent of weight (body size) and growth rate, daughters of feed-efficient bulls (based on NFI) will not necessarily be taller or later maturing. Net Feed intake has a very low phenotypic correlation with fat deposition (0.17) and marbling, therefore selection for NFI can be done without significantly compromising fat deposition. A balanced approach to selection whereby you include fat measurements in your breed objective should further ensure this.
In conclusion, feed costs represent a significant portion of the total cost of beef production, therefore genetic improvement programs for reducing input costs will likely include traits related to feed utilization. In contrast to traditional ratio type measures of efficiency (FCR), residual feed intake is uncorrelated with body weight and growth rate, which at least partially alleviates concerns over the long-term implications of selection and antagonistic correlated responses for mature size and maintenance requirements.
Acknowledegements
Lisa Rumsfeld – Vytelle