HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Crews, D. H. Articles by Kemp, R. A. Search for Related Content PubMed PubMed Citation Articles by Crews, D. H., Jr. Articles by Kemp, R. A.

Weaning, yearling, and preharvest ultrasound measures of fat andmuscle area in steers, bulls, and heifers¹

Agriculture and Agri-Food Canada Research Centre, Lethbridge, Alberta T1J 4B1, Canada

² Correspondence:
5403 1st Avenue South (phone: 403-317-2288; fax: 403-382-3156; e-mail:
dcrews{at}agr.gc.ca).

	Abstract

Top Abstract Introduction Materials and Methods Results and Discussion Implications Literature Cited

 
Longissimus muscle area and fat thickness were measured following weaning, at yearling, and prior to harvest using real-time ultrasound, and corresponding carcass measurements were recorded 3 to 7 d following the preharvest scan in composite steers (n = 116, 447 ± 19 d), bulls (n = 224, 521 ± 11 d), and heifers (n = 257, 532 ± 12 d). Although fat deposition was limited in bulls and heifers from weaning to yearling, coefficients of variation ranged from 8.46 to 13.46% for muscle area, and from 27.55 to 38.95% for fat thickness, indicating that significant phenotypic variance exists across genders. Residual correlations, adjusted for the effects of year of birth, gender, and age at measurement, were high and ranged from 0.79 to 0.87 among ultrasound and carcass measures of muscle area. Residual correlations among ultrasound and carcass measures of fat thickness were also high, ranging from 0.64 to 0.86. Weaning and/or yearling ultrasound muscle area yielded similarly accurate predictions of carcass muscle area. Yearling ultrasound fat thickness accounted for 13% more of the observed variance in carcass fat thickness than the weaning ultrasound measure in single-trait prediction models. When both weaning and yearling ultrasound measures were used to predict carcass fat thickness, partial R² values were 0.15 and 0.61 for weaning and yearling ultrasound fat thickness, respectively. The difference between predicted and carcass measures with respect to muscle area (fat thickness) was less than 6.45 cm² (2.5 mm) for 80.2 to 88.9% (90.3 to 95%) of animals. Preharvest ultrasound measures yielded standard errors of prediction of less than 4.95 cm² for muscle area and 1.51 mm or less for fat thickness. These results indicate that ultrasound measures taken between weaning and yearling provide accurate predictors of corresponding carcass traits in steers, bulls, and heifers.

Key Words: Accuracy • Beef Cattle • Carcass Composition • Ultrasound

	Introduction

Top Abstract Introduction Materials and Methods Results and Discussion Implications Literature Cited

 
Genetic evaluation and improvement programs for longissimus muscle area, fat thickness, and other component and composite measures of yield have traditionally relied on data collection from progeny tests. There is an increasing interest in the use of real-time ultrasound (RTU) as a noninvasive and cost-effective method to measure body composition in candidate replacement beef cattle. Potentially, RTU could be used to increase the relative amount of genetic information available to estimate carcass EPD and make selection decisions (Bertrand et al., 2000; Crews and Kemp, 2001).

Studies have shown that preharvest RTU measurements are highly repeatable (e.g., Brethour, 1992; Herring et al., 1994) and correlate with corresponding carcass measurements (e.g., Perkins et al., 1992; Herring et al., 1994; Hassen et al., 1998). There is a lack of recent literature, however, comparing accuracy of RTU measurements taken at ages other than shortly before harvest.

Bergen et al. (1997) reported that RTU traits in performance-tested beef bulls had sufficiently large variance and heritability to be valuable in genetic improvement programs for carcass traits. Effective evaluation and selection programs for replacement beef cattle should be based on accurate RTU measurements; however, research characterizing RTU accuracy among cattle of different genders is limited.

Research is needed that evaluates RTU in breeding as well as slaughter animals, including measurements taken prior to making selection decisions. The objective of this study, therefore, was to characterize the accuracy of RTU measurements from beef bulls, heifers, and steers at weaning, yearling, and preharvest.

	Materials and Methods

Top Abstract Introduction Materials and Methods Results and Discussion Implications Literature Cited

 
Data
Composite (0.25 Charolais, 0.25 Simmental, 0.44 British [Angus, Hereford, Shorthorn], 0.06 Limousin) steers, bulls, and heifers were produced at the Agriculture and Agri-Food Canada Research Substation at Onefour, Alberta, in 1996 and 1997. Calves were born between late February and mid-May each year and were weaned in late October when the average calf age was 200 d. A sample of bull calves (n = 60) were castrated at weaning each year. Details of the development of this stable composite breed were given by Mwansa et al. (2000).

Intact bulls and heifers were placed in drylot at weaning and fed a growing ration resulting in ADG of 1.07 and 0.70 kg•d^-1, respectively. The postweaning growth period continued for 196 d, after which bulls and heifers were transported to the Lethbridge Research Centre (LRC) feedlot and fed a finishing ration for 70 to 100 d prior to harvest. Steers were transported following weaning to the LRC feedlot and fed a growing ration (150 d, 1.13 kg•d^-1) followed by a finishing ration (90 to 120 d, 1.34 kg•d^-1) until designated for harvest when live weight reached a minimum of 500 kg.

Real-time ultrasound images were collected on all animals three times, including approximately 60 d following weaning after acclimation to postweaning facilities, near 1 yr of age, and 3 to 7 d prior to harvest. Images were collected using an Aloka SSD-1100 Flexus RTU unit (Aloka Co. Ltd., Tokyo, Japan) with a 17.2-cm, 3.5-MHz probe. The probe used is identical to that used by the Aloka 500V RTU unit (e.g., Hassen et al., 1998). Animal preparation and image collection procedures were according to Beef Improvement Federation guidelines (BIF, 1996). Digitized images were interpreted using Jandel Sigma Scan Pro (Jandel Scientific, San Rafael, CA) image analysis software. Subcutaneous fat thickness was measured at the 12 to 13th rib interface over the longissimus muscle, two-thirds the distance from the spine between the medial and lateral muscle ends, corresponding to the Canadian carcass grading site. The perimeter of the longissimus muscle was traced from the digitized image and muscle area was computed by the software. All RTU images were taken by a single technician and were subsequently interpreted by a second technician.

Bulls and heifers were processed at a commercial packing facility and steers were processed at the Lacombe Research Centre. Following routine processing procedures, whole carcass data were collected 24 to 40 h postmortem on all animals, including subcutaneous fat thickness and longissimus muscle area by a certified beef grader according to standards of the Canadian Meat Grading Agency.

Data Editing and Analyses
The final data set consisted of RTU and carcass observations (n = 597) on bulls (n = 224), heifers (n = 257), and steers (n = 116). All analyses were conducted using SAS (Ver. 8.2, SAS Inst., Inc., Cary, NC). Weaning and yearling RTU measurements were used as predictors of corresponding carcass measurements. The prediction model included the main effects of birth year and gender. The interaction of birth year with gender accounted for relatively small portions (P > 0.10) of observed variance in response variables; therefore, this effect was dropped from the final model. Ultrasound and carcass variables were adjusted for the linear effects of age at measurement. Because genders were harvested at different ages, linear age adjustments were made within gender.

Prediction models were fit whereby portions of variance in carcass traits accounted for by RTU measurements at weaning, yearling, or both, were estimated. Residual correlations, bias, and standard errors of prediction have been used to characterize the accuracy of preharvest RTU measurements in several recent studies (Hassen et al., 1998; Herring et al., 1994; Perkins et al., 1992). In addition to these variables, the percentages of animals of each gender that had absolute values for the difference between RTU and carcass measures less than 6.45 cm² for muscle area, or 3 mm for fat thickness, were calculated. Similarly, in the case of prediction models including weaning and/or yearling RTU measurements, animals with predicted and actual carcass measurements that differed by less than 6.45 cm² for muscle area or 3 mm for fat thickness were classified as accurate, whereas those with greater differences were classified as inaccurate.

	Results and Discussion

Top Abstract Introduction Materials and Methods Results and Discussion Implications Literature Cited

 
Gender Effects on Muscle Area.
Least squares means for RTU and carcass measures of muscle area and fat thickness are reported in Table 1. Weaning muscle area was smaller (P < 0.01) for heifers (39.07 cm²) than for bulls (48.15 cm²) or steers (45.21 cm²). Relative muscle area growth rates from weaning to yearling were 43, 34, and 31% for steers, bulls, and heifers, respectively, probably reflecting differences in ADG. At yearling, steer and bull muscle area measurements were similar, but larger (P < 0.01) than yearling heifer muscle area. The smaller increase in muscle area from yearling to preharvest of steers was mostly because steers were harvested approximately 75 to 85 d younger (442 ± 19 d) than bulls (516 ± 12 d) or heifers (530 ± 12 d). Muscle area deposition rates during the period between yearling and preharvest measurements were approximately 0.19, 0.21, and 0.18 cm²•d^-1 for steers, bulls, and heifers, respectively. Prior to harvest, RTU muscle area measurements were similar between steers and heifers, and both were smaller (P < 0.01) than those of bulls. Carcass muscle area was likewise similar between steers and heifers and smaller (P < 0.01) than in bulls.

When weaning scans were collected, steers had been consuming a higher energy diet than bulls and heifers for approximately 60 d. Steer fat thickness (5.73 mm) was greater (P < 0.01) than both bull (3.12 mm) and heifer (3.31 mm) fat thickness at weaning. The differences noted for weaning measurements were greater at yearling when steers (10.1 mm) had more (P < 0.01) fat than bulls (3.06 mm) or heifers (4.36 mm). Yearling heifers had more (P < 0.05) fat than did yearling bulls. Least squares means indicated that weaning and yearling RTU fat thickness measurements of bulls were not different (P > 0.10). It appears from these results that nutritional level was limiting fat deposition in bulls. Wilson (1992) noted that the small amount and low variability of fat thickness among young beef bulls, due to management and level of nutrition, may lead to difficulties in accurately predicting genetic differences in fat deposition potential. Prior to harvest, steers were fatter (P < 0.01) than bulls and heifers, even though steers were younger when preharvest measurements were collected. Gender rankings were similar for yearling and preharvest RTU and carcass measures of fat thickness with steers fattest, heifers intermediate, and bulls leanest.

Correlations Among Ultrasound and Carcass Measures.
Table 2 contains residual correlations among RTU and carcass measures of muscle area and fat thickness. Residual correlations are adjusted for effects in the model (namely, year, gender, and age at measurement). Muscle area measurements taken at weaning, yearling, and prior to harvest had high and positive residual correlations ranging from 0.79 to 0.86, indicating that repeated measures of muscle area from the same animal are similar. The overall repeatability of two preharvest RTU muscle area measures in young bulls was 0.94 in the report of Bergen et al. (1996). However, in that study, the two measures were taken within a very short interval. Similarly, Hassen et al. (1998) reported repeatability estimates for RTU muscle area of 0.97 when the two measurements were taken on consecutive days prior to harvest. Weaning and yearling RTU muscle area measurements had residual correlations of 0.86 with carcass muscle area, indicating a highly positive and similar association between carcass muscle area and its RTU indicators at weaning and yearling. The residual correlation between preharvest RTU and carcass muscle area was 0.87. These results compare favorably with those of previous studies showing moderate to high correlations between preharvest RTU and carcass measurements of muscle area. Smith et al. (1992) reported simple correlations of 0.43 and 0.63 between preharvest and carcass muscle area measurements in two studies. Hassen et al. (1998) reported simple and rank correlations of 0.48 and 0.44, respectively, between preharvest and carcass muscle area. Higher correlations of 0.60 (Perkins et al., 1992) and 0.52 to 0.72 for multiple technicians (Herring et al., 1994) have also been reported between RTU and carcass muscle area. The similarity among correlations of RTU measurements with carcass muscle area indicates that RTU measurements collected between weaning and harvest may give similarly accurate predictions of carcass muscle area. Rank correlations among RTU and carcass muscle area measurements (not reported) were high and positive, and followed the same trend as the residual correlations reported in Table 2.

Weaning and Yearling Ultrasound Prediction Models.
Table 3 contains a summary of the RTU models used to predict carcass measures of muscle area and fat thickness. It was of interest to investigate the predictive power of RTU measurements taken at weaning and yearling ages. In the case of bulls and heifers, these predictions would potentially be of use in making selection decisions. Weaning and yearling RTU measurements may be used to place steers into more uniform management groups during the postweaning period. Prediction models for carcass traits using weaning and yearling RTU predictors were evaluated on the basis of total model R² as well as root mean square error (RMSE), where higher R² and lower RMSE are indicative of models that result in more accurate predictions of carcass measurements.

The single-trait prediction model for carcass fat thickness, which included only weaning RTU measurements, resulted in model R² of 0.73 and RMSE of 1.70 mm. The partial R² of 0.59 for weaning RTU fat thickness indicates that slightly more than half of the variance in carcass fat thickness was attributable to variance in the weaning RTU measurement. Yearling RTU fat thickness provided a better single-trait prediction of carcass fat thickness, with higher model R² (0.80) and lower RMSE (1.44 mm) than that for the weaning prediction model. Additionally, the partial R² associated with yearling RTU fat thickness was 0.72, suggesting that a higher proportion of carcass fat thickness variation was due to the yearling RTU measurement compared to the weaning RTU measurement. The inclusion of both weaning and yearling RTU fat thickness measurements increased R² to 0.83 and decreased RMSE by 7% to 1.34 mm vs the single-trait yearling prediction model. The relative amount of carcass fat thickness variance attributable to the yearling RTU measurement was more than four times that attributable to the weaning measurement, as evidenced by partial R² values of 0.15 and 0.61 for the weaning and yearling RTU measurements, respectively. Similar to correlation results noted previously, yearling RTU measurements provided better predictions of carcass fat thickness, and when both weaning and yearling RTU measurements were available, significantly higher portions of carcass fat thickness variance were attributed to the yearling RTU measurement. These results suggest that yearling RTU fat thickness measurements are preferable to RTU measurements taken at weaning for the prediction of carcass fat thickness. Bergen et al. (1997) showed that end-of-test RTU fat thickness was better predicted by RTU measurements that were taken nearer to the end of test in young beef bulls. Prediction model minimum residual standard deviations decreased and average R² increased across five breeds of bulls as end-of-test fat thickness was predicted by RTU measurements taken later in the test in that study. Bergen et al. (1997) concluded that fat thickness development during the postweaning test was less predictable and therefore it was difficult to predict end-of-test RTU fat thickness from measurements taken earlier in the test.

Percentages of animals receiving accurate carcass predictions with the prediction models are presented in Table 4. Muscle area predictions that differed from carcass muscle area by less than 6.45 cm² and fat thickness predictions that differed from carcass fat thickness by less than 2.5 mm respectively, were considered accurate. There was a numerical trend for the percentage of animals with accurate predictions to increase as the RTU predictor was taken nearer to harvest. Whereas 80.2% of animals had accurate muscle area predictions based on weaning RTU measurements, 81.1% had accurate predictions based on the yearling RTU measurement. The percentage of animals with accurate fat thickness predicted values increased from 90.3 to 93.5% when yearling RTU fat thickness replaced the weaning RTU measurement in a single-trait model. Further, predicted carcass values were accurate for 88.9 and 95% of animals for muscle area and fat thickness, respectively, when both weaning and yearling RTU measurements were used to predict carcass measurements.

When expressed as a percentage of carcass muscle area, the absolute value of bias was between 4 and 6% of the carcass measurement in this study. Similar absolute bias ratios (5 to 9.4%) for muscle area were reported by Perkins et al. (1992) and Hassen et al. (1998).

Standard errors of prediction for muscle area were similar among steers (4.49 cm²), bulls (4.93 cm²), and heifers (4.75 cm²). In this case, two-thirds of all animals would have preharvest muscle area measurements that were within 4.49 to 4.93 cm² of carcass measurements. Muscle area standard errors of prediction between 5.95 and 9.52 cm² have been reported in steers and heifers (Herring et al., 1994; Bergen et al., 1996; Hassen et al., 1998). The percentage of steers, bulls, and heifers with preharvest RTU muscle area measurements that differed from carcass measurements by less than 6.45 cm² was 100, 100, and 99.6%, respectively. In the study by Perkins et al. (1992), 53% of steers and heifers had absolute muscle area bias values less than 6.5 cm². Similarly, Smith et al. (1992) showed that 47 and 54% of steers had absolute muscle area bias values less than 6.45 cm² in two experiments.

Preharvest RTU fat thickness measures were, on average, lower than carcass measures for steers, but were higher than carcass measurements for bulls and heifers. However, the negative mean bias of steers was not different (P > 0.05) from zero. The mean bias of -0.21 mm for steers compares favorably with the value of -0.17 cm reported by Hassen et al. (1998), but was higher than the values of 0.01 cm for steers and -0.01 cm for heifers reported by Perkins et al. (1992).

Absolute bias was 1.53, 1.07, and 1.32 mm for steers, bulls, and heifers, respectively. Based on RTU data from 616 beef bulls, Bergen et al. (1996) reported an absolute bias value for fat thickness of 1.2 mm, similar to the results in this study for bulls. Absolute bias values for fat thickness were 0.20 cm and 0.17 cm for steers and heifers, respectively, in Perkins et al. (1992). Similar absolute bias or deviation values (0.20 to 0.29 cm) were reported for fat thickness among steers and heifers by Herring et al. (1994) and Hassen et al. (1998).

The percentage of carcass fat thickness represented by absolute fat thickness bias ranged from 12.02% for steers to 32.02% for bulls, indicating that error in fat thickness prediction with preharvest RTU measurements was larger than that previously noted for muscle area. Similar trends were reported by Perkins et al. (1992) and Hassen et al., (1998).

Standard errors of prediction for fat thickness were 1.40, 0.87, and 1.51 mm for steers, bulls, and heifers, respectively. The fat thickness standard error of prediction reported for bulls by Bergen et al. (1996) was 1.6 mm, nearly twice that of this study. However, the bulls in Bergen et al. (1996) had average carcass fat thickness of 6.0 mm, which was approximately 1.5 mm greater than the bulls in this study. Standard errors of prediction for steers and heifers in the reports of Herring et al. (1994) and Hassen et al. (1998) were higher (0.25 to 0.33 cm) than the values in this study (0.87 to 1.51 mm).

The difference between preharvest RTU and carcass fat thickness was less than 2.5 mm for more than 98% of steers and bulls, and was less than 2.5 mm for 84.8% of heifers. Faulkner et al. (1990) found that 72% of steers and heifers had absolute bias values for fat thickness less than 2 mm. Similar results were reported by Smith et al. (1992), where 74 and 62% of steers had preharvest RTU and carcass fat thickness measurements that differed by less than 2.54 mm. In the study by Perkins et al. (1992), 75% of steers and heifers had absolute bias values for fat thickness that were less than 2.5 mm. These results support previous studies indicating that preharvest RTU measurements provide accurate predictions of carcass traits.

	Implications

Top Abstract Introduction Materials and Methods Results and Discussion Implications Literature Cited

 
Ultrasound measurements of muscle area and fat thickness taken near weaning and yearling ages can be used to predict corresponding carcass measurements in beef steers, bulls, and heifers. Predictions based on yearling measurements were more accurate than those based on weaning measurements for fat thickness; however, predictions based on weaning vs yearling measurements were similar for muscle area. Two-trait models, including both weaning and yearling predictors, were only marginally more accurate than models including only yearling predictors. Approximately 80 to 89% of predicted values were within 6.45 cm² of carcass values for muscle area, and approximately 90 to 95% of predicted values were within 2.5 mm of carcass values for fat thickness. Preharvest ultrasound measurements of steers, bulls, and heifers were highly correlated with carcass measurements. Preharvest standard errors of prediction were less than 4.95 cm² for muscle area and 1.51 mm or less for fat thickness.

	Footnotes

 
¹ AAFC-LRC contribution number 38701038. These data were collected with funding support from the Canadian Beef Industry Development Fund for project 95H022. The authors gratefully acknowledge the contributions of the staff at the Onefour Research Substation and the Lethbridge Research Centre feedlot for cattle management and live animal data collection. The assistance of J. Aalhus and W. Robertson at the Lacombe Research Centre in collection of steer carcass data is also acknowledged.

Received for publication February 18, 2002. Accepted for publication July 9, 2002.

	Literature Cited

Top Abstract Introduction Materials and Methods Results and Discussion Implications Literature Cited

 


BIF. 1996. Guidelines for Uniform Beef Improvement Programs. 7th ed. Kansas State Univ., Colby.

Bergen, R. D., J. J. McKinnon, D. A. Christensen, and N. Kohle. 1996. Prediction of lean yield in yearling bulls using real-time ultrasound. Can. J. Anim. Sci. 76:305–311.

Bergen, R. D., J. J. McKinnon, D. A. Christensen, N. Kohle, and A. Belanger. 1997. Use of real-time ultrasound of evaluate live animal carcass traits in young performance-tested beef bulls. J. Anim. Sci. 75:2300–2307.[Abstract/Free Full Text]

Bertrand, J. K., D. W. Moser, and W. O. Herring. 2000. Beef genetic evaluation programs for carcass traits: current situation and future possibilities. J. Anim. Sci. (Suppl. 1):57(Abstr.).

Brethour, J. R. 1992. The repeatability and accuracy of ultrasound in measuring backfat of cattle. J. Anim. Sci. 70:1039–1044.[Abstract]

Crews, D. H., Jr., and R. A. Kemp. 2001. Genetic parameters for ultrasound and carcass measures of yield and quality among replacement and slaughter beef cattle. J. Anim. Sci. 79:3008–3020.[Abstract/Free Full Text]

Faulkner, D. B., D. F. Parrett, F. K. McKeith, and L. L. Berger. 1990. Prediction of fat cover and carcass composition from live and carcass measurements. J. Anim. Sci. 68:604–610.

Hassen, A., D. E. Wilson, R. E. Willham, G. H. Rouse, and A. H. Trenkle. 1998. Evaluation of ultrasound measurements of fat thickness and longissimus muscle area in feedlot cattle: Assessment of accuracy and repeatability. Can. J. Anim. Sci. 78:277–285.

Herring, W. O., D. C. Miller, J. K. Bertrand, and L. L. Benyshek. 1994. 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.[Abstract]

Moeller, S. J., and L. L. Christian. 1998. Evaluation of the accuracy and repeatability of real-time ultrasonic measurements of backfat and loin muscle area in swine using multiple statistical analysis procedures. J. Anim. Sci. 76:2503–2514.[Abstract/Free Full Text]

Mwansa, P. B., R. A. Kemp, D. H. Crews, Jr., J. P. Kastelic, D. R. C. Bailey, and G. H. Coulter. 2000. Comparison of models for genetic evaluation of scrotal circumference in crossbred bulls. J. Anim. Sci. 78:275–282.[Abstract/Free Full Text]

Perkins, T. L., R. D. Green, and K. E. Hamlin. 1992. Evaluation of ultrasonic estimates of carcass fat thickness and longissimus muscle area in beef cattle. J. Anim. Sci. 70:1002–1010.[Abstract]

Smith, M. T., J. W. Oltjen, H. G. Dolezal, D. R. Gill, and B. D. Behrens. 1992. Evaluation of ultrasound for prediction of carcass fat thickness and longissimus muscle area in feedlot steers. J. Anim. Sci. 70:29–37.[Abstract]

Wilson, D. E. 1992. Application of ultrasound for genetic improvement. J. Anim. Sci. 70:973–983.[Abstract]

This article has been cited by other articles:

				P. B. Wall, G. H. Rouse, D. E. Wilson, R. G. Tait Jr., and W. D. Busby Use of ultrasound to predict body composition changes in steers at 100 and 65 days before slaughter J Anim Sci, June 1, 2004; 82(6): 1621 - 1629. [Abstract] [Full Text] [PDF]

This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Crews, D. H. Articles by Kemp, R. A. Search for Related Content PubMed PubMed Citation Articles by Crews, D. H., Jr. Articles by Kemp, R. A.