• Introduction
• Measuring Feed Efficiency
  • Residual feed intake (RFI)
• Changes Over the Years
• Selecting for Feed Efficiency
• Impact of selecting for low RFI
  • Relationship between feed efficiency and other important production aspects

Introduction

The figure below shows how, for the cow herd portion only on a farm, the costs of production resulted in negative returns on investment for the average of all Alberta AgriProfits producers 11 out of 16 years. The low cost producer (the top 1/3 of the Agriprofits participants) saw negative returns on investment 6 out of 16 years.  Considering the tough times in 2003 with BSE and the increasing feed prices from 2006 onward, knowing that 70% of beef production costs are feed related, the targeted selection for improved feed efficiency in the cow herd will only improve the return on investments (ROI’s).  No one wants to be that average producer, we all want to be above average.  We have to watch our inputs and outputs and focus on those aspects that result in long term gain.

Measuring Feed Efficiency

If you ask an average cattle producer how they measure feed efficiency in their herd, most would say by looking at the feed to gain ratio (Feed:Gain) or the feed conversion ratio (FCR).  Basically, this is the calculation of the feed consumed per unit of weight gained.  However, what this measure does not tell you is what the individual animals are eating. It only gives you a group average. While a group average might be useful in a feedlot situation, it really is of little value to a breeding herd where you want to make progress through genetic selection.  Many beef cattle breed associations have adopted a slightly different method of evaluating individual feed efficiency, called residual feed intake, or RFI.

Residual feed intake (RFI)

Residual feed intake is defined as the difference between an animal's actual feed consumed, or eaten, and the animal’s calculated feed requirements based on its body weight and ADG during a standardized test period. Essentially, RFI describes the variation in feed intake that remains after the requirements for maintenance and growth have been met. Efficient animals eat less than expected and have a negative or low RFI, while inefficient animals eat more than expected and have a positive or high RFI. 

More recently, RFI values have been adjusted for body fatness (RFIfat), thus attempting to render RFI independent of carcass fatness in slaughter cattle and later maturity or fattening in replacement heifers and bulls.  Similarly, another measure referred to as residual gain (RG) is adjusted for body size and dry matter intake (DMI).  It represents animals with superior gain at equal levels of body weight and DMI. A trait that combines both RFI and RG, referred to as residual intake and gain (RIG), represents metabolically efficient, fast growing animals that consume less feed.  These latter two measures of feed efficiency should also be adjusted for body composition using final off-test ultrasound backfat  thickness, marbling score and/or ribeye area. These measures of feed efficiency are heritable and either moderately (RFI vs. RG) or highly (RG vs. RIG) correlated with each other.   

Changes Over the Years

We know that other livestock species have made improvements in feed:gain ratios over the years through both genetic and non-genetic selection.  Take the pig as an example, FCR has improved from 3.8 lbs to 2.6 lbs of feed per pound of gain from 1972 to 2007.  During these 35 years, the pig’s final market weight also rose from 220 lbs to 275 lbs.  While it is unreasonable for beef producers to expect to achieve the feed efficiency levels of pigs and chickens, due to the physiological differences of beef cattle, it is important to identify cattle that are genetically superior at converting feedstuffs to pounds of meat.

For the beef cow, both the measures of DMI and ADG are related to body size, growth and composition of gain.  Thus, selection for improved FCR has resulted in cattle that grow faster (increased ADG), have increased mature size, and increased maintenance and feed requirements.  We’ve already been doing this and we produced a larger framed cow who ate more. Figure 3 shows the feed maintenance requirements for cows over this 50 year period.  While it’s true that the cow size increased, so did their feed requirements - substantially.

If you take a look at the show ring heifer champions over the years during this same time period, you’ll see a drastic change in frame size from the 50’s to the early 80’s and a return to a more moderate frame size by the early 2000’s.  What we still don’t know about these replacement females is how much they ate for the performance they had.  On the other hand, we do know that these breeders selected these heifers based on more than one trait.  Structural correctness, conformation, docility, and their ability to breed and raise a calf were all considerations in their breeding programs; so we can’t forget that.  Even though we have a great tool to measure feed efficiency in the RFI trait, it has to be taken into account with the other traits of economic value.  For a cow-calf producer, fertility is 10 times more important than carcass traits and 5 times more important than growth traits.  Single trait selection is never a wise decision nor a practical goal to pursue.

Selecting for Feed Efficiency

Seedstock producers and breed associations have effectively used expected progeny differences (EPD’s) to improve the genetic merit of their cattle.  However, these have been primarily for traits including growth and carcass which have put an emphasis on income and revenue generation leading producers to place a high value and level of importance on these traits to sustain their operation.  What has been forgotten to some extent is the selection for factors that could lower costs within the production cycle, like feed efficiency.   Measuring and selecting for the inputs and not just the outputs needs some attention for the beef operation to continue generating income, but also to enhance sustainability and save costs.   Selecting cattle for their feed efficiency using the RFI trait is the best measure we currently have as a direct measure of metabolic efficiency, or energy conservation because it is independent of body weight, average daily gain and backfat thickness.  In any population there is variation in feed efficiency, and there will be individuals that can achieve high rates of gain with low feed intakes just as there will be individuals achieving low rates of gain with high feed intakes and others in between.  Our challenge comes in measuring cattle for this trait, interpreting the numbers and using the data for genetic progress.

Figure 4 compares the progress that has been made in dry matter intake and the resulting feed costs throughout the 1990’s at an Australian Research Centre in regards to actual selection for feed efficient cattle by using RFI.  The negative RFI (high efficiency cattle) have reduced their dry matter intake per day by close to 0.5 kg resulting in significant feed savings to the beef operation. However, given that multi-trait breeding goals will be pursued by the industry, the researchers assumed an annual rate of response in RFI of -0.08 kg DM/day (0.8%/year) in a 25-year simulation compared to not selecting for RFI. Much progress can be made in improving feed efficiency well into the future as each generation improves after targeted selection for the trait.

Currently, the easiest way to select for feed efficiency (if you are not testing your own cattle) is to purchase feed efficient or negative RFI bulls to use on your cow herd.  Typically RFI is measured in young cattle (7-10 months of age) in feedlot pens fitted with feeding stations designed to automatically monitor individual animal feed intake over a 70 day test (e.g., Figure 5. GrowSafe Systems Ltd., Airdrie, Alberta, Canada) following a three week adjustment to their test diet.  Cattle are weighed before feeding on two consecutive days at the start and end of the test period and at approximately 14-28 day intervals. They are also measured for ultrasound backfat thickness (mm), rib eye area (cm2) and marbling score at the start (optional) and end of the test period.

Impact of selecting for low RFI

Several researchers around the world, including Dr. John Basarab, an Alberta Agriculture and Rural Development  Beef Research Scientist, have been studying this trait for more than 15 years.  They have come to the following conclusions about what selection for feed efficient cattle means to the beef industry.

Research has shown that selection for low RFI (efficient cattle) will:

1. Have no effect on growth, carcass yield & quality grade
2. Reduce feed intake at equal weight and ADG
3. Improve feed to gain ratio by 10-15%
4. Reduce net energy of maintenance and reduce methane and manure production (reducing the carbon footprint of cattle)
5. Have little if any effect on age at puberty
6. Have no effect on calving pattern in first calf heifers
7. Have no negative effect on pregnancy, calving or weaning rate
8. Have little effect on bull fertility
9. Have a positive effect on body fatness or weight particularly during stressful periods
10. Will reduce feed costs
    • $0.07-0.10/hd/d feeders
    • $0.11-0.12/hd/d in cows

If these ten reasons to select for feed efficient cattle are not enough to convince you it’s an important trait to pursue, it is likely because you are concerned about the relationships RFI has to other traits of importance.  Because RFI is a relatively new trait, there are questions regarding its effect on other traits and its’ repeatability at different stages of an animal’s life, on different diets and in different environments.

By looking at the cows below, you likely have a preference for one over the other when their feed efficiency isn’t known.  When you find out they both weaned calves of similar weights and they both were pregnant, you are probably inclined to find the deep bodied, more feminine looking cow on the right as more appealing.  When we look at RFI scores and see this same cow ate 2.83 kg more per day (6.2 lbs) than the average cow in the herd and 5.4 kg (11.9 lbs.) than the other cow (Figure 7), you’ll probably reconsider knowing the impact on feed costs for a herd of 100’s or 1000’s of these feed inefficient cattle.  These are extremes in a herd and illustrate how conformation alone doesn’t tell you the whole story on productivity and performance.  Granted, these are large cows, but the concept of feed efficiency is the same for other breeds and sizes of cows.  The argument has been made by producers that their 1100 lb mature cows are all efficient because they are smaller.  Remember, RFI is independent of body size and weight, average daily gain and backfat thickness and variation and extremes exist in all populations. 

Relationship between feed efficiency and other important production aspects

Let’s now consider some of the relationships between RFI and other traits of importance.  Many factors affect the actual feed intake (DMI) of cattle such as body size, growth, body composition, gender, age, season, ambient temperature, physiological status, previous nutrition and diet. Most of these factors are either equal between animals during a standardized feed intake test (e.g., gender, season, ambient temperature and physiological status) or are adjusted for, such as body size, body composition, and growth so that we can make direct comparisons between animals.  However, considerable within- and between-animal variation does exist in DMI and measures of feed efficiency.

Diet Type and Breed Type

RFI measured on a grower diet and then again on a finisher diet is positively correlated, meaning the animals tend to rank similarly on both diets when tested.  It is also true of RFI measured post-weaning in heifers and RFI measured again later in life as mature cows. However, other research showed that some animals do re-rank, meaning some will have a positive RFI or be inefficient in one test and then when tested again are efficient or have a negative RFI.  This level of re-ranking for RFI, DMI and ADG occurred whether the diet changed from a grower to finisher diet or stayed the same from feeding period  to feeding period.  Such re-ranking was due to: 1) body weight and feed intake measurement error, 2) animal variation in response to compensatory gain, 3) animal variation in efficiency with animal maturity and, 4) animal variation in diet digestibility due to differences in feeding behavior, rate of passage and rumen microbial population. Preliminary data from the Lacombe Research Centre, Canada, also confirms the moderate to strong repeatability of RFI over different stages of the animal’s life.  Replacement heifers identified as –RFI and +RFI when they were 8-12 months of age and fed a 90:10% barley silage and barley grain diet (as fed; -0.373 vs. 0.365 kg DM/day) were also -RFI and +RFI when measured again as 4-7 year old cows and fed a 70:30% grass hay and barley straw cube diet (as fed; -0.375 vs. 0.459 kg DM/day). These results indicate that RFI is consistent across different stages of an animal’s life.  Although, there may be a need for different test criteria (e.g., forage vs. grain-based diets) when selecting terminal and maternal bulls.  Breed types destined for maternal purposes should be tested on forage diets whereas those breed types designed for terminal sire purposes be tested on grain-based diets.

Body Size and Carcass Traits

RFI is not related to pre- and post-weaning growth, body size, slaughter weight and carcass traits in beef cattle and the phenotypic and genetic correlations are near zero.  Experiments have shown no difference in carcass weight, dressing percentage, or marbling grade between cattle of positive and negative RFI values.  However, in an Australian study, the muscle of efficient animals was found to be slightly leaner and also have slightly more calpastatin than inefficient steers, which may negatively affect meat tenderness.  Tenderness is being monitored in efficient animals to see if these results are repeatable in other cattle populations.  RFI is moderately to highly correlated with feed intake and feed conversion ratio (FCR). This implies that selection for -RFI will decrease feed intake at equal levels of body weight, growth and body fatness, and will improve feed-to-gain ratio in feeder cattle and growing replacement heifers.

Methane Emissions

The fact that efficient cattle have decreased feed intake at equal levels of body weight, growth and body fatness also implies that selection for low RFI will decrease methane (CH4) emissions (g/animal/day) because methane emissions are proportional to feed intake.  Generally, the higher the DMI, the higher the methane emissions are.  These estimated reductions in methane emissions of 9-12% also coincide with a 15-17% reduction in manure production.  Improvements to feed efficiency will influence the carbon footprint of cattle making beef more sustainable.

After 25 years of selection for –RFI in an Australian simulation model, the efficient 120-cow beef herd had lower GHG emissions by 101 t CO2e per year or 0.844 t CO2e per cow per year compared with the average 120-cow herd. In addition, the carbon footprint of the efficient herd was 14% lower than that of the cow herd not selected for RFI (19.82 vs. 23.06 kg CO2e/kg carcass beef) and the total farm area decreased by 13%.  These estimates of GHG reduction are conservative as improved DM digestibility in –RFI cattle and improved accuracy and rate of genetic change resulting from genomic enhanced breeding values were not considered.

Feeding Behaviours and Temperament

Feeding behaviours that are collected as part of the RFI test suggest that inefficient (+RFI) cattle use about 5% more energy in feed related activities and possibly use less time ruminating.  They may also be more reactive to stressors since they visit the feed bunks (9-22%) more often each day and have more feeding during the night periods.  Inefficient cattle may also be less docile and more nervous, in regards to their temperaments, compared to efficient cattle.

Body Condition and Adaptability

Observations of beef cows in extensive Canadian winter conditions has shown that –RFI (efficient) cows actually maintain themselves in better body condition score with no differences in productivity compared with their +RFI herd mates. Dams that produced -RFI progeny consistently had 2-3 mm more back fat thickness, on average, over the 12th and 13th ribs and lost less weight during early lactation (pre-calving to pre-breeding) than mothers that produced +RFI progeny.  In addition, –RFI (efficient) heifers calving for the first time had lower calf deaths within 30 days of birth than +RFI (inefficient) heifers. Lower calf death loss suggests that the improved early life survival of calves from -RFI mothers may be due to their improved feed efficiency resulting from more available nutrients and a better uterine environment compared with +RFI mothers.  Recent research from the Lacombe Research Centre confirm these findings in that –RFI cows gained more body fat and body weight than +RFI cows when both groups swath grazed forages for the first time during Canadian winters where night time temperatures dropped below -20° C and animals grazed through the snow from November to March. Previous to this, both –RFI and +RFI young cows had been wintered together in smaller holding areas and fed barley silage to meet their nutritional requirements.  Even though efficient cattle have documented lower feeding event duration and frequency and lower feed intake when bunk fed in an RFI test, this does not mean that –RFI animals cannot compete or acquire forages during extensive grazing. Instead it may imply that efficient animals are more adaptable and less susceptible to stress than +RFI or inefficient animals.

Fertility and Productivity

The relationships of RFI on fertility and productivity in heifers and cows have recently been reviewed showing, -RFI and +RFI cows and heifers were similar in culling, pregnancy, calving and weaning rate, calving pattern and kilogram of calf weaned per mating opportunity (in both Canadian and Australian data). However, -RFI (efficient) cows calved 5-6 d later in the year than +RFI (inefficient) cows. When RFI was adjusted for body fatness (final off-test backfat thickness; RFIfat) no differences were observed in percentage of -RFIfat and +RFIfat heifers reaching puberty by 10, 11, 12, 13, 14 or 15 months of age nor in the percentage of calves born by day 28 of the calving season. Calving difficulty, age at first calving, calf birth weight, calf pre-weaning ADG, calf actual and 200-d weaning weight and heifer productivity, expressed as kg calf weaned per heifer exposed to breeding, were also similar between -RFI and +RFI heifers. Figure 8 below shows how –RFI (efficient) heifers appear to reach puberty later and get pregnant later in the breeding season compared to +RFI (inefficient) heifers.  However, this small difference is likely a feature of the RFI testing procedure itself.  Heifers reaching puberty near the start of the test period may actually have greater energy expenditures (5% greater) because they are cycling throughout the test due to their sexual development and greater activity compared to heifers that reach puberty near the end of an RFI test.  So, this explains why they may breed and calve somewhat later.  What is important is that all the heifers reached puberty by 15 months of age and all heifers were pregnant before 40 days of a breeding season; both suitable management targets.

Bull Fertility

Fertility of young bulls, as measured by scrotal circumference, breeding soundness evaluation, calves born per sire and semen characteristics, for the most part has been unrelated to RFI, though several weak associations have been observed with sperm morphology and motility.  What this is suggesting is that perhaps the efficient –RFI bulls are younger and have less developed sperm.  These observations may also reflect the need to adjust RFI for off-test ultrasound backfat thickness and feeding behaviors in an effort to prevent the selection for later maturing bulls.  A study at the University of Alberta, Kinsella herd showed there was no difference in the number of calves sired by –RFI bulls compared to +RFI bulls.  We have to be careful to not interpret poor sperm morphology with infertility since libido in addition to other aspects of a breeding soundness evaluation are important to ensure any bull, regardless of RFI status, is acceptable to be put into a breeding situation. 

Data continues to be collected from collaborative research projects focused on feed efficiency and residual feed intake both in Alberta and internationally.  Careful interpretation of the data when applying or adopting the technology to your beef operation is up to you to make the most of it.  While there exists a large variation in the range of RFI values in animals, more than 35%, and because the trait is moderately heritable, significant genetic progress can be achieved in breeding programs resulting in cost saving benefits.  For now, because we can’t possibly test all cattle for RFI, contact your breed association to get a list of RFI tested sires for sale at upcoming bull sales.  Introducing sires with a known RFI value is a first step to moving you cow herd toward increased feed efficiency.  However, with time and continued improvement in technologies, the ability to detect efficient animals will improve and increase our ability to select superior animals.

Feedback

Feedback and questions on the content of this page are welcome. Please e-mail us.

Acknowledgements

Thanks to Dr. Susan Markus, Beef Research Scientist, Alberta Agriculture and Rural Development, for contributing her time and expertise to writing this page.