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Selecting for improved Feed Efficiency

Selecting for improved Feed Efficiency

By the spring of 2009, it will be pretty clear to cow/calf producers that feed cost is the largest variable cost on their operations

By the spring of 2009, it will be pretty clear to cow/calf producers that feed cost is the largest variable cost on their operations. In response, producers need to realize that in the “profitability equation” (where profit = revenue – expenses) feed cost is the largest variable over which they have control. And, in the face of rising feed costs, we’re way behind in the genetic selection for improved feed efficiency.

The ability to reduce feed intake (and therefore feed cost) without negatively affecting reproduction, growth, carcass performance, or meat quality is becoming a priority in beef cattle selection programs. Until recently, the seedstock industry focused primarily on developing genetic predictions only for growth and carcass traits, primarily since they were easy and inexpensive to measure.

Selection for growth and carcass performance has resulted in substantial genetic improvement. Unfortunately, these traits only focus on the ‘revenue’ side of the profitability equation. Further, most producers have inadvertently focused on maximizing production of these traits in an attempt to maximize revenue, with limited consideration for cost. In contrast, efforts to develop expected progeny differences (or EPDs) for key ‘cost’ traits, such as feed efficiency, are not yet widespread.

Measuring Feed Efficiency is Hard
Unfortunately, there are two major challenges associated with genetically predicting feed efficiency: 1) historical methods used to calculate and select for feed efficiency are generally lacking, flawed, and/or unproven, and 2) collecting daily feed intake on individual cattle is very expensive.

Calculation Challenges. Historically, feed efficiency has been primarily measured and reported as a ratio – the Feed Conversion Ratio or FCR. It is calculated by dividing the amount of feed consumed by the number of pounds gained. So, for an animal that consumes 21 lbs of feed (on a dry matter basis) and gains 3 lbs, its FCR would be 7 (21 lbs ÷ 3 lbs = 7).

The challenge with using the simple FCR calculation is that it ignores an animal’s body weight, rate of gain, and composition (i.e. amount of fat stores). As a result, selection based on FCR unintentionally leads to animals that are faster gaining but also have a greater mature size. In some cases, this can lead to deleterious effects on reproduction and profitability.

High Cost of Data Collection. Collecting individual daily feed intake on seedstock cattle is very expensive. Unless animals are fed alone in individual pens, the only methods to collect individual intake data for cattle in group pens require the use of costly technologies.

Calan gates have been around for decades, and have been used extensively by most land-grant universities. However, labor is needed to operate and manage them. GrowSafe, a recently-developed alternative from Canada, allows large pens of animals to be evaluated for individual feed intake with limited labor required.

Beyond collecting daily feed intake data on individual animals, cattle weight gain must also be measured regularly (typically every 2 weeks during a 70-day test) in order to effectively characterize feed efficiency. The high frequency of weighing is due to the significant variation that occurs with body weight due to weather, water intake, health, etc.

A final challenge in determining feed efficiency during a test relates to variation among test locations. To generate valuable data, uniformity in rations, rates of gain, and test length is needed.

We’re Playing Catch-up
The U.S. beef industry is in dire need of two things: 1) agreement on how best to measure and genetically-predict feed efficiency, and 2) an elaborate infrastructure to evaluate cattle individually for feed intake during a uniform test period (such as the tests that occurred during the heyday of central bull test stations).

In addition to generating a large amount of feed efficiency data, accurate methods to predict feed efficiency are needed. This might include the analysis of tissue samples (for blood hormone concentrations), low-cost genetic markers, or correlated traits that can be measured easily.

oday, there are really no widespread genetic predictions for feed efficiency in beef cattle. However, a few years ago some breed associations began offering a genetic prediction for differences in the amount of dietary energy required by daughters of a bull. These new EPDs include the Maintenance Energy (ME) EPD from the Red Angus Association of America, and the Cow Energy Value ($EN) EPD from the American Angus Association.

Unfortunately, the units associated with these two EPDs are not consistent. The Maintenance Energy (ME) EPD is reported on a megacalorie (Mcal) per month basis, while the Cow Energy Value ($EN) EPD is expressed in dollars saved per cow per year. Therefore, a negative ME EPD is considered favorable while a negative $EN is unfavorable (Table 1).

The ME EPD assumes that the energy content of average quality range forage is 0.86 Mcal/lb (on a dry matter basis). Therefore, the offspring of a sire with an ME EPD of +6 will require approximately 7 lbs (6 ÷ 0.86 = 7) more feed each month (on a dry matter basis) compared to offspring of a sire with an ME EPD of 0.

Data used for the creation of these EPDs does not include any actual feed intake data collected during a specified test. Instead, previously-available data that correlate to cow energy requirements were used: mature cow body weight at weaning (adjusted for body condition score) and Milk EPD. This is based on the fact that a sire producing daughters with greater milk production (i.e. higher Milk EPDs) and more growth (as seen by larger mature sizes) will require more dietary energy to maintain her body weight.

Australian seedstock producers have taken a different approach to predicting feed efficiency. The Angus Society of Australia publishes an expected breeding value or EBV (generally equivalent to an EPD) for a trait referred to as Net Feed Intake. This trait, also referred to more commonly in the U.S. as Residual Feed Intake (RFI), is an estimate of the genetic difference in feed intake after growth rate and body weight have been accounted for. It is an alternative method of characterizing feed efficiency in beef cattle, and is based on actual feed intake data.

Predicting Feed Efficiency Tomorrow
To build on the currently available Maintenance Energy and Cow Energy Value EPDs in the U.S., the evaluation of seedstock cattle for RFI instead of the traditional Feed Conversion Ratio has begun. An animal’s RFI value is the difference (in pounds) between the animal’s actual feed intake and its predicted feed intake. These two numbers are acquired easily, but still require that an animal’s daily feed intake and bi-weekly weight are recorded during a uniform test period.

The first value – an animal’s actual feed intake – is collected daily during a standard 70-day post-weaning test of an entire contemporary group of calves (from the same management group, cohort, and sex). The second value – the animal’s predicted feed intake – is generated from a statistical calculation (known as a regression) which compares the animal’s feed consumption, weight, and gain with that of its contemporaries.

An animal’s RFI value is reported as the number of pounds of feed (on a dry matter basis) that it actually consumed compared to what it was predicted to consume. Therefore, an RFI of –2.0 indicates that an animal consumed 2 lbs less per day at the same rate of gain than an animal with an RFI of 0.0. Thus, a negative RFI value is considered desirable.

Amazingly, the RFI trait appears to be independent of growth rate (average daily gain), which enables the selection of more efficient animals without affecting performance or mature weight. The relationship among RFI and carcass performance or reproduction traits has not yet been studied as extensively; however, preliminary data indicate that RFI is probably independent of these traits as well.

In a typical group of yearling steers receiving a growing ration (high in forage), it appears that variation in feed intake of over 35% is common. For instance, in a group of 54 Angus steers evaluated for RFI during a 70-day test at the University of Idaho, 2 steers gained an average of 3.2 lbs/day but consumed 27 and 38 lbs of feed (dry matter basis), respectively. This difference of 11 lbs of feed per day represents the typical variation inherent in any beef cattle population.

RFI is becoming the broadly accepted ‘gold standard’ for measuring feed efficiency. Due to the variation of RFI within a population, and the fact that RFI is moderately heritable, it offers a genetic selection method to improve beef cattle feed efficiency without negatively affecting growth rate, mature size, or performance. In Australia, selection of parents with low RFI values (considered efficient) resulted in progeny that consumed less feed as yearlings but weighed the same at harvest as offspring from high RFI (inefficient) parents.

Alternatives to RFI Feed Intake Tests?
Today, the most reliable data result from actually measuring RFI in multiple progeny during a standard 70-day post-weaning test. Yet, one of the greatest hurdles to implementing widespread selection based on RFI is the cost of identifying sires with superior RFI values. In response, researchers have recently begun to search for useful indicator traits for RFI including blood hormone concentrations and candidate genes to reduce the cost of determining RFI values.

Currently, DNA marker technology has enabled two companies to offer genetic tests for feed efficiency: Bovigen (a division of Pfizer) offers the Genestar test, and Merial offers the Igenity profile.

The Genestar test uses four DNA markers that were identified as being related to RFI based on data from cattle evaluated for RFI. Genestar results are reported on a scale of 0 to 8 “stars,” where more are considered better (an animal with more stars vs. another will eat less but gain the same). Bovigen has reported that these four markers collectively explain 15% of the difference in intake among animals.

The Igenity profile differs in that it reports results for both RFI and feed intake, and also that it is only available for Bos Indicus-influenced cattle (e.g. Zebu or heat-adapted breeds such as Brahman). However, it is reported on a scale of 1 to 10 where a one-point difference in RFI equals 0.6 lbs/day of feed required for the same rate of gain. Thus, an RFI score of 1 is superior (where an animal requires less feed for growth and maintenance) compared to a 10.
Since these tests are very new, it is not yet clear how much genetic improvement in feed efficiency they will enable seedstock producers to achieve. Also, both tests only include a very small number of markers, even though a very large (but unknown) number of markers actually influence feed efficiency.

Much of the initial research to create these tests was conducted in Australian cattle. But, more importantly, the cattle were evaluated for RFI while receiving a grain-based finishing diet. In the U.S., initial indications are that cattle should really only be evaluated for RFI during the growing phase when a forage-based diet is fed. This enables cattle to be evaluated at a time when body composition (relative amounts of muscle, fat, and bone) is similar across the contemporary group. In contrast, composition is usually more varied during the finishing phase when mostly grain is fed.

The National Beef Cattle Evaluation Consortium has initiated a Commercial DNA Test Validation Program to independently verify genetic tests offered by genomics companies. Updates on the status of the validations are available. It is essential that data from indicator traits or genetic tests be validated and referenced to absolute measures of RFI before their adoption is widespread.

The Bottom Line
The days of cheap feed are over. As a result, the U.S. beef industry must undertake the monumental task of genetically improving the feed efficiency of our cattle. Substantial costs to collect crucial feed intake and weight gain data will be shouldered initially by seedstock producers. However, commercial bull buyers will soon be placing increasing emphasis on the genetic prediction of feed efficiency, most likely through the genetic prediction of traits like RFI.

Until an adequate number of sires can be evaluated for feed efficiency to create an RFI EPD, and DNA tests are validated for their accuracy, it is crucial for producers to focus on how best to incorporate feed efficiency into their selection programs. Economically-important traits such as reproduction and eating quality cannot be ignored at the expense of improving feed efficiency. If that occurs, the beef industry will give up its competitive advantage of unparalleled palatability to the pork and poultry industries, and we’ll never be able to compete with them on feed efficiency.