EFFECT OF RACTOPAMINE HYDROCHLORIDE ON BEEF CARCASS COMPOSITION AND ESTIMATES OF INTERMUSCULAR FAT KARY RIGDON KENT, B.S. A THESIS MEAT SCIENCE

Transcription

1 L.^ EFFECT OF RACTOPAMINE HYDROCHLORIDE ON BEEF CARCASS COMPOSITION AND ESTIMATES OF INTERMUSCULAR FAT by KARY RIGDON KENT, B.S. A THESIS IN MEAT SCIENCE Submitted to the Graduate Faculty of Texas Tech University in Partial Fulfillment of the Requirements for the Degree of MASTER OF SCIENCE Approved Accepted May 1990

2 ACKNOWLEDGMENTS Deep appreciation is extended to my advisor and friend Dr. Gordon W. Davis for his guidance and counsel during my Master's program. Appreciation is also extended to Dr. C. Boyd Ramsey and Dr. Rodney L. Preston for their assistance in completion of my degree. I would also like to thank Dr. Robert C. Albin, Dr. Steve Bartle, Dr. Leslie Thompson, David McNeese, Alan Schluter, Monica Hightower and Kenny Wu for their cooperation and friendship. I thank project director Dr. Lamar H. Carrol of Lilly Research Laboratories for his cooperation and attention to detail in completion of this investigation. Most importantly, I am deeply thankful for the love and encouragement of my wife, Jennifer, and my daughter, Kelsea. I am also deeply thankful for the support of my parents, Wendell and Sydney Kent, and my father and motherin-law, Jerry and Nelda Gortney. 11

3 TABLE OF CONTENTS ACKNOWLEDGMENTS ABSTRACT LIST OF TABLES LIST OF FIGURES ii V vii ix CHAPTER I. INTRODUCTION 1 II. LITERATURE REVIEW 3 Ractopamine hydrochloride 3 Beef carcass composition 4 III. EXPERIMENTAL PROCEDURES 8 Basic design 8 Carcass selection 10 Carcass grading 10 Carcass estimates 11 Carcass fabrication 13 Grinding and mixing 16 Sampling 16 Proximate analysis 17 Statistical analysis 18 IV. RESULTS AND DISCUSSION 19 Effect of ractopamine hydrochloride on beef carcass composition 19 Effect of intermuscular fat on beef carcass composition

4 V. CONCLUSIONS 45 LITERATURE CITED 4 7 APPENDICES A. DATA SHEET FOR CARCASS TRAITS 51 B. INTERMUSCULAR FAT ESTIMATE SCALE 53 C. EXAMPLES OF INTERMUSCULAR FAT ESTIMATES 55 D. DATA SHEET FOR CARCASS FABRICATION 58 IV

5 ABSTRACT A total of 160 predominantly Angus, medium-framed steers (389 kg) were fed a finishing diet for 42 to 49 d. Steers (452 kg) then were estimated to be 4 6 d from slaughter condition, allotted to five blocks [weight and fat thickness (FTK) at 12th rib] and ractopamine hydrochloride (RH) was introduced into their diet (0, 10, 20 or 30 ppm). Carcasses were evaluated 24 h postmortem by three experienced evaluators for USDA yield grade (YG) and quality grade factors, nine subcutaneous (SC) fat indicators and four intermuscular (IM) fat indicators. Right sides (n = 40) varying in composition (YG 1.1 to 3.8) then were randomly selected (2 per block per treatment) for evaluation/determination of 10 carcass traits, four chemical traits (fat, moisture, protein and ash), two measures of cutability, and total IM fat from the round, loin, rib and chuck. Marbling score, adjusted FTK, ribeye area (REA) and USDA grade (yield and quality) were not influenced by RH treatment. Percentage IM fat, SC fat, boneless defatted primal cuts (round, loin, rib and chuck) were not influenced by RH treatment. No differences were found across RH treatments among four chemical traits (fat, moisture, protein and ash). Increased feeding levels of RH may be required to realize improvement in beef carcass composition. Simultaneous consideration of adjusted FTK, V

6 REA, kidney, pelvic and heart fat percent (KPH) and hot carcass weight (HCW) accounted for 60.4% of the observed variation in percentage of chemical carcass fat, whereas, an equation containing an IM fat estimate (IM fat estimate at the 12th rib, REA, KPH and HCW accounted for 59.4% of the observed variation. Simultaneous consideration of adjusted FTK, REA, KPH and HCW accounted for 58.9% of the observed variation in cutability (boneless, closely trimmed retail cuts from the round, loin, rib and chuck containing 6 mm SC fat and zero IM fat), while an equation containing an IM fat estimate (IM fat estimate at 12th rib, REA, KPH and HCW) accounted for 64% of the observed variation. These data suggest SC fat can be removed via hot fat trimming and cutability can be reliably predicted using an IM fat estimate at the 12th rib instead of adjusted FTK. VI

7 LIST OF TABLES 1. EXPERIMENTAL DESIGN, 2. LEAST SQUARE MEANS AND STANDARD ERROR OF THE MEANS (SEM) ACROSS TREATMENTS FOR VARIOUS CARCASS TRAITS AND CHEMICAL ASSAYS LEAST SQUARE MEANS AND STANDARD ERROR OF THE MEANS (SEM) ACROSS TREATMENTS FOR SIDE MEASURES OF MASS, MUSCLING, FATNESS AND CUTABILITY LEAST SQUARE MEANS AND STANDARD ERROR OF THE MEANS (SEM) ACROSS TREATMENTS FOR MEASURES OF MASS, MUSCLING, FATNESS AND CUTABILITY FOR THE CHUCK LEAST SQUARE MEANS AND STANDARD ERROR OF THE MEANS (SEM) ACROSS TREATMENTS FOR MEASURES OF MASS, MUSCLING, FATNESS AND CUTABILITY FOR THE RIB LEAST SQUARE MEANS AND STANDARD ERROR OF THE MEANS (SEM) ACROSS TREATMENTS FOR MEASURES OF MASS, MUSCLING, FATNESS AND CUTABILITY FOR THE LOIN LEAST SQUARE MEANS AND STANDARD ERROR OF THE MEANS (SEM) ACROSS TREATMENTS FOR MEASURES OF MASS, MUSCLING, FATNESS AND CUTABILITY FOR THE ROUND SIMPLE CORRELATION COEFFICIENTS RELATING CERTAIN CARCASS TRAITS TO FOUR COMPOSITIONAL INDICES SIMPLE CORRELATION COEFFICIENTS RELATING VARIOUS SUBCUTANEOUS (SC) FAT ESTIMATES TO FOUR COMPOSITIONAL INDICES SIMPLE CORPiELATION COEFFICIENTS RELATING INTERl^lUSCULAR (IM) FAT ESTIMATES TO FOUR COMPOSITIONAL INDICES REGRESSION EQUATIONS EMPLOYING VARIOUS FAT ESTIMATES PREDICTING FOUR COMPOSITIONAL INDICES 37 vii

8 12. REGRESSION EQUATIONS PREDICTING CHEMICAL CARCASS FAT REGRESSION EQUATIONS PREDICTING INTERMUSCULAR FAT PERCENT OF SIDE REGRESSION EQUATIONS PREDICTING CUTABILITY I REGRESSION EQUATIONS PREDICTING CUTABILITY II 43 Vlll

9 LIST OF FIGURES 1. Intermuscular fat estimate locations Interface of 5th and 6th rib 14 IX

10 CHAPTER I INTRODUCTION Improvement in feedlot performance and product composition is a past and current goal of the cattle industry. Numerous drugs such as Ralgro and Synevex currently are available and utilized by feeders to improve cattle performance. Other experimental drugs such as cimaterol and clenbuterol have been reported to improve beef carcass composition (Miller et al., 1988; Ricks et al., 1984). Ractopamine hydrochloride (RH) is another feed additive (repartitioning agent) under recent study in swine. Crenshaw et al. (1987) reported the feeding of RH enhanced carcass leanness and muscularity of butcher hogs. No formal research has been conducted to determine the effects of RH feeding on the composition of beef cattle. Therefore, our first objective was to determine the effects of RH feeding on carcass traits and composition of the major primal cuts of the beef carcass. Changes in the packing industry in the 1980's have included: discontinued use of shrouds, implementation of spray chilling, decoupling of USDA yield and quality grades (USDA, 1989) and hot fat trimming. Methodology for grading beef carcasses also is not immune to change. Reasonably accurate estimation of

11 -^««" cutability of a hot fat trimmed carcass will require an alternative measure of total carcass fatness. Since subcutaneous (SC) fat has been altered by hot fat trimming or other trimming (inspectors, hide puller, packer) the only plausible remaining fat indicators are various intermuscular (IM) fat depot sites. Following trimming, IM fat will remain intact, protected by overlying muscles. Little, if any research has been conducted for identifying specific locations on a carcass to accurately predict carcass fatness without the use of a SC fat measurement. A need exits for studies concerning IM fat and its effect on the value-based marketing of the beef carcass. Therefore, the second objective of this study was to determine and compare various IM fat depots in a beef carcass as predictors of carcass composition and potential use in a yield grade equation designed for application to carcasses trimmed of SC fat.

12 CHAPTER II LITERATURE REVIEW Ractopamine hydrochloride. Numerous drugs have been introduced which act as repartitioning agents when fed to cattle, sheep and swine. A repartitioning agent can be defined as an exogenous substance which redirects the flow of nutrients away from fat deposition and towards muscle deposition (Ricks et al., 1984). Included among these agents are B-agonists, such as clenbuterol, cimaterol and RH. Extensive studies using clenbuterol and cimatrol as top coat dressings on rations have been conducted which show these agents decrease fat deposition while increasing muscle deposition in beef (Miller et al., 1988; Ricks et al., 1984) and in lambs (Baker et al., 1984; Beerman et al., 1986). Ractopamine hydrochloride is a phenethanolamine based upon its chemical structure. It has been studied in finisher swine with results similar to those of other betaagonists. Pork carcass leanness can be increased with increased dietary RH (Hancock et al., 1987; Prince et al., 1987; Crenshaw et al., 1987). Crenshaw et al. (1987) and Prince et al. (1987) also reported an increase in longissimus muscle area at the 10th rib in swine with increased feeding of RH.

13 4 Beef carcass composition. Several modifications of the official beef grading standards have been made since their inception in Most of these changes were designed to make the grades more useful tools for identifying value-determining differences in beef. Murphey et al. (1960) reported the single best indicator of beef carcass cutability was a SC fat measurement opposite the 12th rib. Subsequent studies by Allen et al. (1968), Abraham et al. (1968), Hedrick et al. (1969), Crouse et al. (1975) and Crouse and Dikeman (1976), confirmed Murphey's results. However, due to changes in beef production and slaughtering techniques during the late 1960's and early 1970's, a need existed to re-evaluate the accuracy of the 12th rib measurement in cutability determinations. Abraham et al. (1980) reported a significant increase in accuracy of cutability prediction by adjusting the measured FTK opposite the 12th rib to account for nonuniform SC fat deposition and for fat removed during the dehiding process. Significant changes have been made in slaughter and grading procedures employed by the beef industry. Various changes could reduce the validity of adjusted FTK in determining the cutability of the beef carcass since the IM fat will remain intact following trimming of the SC fat. This fat is visible only in two locations until breaking of the carcass into primal cuts. Abraham et al. (198 0)

14 recognized the importance of IM fat and reported substantial improvement in predicting cutability when actual percentage fat trim (SC and IM fat) was used instead of adjusted FTK. For practical reasons, this measure was found unfeasible in a rail grading system. Several researchers have reported yield grade to be the most reliable and readily accessible means of determining carcass composition (Ramsey et al., 1962; Crouse et al., 1975; Abraham et al., 1980). However, most agree with Powell and Huffman (1968) that chemical analysis of the entire carcass is the most accurate estimate of carcass composition. Retail yield percent and separable lean percent of a carcass are other endpoints many researchers have used to determine the value of a carcass. Many, if not all, of these studies have used some form of SC fat measurement to meet their objectives. Brungardt and Bray (19 63) used the SC fat measurement at the 12th rib and percent trimmed round to derive their equation for percent retail yield. Johnson et al. (1989) also used an adjusted FTK measurement along with superficial pectoral weight to derive their equation predicting separable lean from the forequarter. Cole et al. (1962) reported FTK opposite the ribeye was associated more highly with separable carcass lean than was REA.

15 Other methods of determining carcass composition include use of specific gravity with both good (Garrett and Hinman, 1969; Ferrell et al., 1976) and less acceptable results (Powell and Huffman, 1968; Waldman et al., 1969; Fortin et al., 1980). Another is the composition of the 9th-10th-llth rib section first reported by Hankins and Howe (1946). Fat deposition among breed types, sex and age has been extensively studied. Jones et al. (1980) reported dairy type cattle deposited greater amounts of IM fat in the chuck than Hereford cattle. Bulls deposited greater amounts of IM fat in the chuck and round than heifers, however, heifers deposited greater amounts of SC fat than bulls. Murphey et al. (1985) reported heifers deposited more SC fat than steers in the udder/cod, chuck and rump regions. Shahin and Berg (1985a) reported the double muscling trait decreased SC fat more than IM fat deposition. Shahin and Berg (1985b) suggested, as animals are selected for decreased SC fat deposition, an indirect selection for increased IM fat might be occurring. Intermuscular fat is a late-developing depot and its contribution to total fat does not decrease as fattening progresses (Cianzio et al., 1982). Therefore, the relevance of IM fat in determining carcass cutability and subsequent carcass value needs to be addressed.

16 In summary, yield grade has been considered the most accurate and feasible method for predicting beef carcass composition under industry conditions. However, should slaughter and dressing procedures move towards hot fat trimming, the best carcass composition indicator (adjusted FTK) used in the yield grade equation will be lost.

17 CHAPTER III EXPERIMENTAL PROCEDURES Basic design. A total of 200 medium-framed black and black baldy steers, predominantly Angus, were purchased from a private ranch near Ringling, Oklahoma. The steers, kg average, were shipped to the Burnett Center, Texas Tech University (TTU) Agricultural Research Center, New Deal, Texas, in November, The steers were immediately penned and gradually placed on a finishing ration (corn silage, 12%; cottonseed hulls, 7.6%; steamflaked sorghum grain, 69.2%; protein, minerals, and vitamins). Steers which were sick, injured or otherwise not performing as expected then were culled from the experiment. When steers were estimated to be 4 6 d from slaughter, via real time ultrasound measurement of FTK at the 12th rib, animals were weighed and assigned to four treatments consisting of five blocks per treatment based on weight and FTK (20 pens, eight head per pen). At this time, RH was introduced to the diet at 0, 10, 2 0 or 3 0 ppm (Table 1). Following the 46-d experimental feeding period, weights and ultrasound FTK measures were obtained for each animal. Steers were immediately transported 150 km to Excel, Corp. in Friona, Texas, for slaughter. Slaughter was performed about 2 h after cattle arrived under normal 8

18 ^ ^ ^ ^ TABLE 1. EXPERIMENTAL DESIGN Ractopam; Lne hydrochloride, ppm Block ^ ^Number of carcasses, total n = 40

19 10 industry conditions (chain speed of 275 cattle per hour). Slaughter sequence was recorded by ear tag number at time of bleeding and each carcass then was assigned a sequence number. Kidneys were removed during evisceration and all carcasses were scored (estimation of weight removed) for trim defects occurring during slaughter. Carcasses were spray chilled and not shrouded during the 24-h chilling time in a -2 C chill cooler. Carcass selection. Carcasses which were excessively trimmed during slaughter due to bruises, cleanliness or hide puller defects were excluded from the selection group. Carcasses, n = 40 (Table 1), then were randomly selected within block based on HCW ( kg HCW from the mean of the block) for further study. Carcass grading. All USDA yield and quality grade factors (Appendix A) were obtained by three trained evaluators 24 h postmortem in the Excel beef carcass sales cooler (3 C). Each evaluator individually determined the adjusted FTK for each carcass. A group discussion was conducted for any carcasses when a range of 3 mm or more existed among the evaluators before a final estimate was obtained. Ribeye area was determined to the nearest.5 cm by an average of two independent measurements. When the independent REA measurements varied by more than 2 cm^, two

20 11 additional independent measurements were made until a precise and accurate measurement was determined. Kidney, pelvic and heart fat, including an additional.9 kg to account for the kidneys removed at time of slaughter, was determined by the average of estimates to the nearest.5% among three independent evaluations. Marbling score was determined by the arithmetic average, to the nearest 10% within marbling score, among three independent evaluations. Marbling score was reevaluated and discussed if the range of independent evaluations was greater than 30% within or across marbling scores. Carcass estimates. Sites of SC fat estimation (Appendix A) included: adjusted FTK opposite the 12th rib, the rib-plate juncture at the 12th rib, over the loin edge, rump, outside round, inside round, chuck, brisket and the cod region. Estimates of IM fat (Appendix A) were obtained based on an 8 point scale (8 = no IM fat, 1 = extremely high amount of IM fat. Appendix B). Locations of the IM estimates were: interface of the 12th and 13th rib (Appendix C) between the longissimus and the spinalis dorsi muscles (Figure 1, site A), the acorn area between the longissimus and the SC fat layer (Figure 1, site B), the multifidus dorsi and the intercostal muscles (Figure 1, site C) ; rib-plate juncture at the interface of the 12th

21 12 Figure 1. Intermuscular fat estimate locati ons

22 13 and 13th rib between the longissimus costarum muscle and the rib immediately lateral to the tip of the longissimus muscle to a point 10 cm lateral of the longissimus muscle (Figure 1, site D) ; the kidney, pelvic and heart fat regions; and, dorsal two-thirds of the interface of the 5th and 6th ribs (Figure 2). Carcass fabrication. Right sides of the 40 selected carcasses were quartered and shipped 150 km to the Texas Tech University Meat Laboratory in Lubbock, Texas, via refrigerated truck 3 6 to 48 h postmortem. Carcass quarters then were held in a 3 C cooler until fabrication at 48 to 168 h post-mortem in a 7 C processing room. Carcasses then were weighed and fabricated via the following procedure to obtain cutability and IM fat values. All carcasses were standardized prior to fabrication to reduce influences of slaughter, dressing and shipping procedures: the hanging tender was removed and the spinal cord and accompanying related fat were removed. Carcasses then were weighed. All pelvic and heart fat was removed and weighed. Kidney fat in excess of 6 mm over the tenderloin muscle was removed and weighed. The skankless round was obtained by cutting the drop loin from the wholesale round between the juncture of the 4th and 5th sacral vertebrae and 2.5 cm anterior to the aitch bone. The hind shank then was removed between the

23 14 ^ 2 Figure 2- interface of

24 15 natural seam of the outside round and the shank muscles, continuing through the joint between the tibia and femur. The loin was obtained via removal of the flank. Removal was along a line starting at the cap muscle on the lateral edge of the sirloin end extending to a point on the loin end determined by the side weight. The flank was removed 23 cm lateral to the tip of the last thoracic vertebra for sides weighing under 13 6 kg. The flank was removed 24 cm lateral to the tip of the last thoracic vertebra for sides weighing over 13 6 kg. The rib was obtained by separating the cross cut chuck (chuck, brisket and foreshank) from the rib and plate by a cut between the 5th and 6th rib. The plate was removed from the rib along a line extending from a point on the rib end 8 cm lateral to the tip of the longissimus muscle to a point on the blade end 10 cm lateral to the tip of the longissimus muscle. The square cut chuck was obtained by removing the brisket and foreshank along a line perpendicular to the blade face, intersecting a point immediately dorsal to the lateral condyle of the humerus. The secondary primals (hind shank, flank, plate, brisket and foreshank) then were weighed and fabricated into lean, fat and bone (including heavy connective tissue).

25 "Ssy'^' 16 The major primals (shankless round, loin, rib and square cut chuck) were weighed. All bones and heavy connective tissue then were removed from the primals. Weights were obtained for total boneless tissue and total bone (including heavy connective tissue). Subcutaneous fat in excess of 6 mm was removed and weights were obtained for SC fat and the remaining primal boneless tissue. All IM fat then was removed and weights were obtained for total IM fat and the remaining trimmed boneless tissue from the primal. The data sheet used for recording fabrication weights is shown in Appendix D. Grinding and mixing. Three subunits of soft tissue from the carcass then were separated prior to grinding. The subunits consisted of: (A) trimmed boneless tissue and IM fat from the square cut chuck, rib and loin, (B) trimmed, boneless tissue and IM fat from the round and all soft tissue from the secondary primals excluding the cod fat, and (C) SC fat in excess of 6 mm removed from the major primals and the cod fat. All subunits then were individually mixed, ground through a 6-mm plate, mixed and reground through a 3.3-mm plate with a dual Hollymatic Model GMG 180A Mixer/Grinder. Sampling. A 20% by weight randomly selected unit of ground beef was obtained from each subunit and this sample was mixed and ground through a 3.3-mm plate for obtaining proximate analysis samples. Following the final grind, two

26 kg samples were randomly selected, frozen with liquid nitrogen (-196 C) and powdered for 3 0 sec in a Robot Coupe. Six 150-g powdered samples were obtained, packaged in Whirl Paks and labeled A, B and C (from 2.3-kg sample 1) and D, E and F (from 2.3-kg sample 2). Samples A, B, D and E were assigned as primary samples for proximate analyses in duplicate. Samples C and F were assigned as backup samples for proximate analysis to be used for reruns. All samples were stored in a -40 C freezer until proximate analyses were performed. Proximate analysis. AOAC, 1980 were followed. Methods for analyses described in Ash for the boneless tissue was determined in duplicate from sample A. A rerun was deemed necessary if the variation between duplicates was greater than 10%. Analyses for moisture, protein and fat were run in duplicate from each sample of A, B, D and E. Reruns were performed on samples which varied more than 5% within a sample set. Reruns then were performed on samples which varied more than 10% between averages of sample A versus sample B and sample D versus sample E. Sample C was utilized for sample A and B reruns. Sample F was utilized for sample D and E reruns. Following all reruns, the arithmetic average of all qualifying samples was reported as the value for ash, moisture, protein and fat percentages for each of the 40 carcass sides fabricated.

27 18 Statistical analysis. One-way analysis of variance was employed to determine differences across treatments for grading factors, carcass traits and major primal cut and fatness traits (SAS, 1986). Multiple regression techniques were employed to determine prediction values for IM fat estimates and cutability estimates of the carcasses (SAS, 1986).

28 CHAPTER IV RESULTS AND DISCUSSION Effect of ractopamine hydrochloride on beef carcass composition. Least square means and coefficients of variation for carcass traits and chemical assays across RH treatment levels are shown in Table 2. No significant differences (linear or quadratic) were found for 10 carcass and 4 chemical traits across treatment, however, among the three RH treated groups the 10-ppm treatment had the highest percent ash (boneless tissue). A variation of only.07 was found for yield grade across treatments. Further, a range in carcass chemical fat was 1.61% across treatments. These findings differ from those of Hancock et al. (1987), Prince et al. (1987) and Crenshaw et al. (1987) who found increased RH feeding (10, 2 0 and 3 0 ppm) positively affected carcass leanness and muscling in pigs. Ractopamine feeding did not alter marbling score. In contrast. Miller et al. (1989) reported significant decreases in marbling score for heifers when fed clenbuterol (64 ml/dose of a sucrose based top dressing), a beta-agonist. Shown in Table 3 are the least square means and coefficients of variation for side measures of mass, muscling, fatness and cutability across treatments of RH feeding. No significant differences (linear or quadratic) 19

29 TABLE 2. LEAST SQUARE MEANS AND STANDARD ERROR OF THE MEANS (SEM) ACROSS TREATMENTS FOR VARIOUS CARCASS TRAITS AND CHEMICAL ASSAYS 20 Ractopamine hydrochloride, ppm Trait^ Carcass Traits Hot carcass wt., kg Forequarter wt., kg Hindquarter wt., kg Fat thickness, mm Adjusted fat thickness, mm Ribeye area, cm^ Actual KPH, % USDA Yield Grade Marbling score USDA Quality Grade^ SEM 302.6' 76. r 71.2^ 9.7^ 307.2^ 76.9^ 71.8' 9.8^ 306.5' 77.7^ 71.1' 8.7^ 305.3^ 77.1' 7 0.6' 9.3' ^ 11.3^ 10.3^ 10.6^ ^ 80.02^ 78.74^ 78.35^ ^ 2.24^ 2.22^ 2.19^ ^ 2.67^ 2.60^ 2.64^ ^ 502.0^ 502.0^ 483.0^ ^ 18.5^ 18.2^ 18.0^.33 Chemical assays ash, % 74'.79 be.70 bd.67 bd.04 protein, % 16.30' 15.77^ 16.31^ 16.21^.23 moisture, % 57.64' 56.47^ 57.61^ 57.73^.72 fat. % 24.52' 26.13^ 24.45^ 24.53^.98 ^KPH = kidney, pelvic and heart fat. ^'^'^Means on a line with common superscript are not different (P >.05). 500 = small ^, 450 = slight^. ^17 = USDA Select-minus; 18 = USDA Select-plus.

30 TABLE 3. LEAST SQUARE MEANS AND STANDARD ERROR OF THE MEANS (SEM) ACROSS TREATMENTS FOR SIDE MEASURES OF MASS, MUSCLING, FATNESS AND CUTABILITY 21 Ractopamine hydrochloride, ppm^ Trait^ SEM Measure of mass Side wt, kg Measures of muscling CUT I wt, kg CUT II wt, kg Measures of fatness SC fat wt, kg SC fat, % IM fat wt, kg IM fat, % Measures of cutability CUT I, % CUT II, % ^None of the treatment differences were significant (P >.05). ^CUT I = boneless tissue, 6 mm SC fat; CUT II = boneless tissue, 6mm SC fat, 0 mm IM fat; SC = subcutaneous, IM = intermuscular.

31 were found across treatment for measures of mass, muscling, 22 fatness or cutability. Results of this study show IM fat trim (7.29% to 7.94% of side weight) was much higher than SC fat trim (2.47% to 3.18% of side weight). The higher trim values for IM were due to trimming all IM fat in contrast to removing SC fat to 6 mm in the present study. However, Tatum et al. (1990) reported SC fat levels to be higher (51.5% to 52.5% of total fat) than IM fat levels (33.7% to 34.6% of total fat) for carcasses produced from progeny sired by Piedmontese, Gelbvieh or Red Angus. Tatum et al. (1990) based fat levels on percentage of total dissectable fat from the entire carcass. Conversely, our study basis is all IM fat and SC fat in excess of 6 mm from the four major primals expressed as a percentage of side weight. Cutability of boneless closely trimmed (6 mm SC) retail cuts containing no IM fat (CUT II) may be a more accurate estimate of the actual value of the carcass. Similarly, Abraham et al. (1980) reported actual fat trim may be the best indicator of beef carcass composition. It is probable retailers would appreciate this type of information; however, it is currently not feasible for the packer because of the investment required to implement such a labor intensive program resulting in much lower total yield. Although health authorities, consumers and the National Live Stock and Meat Board all agree we need less

32 23 fat, the packer and retailer are profit driven and leave as much IM and SC fat intact as the consumer will buy. Least square means and coefficients of variation across treatment for measures of mass, muscling and cutability for the chuck are shown in Table 4. No differences (linear or quadratic) were significant. Subcutaneous fat removed from the chuck (.3% to.48%) represents only 10% to 15% of the total SC fat trim from the side (Table 2), whereas, IM fat trim from the chuck (3.69% to 3.99%) represents over 50% of the IM fat trim in the side (Table 2). Cutability measures for the chuck based on IM fat removed (CUT II) were about 14% lower than cutability measures based on IM fat not removed (CUT I) thus implicating IM fat as a major component of the beef chuck. Means for thirteen measures of mass, muscling, fatness and cutability for the rib (Table 5) show no differences (P >.05) across treatment. Subcutaneous and IM fat trim levels showed relatively low contributions to the total SC and IM fat trim percentages of the side (Table 2). Cutability measures for no IM fat removed (CUT I) showed the rib to have the lowest cutability among the four primals, most likely because of the greater amount of bone relative to the weight of the rib. Cutability measures for no IM fat removed (CUT I) were about 12% higher than cutability measures for all IM fat removed (CUT II), thus

33 TABLE 4. LEAST SQUARE MEANS AND STANDARD ERROR OF THE MEANS (SEM) ACROSS TREATMENTS FOR MEASURES OF MASS, MUSCLING, FATNESS AND CUTABILITY FOR THE CHUCK 24 Ractopamine hydr ochloride t, ppm^ Trait^ SEM Measure of mass Chuck wt, kg Measures of muscling CUT I wt, kg CUT II wt, kg Measures of fatness SC fat wt, kg SC fat, % of chuck SC fat, % of side IM fat wt, kg IM fat, % of chuck IM fat, % of side Measures of cutability CUT I, % of chuck CUT I, % of side CUT II, % of chuck CUT II, % of side ^None of the treatment differences were significant (P >.05). 'CUT I = boneless tissue, 6 mm SC fat; CUT II boneless tissue, 6 mm SC fat, 0 mm IM fat; SC - subcutaneous, IM = intermuscular.

34 TABLE 5. LEAST SQUARE MEANS AND STANDARD ERROR OF THE MEANS (SEM) ACROSS TREATMENTS FOR MEASURES OF MASS, MUSCLING, FATNESS AND CUTABILITY FOR THE RIB 25 Ractopamine hydrochloride, ppm' Trait^ SEM Measure of mass Rib wt, kg Measures of muscling CUT I wt, kg CUT II wt, kg Measures of fatness SC fat wt, kg SC fat, % of rib SC fat, % of side IM fat wt, kg IM fat, % of rib IM fat, % of side Measures of cutability CUT I, % of rib CUT I, % of side CUT II, % of rib CUT II, % of side ^None of the treatment differences were significant (P >.05). ^CUT I = boneless tissue, 6 mm SC fat; CUT II = boneless tissue, 6 mm SC fat, 0 mm IM fat; SC =.subcutaneous, IM = intermuscular.

35 .» 26 implicating IM fat as a major component of the rib. Cutability percentages of no IM fat removed (CUT I) were similar to a 5% value reported by Romans et al. (1985). Least square means and coefficients of variation for measures of mass, muscling and cutability across treatment levels for the loin are shown in Table 6. The weight of the loins in the 3 0 ppm RH feeding treatment was the lowest (P <.05). No other significant differences among means were found across treatments, although several trends were evident. A linear trend (P <.10) showed subcutaneous fat trim weight from the loin decreasing (1.51 kg to.87 kg) across treatment. Another linear trend (P <.10) showed SC fat trim (% of side) from the loin decreasing (1.0% to.6%) as RH feeding level increased (0 ppm to 3 0 ppm). Intermuscular fat trim weight, as well as percent of loin and percent of side IM fat trim, displayed quadratic trends (P <.10) across treatment with the control group possessing the lowest value in all three cases. The cutability estimate based on all IM fat removed (CUT II) displayed a quadratic trend (P <.10) while the estimate including IM fat showed both a linear (P <.10) and a quadratic trend (P <.10) with the 30 ppm treatment level yielding the highest percent in both instances. Subcutaneous fat trim levels (Table 6) represented about 30% of the total SC fat trim (Table 2) from the side. Intermuscular fat trim levels (Table 6) represented about

36 TABLE 6. LEAST SQUARE MEANS AND STANDARD ERROR OF THE MEANS (SEM) ACROSS TREATMENTS FOR MEASURES OF MASS, MUSCLING, FATNESS AND CUTABILITY FOR THE LOIN 27 Ractopamine hydrochloride, ppm Trait^ SEM Measure of mass Loin wt, kg 24.19' 24.56' 24.24' 23.15' 55 Measures of muscling CUT I wt, kg 17.22^ 17.37^ 17.12^ 17.34^.42 CUT II wt, kg 14.59*^ 14.42^ 14.21^ 14.48^.46 Measures of fatness SC fat wt, kg SC fat, of loin SC fat. % of side IM fat wt, kg IM fat, % of loin IM fat, % of side ^ ' ^ i.oo' ^ ' ^ ^ ^ Measures of cutability CUT I, % of loin CUT I, % of side CUT II, % of loin CUT II, % of side ^ ^ ^ ^ CUT I = boneless tissue, 6 mm SC fat; boneless tissue, 6 mm SC fat, 0 mm IM fat; subcutaneous, IM = intermuscular. CUT II = SC = ^'^Means different (P on a line with common superscript are not >.05).

37 28 24% of the total IM fat trim (Table 2) from the side. Based on percent of primal, the loin possessed more SC fat and less IM fat than the rib and chuck (Table 5 and Table 4, respectively). with higher RH feeding levels, it would be interesting to observe if RH would significantly decrease SC fat over the loin. much value to the industry. If so, this would be of Table 7 contains the least square means and coefficients of variation across treatment for measures of mass, muscling and cutability for the round. No significant differences were found across treatment. Surprisingly, SC fat weight and percent of side values were highest for the round among the four primals. However, IM fat weight and percent of side values were about the same as the loin, higher than the rib and lower than the chuck. In conclusion, RH feeding did not significantly affect carcass or chemical traits. Ractopamine hydrochloride feeding did not affect carcass composition as a whole or among primal cuts (round, loin, rib and chuck). Finally, the best cutability end point may be boneless, closely trimmed (6 mm SC fat, zero IM fat) retail cuts from the round, loin, rib and chuck. However, at the present time this labor intensive form of cutability it is not economically feasible. More studies need to be conducted in the area of true cutability and the determination of the actual value of a beef carcass. If major beef retailers

38 TABLE 7. LEAST SQUARE MEANS AND STANDARD ERROR OF THE MEANS (SEM) ACROSS TREATMENTS FOR MEASURES OF MASS, MUSCLING, FATNESS AND CUTABILITY FOR THE ROUND 29 Ractopam ine hydrochlorid* 2, ppm^ Trait^ SEM Measure of mass Round wt, kg Measures of muscling CUT I wt, kg CUT II wt, kg Measures of fatness SC fat wt, kg SC fat, % of round SC fat, % of side IM fat wt, kg IM fat, % of round IM fat, % of side Measures of cutability CUT I, % of round CUT I, % of side CUT II, % of round CUT II, % of side ^None of the treatment differences were significant (P >.05). ^CUT I = boneless tissue, 6 mm SC fat; CUT II = boneless tissue, 6 mm SC fat, 0 mm IM fat; SC = subcutaneous, IM = intermuscular.

39 30 were truly aware of the major effect of excess (greater than 6 mm) SC fat and IM fat of the chuck and rib on their retail yield, a much clearer signal could be sent back to the packer/feeder/breeder that fat must be reduced. The consumer does not want the excess fat (SC or IM) ; therefore, someone else must assume the loss, most likely the retailer and ultimately the consumer in excess calories consumed or plate waste. Effect of intermuscular fat on beef carcass composition. Shown in Table 8 are simple correlation coefficients relating carcass grading factors to four composition indices. Adjusted FTK was most closely related to chemical carcass fat, cutability I (boneless tissue with 6 mm SC fat) and cutability II (boneless tissue with 6 mm SC fat and no IM fat) with r =.77, -.62 and -.70 (P <.05), respectively. In agreement with Abraham et al. (1980) adjusted FTK was more closely related to all composition indices than was the actual FTK. Fat thickness, actual and adjusted, were poorly correlated (r =.30 and.37, respectively) to IM fat percent of side weight. In support of these data, Shahin and Berg (1985b) reported IM fat and SC fat depots develop at relatively different rates. Ribeye area was also highly correlated (r = -.53) with chemical carcass fat percent. Surprisingly, REA was the highest related ( r = -.44) among grade factors to IM

40 31 TABLE 8. SIMPLE CORRELATION COEFFICIENTS RELATING CERTAIN CARCASS TRAITS TO FOUR COMPOSITIONAL INDICES Carcass trait Chemical fat, % Cutability I^ Cutability 11^ Intermuscular fat, %^ Actual fat thickness. mm ** kk Adjusted fat thickness. Ribeye area. KPH, %^ mm 2 cm*^,11 k-k k-k * kk kk **.37 A A * * Hot carcass weight, kg ** -.07 Marbling score kk *. 37 ^Boneless, closely trimmed (6 mm subcutaneous fat) tissue from the round, loin, rib and chuck. Boneless, closely trimmed (6 mm subcutaneous fat, 0 mm intermuscular fat) tissue from the round, loin, rib and chuck. *-^Percent of side wt. ^KPH, % = actual kidney, pelvic and heart fat percent *(P <.05). ** (P <.01).

41 32 fat percentage. Kidney, pelvic and heart fat percent was not correlated to IM fat percent of the side (r =.0) in contrast to Abraham et al. (1980) who reported high correlations (r =.59). Ribeye area was more closely related to cutability II (r =.45) than to cutability I (r =.26) which may be explained by realizing cutability II includes no IM fat, therefore allowing muscle to comprise a greater percent of the index. Marbling score was also higher correlated to cutability II (r = -.31) than to cutability I (r = -.14) reinforcing the idea that cutability II may be a better estimate of actual carcass value. Table 9 shows the simple correlation coefficients relating nine SC fat estimates to four indices of composition. All estimates were highly correlated (r =.70 to.82) with chemical carcass fat percent. These data indicate estimations of SC fat depots can be made subjectively with some degree of certainty. Subcutaneous fat estimations showed increased correlations (Table 9) with IM fat percent over those of the grading factors (Table 8), however, all r values still were relatively low (r =.39 to.47). Correlations relating SC fat estimates over the rib-plate juncture and over the loin edge with cutability I and II were equivalent and highest among the SC fat estimates. All SC fat estimates (excluding the

42 TABLE 9. SIMPLE CORRELATION COEFFICIENTS RELATING VARIOUS SUBCUTANEOUS (SC) FAT ESTIMATES TO FOUR COMPOSITIONAL INDICES 33 Location of SC fat estimate Chemical Cutability Cutability fat, % II Intermuscular fat. %^ Opposite ribeye.80 Rib-plate juncture.75 Loin edge.75 Rump.77 Outside round.73 Inside round.75 Cod.70 Brisket.75 Chuck.82 ** kk kk kk kk kk kk kk kk ** ** ** ** ** ** ** ** ** ** ** ** kk kk kk kk kk kk ^Boneless closely trimmed(6 mm) tissue with no intermuscular fat removed from the round, loin, rib and chuck. ^Boneless, closely trimmed (6 mm) tissue with all intermuscular fat removed from the round, loin, rib and chuck. *^Percent of right side wt. *(P <.05) ** ** ** ** ** ** 45 ** kk (P <.01).

43 34 brisket location), however, were highly correlated to both indices of cutability. Table 10 shows the simple correlation coefficients relating IM fat estimates with chemical carcass fat, IM fat percent and the two measures cutability. Among four IM fat locations for estimation of total carcass chemical fat, IM fat at the 12th rib was the single best predictor (Table 10). The area of the 12th rib is a highly studied location in terms of carcass composition research. Surprisingly, IM fat at the 12th rib has not been previously studied. Due to the location of this estimate, it would lend itself to easy implementation into a value based marketing plan utilizing beef carcass composition estimates especially for hot fat trimmed carcasses. The IM fat estimate with the second highest correlation was the estimate at the ribplate juncture, however, this estimate showed a low correlation with IM fat percent of side. The kidney, pelvic and heart fat area and 5th rib estimates had the lowest correlation with chemical carcass fat; and, they are less logical for use in a value-based marketing plan utilizing rail grading methods for carcass composition estimation. Among the IM fat estimates, the 12th rib and the ribplate juncture were most highly correlated with cutability II (Table 10). The estimate at the 12th rib and the 5th/6th rib interface were modestly correlated to percent

44 TABLE 10. SIMPLE CORRELATION COEFFICIENTS RELATING INTERMUSCULAR (IM) FAT ESTIMATES TO FOUR COMPOSITIONAL INDICES 35 Location of IM fat estimate^ Chemical carcass fat, % Cutability Cutability 11^ IM fat. r 12th rib -.72 **.53 ** 71 ** -.54 ** RP juncture -.70 kk.64 ** 72 ** -.39 KPH area -.62 kk 56 ** 63 ** th rib -.55 kk ** -.51 ** Average -.77 kk.63 ** 79 ** -.54 ** ^RP = rib-plate at 12th rib; KPH = kidney, pelvic and heart fat; average = mean of four IM fat estimates. Boneless tissue, 6 mm subcutaneous fat, from the round, loin, rib and chuck. ^Boneless tissue, 6 mm subcutaneous fat, 0 mm IM fat, from the round, loin, rib and chuck. ^Percent of side wt. (P <.05). k k (P <.01).

45 36 IM fat (r = -.54 and -.51), and the average of the estimates did not show an increase (r = -.54). Higher correlations were observed for all IM fat estimates to cutability II than to cutability I. This relationship adds support to the philosophy that cutability II (IM fat removed) is a superior indicator of true carcass value. Although the average of the nine SC fat estimates were consistently the most highly correlated to the four compositional indices (Table 10), it is not feasible in an industry situation for predicting carcass fatness because of the unexposed 5th/6th rib interface at the time of carcass evaluation. Intermuscular fat estimates at the 12th rib and the rib-plate juncture were selected, due to their higher correlation coefficients and logic, for use in multiple regression equations for comparison to the adjusted FTK estimate currently used in the yield grade equation. Thus, adjusted FTK at the 12th rib and IM fatness estimates at the 12th rib and rib-plate juncture were evaluated individually to determine their specific influence in predicting chemical fat, IM fat percent and cutability. Adjusted FTK explained the most variation in chemical carcass fat (58.8%) while IM fat estimate at the 12th rib explained 51.6% of the observed variation (Table 11). The IM fat estimate at the rib-plate juncture (Table 11) was associated with the greatest amount of the observed

46 37 TABLE 11. REGRESSION EQUATIONS EMPLOYING VARIOUS FAT ESTIMATES PREDICTING FOUR COMPOSITIONAL INDICES Composition Fat index^ estimate R^ SEE^ Chemical fat, %: Cutability I: Cutability II: IM fat of side, %: Adjusted fat thickness IM fat estimate at 12th rib IM fat estimate at rib-plate Adjusted fat thickness, mm IM fat estimate at 12th rib IM fat estimate at rib-plate Adjusted fat thickness, mm IM fat estimate at 12th rib IM fat estimate at rib-plate Adjusted fat thickness, mm IM fat estimate at 12th rib IM fat estimate at rib-plate ^Cutability I = boneless, closely trimmed (6 mm subcutaneous fat) tissue from the round, loin, rib and chuck; Cutability II = boneless, closely trimmed (6 mm subcutaneous fat, 0 mm IM fat) tissue from the round, loin, rib and chuck, IM = intermuscular. ^SEE = standard error of the estimate.

47 38 variation (51.5%) in cutability I compared to adjusted FTK which was associated with 38.4% of the observed variation. The IM fat estimates were equally associated with cutability II (51.5%) compared to adjusted FTK (48.9%). The IM fat estimate at the 12th rib (Table 11) was associated with the greatest amount of variation of percent IM fat (29.0%) while adjusted FTK was associated with less of the observed variation (13.4%) as expected. Data in Table 11 clearly indicate IM fat estimated at the 12th rib is about equal to adjusted FTK at the 12th rib as an index to carcass composition. Adjusted FTK and IM fatness estimates at the 12th rib and rib-plate juncture were combined individually with the other yield grading factors for use in multiple regression equations to further evaluate their role in predicting carcass chemical composition, IM fat percent of side and cutability. Shown in Table 12 are the regression equations predicting chemical carcass fat. Equation 1 employing three traits selected by Murphey et al. (19 60) plus adjusted FTK at the 12th rib as the best indicator for fatness (Abraham et al., 1980), was associated with 60.7% of the observed variation in chemical carcass fat. When the IM fat estimate at the 12th rib was used in place of adjusted FTK (Equation 2), a reduction of only.5% was realized (R^ =.602). However, the introduction of the IM

48 TABLE 12. REGRESSION EQUATIONS PREDICTING CHEMICAL CARCASS FAT 39 Equation Independent variables^ Intercept b-value R^ SEE' Adjusted fat thickness, mm Kidney, pelvic and heart fat, Ribeye area, cm^ Hot carcass weight, kg % IM fat estmate at 12th rib Kidney, pelvic and heart fat, % 1.11 Ribeye area,cm^ -.08 Hot carcass weight, kg -.02 IM fat estimate at rib-plate juncture Kidney, pelvic and heart fat, % Ribeye area, cm Hot carcass weight, kg ^IM = intermuscular *SEE = standard error of the estimate.

49 40 fat estimate at the rib-plate juncture as the fat predictor (Equation 3) dropped the R^ value to 53.1%. Table 13 shows the regression equations predicting IM fat percent of the side using the same equations as Table 12. Although none of the equations proved to be highly effective in predicting percent IM fat (R^ =.251 to.355), Equation 2, utilizing the IM fat estimation at the 12th rib, was associated with the greatest amount of variation (R^ =.355). All equations in Table 14 possessed similar R^ values (.542 to.564). These data indicate percent boneless, closely trimmed (6 mm SC fat) retail cuts from the round, loin, rib and chuck can be predicted with the SC fat intact or hot fat trimmed without loss of accuracy (Table 14) when an IM fat estimate is employed into the yield equation. Equations using the same independent variables then were employed in Table 15 which shows the regression equations predicting carcass cutability based on boneless closely trimmed tissue with 6 mm SC fat and no IM fat. Equation 2 (IM fat estimate at 12th rib) was the most accurate equation due to the association of 64.5% of the observed variation while Equations 1 and 3 were equivalent (59.1%). As discussed above, this cutability value may be the best indicator of true carcass value for use in a value-based beef marketing system. The IM fat estimation at the 12th rib is logical and feasible when considering

50 41 TABLE 13. REGRESSION EQUATIONS PREDICTING INTERMUSCULAR FAT PERCENT OF SIDE Equation Independent variables^ Intercept b-value R2 SEE^ 1 Adjusted fat thickness, mm Kidney, pelvic and heart fat, % -.42 Ribeye area, cm^ -.06 Hot carcass weight, kg.01 2 IM fat estimate at 12th rib Kidney, pelvic and heart fat, % 2 Ribeye area, cm Hot carcass weight, kg.00 3 IM fat estimate at rib-plate juncture Kidney, pelvic and heart fat, % Ribeye area, cm -.06 Hot carcass weight, kg.01 ^IM = intermuscular. t»see = standard error of the estimate

51 TABLE 14. REGRESSION EQUATIONS PREDICTING CUTABILITY I^ 42 Equation Independent variables^ Intercept b-value R2 SEE^ 1 Adjusted fat thickness, mm Kidney, pelvic and heart fat, % Ribeye area, cm^ -.01 Hot carcass weight, kg -.03 IM fat estimate at 12th rib Kidney, pelvic and heart fat, % 1.56 Ribeye area, cm^.01 Hot carcass weight, kg -.03 IM fat estimate at rib-plate juncture Kidney, pelvic and heart fat. Ribeye area, cm'^ % Hot carcass weight, kg -.03 ^Percent ofboneless, closely trimmed (6 mm subcutaneous fat) retail cuts from the round, loin, rib and chuck. ^IM = intermuscular. ^SEE = standard error of the estimate.

52 TABLE 15. REGRESSION EQUATIONS PREDICTING CUTABILITY 11^ 43 Equa- Independent tion variables^ Intercept b-value R^ SEE c Adjusted fat thickness, mm Kidney, pelvic and heart fat, % -.58 Ribeye area, cm^.07 Hot carcass weight, kg -.04 IM fat estimate at 12th rib Kidney, pelvic and heart fat, % Ribeye area, cm^.06 Hot carcass weight, kg -.03 IM fat estimate at rib-plate juncture Kidney, pelvic and heart fat, % Ribeye area, cm -08 Hot carcass weight, kg -.04 ^Percent of boneless, closely trimmed (6 mm subcutaneous fat, 0 mm IM fat) retail cuts from the round, loin, rib and chuck. ^IM = intermuscular. ^SEE = standard error of the estimate.