The Use of Ultrasound Measurements in Beef Breeding Programs
Livestock Update, December 1999
Scott P. Greiner, Ph.D., Extension Animal Scientist, Beef, Virginia Tech
Due to the decline in market share over the past two decades, the beef industry has been challenged to shift from being a commodity-driven to a consumer-driven business. Providing consumers with the lean, palatable, wholesome product they desire has increased focus on the end product by all segments of the industry. Growth in alliance and specification programs, as well as carcass merit-based pricing systems are a testimony to these changes. These forms of value-based marketing have increased the emphasis placed on carcass traits by producers, as financial rewards are available for those providing a superior product.
Greater focus on the end product has stimulated demand for genetic evaluation of carcass traits. However, collection of progeny carcass data for use in expected progeny difference calculation by breed associations is time consuming, expensive, and requires extensive cooperation by various segments of the industry. In addition, the past inability to measure carcass traits on breeding animals has limited the amount of data available for these genetic evaluations. The use of real-time ultrasound has tremendous potential to alleviate these shortcomings. Scanning of yearling seedstock for carcass merit would reduce the dependency on progeny testing and shorten the time interval required for evaluation. Additionally, incorporation of ultrasound into structured sire evaluations would allow carcass merit to be evaluated at a proper endpoint and allow for maintenance of contemporary groups which are frequently disrupted by marketing procedures. However, these possibilities are contingent on the ability of real-time ultrasound to measure carcass traits in the live animal in a consistently accurate manner.
The use of ultrasound for fat and muscle prediction in live beef cattle is not a new technology, as it has been used for over 35 years to determine body composition. Over time, technological advancements have improved ultrasound equipment and likewise improved accuracy of carcass trait prediction. Development of a longer ultrasound transducer or probe, specifically designed for cattle use, has been the major advancement in ultrasound hardware. This longer probe allows for imaging of the entire ribeye muscle and has resulted in improved accuracy of this trait.
Adaptation of ultrasound as a tool for genetic improvement by beef cattle breeders over the last ten years has been largely dependent on their confidence, or lack of confidence, in the accuracy of the technology. Generally, the term accuracy has been used to refer to the relationship between an ultrasound measurement taken on the live animal and the same measurement taken on the carcass in the cooler. Many studies have been conducted over the years to define the variability in ultrasound's ability to predict carcass measurements. This variability can be attributed to several factors including type of ultrasound machine and magnitude of the measurement itself (ribeye size, level of fat thickness). However, the majority of the variability in accuracy of prediction can be attributed to the ultrasound technician. Technician error arises as a result of both the image collection process as well as the interpretation/tracing of the image for measurement determination (Duello, 1993; Herring 1994a).
Due to the variation in technician proficiency, the Beef Improvement Federation has developed certification standards to measure technician accuracy. Breed associations have utilized certified technicians for compilation of ultrasound data for use in genetic evaluations. There are three accuracy criteria that are used to certify each technician: 1) Standard error of prediction- standard deviation of the difference between ultrasound and carcass measurement, measure of the technician's ability to rank or predict differences between animals correctly; 2) Standard error of repeatability- measure of the technician's consistency (repeated measurements on the same animal); and 3) Bias- measure of the average difference between a technician's estimate and the carcass measurement, not related to technician's ability to rank animals or predict differences between animals. These certification standards are useful for understanding achievable levels of accuracy with ultrasound.
|1997 BIF Ultrasound Certification Standards|
The certification standards for standard error of prediction indicate that 67% of the time, ultrasound fat thickness measurements are within .10 inches of carcass measurements. Likewise, proficient technicians are within 1.2 square inches of the carcass measurement 67% of the time for ribeye area.
Percent Intramuscular Fat:
Marbling may be objectively measured in live cattle using real-time ultrasound and is reported as percent fat in the ribeye muscle. Percent fat correlates with a USDA grader's subjective visual evaluation of marbling in a beef carcass and is the primary component for carcass quality pricing. Relative to fat thickness and marbling, however, marbling can be assessed with somewhat less accuracy than fat thickness or ribeye area in live cattle (see table above).
Research studies have found a relatively high correlation of .75 between ultrasound-predicted percent fat in the live animal and the actual percent fat in the carcass ribeye (Wilson et al., 1998a). We would not expect this relationship to be perfect, as marbling scores are subjective and influenced by a USDA grader's assessment of texture and distribution of intramuscular fat as well as color of the lean. On the other hand, percent intramuscular fat is an objective measure determined by chemical analysis. The following table outlines the relationship between intramuscular fat percentage and the USDA quality grading system.
|Relationship Between Chemical % Intramuscular Fat and USDA Quality Grades|
Due to sex differences, bulls will have significantly lower percent intramuscular fat values than steers. When bulls and steers are slaughtered at a common age endpoint, steers have from 2 to 2.5% more intramuscular fat than bulls (Wilson, 1995). Therefore, steer mates to a bull with 2.5% intramuscular fat (Standard) would have approximately 5.0% intramuscular fat (low Choice).
It is important to note that individual carcass trait measurements are only indicators of total carcass composition, and ultrasound serves as a mechanism by which we can predict these predictors. Therefore, the ability of ultrasonic measurements to predict retail product yield relative to carcass measurements is important if ultrasound is going to be used as a means to improve end product.
Due to the expense involved in collecting carcass cut-out data, relatively few studies have examined the efficacy of using ultrasound/live animal measures to predict beef carcass retail yield. Recent studies have shown that prediction of retail yield is only slightly less effective using ultrasound measures of fat thickness and ribeye area compared to actual carcass measures (Herring et al., 1994b; Williams et al., 1997).
The predictive value of various ultrasonic and carcass measurements for a study conducted at the U.S. Meat Animal Research Center is summarized in the following table (Greiner, 1997). This study was conducted over a two year period and involved 534 steers representing six sire breed groups. Carcasses were fabricated into boneless, totally trimmed retail product and ultrasound as well as carcass measures were used to predict retail product yield. Ribeye area and fat thickness are the two traits most closely related to beef carcass retail product. Fat thickness and percent retail product are inversely related, with increasing levels of fat thickness resulting in a lower percentage of the carcass as saleable retail product. When done properly, ultrasound and carcass measurements of 12-13th rib fat thickness both account for a similar amount of the variation in percentage of retail product (54%). It has been hypothesized that ultrasonic assessment of fat thickness may be superior to carcass measurements due to hide pulls and disruption of the fat layer during carcass processing. In contrast to 12-13th rib fat thickness, ribeye area explains a small percentage of the variation in percentage of retail product. Carcass ribeye explained 6% more of the variation in retail product percentage than did ultrasound ribeye area when each was used as a single predictor. It appears that ultrasonic measurements of fat thickness are as predictive as carcass measures for retail product yield, whereas ribeye area measured on the carcass is more highly related to retail yield parameters than ultrasonic ribeye area.
An ultrasonic estimate of rump fat (measured between hooks and pins, parallel to the vertebrae has shown promise as an additional indicator of body composition. It is thought that this measurement will be more useful on lean cattle (bulls), as they may exhibit more variation in fat deposition over the rump that at the 12-13th rib (Bertrand and Kriese, 1995).
Ultrasound measurements of 12-13th rib fat, ribeye area, rump fat, and live weight used together accounted for 61% of the variation in percentage of retail product in this study. This compares favorably to the 65% explained by current USDA Yield Grade measurements. These results, along with other studies, confirm ultrasound is a useful predictor of carcass composition in live beef cattle.
The power of ultrasound resides in the ability to quickly amass large amounts of data, through the scanning of yearling bulls and heifers, for use in carcass trait genetic evaluations. To date adoption for this use has been slow due to differences in technician proficiency and variability in software for measurement determination. However, the American Angus Association has initiated a research project to investigate the use of ultrasound data collected on yearling bulls and heifers to supplement their carcass database. The project involves the use of a centralized processing laboratory, in which all measurements are performed. Approved technicians collect images in the field, and then send them to the processing lab where the actual measurements are made by trained, highly skilled interpretation technicians. This process was designed to insure credibility, timeliness, and accuracy of the ultrasound measurements as well as serve as a quality control mechanism for data collected. Breeders receive ultrasound data back in much the same form as growth performance records, including contemporary group means and individual ratios.
The preliminary results of this research were released in September, 1999. Over 30,000 animal records had been collected since the start of the project in January, 1998. EPDs for ultrasound traits were calculated for 2,153 bulls. To put this in perspective, the fall 1999 Angus Sire Evaluation lists a total of 2,378 bulls with carcass EPDs which are the result of 45,851 progeny carcass records. These progeny carcass records have been assembled over the last 15 years, or since the inception of the sire carcass testing program. This emphasizes a primary advantage to ultrasound- generating a large database in a relatively short period of time. Heritability estimates from the research are also very encouraging: % intramuscular fat- .30, ribeye area- .36, rib fat- .34, % retail product- .35, and rump fat- .39. These heritabilities are equal to or higher than those reported for the carcass evaluation, indicating that ultrasound can accurately measure these traits.
Until the time that ultrasound data is fully incorporated into carcass trait genetic evaluations, breeders are faced with the use of adjusted data for selection decisions. As with any performance trait, proper contemporary group identification is essential. Currently, most ultrasound measurements are being adjusted to a common age endpoint (365 day), much like carcass data. Yearling bulls should be scanned when they are between 320 and 440 days of age. All bulls within a contemporary group should be scanned on the same day to minimize potential environmental differences that may influence image quality. This is most important for percent intramuscular fat prediction.
Proper use of ultrasound data involves understanding its limitations. As an example, the accuracy of the measurements is not definitive enough to correctly rank the top 3 or 4 bulls within a contemporary group for a particular trait. For seedstock producers, sire group effects should be of most interest. On the other hand, ultrasound is certainly useful to distinguish which bulls are in the upper third vs. lower third for a particular trait, or sorted into high, average, and low categories. Additionally, potential outliers for traits of interest may be considered as candidates for carcass testing. Objective ultrasound measurements also compliment visual evaluation in bull selection. Ultrasound measurements, combined with pedigree information can serve as a useful selection tool in beef breeding programs.
Bertrand, J. K. and L. A. Kriese. 1995. Genetic evaluation of carcass traits: Results, questions and concerns. Proceedings of 5th BIF Genetic Prediction Workshop.
Duello, D. A. 1993. The use of real-time ultrasound measurements to predict composition and estimate genetic parameters of carcass traits in live beef cattle. Ph.D. Thesis. Iowa State Univ., Ames.
Greiner, S. P. 1997. The use of real-time ultrasound and live animal measurements to predict carcass composition in beef cattle. Ph.D. Thesis. Iowa State Univ., Ames.
Herring, W. O., D. C. Miller, J. K. Bertrand, and L. L. Benyshek. 1994a. Evaluation of machine, technician, and interpreter effects on ultrasonic measures of backfat and longissimus muscle area in beef cattle. J. Anim. Sci. 72:2216-2226.
Herring, W. O. S. E. Williams, J. K. Bertrand, L. L. Benyshek, and D. C. Miller. 1994b. Comparison of live and carcass equations predicting percentage of cutability, retail product weight, and trimmable fat in beef cattle. J. Anim. Sci. 72:1107-1118.
Williams, R. E., J. K. Bertrand, S. E. Williams, and L. L. Benyshek. 1997. Biceps femoris and rump fat as additional ultrasound measurements for predicting retail product and trimmable fat in beef carcasses. J. Anim. Sci. 75:7-13.
Wilson, D. E. 1995. Breeding Programs that compete in a value-based market (seedstock). In: Beef Cattle Value Based Marketing. Iowa State Univ. Extension.
Wilson, D. E., G. H. Rouse, and S. P. Greiner. 1998a. Relationship between chemical percentage intramuscular fat and USDA marbling score. ISU Beef Research Report. A.S. Leaflet R1529.
Wilson, D. E., G. H. Rouse, and C. L. Hays. 1998b. AAACUP Research Update. In: Handbook American Angus Assoc. Centralized Ultrasound Processing.