T. Smith, J. D. Domingue, J. C. Paschal, D. E. Franke, T. D. Bidner and G. WhippleGenetic parameters for growth and carcass traits of Brahman steers

published online March 5, 2007J ANIM SCI 

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Running Head: Genetic parameters for Brahman steers 123

Genetic parameters for growth and carcass traits of Brahman steers1,2 45

T. Smith*3, J. D. Domingue†, J. C. Paschal‡, 6D. E. Franke†, T. D. Bidner†, and G. Whipple§ 7

8*University of Louisiana at Monroe, †LSU Agricultural Center, Baton Rouge, ‡Texas A&M 9

Research and Extension Center, Corpus Christi, and §Woodland Mills, TN. 1011

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1Approved for publication by the Director of the Louisiana Agric. Exp. Stn. as Manuscript No. 23

06-18-0301. 24

2Acknowledgement: The authors thank Manual A. Persica III, and John T. Carothers, Research 25

Associates in the Department of Animal Sciences, for assistance in preparing, aging, and cooking 26

steaks and in obtaining shear force data for this project. 27

3Correspondence: phone 318-342-1785; fax 318-342-1779; email: smith@ulm.edu. 28

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ABSTRACT: Spring born purebred Brahman bull calves (n = 467) with known pedigrees and 29

sired by 68 bulls in 17 private herds in Louisiana were purchased at weaning from 1996 through 30

2000 to study variation in growth, carcass, and tenderness traits. After purchase, calves were 31

processed for stocker grazing on ryegrass, fed in a south Texas feedlot, and processed in a 32

commercial facility. Carcass data were recorded 24 hr postmortem. Muscle samples and primal 33

ribs were taken to measure calpastatin activity and shear force. An animal model was used to 34

estimate heritability, genetic correlations, and sire EPD. Relatively high heritability estimates 35

were found for BW at slaughter (0.59 ± 0.16), hot carcass weight (0.57 ± 0.15), longissimus 36

muscle area (0.50 ± 0.16), yield grade (0.46 ± 0.17), calpastatin enzyme activity (0.45 ± 0.17), 37

and carcass quality grade (0.42 ± 0.16); moderate heritability estimates were found for hump 38

height (0.38 ± 0.16), marbling score (0.37 ± 0.16), fat thickness (0.36 ± 0.17), feedlot ADG (0.33 39

± 0.14), 7-d shear force (0.29 ± 0.14); and 14-d shear force (0.20 ± 0.11); relatively low 40

heritability estimates were found for skeletal maturity (0.10 ± 0.10), lean maturity (0.00 ± 0.07) 41

and percent kidney, pelvic, and heart fat (0.00 ± 0.07). Most genetic correlations were between -42

0.50 and +0.50. Other genetic correlations were 0.74 ± 0.27 between calpastatin activity and 7-d 43

shear force, 0.72 ± 0.25 between calpastatin activity and 14-d shear force, -0.90 ± 0.30 between 44

yield grade and 7-d shear force, and -0.82 ± 0.27 between fat thickness and 7-d shear force. 45

Heritability estimates and genetic correlations for most traits were similar to estimates reported 46

in the literature. Sire EPD ranges for carcass traits approached those reported for sires in other 47

breeds. The magnitude of heritability estimates suggests that improvement in carcass yield, 48

carcass quality, and consumer acceptance traits can be made within the Brahman population. 49

KeyWords: Brahman steers, carcass traits, genetic parameters. 50

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INTRODUCTION 52

The Brahman is the most common tropically adapted breed in the Gulf Coast Region. 53

Many commercial cow-calf producers in the region use Brahman crossbred cows in their herds 54

because of their reproductive and maternal advantages. However, Damon et al. (1960), DeRouen 55

et al. (1992), and Wheeler et al. (2001) reported that meat from Brahman cattle is less tender than 56

meat from non-Brahman cattle. Also, Luckett et al. (1975), Johnson et al. (1990) and O'Conner 57

et al. (1997) reported that shear force of meat increased as the percentage of Bos indicus 58

inheritance increased in crossbreds. Additionally, Damon et al. (1960), Wheeler et al. (2001) and 59

DeRouen et al. (2002) reported that carcasses of Brahman steers had lower marbling scores than 60

non-Brahman steers, resulting in lower carcass quality grades. 61

With the emphasis being placed on carcass and tenderness traits in the beef cattle industry 62

today, obtaining information on heritabilities and genetic correlations of these traits is necessary 63

in order to design a scheme to improve purebred Brahman cattle. Most reviews of genetic 64

parameters for carcass traits have been from Bos taurus cattle (Marshall, 1994; Koots et al., 65

1994; Utrera and Van Vleck, 2006). Crews and Franke (1998), Elzo et al. (1998), and Riley et al. 66

(2002; 2003) published genetic parameters for carcass traits of Brahman and Brahman crossbred 67

cattle. Johnston et al. (2003) reported slightly higher heritability estimates for shear force of 68

tropically adapted breeds in Australia than for temperate breeds. 69

In order to learn more about genetic variation in the Brahman breed, the objective of this 70

study was to gain additional information about heritabilities and genetic correlations for 71

postweaning growth, carcass, and tenderness traits in purebred Brahman steers and to predict 72

EPD of sires represented in the sample of steers. 73

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MATERIALS AND METHODS 74

Paternal half-sib Brahman male calves (n = 467) sired by 68 bulls were purchased from 75

17 purebred Brahman breeders in Louisiana over five yr (1996 to 2000). Calves were spring 76

born, weaned in the fall, and transported from breeders’ farms to the LSU Agricultural Center 77

Central Station (AGCCS) in Baton Rouge. Owners of these Brahman herds indicated their sires 78

were selected on the basis of some combination of weight at 12 or 24 mo of age, muscle 79

thickness, breed character, parental or individual show ring performance, or pedigree. None of 80

the producers considered carcass merit in sire selection. Most bull calves purchased from 81

producers were average or above for weaning weight in that herd-year group. The LSU 82

Agricultural Center Animal Use and Care Committee approved managerial aspects of this 83

research. 84

Management 85

Calves were castrated, dehorned if necessary, given appropriate vaccinations and 86

dewormed within two wk after arrival at the AGCCS. Each calf was assigned an identification 87

number for data collection and for association with its ancestral pedigree. After processing, 88

calves were placed on regrowth common bermudagrass (Cynadon dactylon) pastures with 2.3 kg 89

of a high roughage corn based diet (12% total protein) per head*d-1. Bermudagrass hay was 90

available at all times. Calves were placed on ryegrass pasture (Lolium multiflorum) about 91

December 1 each year, stocked at approximately 730 kg of calf per ha, and grazed for an annual 92

average of 120 d. Steers were implanted with Synovex before placement on ryegrass the first 93

yr and with Ralgro the remaining four yr. Upon completion of the grazing period steers were 94

shipped to a feedlot in south Texas for finishing. 95

Feedlot and Slaughter 96

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Steers were weighed upon arrival at the feedlot, implanted with Ralgro, and placed in one 97

pen for feeding. Steers were harvested in two or three groups each yr. When a group of steers in 98

the pen reached an estimated average of 7 to 10 mm fat thickness and a BW of 500 to 570 kg, 99

that group was harvested. Time of harvest for each group was visually estimated by trained 100

feedlot personnel. Steers were fed an average of 148 d in the feedlot over the 5 yr. Steers were 101

processed at Sam Kane Beef Processors in Corpus Christi, TX at an average age of 545 d. 102

Carcasses were electrically stimulated with high voltage during the slaughter process. After a 24-103

hr chill, carcasses were ribbed and carcass data recorded. A 15-g longissimus muscle sample was 104

collected at this time for measurement of calpastatin enzyme activity. Calpastatin activity was 105

determined at Central Community College in Hastings, NE, following the procedures of Whipple 106

et al. (1990a) and Shackelford et al. (1994). Calpastatin activity was not measured the last year 107

of the study. 108

Cooking and Shear Force Measurements 109

A boneless wholesale rib (#112; NAMP, 1997) was obtained from the right side of each 110

carcass at the time the carcasses were processed. The ribs were transported by refrigerated truck 111

to the Louisiana State University Animal Sciences Department Meats Laboratory. Two 2.54-cm 112

thick steaks were cut from the small end of each rib section, trimmed of outside fat and 113

connective tissue, vacuum packaged, and randomly assigned to aging for 7- or 14-d, 114

respectively. After the steaks were aged the appropriate time at 4°C they were frozen at -20°C. 115

When steaks from all steers had been aged and frozen, steaks were thawed for 24 h at 4°C and 116

then broiled to an internal temperature of 70°C (medium doneness) on a Farberware Open-117

Hearth Broiler (Model FSR200; Faberware Co., Bronx, NY). Internal temperatures were 118

monitored by 30-ga., type-T constantan-copper thermocouple connected to a strip chart recorder 119

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(Honeywell, Inc., Fort Washington, PA). Steaks were turned once at about 35°C and removed at 120

70°C. After steaks were held for 24 hr at 4°C, six 1.27-cm cores were removed from each steak 121

parallel to the orientation of the muscle fibers. Cores were sheared with a Model 4501 Instron 122

Universal Testing Machine (Instron Corp., Canton, MA) equipped with a Warner-Bratzler V-123

blade shearing attachment with a cross-head speed of 100 mm/min. The average of the six shear 124

force measurements on each steak was used as the shear force observation for each steer. This 125

procedure follows guidelines established by the American Meat Science Association (AMSA, 126

1995). 127

Statistical Analysis 128

The Multiple Trait Derivative Free Restricted Maximum Likelihood (MTDFREML) 129

programs of Boldman et al. (1995) were used to estimate heritability, genetic correlations 130

between all traits, and sire EPD. The MIXED procedure of SAS (SAS Inst. Inc., Cary, NC) was 131

used to obtain starting additive genetic and residual variances for MTDFREML. Proc MIXED 132

included sire as a random effect, and contemporary group (yr x harvest group) and the linear 133

covariate of slaughter age as fixed effects. Sires were confounded with herd, however herd was 134

not a significant source of variation in early analyses. Artificial insemination was not used across 135

the private herds. Connectedness across herds was assumed to occur through the numerator 136

relationship matrix, A, used in the animal model (Kennedy and Trus, 1993). The fact that all 137

herds were located in Louisiana and that breeders often exchanged germplasm most likely 138

improved this assumption. 139

Four-generation pedigrees were available for all steers. A total of 2,155 animals 140

contributed information to the A matrix. Heritabilities and sire breeding values were estimated 141

with single-trait analyses in MTDFREML while two-trait analyses in MTDFREML were used to 142

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estimate phenotypic and genetic correlations. To obtain estimates of SE for the two-trait 143

analyses, the data were edited to include only steers that had observations for those two traits. 144

Analyses were run initially at a convergence of 10-6 and then rerun to a convergence of 145

the simplex of 10-9. Cold restarts were made to insure the global maximum was reached. This 146

was assumed when the -2(log likelihood) did not change to the second decimal place. Variances 147

and co-variances obtained from the analyses were assumed to be based on a constant age at 148

slaughter endpoint. Slaughter age was used to adjust for the range of birth dates in the calves. 149

Contemporary groups were determined by the year and group in which each steer was harvested. 150

Thirteen contemporary groups were involved in the study with an average of 33 steers per group. 151

Response variables based on objective observations included feedlot ADG, BW at 152

slaughter, hot carcass weight, fat thickness, longissimus muscle area, quality grade, yield grade, 153

calpastatin enzyme activity, shear force after 7- and 14-d aging, and hump height. Skeletal and 154

lean maturity, percent kidney, pelvic and heart fat, and marbling score data were visually 155

estimated at ribbing of carcasses. Yield grade was calculated from an equation from the meats 156

manual of Boggs and Merkel (1979). Subjective measurements were determined by the same 157

trained meats specialist all five yr of the study. Ribeye area was determined using a direct grid 158

reading. 159

RESULTS AND DISCUSSION 160

Performance and Carcass Data 161

Descriptive statistics for growth, carcass, and tenderness traits are given in Table 1. A 162

total of 430 steers contributed data to most responses. Calpastatin activity was limited to 355 163

observations. Average BW at slaughter and fat thickness was within the range of criteria given 164

feedlot personnel for harvesting slaughter groups. Slaughter and carcass weights were slightly 165

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higher and fat thickness was slightly less than Brahman steers and heifers fed and harvested in 166

Florida (Riley et al., 2002). 167

Variance Components and Heritabilities 168

Heritability estimates for traits discussed in this study are presented in Table 2. High 169

heritability estimates (>0.40) were found for BW at slaughter, hot carcass weight, longissimus 170

muscle area, quality grade, yield grade, and calpastatin activity. Moderate estimates of 171

heritability (0.20 to 0.39) were obtained for feedlot ADG, fat thickness, marbling score, 7- and 172

14-d shear force, and hump height, while low estimates of heritability (<0.20) were found for 173

skeletal maturity, lean maturity, and percent kidney, pelvic and heart fat. 174

The estimate of heritability for feedlot ADG (0.33 ± 0.14) was similar to an estimate of 175

0.36 ± 0.09 reported by Gregory et al. (1995) for purebred and composite populations of cattle. 176

The estimates of heritability for BW at slaughter (0.59 ± 0.16) and hot carcass weight (0.57 ±177

0.15) were the highest in the study and were similar to mean estimates of 0.52 ± 0.14 and 0.45 ±178

0.12 reported by Koots et al. (1994) and estimates of 0.47 and 0.55 reported by Riley et al. 179

(2002). Utrera and Van Vleck (2006) reported a mean heritability of 0.42 for carcass weight 180

adjusted to a constant age. Lower estimates ranging from 0.15 ± 0.11 to 0.28 ± 0.08 were also 181

reported for these traits (Gregory et al., 1995; Wulf et al., 1996). 182

Our estimate of heritability for longissimus muscle area was 0.50 ± 0.16. This estimate is 183

lower but not different from estimates of 0.62, 0.65 ± 0.13, and 0.69 ± 0.14 reported by Van 184

Vleck et al. (1992) and Wheeler et al. (1996; 2001). Marshall (1994) and Koots et al. (1994) 185

reported mean estimates of 0.37 and 0.43, respectively for longissimus muscle area. Utrera and 186

Van Vleck (2006) reported a mean heritability estimate of 0.41 for longissimus muscle area from 187

36 estimates. 188

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The heritability estimate for fat thickness was 0.36 ± 0.17. This estimate is larger than 189

the 0.25 ± 0.08 reported by Gregory et al. (1995) and smaller than those reported by Wheeler et 190

al. (1996; 2001) and Marshall (1994) (0.44 to 0.84 ± 0.14) and the estimate of 0.63 reported by 191

Riley et al. (2002). Utrera and Van Vleck (2006) reported a mean heritability estimate of 0.41 for 192

adjusted fat thickness on 36 estimates. 193

For marbling score, the heritability estimate of 0.37 ± 0.16 found in this study was lower 194

than the range of estimates (0.43 to 0.93 ± 0.02) reported for marbling score by several authors 195

(Van Vleck et al., 1992; Shackelford et al., 1994; Wheeler et al., 2001). Wulf et al. (1996) 196

reported a lower estimate at 0.16 ± 0.11. Riley et al. (2002) reported a heritability estimate for 197

marbling score on Brahman steers and heifers of 0.44. Marshall (1994) reported a mean estimate 198

of 0.35 on 9 estimates whereas Utrera and Van Vleck (2006) reported a mean heritability 199

estimate of 0.45 on 29 estimates. Estimates of heritability for carcass quality grade were limited. 200

Riley et al. (2002) reported a heritability estimate for carcass quality grade of 0.47 that is similar 201

to our estimate of 0.42 ± 0.16.202

The estimate of heritability for yield grade was 0.46 ± 0.17, which is lower than estimates 203

reported by Wheeler et al. (1996; 2001) (0.76 ± 0.13, 0.85 ± 0.14) and Wulf et al. (1996) (0.76 ±204

0.26). Estimates of heritability for skeletal and lean maturity were not different from zero (0.10 ±205

0.10 and 0.00 ± 0.08, respectively). No literature estimates were found for these comparisons. 206

All steers were classified as A-maturity, therefore genetic variation for maturity was relatively 207

small. 208

The heritability estimate for percent kidney, pelvic, and heart fat was not different from 209

zero (0.00 ± 0.08). Elzo et al. (1998) reported low estimates of heritability for percent kidney, 210

pelvic, and heart fat ranging from .01 to .14 in several groups of cattle. Moderate levels of 211

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heritability for percent kidney, pelvic, and heart fat (0.32 ± 0.12; 0.28 ± 0.12) were reported by 212

Wheeler et al. (1996; 2001). A relatively high mean estimate of heritability for percent kidney, 213

pelvic, and heart fat of 0.48 on 8 estimates was reported by Utrera and Van Vleck (2006). 214

Heritability estimates for percent kidney, pelvic, and heart fat from dissected carcasses may be 215

larger than when KPH is subjectively measured by carcass observation. 216

The heritability estimate for hump height in this study was 0.38 ± 0.16. Riley et al. 217

(2002) reported an estimate of 0.54 for purebred Brahman cattle. Sherbeck et al. (1996) found 218

that shear force increased as hump height in Brahman crossbred cattle increased. 219

Heritability for calpastatin activity was 0.45 ± 0.17 and slightly lower than estimates 220

reported by Wulf et al. (1996), Marshall (1994), and Shackelford et al. (1994) of 0.52 ± 0.21,221

0.70, and 0.65 ± 0.19, respectively. However, our estimate was higher than those reported by 222

O’Conner et al. (1997) and Riley et al. (2003), that were 0.15 ± 0.15 and 0.07 respectively. 223

Estimates of heritability for shear force after different aging times have been variable, 224

ranging from 0.06 to 0.37 (Wulf et al., 1996; O’Conner et al., 1997; Wheeler et al., 1996; Riley 225

et al., 2003). Crews and Franke (1998) found that heritability for shear force decreased (0.24 to 226

0.02) as Brahman breeding decreased. This is contrary to the report of Elzo et al. (1998) who 227

reported higher heritability estimates as percent Brahman decreased (0.17 to 0.58). The 228

estimates of heritability in this study for shear force at 7-d and 14-d of aging were 0.29 ± 0.14229

and 0.20 ± 0.11, respectively. These values are consistent with most of the reports in the 230

scientific literature. However, Shackelford et al. (1994) reported an estimate of 0.53 ± 0.15231

across groups of cattle. 232

Estimates of heritability for carcass and shear force traits were reported from temperate 233

and tropical breeds of cattle in Australia. Johnston et al. (2003) reported the heritability of shear 234

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force was slightly larger for tropical breeds (0.30; Brahman, Belmont Red and Santa Gertrudis) 235

than for temperate breeds (0.09; Angus, Hereford, Murray Gray and Shorthorn). However, 236

Reverter et al. (2003) in a companion paper reported that heritability estimates for carcass traits 237

were similar for tropical and temperate breeds. 238

Ferguson et al. (2000) reported that electrical stimulation of carcasses prior to chilling 239

resulted in lower shear force and in lower calpastatin enzyme activity. We were not able to 240

determine the effect of electrical stimulation on shear force and calpastatin activity in these cattle 241

as all were electrical stimulated. It is not clear if electrical stimulation influenced the magnitude 242

of genetic parameters estimated for these traits. 243

Phenotypic and Genetic Correlations 244

Phenotypic and genotypic correlations are given in Table 3. Most phenotypic 245

correlations were relatively small with values less than 0.30. Lean maturity and percent kidney, 246

pelvic, and heart fat were not included in the two-trait analyses because their estimated additive 247

genetic variance was zero. Feedlot ADG was positively correlated with BW at slaughter (0.67) 248

and hot carcass weight (0.61). Body weight at slaughter was also positively correlated (0.90) 249

with hot carcass weight. Longissimus muscle area was positively correlated with BW at 250

slaughter (0.31) and hot carcass weight (0.40). Yield grade was positively correlated with fat 251

thickness (0.79) and negatively correlated with longissimus muscle area (-0.49). Fatter carcasses 252

were associated with higher yield grades and smaller longissimus muscle areas. 253

Most genetic correlations were between -0.50 and +0.50. Standard errors associated with 254

the genetic correlations averaged 0.30 and ranged from 0.01 to 0.50. Genetic correlations 255

between feedlot ADG and BW at slaughter and ADG and hot carcass weight were 0.71 ± 0.15,256

and 0.56 ± 0.18, respectively. Hot carcass weight was also genetically correlated with 257

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longissimus muscle area (0.45 ± 0.19) and marbling score (0.51 ± 0.23). The genetic correlation 258

between yield grade and fat thickness was relatively high in this study (0.77 ± 0.12) but lower 259

than values reported by Wheeler et al. (1996; 2001) (0.86 ± 0.04 and 0.89 ± 0.03). Yield grade 260

was highly correlated genetically with longissimus muscle area (-0.66 ± 0.16). Wheeler et al. 261

(1996; 2001) reported large genetic correlations between yield grade and longissimus muscle 262

area (-0.79 ± 0.21; -0.72 ± 0.19). Marbling score was highly correlated (0.99 ± 0.02) genetically 263

with quality grade because marbling score is the main indicator of carcass quality grade. 264

Calpastatin enzyme activity was negatively correlated genetically with hot carcass weight 265

(-0.69 ± 0.24) but positively correlated with shear force after steaks were aged for 7- (0.74 ±266

0.28) and 14-d (0.72 ± 0.26). Whipple et al. (1990b) identified calpastatin activity as one 267

possible cause for the difference in tenderness between Bos indicus and Bos taurus crosses. 268

Whipple et al. (1990a) and Shackelford et al. (1991) found that calpastatin activity at 24 hr 269

postmortem was strongly associated with beef tenderness (r = 0.66 and 0.39, respectively). Other 270

researchers (Marshal, 1994; Shackelford et al., 1994; Wulf et al., 1996) reported high positive 271

correlations of 0.58 and 0.50 ± 0.22 between calpastatin enzyme activity and shear force. 272

Shear force at 7-d and 14-d of aging was negatively correlated genetically with yield 273

grade (-0.90 ± .30 and -0.66 ± 0.30, respectively). Wheeler et al. (2001) also found a negative 274

genetic correlation between shear force and yield grade at 7- (-0.50 ± 0.26) and 14-d (-0.41 ±275

0.28) of aging. Seven-day shear force was also negatively correlated with fat thickness at -0.82 ±276

0.27. Wheeler et al. (2001) also reported a negative genetic correlation (-0.41 ± 0.25). Shear 277

force has been known to be greater in carcasses with less fat thickness due to cold shortening 278

(Koohmaraie et al., 1996; King et al., 2003). Bidner et al. (1997) showed that removing the back 279

fat from carcasses resulted in faster cooling of the carcass, a higher pH, and a higher shear force. 280

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We do not know if cold shortening is responsible for the high genetic correlation between fat 281

thickness and shear force in these data. The genetic correlations between 7-d shear force and 282

yield grade and 7-d shear force and fat thickness indicate that selection for improved tenderness 283

may be associated with increased fat thickness and low yielding carcasses. However, EPD of 284

approximately 30% of the sires with negative EPD for 7-d shear force were associated with 285

negative EPD for yield grade and for fat thickness. This indicates that it is possible to find sires 286

in this sample that would improve 7-d shear force and not cause fatter or lower yielding 287

carcasses. The phenotypic correlation between fat thickness and shear force was near zero. 288

The genetic correlation for fat thickness and marbling score was 0.04 ± 0.33. Our finding 289

was similar to low values ranging from -0.19 to 0.26 ± 0.24 (Crews et al., 2004; Wilson et al., 290

1993; Hirooka et al., 1996; Wheeler et al., 1996; Shanks et al., 2001; Pariacote et al., 1998). 291

When analyzing data from purebred Brahman cattle, Elzo et al. (1998) and Riley et al. (2002) 292

reported estimates of 0.03 and 0.56, respectively. Moderate values of 0.42 ± 0.14 and 0.44 ± 0.18293

were reported by Wheeler et al. (2001) and Gregory et al. (1995). 294

Marbling score was not associated genetically with shear force at 7 (0.08 ± 0.34) or 14 295

days (-0.02 ± .36) of aging. Wheeler et al. (1994) reported that the small positive association of 296

marbling score with palatability was similar in Bos taurus and Bos indicus cattle and that 297

marbling explained at best only 5% of the variation in palatability traits. Dikeman et al. (2005) 298

said that selection for marbling would result in little improvement in meat tenderness. In a 299

summary of several papers, Marshall (1994) reported a range of estimates from -0.25 to -0.53. 300

Results by Elzo et al. (1998) gave a value of -0.06 for purebred Brahman cattle while Sherbeck 301

et al. (1996) showed similar findings with small relationships between marbling score and 302

tenderness on steers of varying percentages of Brahman inheritance. Moderate values were 303

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reported by Wheeler et al. (2001) when aging steaks for 7 (-0.27 ± 0.27) and 14 days (-0.30 ±304

0.30). 305

Expected Progeny Differences 306

Expected progeny differences were calculated for each of the 68 sires. Descriptive 307

statistics of the sire EPD are given in Table 4. The mean EPD for each trait was near zero. 308

Ranges of sire EPD for the traits in this study are similar to ranges for carcass trait EPD of the 309

230 bulls in the 2006 American Brahman Breeders Association Sire Summary (American 310

Brahman Breeders Association, Houston, TX). Interestingly, ranges of sire EPD for carcass 311

weight and longissimus muscle area in this study were generally similar to those in the 2006 312

Angus sire summary (www.angus.org/sireeval/averages.html), but Angus bulls had greater range 313

for marbling score and for fat thickness. Sire EPD for shear force after a 14-d aging period in 314

103 Simmental, 23 Shorthorn, and 69 Hereford bulls involved in the National Cattlemen’s Beef 315

Association Carcass Merit Project were similar across breeds and ranged from -0.48 to 0.36 kg 316

(Dikeman et al., 2005). Ranges for Simbrah sire EPD for carcass traits were generally similar to 317

those in this study (www.simmental.org/simmapp/evalstats/). 318

Ranges of sire EPD found in this study and magnitude of genetic parameters discussed 319

earlier indicate sufficient genetic variation in these cattle to select for genetic improvement of 320

most important carcass characteristics. It is recognized that steers used in this study were not a 321

random sample of the U. S. Brahman population, but rather a sample of calves from participating 322

Brahman breeders in Louisiana. 323

IMPLICATIONS 324

The magnitude of genetic parameters estimated for carcass and tenderness traits in a 325

sample of Brahman steers indicates that selection within the Brahman breed may improve 326

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carcass quality and consumer related traits. However, selection of some sires for improvement in 327

tenderness may result in fatter and less yielding carcasses. Further research is needed to 328

determine if these correlations are as high in Brahman cattle as found in this study. The ranges of 329

Brahman sire EPD for carcass quality and tenderness traits were not radically different from EPD 330

ranges of sires in other breeds. 331

332LITERATURE CITED 333

334AMSA. 1995. Research guidelines for cookery, sensory evaluations, and instrumental 335

tenderness measurements of fresh meat. Am. Meat Sci. Assoc., Chicago, IL. 336337

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Table 1. Descriptive statistics for growth, carcass, and tenderness traits 482Trait n Mean SD Min Max CV 483Slaughter age 430 545.64 51.26 389.00 665.00 9.39 484

485Feedlot ADG, kg 430 1.49 0.23 0.64 2.51 15.67 486

487BW at slaughter, kg 430 556.87 55.80 335.45 679.55 10.02 488

489Hot carcass weight, kg 430 336.45 36.89 195.95 422.75 10.96 490

491Fat thickness, cm 430 0.87 0.42 0.13 2.80 47.87 492

493Skeletal maturity1 429 154.22 9.05 130.00 240.00 5.87 494

495Lean maturity2 425 151.29 12.09 120.00 200.00 7.99 496

497Loin muscle area, cm2 430 85.98 8.72 58.70 109.70 10.14 498

499Kidney, pelvic and heart fat, % 430 2.12 0.43 0.50 3.50 20.49 500

501Marbling score3 430 390.30 61.68 220.00 680.00 15.80 502

503Quality grade4 430 676.95 44.12 413.00 793.00 6.52 504

505Yield grade 430 2.34 0.68 0.80 4.70 29.05 506

507Calpastatin5 355 4.51 1.22 1.83 9.16 27.00 508

5097 day shear force, kg 428 4.57 1.21 1.96 9.89 26.54 510

51114 day shear force, kg 427 3.85 0.86 1.67 7.04 22.25 512

513Hump height, cm 420 19.36 3.30 10.20 30.50 17.03 5141Maturity scores 100 to 199 = A grade maturity, 200 to 299= B grade maturity, etc. 5152Maturity scores 100 to 199 = A grade maturity, 200 to 299= B grade maturity, etc. 5163200 to 299 Traces; 300 to 399 = Slight; 400 to 499 = Small; 500 to 599 = Modest, etc. 5174500 to 599 = Standard; 600 to 699 = Select; 700 to 799 = Choice; 800 to 899 = Prime. 5185Units of calpastatin activity per gram of muscle. 519

520

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Table 2. Additive genetic and residual variances and estimates of heritability 521Trait Additive variance Residual variance Heritability 522Feedlot ADG, kg 0.013 0.026 0.33 ± 0.14 523

524Slaughter weight, kg 1112.693 793.057 0.59 ± 0.16 525

526Hot carcass weight, kg 483.014 370.513 0.57 ± 0.15 527

528Fat thickness, cm 0.049 0.087 0.36 ± 0.17 529

530Skeletal maturity score1 6.721 62.194 0.10 ± 0.10 531

532Lean maturity score2 0.619 124.054 0.00 ± 0.08 533

534Longissimus muscle area, cm2 34.490 33.857 0.50 ± 0.16 535

536Kidney, pelvic and heart fat, % 0.000 0.167 0.00 ± 0.08 537

538Marbling score3 1170.077 1993.964 0.37 ± 0.16 539

540Quality Grade4 672.108 933.952 0.42 ± 0.16 541

542Yield grade 0.169 0.198 0.46 ± 0.17 543

544Calpastatin5 0.374 0.462 0.45 ± 0.17 545

5467-d shear force, kg 0.291 0.727 0.29 ± 0.14 547

54814-d shear force, kg 0.120 0.476 0.20 ± 0.11 549

550Hump height, cm 4.028 6.607 0.38 ± 0.16 5511Maturity scores 100 to 199 = A grade maturity, 200 to 299= B grade maturity, etc. 5522Maturity scores 100 to 199 = A grade maturity, 200 to 299= B grade maturity, etc. 5533200 to 299 Traces; 300 to 399 = Slight; 400 to 499 = Small; 500 to 599 = Modest, etc. 5544500 to 599 = Standard; 600 to 699 = Select; 700 to 799 = Choice; 800 to 899 = Prime. 5555Units of calpastatin activity per gram of muscle. 556

557558

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Table 3. Phenotypic and genetic correlations among growth, carcass and tenderness traits1

Trait2 ADG SLWT HCWT FT SMAT LMA MS

ADG, kg 0.71 ± 0.14 0.56 ± 0.17 -0.13 ± 0.33 -0.48 ± 0.45 0.16 ± 0.27 0.27 ± 0.28

SLWT, kg 0.66 0.94 ± 0.03 0.10 ± 0.27 -0.26 ± 0.44 0.30 ± 0.21 0.33 ± 0.24

HCWT, kg 0.61 0.89 0.08 ± 0.26 -0.24 ± 0.43 0.45 ± 0.19 0.51 ± 0.22

FT, cm 0.11 0.16 0.25 -0.27 ± 0.50 -0.25 ± 0.27 0.04 ± 0.33

SMAT -0.03 0.07 0.10 0.04 0.11 ± 0.43 -0.45 ± 0.47

LMA, cm2 0.20 0.31 0.39 -0.07 0.12 0.17 ± 0.28

MS 0.14 0.15 0.21 0.11 0.01 0.04

QG 0.13 0.10 0.16 0.12 0.00 0.05 0.81

YG 0.18 0.25 0.29 0.78 -0.01 -0.48 0.13

CALP 0.03 -0.03 0.08 -0.11 0.02 -0.03 -0.08

SF7, kg -0.06 -0.03 0.00 -0.02 0.05 0.05 -0.13

SF14, kg 0.03 0.00 -0.03 -0.02 -0.02 0.12 -0.02

HUMP, cm 0.23 0.02 0.26 0.21 -0.01 0.02 0.21Continued

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Table 3. Continued

Trait2 QG YG CALP SF7 SF14 HUMP

ADG, kg 0.09 ± 0.30 0.06 ± 0.29 -0.18 ± 0.31 -0.17 ± 0.34 -0.18 ± 0.35 -0.41 ± 0.30

SLWT, kg 0.00 ± 0.25 0.24 ± 0.23 -0.41 ± 0.26 -0.37 ± 0.28 -0.36 ± 0.30 -0.22 ± 0.26

HCWT, kg 0.23 ± 0.24 0.16 ± 0.23 -0.69 ± 0.24 -0.41 ± 0.28 -0.47 ± 0.30 -0.29 ± 0.26

FT, cm 0.46 ± 0.29 0.77 ± 0.12 -0.56 ± 0.32 -0.82 ± 0.27 -0.36 ± 0.38 -0.20 ± 0.35

SMAT -0.44 ± 0.45 -0.41 ± 0.46 0.57 ± 0.49 0.22 ± 0.49 0.27 ± 0.48 -0.62 ± 0.50

LMA, cm2 -0.04 ± 0.27 -0.66 ± 0.16 -0.43 ± 0.30 -0.04 ± 0.31 0.19 ± 0.32 -0.37 ± 0.29

MS 0.99 ± 0.01 0.13 ± 0.30 -0.51 ± 0.41 0.08 ± 0.34 -0.02 ± 0.36 0.17 ± 0.31

QG 0.38 ± 0.27 -0.44 ± 0.38 0.14 ± 0.32 0.10 ± 0.34 0.04 ± 0.30

YG 0.11 -0.36 ± 0.30 -0.90 ± 0.30 -0.66 ± 0.30 -0.07 ± 0.30

CALP -0.06 -0.07 0.74 ± 0.27 0.72 ± 0.25 -0.23 ± 0.29

SF7, kg -0.09 -0.05 0.26 1.00 ± 0.32 -0.43 ± 0.33

SF14, kg 0.02 -0.11 0.26 0.26 -0.14 ± 0.37

HUMP, cm 0.17 0.22 -0.02 -0.04 0.051Phenotypic correlations are in the lower triangle and genetic correlations with standard errors are in the upper triangle.2ADG = feedlot average daily gain, SLWT = slaughter weight, HCWT = hot carcass weight, FT = fat thickness, SMAT = skeletal maturity, LMA = longissimusmuscle area, MS = marbling score, QG = quality grade, YG = yield grade, CALP = units of calpastatin activity per gram of muscle, SF7 = shear force of 7-d agedsteaks, SF14 = shear force of 14-d aged steaks, and HUMP = hump height

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Table 4. Descriptive statistics for sire growth, carcass, and tenderness trait EPDTrait Mean Min Max SDFeedlot ADG, kg 0.01 -0.07 0.12 0.04

Slaughter weight, kg 2.45 -28.16 25.73 12.74

Hot carcass weight, kg 1.18 -19.40 17.61 8.56

Fat thickness, cm -0.01 -0.14 0.16 0.06

Skeletal maturity1 -0.05 -0.88 2.17 0.43

Loin muscle area, cm2 0.19 -3.30 6.87 1.98

Marbling score2 1.18 -19.71 22.60 9.98

Quality grade3 0.74 -25.39 18.86 8.01

Yield grade -0.01 -0.31 0.22 0.13

Calpastatin4 0.00 -0.36 0.61 0.18

7 day shear force, kg -0.01 -0.36 0.45 0.15

14 day shear force, kg 0.00 -0.16 0.33 0.09

Hump height, cm 0.07 -1.11 1.81 0.591100 to 199 = A maturity.2200 to 299 = Traces; 300 to 399 = Slight; 400 to 499 = Small; 500 to 599 = Modest, etc.3500 to 599 = Standard; 600 to 699 = Select; 700 to 799 = Choice; 800 to 899 = Prime.4Units of calpastatin activity per gram of muscle.

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