LM Steaks Research Articles

Zilpaterol hydrochloride lowers marbling score by dilution of marbling and depression of intramuscular adipocyte volume in M. longissimus dorsi of beef steers

We hypothesized that zilpaterol hydrochloride (ZH) depresses marbling scores in beef cattle by dilution of the intramuscular (i.m.) adipose tissue in the longissimus thoracis (LT) by increased muscle cross-sectional area. Crossbred steers were treated with ractopamine hydrochloride (RH; 28 d) or ZH (20 d) or no β-adrenergic agonist (CON). ZH increased LT cross-sectional area (P < .001) and depressed rib fat depth (P < .001), USDA marbling score (P < .05), percent LT lipid (P < .02), total lipid in a 2.54 cm-thick LM steak (P < .05) and most LT lipid fatty acids (P ≤ .05),but had no effect on mean i.m. adipocyte volume (P = .15). ZH increased the relative volume proportion of smaller i.m. adipocytes (250 to 500 pL) and decreased the proportion of larger i.m. adipocytes (2000 and 3000 pL) (P < .05). We conclude that ZH reduces marbling score both by dilution of the marbling and a depression of i.m. adipocyte relative volumes.

Comparison of meat quality and health implications of branded and commodity beef

The primary objective was to compare the quality attributes of steaks from “naturally raised” branded beef programs (NAT) with steaks from commodity beef (CONV) with similar marbling specifications. Ribeye rolls were purchased from 5 branded programs with identical marketing claims (no dietary antibiotic or ionophore inclusion and no growth promotants) and 2 major beef packing companies and were wet-aged at 2°C for 14 d from the box date. After wet aging, ribeye rolls were removed from vacuum packaging and pH of the LM was measured before steaks were cut for fresh instrumental color, fatty acid analysis, antibiotic residue testing, Warner-Bratzler shear-force determination, and consumer sensory evaluation. The LM pH did not differ (P = 0.072) between CONV and NAT ribeye rolls, but CONV LM had lesser (P = 0.014) L* values than NAT LM. Although CONV LM had greater (P = 0.019) proportions of 18:1 trans fatty acids than NAT LM, concentrations of SFA (P = 0.799), monounsaturated fatty acids (P = 0.724), and PUFA (P = 0.420) were not different between CONV and NAT. Penicillin G residues were detected in 2 NAT steaks, but no antibiotic residues were detected in the CONV LM steaks. Neither Warner-Bratzler shear-force values nor consumer panelists’ sensory ratings differed (P ≥ 0.166) between CONV and NAT. There was little to no difference in fresh beef color, fatty acid composition, or cooked beef palatability between steaks from CONV and NAT, especially when cattle were fed high-concentrate finishing diets.

Effects of United States Department of Agriculture carcass maturity on sensory attributes of steaks produced by cattle representing two dental age classes.

This study examined the effects of USDA carcass maturity on sensory properties of LM steaks produced by cattle representing 2 dental age classes. Carcasses identified for use in the experiment were produced by steers and heifers classified as either <30 mo of age (MOA) or ≥30 MOA at the time of slaughter using dentition. Within each dental age class, carcasses were selected to represent 2 maturity groups and 3 marbling categories, resulting in 12 dental age × maturity × marbling subclasses, each consisting of 50 carcasses. Maturity groups consisted of carcasses classified by USDA graders as either A to A (A) overall maturity or B to D (B-D) overall maturity; marbling categories consisted of carcasses with instrument marbling scores of Slight to Slight (SL), Small to Small (SM), or Modest to Moderate (MT-MD). Carcasses were selected in pairs so that each carcass chosen to represent the B-D-maturity group was paired with an A-maturity carcass of the same sex and marbling score (±50 marbling units). Strip loin (LM) steaks were obtained from both sides of each carcass. After a 14-d aging period, 1 LM steak was measured for Warner-Bratzler shear force (WBSF) and slice shear force (SSF), whereas the other LM steak was used for sensory analysis by a trained descriptive attribute panel. No differences ( > 0.05) in LM tenderness, juiciness, or flavor were detected between carcass maturity groups in either dental age class. Advanced dental age (≥30 MOA), however, was associated with more intense ( < 0.05) grassy and bloody/serumy flavors and decreased ( < 0.05) tenderness within the SL marbling group. Marbling score effectively stratified carcasses (MT-MD > SM > SL) according to differences ( < 0.0001) in LM tenderness, juiciness, beefy/brothy flavor, and buttery/beef fat flavor. In addition, increased marbling was associated with lesser ( < 0.01) intensities of bloody/serumy, livery/organy, and grassy flavors as well as smaller ( < 0.0001) values for WBSF and SSF. Results of this study suggest that USDA carcass maturity does not effectively identify differences in LM sensory attributes in the population of beef carcasses routinely offered for grading in today's U.S. commercial beef processing facilities.

Effects of USDA carcass maturity on sensory attributes of beef produced by grain-finished steers and heifers classified as less than 30 months old using dentition1

This study compared sensory properties of LM steaks from A maturity and B maturity or older carcasses that were produced by grain-finished steers and heifers classified as less than 30 mo old at the time of slaughter using dentition. Carcasses were selected to represent 2 maturity groups and 3 marbling categories within each maturity group, resulting in 6 maturity × marbling subclasses, each subclass consisting of 75 carcasses. Maturity groups consisted of carcasses classified by USDA graders as either A(00) to A(99) overall (A) maturity or B(00) to C(99) overall (B-C) maturity; marbling categories consisted of carcasses with instrument marbling scores of Slight (SL), Small (SM), or Modest(00) or greater (MT+). Carcasses were selected in pairs so that each carcass chosen to represent the B-C maturity group was paired with an A maturity carcass of the same sex and marbling score (± 30 marbling units). Strip loin (LM) steaks were obtained from both sides of each carcass. After a 14-d aging period, 1 LM steak was measured for Warner-Bratzler shear force (WBSF) and slice shear force (SSF), whereas the other LM steak was used for sensory analysis by a trained descriptive attribute panel. No differences (P > 0.05) in WBSF, SSF, or sensory panel ratings for tenderness, juiciness, or flavor were detected between LM steaks from carcasses classified as A maturity and steaks from B-C maturity carcasses. However, marbling categories effectively stratified carcasses (MT+ > SM > SL) according to differences (P < 0.0001) in LM tenderness, juiciness, meaty/brothy flavor, and buttery/beef fat flavor. Increased marbling also was associated with lesser (P < 0.01) intensities of bloody/serumy and livery/organy flavors and reduced (P < 0.01) values for WBSF and SSF. Of the traits tested, only bloody/serumy flavor was affected (P < 0.05) by the maturity × marbling interaction. Interaction means showed that LM steaks from B-C maturity carcasses with SL marbling had a less intense bloody/serumy flavor than did steaks from A maturity carcasses with SL marbling. Results of this study suggest that, when applied to carcasses from grain-finished cattle whose dental ages are less than 30 mo old at the time of slaughter, USDA quality grades would be no less effective in identifying eating quality differences if the A and B-C maturity groups were combined and quality grades were assigned using only marbling.

Effects of feeding extruded full-fat cottonseed pellets in place of tallow as a fat source for finishing heifers on feedlot performance, carcass characteristics, sensory traits, display color, and fatty acid profiles1

The objective of this study was to examine the effects of supplemental feeding of full-fat extruded cottonseed pellets (FFECS) compared with tallow on carcass characteristics, sensory traits, retail display color, and fatty acid profiles, especially CLA isomers in finishing heifers. Twenty-one Angus heifers (450 ± 5 kg) were assigned randomly to 1 of 3 experimental diets: 1) 100% supplemental fat from tallow at 4.1% of ration DM (TAL), 2) a 50:50 ratio of supplemental fat from a combination of tallow at 2.1% and FFECS at 12.8% of ration DM (TAL/ECS), and 3) 100% supplemental fat from FFECS at 25.6% ration DM (ECS). All rations were formulated to contain 7.5% fat on a DM basis. Heifers were individually fed, ad libitum, for 82 d, and BW, G:F, DMI, ADG, and body composition via ultrasound were collected at 3 to 4 wk intervals. After 82 d on feed heifers were slaughtered under federal inspection, and carcass characteristics were measured (at 24 h). The LM was removed for retail display color (1, 3, 6, 10 d), Warner-Bratzler shear force (1, 3, 7, 14, 21 d postmortem aging), sensory analysis (1, 7, 14, 21 d postmortem aging), and fatty acid profile analysis. Subcutaneous fat, including all layers, was removed from the LM for fatty acid profile analysis, and ground beef patties (80:20) were produced with lean from the brisket and fat from the plate for retail color analysis (1, 2, 4, 7 d). Supplemental fat source did not influence feedlot performance for any of the traits measured (P > 0.12) or any carcass traits related to yield, quality, or LM color at the 12th- to 13th-rib interface (P > 0.15). Supplemental fat source did not affect Warner-Bratzler shear force or any sensory traits (P > 0.20), but LM steaks became more tender as postmortem aging time increased up to 14 d (P < 0.01). During retail display of LM steaks and beef patties, the only difference was LM steaks from ECS were darker (lower L* value) than TAL or TAL/ECS steaks (P < 0.02). As display time increased, LM steak and beef patty objective and subjective color deteriorated (P < 0.01). Although feeding FFECS compared with tallow increased linoleic acid (C18:2(n-6)) in both intramuscular and subcutaneous fat (P < 0.04), this did not lead to an increase in total CLA content (P > 0.90). Full-fat extruded cottonseed pellets are interchangeable with tallow in heifer finishing diets without impacting feeding performance, meat quality, shelf life color, or CLA content of adipose sites.

Sampling and aging effects on beef longissimus color stability measurements1

The present study was conducted to determine the repeatability of color stability measurements and to evaluate relationships among color stability data collected under differing sampling and aging protocols. Beef (Bos taurus) carcasses (n = 100) were selected at grading in a commercial facility, after which a LM steak was removed from the 13th rib of each carcass and immediately placed in simulated retail display. Steaks were removed from the remainder of each loin after 14 (duplicate) and 35 d of aging and placed in display. Color attributes [L*, a*, b*, hue angle, chroma, K/S(572)/K/S(525), and overall color change (ΔE)] were determined on d 0, 1, 4, 7, and 11 of display. Duplicate 14-d aged steaks differed (P < 0.05) initially with regard to L*, b*, hue angle, chroma, K/ S(572)/K/S(525), and ΔE. However, changes in these attributes during display were equivalent in the duplicate steaks. Furthermore, repeatability estimates were high for all attributes, particularly when measured late in the display period (R = 0.55 to 0.97 on d 4, 7, and 11 of display). Differences in the trends associated with color change of steaks removed from the carcass after grading and those aged for 14 d were generally insignificant. Changes in color attributes of steaks aged for 35 d before simulated retail display generally were much more rapid than those obtained after grading or those aged for 14 d. Despite differences in the rate of discoloration during simulated retail display, color attributes were moderately to highly correlated (P < 0.05) between aging treatments, though the degree of correlation between attributes varied across days of display. In steaks collected after grading and those aged for 14 d, the greatest correlation was observed in the latter part of the display period with coefficients ranging from 0.61 to 0.94 on d 4, 7, and 11 of display. The greatest correlation between steaks aged for 14 d and those aged for 35 d were detected in the middle portion of the display period, presumably because many steaks aged for 35 d had reached an ultimate level of discoloration by d 11 of display with correlation coefficients ranging from 0.51 to 0.95 on d 4 and 7 of display. Thus, these results indicate that color stability data is highly repeatable and that, although aging impacts color-life, animal variation is consistent across aging times. Furthermore, steaks obtained from carcasses after grading can provide color stability evaluations applicable to steaks from aged subprimals.

Characterizing bovine adipocyte distribution and its relationship with carcass and meat characteristics using a finite mixture model1

The appreciation of adipose tissue complexity has initiated a new era of multifaceted investigations that continue to provide findings in adipocyte biology, but quantitative descriptions of adipocyte distribution are lacking. The first objective was to develop a finite mixture model to model adipocyte bimodal distribution and to correlate these estimates with carcass and meat characteristics. A secondary objective was to demonstrate within-animal observed variability in adipocyte cellularity. Steers were finished on a high-grain diet (n = 14) or grass (n = 16). One 12-cm thick LM steak from each steer was collected during harvest. A probability density function was developed that partitioned the cell diameter population into small and large populations and described the relative proportions of cells for each animal in these 2 distinct populations. Five parameters were estimated through the finite mixture model: the means (μ(1) and μ(2)) and SD (σ(1) and σ(2)) for the small and large adipocyte populations, respectively, and a proportion parameter (p) describing the proportion of the distribution of the smaller adipocyte populations. The proportion parameter for all animals tended to be different (P = 0.07) between groups with the grain presenting a p of 22.5 ± 12.5% and grass 16.2 ± 4.7%. The μ(2) was correlated with yield grade (YG, P = 0.04), and σ(2) with final BW, HCW, dressing percentage, YG, and quality grade score (P = 0.01). When correlating these parameters with the sensory data, μ(2) and σ(2) were correlated with tenderness (P ≤ 0.05), σ(1) and p with juiciness (P ≤ 0.05), and p with overall palatability (P = 0.01). Adipocyte cellularity variability was measured by examining the results from 5 randomly chosen steers from each group (grain and grass). In this subset, the μ(1) and p ranged from 32.1 to 46.1 μm and 1 to 27% for grass-finished steers, and ranged from 33.7 to 41.0 μm and 10 to 48% for grain-finished steers. The μ(2) and (1 - p) ranged from 75.0 to 105.1 μm and 73 to 99% for grass-finished steers, respectively, and ranged from 84.8 to 124.0 μm and 52 to 90% for grain-finished steers, respectively. The finite mixture model provides a quantitative description of the distribution of adipocytes and contributes to explaining adipocyte biology. Adipocyte cellularity variability among samples within an animal is a topic that should be further evaluated, as well as its correlation with other factors, such as gene expression and hormone secretion.

Effects of sequential implanting and ractopamine hydrochloride supplementation on carcass characteristics and longissimus muscle tenderness of calf-fed steers and heifers1

A 4 × 2 factorial arrangement of treatments (4 growth-enhancement treatments × 2 sex classes) was used to quantify effects of initial implanting (I-implant, d 0), terminal implanting (T-implant, d 63), and feeding ractopamine hydrochloride [RAC, 200 mg/(animal/d)] for the last 28 d on feed on carcass characteristics and LM shear force (WBSF) of calf-fed steers (n = 159) and heifers (n = 132). Growth-enhancement treatments included the following: TRT1, T-implant only; TRT2, I-implant and RAC; TRT3, I-implant and T-implant; TRT4, I-implant, T-implant, and RAC. Growth responses (BW and ADG) were measured in 3 segments of the finishing period: 1) d 0 to 63, 2) d 63 to 28 d before slaughter, and 3) final 28 d. Cattle were slaughtered after 152, 166, or 180 d of finishing; carcass data were collected after a 48-h chill; and LM WBSF was measured at 3, 7, 14, 21, and 28 d postmortem. A priori contrasts were constructed to test effects associated with use vs. exclusion of growth enhancement in each segment of the finishing period. The interaction between sex class and treatment was not significant (P > 0.05) for any trait tested, indicating that the 4 treatments elicited similar effects in both sexes. Initial implanting improved (P < 0.001) ADG from d 0 to 63 by 11.5%, terminal implanting improved (P < 0.001) ADG from d 63 to 28 d before slaughter by 15%, and supplementing twice-implanted cattle with RAC enhanced ADG during the final 28 d of finishing by 12%. Effects of I-implant, T-implant, and RAC resulted in LM area increases of 3 cm(2) (P = 0.015), 6 cm(2) (P < 0.001), and 3 cm(2) (P = 0.011), respectively, and HCW responses of 11 kg (P = 0.011), 16 kg (P = 0.001), and 6 kg (P = 0.195), respectively. Initial implanting resulted in a 20-point reduction (P = 0.097) in marbling, and T-implant reduced marbling by 25 points (P = 0.04), whereas marbling score was unaffected (P = 0.236) by RAC supplementation. Cattle that received only 1 implant (TRT1 and TRT2) produced carcasses with greater (P = 0.026) mean marbling scores and greater (P = 0.01) rates of conformity to beef carcass marketing specifications for HCW, quality grade, yield grade, and LM area than did cattle that were implanted twice (TRT3 and TRT4). Values for LM WBSF were not affected (P > 0.05) by initial or terminal implanting; however, RAC supplementation increased (P = 0.007) mean LM WBSF by 0.23 kg, which translated into a reduction (P = 0.007) in predicted consumer acceptance of LM steaks.

Effects of genetic markers and implant strategy on longissimus and gluteus muscle tenderness of calf-fed steers and heifers1

Effects of genotype (GEN) and implant program (IMP) on LM and gluteus muscle (GM) tenderization were investigated using crossbred steer (n = 185) and heifer (n = 158) calves. The 3-marker GeneSTAR Tenderness panel [CAST (calpastatin), CAPN1 316 (µ-calpain), and CAPN1 4751 (µ-calpain)] was used to determine the GEN of each animal (reported as total number of favorable alleles, 0 through 6). Calves were randomly assigned to 1 of 2 IMP, conventional (CNV) or delayed. Cattle in the CNV group were implanted at the beginning of the finishing period with Revalor-IS or Revalor-IH (Intervet Inc., Millsboro, DE), and then reimplanted 59 d later with Revalor-S or Revalor-H (Intervet Inc.). Calves in the delayed group received a single terminal implant (Revalor-S or Revalor-H) administered 45 d after initiation of the finishing period. Warner-Bratzler shear force (WBSF) was measured on LM and GM steaks at 3, 7, 14, 21, and 28 d postmortem. No interactions between the main effects of sex, IMP, or GEN were detected (P > 0.05) for WBSF. An IMP × postmortem aging (age) interaction was detected (P < 0.05) for LM and GM WBSF. For both muscles, steaks from CNV cattle had WBSF values that were approximately 0.2 kg greater (P < 0.05) than the values for steaks from delayed animals, but only during the early postmortem period (3 to 7 d). A linear effect of GEN on WBSF was detected (P < 0.05) for LM and GM steaks. Within each muscle, steaks from cattle with 6 favorable alleles had WBSF values 0.33 kg less than the values for steaks from cattle with 1 favorable allele. The GEN × age interaction was not significant for LM (P = 0.14) or GM (P = 0.20), but a numerical trend was observed for the effect of GEN on WBSF to diminish as age increased. To investigate how genetic markers could be interfaced with current beef carcass quality grading, cattle were sorted into 2 gene marker groups (GMG), ≤3 vs. ≥4 favorable alleles. For both muscles, GMG was effective only at identifying tenderness differences within the Select grade. When aged ≤14 d, Select LM steaks from cattle with ≥4 alleles had smaller (P < 0.05) WBSF values than did LM steaks from animals with ≤3 alleles. Preslaughter factors (sex, IMP, and GMG) controlled in the present study each accounted for less than 7% of the explained variation in tenderness of the test population. Results from this study suggest that the 3 GeneSTAR Tenderness markers were associated with small differences (0.33 kg) in WBSF and may be useful for increasing the consistency of Select beef, but these specific markers accounted for only a minor amount of variation in beef tenderness.

The effects of zilpaterol hydrochloride on carcass cutability and tenderness of calf-fed Holstein steers1

To evaluate the impact of zilpaterol hydrochloride (ZH) on carcass cutability and tenderness of calf-fed Holstein steers, calf-fed Holstein carcasses (n = 102) were selected from a pool of 2,300 steers that were fed 0 or 8.3 mg/kg (DM basis) of ZH. Zilpaterol hydrochloride was supplemented the last 20 d of the finishing period and withdrawn for 3 d before slaughter. Carcasses were selected based on carcass weight as well as predetermined USDA Yield grade categories. For tenderness evaluation, steaks from the strip loin, bottom round, and top round (n = 54 per subprimal) were aged for 14 or 21 d postmortem. Carcasses from ZH-fed steers had more (P < 0.01) saleable yield than carcasses from control-fed steers. Additionally, ZH-fed steers had greater (P < or = 0.01) subprimal yield from the shoulder clod, strip loin, peeled tenderloin, top sirloin butt, bottom sirloin tri-tip, peeled knuckle, inside round, bottom round flat, eye of round, heel, and shank. Furthermore, ZH decreased (P < 0.01) the total amount and percentage of bone and fat trim from the carcass. Moisture loss was not affected by ZH in LM or inside round steaks (P > 0.05); however, ZH increased thawing loss (P = 0.05) but reduced cooking loss (P = 0.05) in bottom round steaks. Shear force values of LM and inside round steaks increased with ZH inclusion (P < 0.01), but there was no difference in bottom round steaks (P > 0.05). Steaks aged for 21 d had smaller (P < 0.01) Warner-Bratzler shear force (WBS) values than 14-d steaks from all 3 subprimals. Trained sensory panelists did not detect any differences (P > 0.05) in sensory juiciness, tenderness, or flavor variables of LM or inside round steaks, except ZH steaks from the LM received smaller scores for sustained juiciness (P = 0.01) and overall tenderness (P = 0.04) than control steaks. Although LM steaks from ZH cattle were tougher than control steaks, the ZH-treated steaks had an average WBS value of 4.10 kg, which would be classified as intermediate in tenderness, with trained panelists rating ZH steaks slightly to moderately tender. Feeding ZH improved carcass cutability of calf-fed Holstein steers; however, tenderness was reduced in LM and inside round steaks. The interaction of postmortem tenderization techniques should be investigated to evaluate their impact on palatability in cattle supplemented with beta-agonists to allow the beef industry to take full advantage of the enhancement in performance and carcass yield.

Perspectives on the application of zilpaterol hydrochloride in the United States beef industry

Zilpaterol hydrochloride (ZH) is a beta-adrenergic agonist approved to be fed at a rate of 8.3 mg/kg (100% DM basis) during the final 20 to 40 d of the finishing period in beef cattle followed by a minimum 3-d withdrawal period antemortem. The Federal Drug Administration (FDA) approved label claims of increased rate of BW gain, improved feed efficiency, and increased carcass leanness. Before the release of ZH for commercial use in 2007, approximately 10 independent research trials at various universities and commercial feedlots were initiated. Articles in recent issues of the Journal of Animal Science are a result of the large comprehensive body of research designed to increase the understanding of the effect of ZH on beef cattle growth, carcass traits, and beef quality. The feeding of ZH for 20 to 40 d with a 3-d withdrawal resulted in significantly increased ADG. The increases equate to an average of 9 kg heavier BW in ZH-fed steers. Hot carcass weight has been shown to increase to a larger degree compared with BW, with an average improvement of 15 kg. Dressing percent is increased by 1.5 to 2.0% with the feeding of ZH. Increases in carcass leanness were reported for cattle fed ZH mainly through a reduction in yield grades. The LM area was increased, along with yield of subprimal cuts from the round, flank, and loin. Warner-Bratzler shear force studies have shown LM steaks from ZH-treated cattle to have increased shear force values of 1.1 to 1.7 kg for 7-d-aged steaks, 0.4 to 1.3 kg for 14-d-aged steaks, and 0.27 to 1.4 kg for 21-d-aged steaks compared with controls. Recent research has suggested that the aging response is normal in ZH steaks. Consumers were able to identify tenderness differences in 14-d-aged Choice steaks from cattle fed ZH for 20 d compared with 14-d-aged steaks from control cattle; this difference was mitigated with 21 d of postmortem aging. Zilpaterol hydrochloride has been shown to increase cattle growth and efficiency as well as lean tissue deposition in the carcass, with some impact on carcass traits such as Warner-Bratzler shear force.

Relationships of behavioral and physiological symptoms of preslaughter stress to beef longissimus muscle tenderness1

Relationships between behavioral and physiological symptoms of preslaughter stress and LM Warner-Bratzler shear force (WBSF) were investigated using Bos taurus steers (n = 79) and heifers (n = 77). Measurements of heart rate, respiration rate, rectal temperature, and concentrations of serum cortisol and plasma epinephrine were used as indicators of stress associated with physical handling and chute restraint, whereas concentrations of cortisol, glucose, lactate, and creatine kinase in blood samples obtained at exsanguination were measured to reflect physiological reactions of animals to transportation stress. Increased plasma epinephrine concentration, indicative of acute handling stress, was associated with elevated heart rate (r = 0.42, P < 0.001) and rectal temperature (r = 0.34, P < 0.001) during restraint, increased plasma lactate (r = 0.22, P = 0.006) and serum creatine kinase (r = 0.28, P < 0.001) concentrations at slaughter, and greater LM WBSF (r = 0.22, P = 0.006). Plasma lactate concentration at slaughter, which reflected an adrenergic stress response to transportation, was associated with lesser final LM pH (r = -0.30, P < 0.001) and greater LM WBSF (r = 0.26, P = 0.002). Categorical analyses of chute and posttransportation behavior scores (calm vs. restless vs. nervous) showed that cattle exhibiting adverse behavioral reactions to handling and chute restraint had increased (P < 0.05) values for plasma epinephrine concentration, heart rate, and rectal temperature during chute restraint, elevated (P < 0.05) plasma lactate concentration at slaughter, and increased (P < 0.05) LM WBSF. In addition, cattle showing behavioral symptoms of stress after transportation had greater (P < 0.05) plasma glucose and lactate concentrations at slaughter and produced LM steaks that were 0.34 kg tougher (P < 0.05) when compared with calm cattle. No carcasses were identified as dark cutters, and LM pH did not differ (P > 0.05) among behavior categories. Grouping cattle according to differences in plasma lactate concentration categorized them according to mean differences in LM WBSF. Moreover, steaks from cattle with the greatest plasma lactate concentrations at slaughter (91st to 100th percentile) had a delayed response to aging that persisted until 14 d postmortem. Stress-induced differences in LM tenderness observed in this study were independent of differences in muscle pH.

Effects of sex and short-term magnesium supplementation on stress responses and longissimus muscle quality characteristics of crossbred cattle1

Calf-fed heifers (n = 72) and steers (n = 72) were supplemented with 4 levels (0, 0.25, 0.50, and 0.75%) of dietary Mg as MgO during the final 14 d of finishing and were commingled 1 d before slaughter (inducing stress by mixing unfamiliar cattle) to examine the effects of sex class and Mg supplementation on stress responses and LM quality characteristics. Heifers and steers exhibited markedly different stress responses. Heifers were more excitable than steers during preslaughter handling events and exhibited a short-term physiological stress response that involved acute sympatho-adrenal activation and resulted in increased meat toughness, without a concomitant increase in muscle pH. Steers, on the other hand, exhibited greater physical activity, associated with agonistic behavior, during the mixing period and therefore produced carcasses with lesser (P = 0.008) LM glycogen concentrations and greater (P = 0.042) 48-h LM pH values, compared with heifers. Steers also produced tougher (P = 0.008) LM steaks than did heifers. Within the range of pH values observed in this study (5.3 to 6.1), positive, linear relationships between 48-h LM pH and mean LM shear force (P < 0.05) were observed in both heifers (r = 0.25) and steers (r = 0.37). Effects of pH on LM shear force (P < 0.05), which were most pronounced at 3 and 7 d postmortem, diminished during postmortem aging and were no longer evident (P > 0.05) once LM samples had been aged for 21 d. Results suggested that toughness of LM steaks from beef carcasses with final LM pH values greater than 5.65 could be problematic unless LM cuts are aged for approximately 18 d or longer. Supplementation with dietary Mg increased (P = 0.011) serum Mg concentration, but had no effect (P > 0.05) on any of the physiological stress indicators or LM quality characteristics measured in this study. There was no evidence to support the premise that Mg supplementation of cattle lessens the effects of preslaughter stress on beef quality characteristics.

Production Characteristics of Pasture-Fed Beef

Twenty pasture-fed steers and 10 pasture-fed heifers were evaluated for relationships among daily BW gain, grazing period, frame size, final weight, and carcass traits (fat thickness, ribeye area, marbling score, and YG). Cattle were wintered for a BW gain of 0.69 ± 0.03 kg/d for 156 d postweaning and were maintained in adjacent, rotationally grazed paddocks containing primarily cool-season grasses. Cattle were slaughtered at a constant age (532.9 d ± 5.7 d) in 6 slaughter groups and carcass data were collected. Three LM steaks were taken from each of the carcasses and consistently labeled for position on the 9th- to 12th-rib section of the LM. One steak was evaluated for Warner-Bratzler shear force. An additional steak was used to determine the total lipid, fatty acid, and cholesterol composition of the steaks. Correlations were determined for the relationship of production and carcass traits with the fatty acid and cholesterol profile. Animal, growth, and carcass traits were generally not strongly related to fatty acid and cholesterol content of cooked steaks from pasture-fed cattle slaughtered at 533 d of age.

Video image analysis as a potential grading system for Uruguayan beef carcasses

A study was conducted in 2 phases to evaluate the effectiveness of 1) the VIAscan Beef Carcass System (BCSys; hot carcass system) and the CVS BeefCam (chilled carcass system), used independently or in combination, to predict Uruguayan beef carcass fabrication yields; and 2) the CVS BeefCam to segregate Uruguayan beef carcasses into groups that differ in the Warner-Bratzler shear force (WBSF) values of their LM steaks. The results from the meat yield phase of the present study indicated that the prediction of saleable meat yield percentages from Uruguayan beef carcasses by use of the BCSys or CVS BeefCam is similar to, or slightly better than, the use of USDA yield grade calculated to the nearest 0.1 and was much more effective than prediction based on Uruguay National Institute of Meat (INAC) grades. A further improvement in fabrication yield prediction could be obtained by use of a dual-component video image analysis (VIA) system. Whichever method of VIA prediction of fabrication yield is used, a single predicted value of fabrication yield for every carcass removes an impediment to the implementation of a value-based pricing system. Additionally, a VIA method of predicting carcass yield has the advantage over the current INAC classification system in that estimates would be produced by an instrument rather than by packing plant personnel, which would appeal to cattle producers. Results from the tenderness phase of the study indicated that the CVS BeefCam output variable for marbling was not (P > 0.05) able to segregate steer and heifer carcasses into groups that differed in WBSF values. In addition, the results of segregating steer and heifer carcasses according to muscle color output variables indicate that muscle maturity and skeletal maturity were useful for segregating carcasses according to differences in WBSF values of their steaks (P > 0.05). Use of VIA to predict beef carcass fabrication yields could improve accuracy and reduce subjectivity in comparison with use of current INAC grades. Use of VIA to sort carcasses according to muscle color would allow for the marketing of more consistent beef products with respect to tenderness. This would help facilitate the initiation of a value-based marketing system for the Uruguayan beef industry.

Effects of feeding zilpaterol hydrochloride with and without monensin and tylosin on carcass cutability and meat palatability of beef steers

An experiment was conducted using 200 beef carcasses to evaluate the effects of feeding zilpaterol hydrochloride with or without monensin and tylosin on carcass cutability and meat sensory variables. The experiment was conducted using a randomized complete block design with treatments arranged as a 2 (no zilpaterol vs. zilpaterol) x 2 (monensin and tylosin withdrawn vs. monensin and tylosin fed) factorial. Cattle (n=3,757) were fed zilpaterol hydrochloride, a beta(2)-adrenergic agonist, for 30 d at the end of the finishing period and withdrawn from zilpaterol hydrochloride for the last 5 d on feed. Five carcasses (weighing between 305 and 421 kg and free of slaughter defects) were selected from each of 40 feedlot treatment pens. Strip loins from the left sides were collected for sensory analysis and Warner-Bratzler shear force (WBSF) testing, and the rib was collected for 9th, 10th, 11th-rib dissections. A subsample of 3 carcass right sides per pen was fabricated into boneless subprimals according to Institutional Meat Purchase Specifications. Carcasses from zilpaterol-fed steers had greater (P <or= 0.008) sub-primal yields of shoulder clod, chuck tender, knuckle, top round, outside round, eye of the round, strip loin, top sirloin butt, bottom sirloin butt ball tip, full tenderloin, and flank steak than steers not fed zilpaterol. In addition, zilpaterol hydrochloride treatment decreased (P=0.002) trimmable fat. Zilpaterol hydrochloride increased (P <or= 0.006) estimated carcass protein and moisture and decreased (P <or= 0.007) estimated carcass and LM fat percentage. For LM WBSF there was a zilpaterol hydrochloride x postmortem aging interaction (P<0.01). The beta(2)-adrenergic agonist increased (P=0.001) LM WBSF at 7, 14, and 21 d postmortem and decreased (P<0.001) trained sensory-panel juiciness, tenderness, and flavor intensity of LM steaks aged for 14 d. A consumer sensory panel also found LM steaks from zilpaterol-fed steers were (P=0.03) less tender than steaks from steers not fed zilpaterol; however, tenderness acceptability and overall acceptability were not affected (P >or= 0.26). For the main effect of monensin and tylosin, withdrawal of monensin and tylosin decreased (P=0.01) consumer juiciness scores, although other yield and compositional measurements were not affected (P >or= 0.07). Zilpaterol is a strong repartitioning agent that increases meat yield through increased protein and decreased fat deposition.

Effects of heifer finishing implants on beef carcass traits and longissimus tenderness1

Effects of finishing implants on heifer carcass characteristics and LM Warner-Bratzler shear force (WBSF) were investigated using commercially fed Continental x British heifers (n = 500). Heifers were blocked by initial BW (block 1, BW > or = 340 kg; block 2, BW < 340 kg) and assigned randomly to 12 treatments that utilized 0, 1, or 2 finishing implants to deliver cumulative dosages of trenbolone acetate (TBA) and estradiol 17-beta (E2) ranging from 0 to 400 mg of TBA and 0 to 40 mg of E2 during the finishing period. Heifers in blocks 1 and 2 were slaughtered after 135 and 149 d on feed, respectively. At these endpoints, the treatment groups did not differ (P > 0.05) in adjusted fat thickness or predicted percentage of empty body fat. Compared with a nonimplanted control, implanting heifers once during finishing increased (P = 0.025) HCW by an average of 7.9 kg without affecting the mean marbling score, the percentage of carcasses grading Choice and Prime, or LM WBSF values. Compared with the use of 1 implant, the use of 2 finishing implants resulted in an additional increase (P = 0.008) in HCW of 6.0 kg. Reimplanting also increased (P < 0.001) LM area, reduced (P = 0.024) the percentage of KPH, and improved (P = 0.004) mean yield grade. However, reimplanted heifers produced a lower (P = 0.044) percentage of carcasses grading Choice and Prime and LM steaks with greater (P < 0.05) WBSF values at all postmortem aging times compared with heifers that were implanted once. Among heifers receiving 2 implants, mean 14-d LM WBSF increased linearly (P < 0.05) as the cumulative, combined dosage of E2 plus TBA increased. Heifers implanted with a combination of E2 plus TBA had larger (P = 0.046) LM areas, lower (P = 0.004) mean marbling scores, and greater LM WBSF values after 3 d (P = 0.001), 7 d (P = 0.001), 14 d (P = 0.003), and 21 d (P = 0.045) of postmortem aging than did heifers implanted with TBA alone. Heifers that received combination implants containing both E2 and TBA also produced fewer (P = 0.005) carcasses with marbling scores of modest or greater compared with heifers that received single-ingredient implants containing TBA alone. Implant treatment effects on LM WBSF gradually diminished as the length of the postmortem aging period increased. Postmortem aging periods of 14 to 28 d were effective for mitigating the detrimental effects of mild or moderately aggressive heifer implant programs on the predicted consumer acceptability of LM steaks.

Effects of adding poultry fat in the finishing diet of steers on performance, carcass characteristics, sensory traits, and fatty acid profiles1

Use of poultry fat in the finishing diets of steers has not been studied as a potential source of added energy. Therefore, 60 Angus crossbred steers were fed 1 of 3 dietary treatments consisting of 1) a corn-soybean meal control diet devoid of added fat; 2) the control diet formulated with 4% tallow; or 3) the control diet formulated with 4% poultry fat. Addition of fat did not (P = 0.17) affect ADG for the 112-d study. The inclusion of tallow in the diet reduced (P < 0.05) ADFI of steers compared with those on the control diet; however, ADFI of steers fed poultry fat did not differ from those fed the control (P = 0.06) or the tallow (P = 0.36) diets. At d 55, steers consuming either fat source had improved (P < 0.05) G:F compared with steers fed the control diet. For the entire 112 d, steers consuming the poultry fat diet gained more efficiently (P < 0.05) than the control steers, and the tallow-fed steers were intermediate and not different from the other groups (P > or = 0.14). The inclusion of fat in the diet did not (P > or = 0.15) affect carcass characteristics. Steaks from the steers consuming diets with added fat were darker (lower L* value; P < 0.05) than the controls; however, dietary treatments did not (P > or = 0.10) affect any other objective color measurements or discoloration scores during retail display. Thiobarbituric acid reactive substances for LM steaks did not differ (P = 0.21) by dietary treatment. The cooked LM steaks from steers fed poultry fat did not (P > or = 0.80) differ in juiciness or flavor intensity from steaks of steers fed the control or tallow diets. There were also no differences (P = 0.18) in off flavors as a result of added dietary fat. In the LM and adipose tissue, percentages of total SFA were increased (P = 0.05) by adding supplemental fat to the diet, regardless of source. In the LM, total MUFA were decreased (P = 0.02) by adding supplemental fat. Conversely, diet did not (P > or = 0.14) affect the proportions of total PUFA in either tissue or total MUFA in the adipose tissue. Results indicated that replacing beef tallow in finishing diets with poultry fat, a more economical energy source, had no detrimental effects on growth performance, carcass characteristics, retail display life, fatty acid profiles, or palatability.

Determining the optimum beef longissimus muscle size for retail consumers1

Research was conducted in two phases to determine the optimum beef LM size for retail consumers. In Phase I, 50 USDA Choice beef carcass sides were selected at a commercial packing plant and assigned to five different categories (10 sides per category) based on LM size: 61 to 68 cm2 (A), 70 to 78 cm2 (B), 80 to 90 cm2 (C), 92 to 103 cm2 (D), and 105 to 119 cm2 (E). Ribeye rolls were retrieved from all carcass sides. Steaks (2.5-cm thick; 14 per ribeye roll) were cut as needed and transported in groups of 35 steaks (seven per LM size category) to a retail grocery store in Brookings, SD, where they were placed into a designated section of the retail meat case. Steaks were tallied every 4 h on weekdays and every 2 h on weekends and holidays to determine the number of monitoring periods that each steak remained in the retail case. Steaks that did not sell within an allotted time were removed from the case and termed "pulled." Time in case and percentage of steaks pulled from the case did not differ among LM size categories (P > 0.16). Quadratic regression indicated that larger LM steaks sold faster (P < 0.05) than average and small LM steaks. Steaks from rib locations 6 and 7 spent more (P < 0.05) time in the case than steaks from rib locations 8 through 12. Steaks from the 7th rib location were more (P < 0.05) likely to be pulled than steaks from the 8th through 12th rib locations. In Phase II, 15 USDA Choice ribeye rolls were selected from a commercial packing plant to represent two LM size categories: 80 to 90 cm2 (AVG; n = 5); and 105 to 119 cm2 (LARGE; n = 10) and cut into 2.5-cm-thick steaks. A portion of the LARGE steaks was subsequently cut in half (HALF). Four display steaks represented each treatment group in each of five random nth price auctions. Seventy-five people were recruited from the Brookings, SD area to participate in the auctions to determine their willingness to pay for the three different types of ribeye steak. Consumers were willing to pay a premium of 1.50 dollars/kg for LARGE ribeye steaks over AVG ribeye steaks (P < 0.05). Consumers discounted HALF ribeye steaks by 1.01 dollars/kg compared with AVG ribeye steaks (P < 0.05). In conclusion, no optimum LM size existed for beef retail consumers; however, a trend existed toward greater demand for larger LM sizes over smaller LM sizes.

Evaluating consumer acceptability and willingness to pay for various beef chuck muscles1

In-home consumer steak evaluations, followed by centralized laboratory-setting auctions, were used to determine consumer (n = 74 consumers) acceptability and willingness to pay for various beef chuck muscles. The infraspinatus (IF), serratus ventralis (SV), supraspinatus (SS), and triceps brachii (TB) from the beef chuck were evaluated against LM steaks from the rib to determine price and trait differentials. Muscles from USDA Choice, boneless, boxed-beef sub-primals were aged 14 d, frozen, and cut into 2.5-cm-thick steaks. Consumers received two steaks from each muscle for in-home evaluations of uncooked steak appearance and cooked steak palatability. After in-home evaluation of steaks, consumers participated in a random nth price auction session to determine willingness to pay for those steaks. Muscles differed (P < 0.05) for overall like of appearance, like of size, like of shape, and like of leanness; LM generally rated the highest. Steaks from the LM rated highest (P < 0.05) for overall like, and steaks from the SS and SV were lowest (P < 0.05) for overall like. Juiciness and beef flavor intensity scores were highest (P < 0.05) for steaks from the LM and IF, whereas SS steaks received the lowest (P < 0.05) juiciness scores, and SS and SV steaks were rated lowest (P < 0.05) for beef flavor intensity. Average auction price differentials differed (P < 0.05) from the LM, and were -0.71 dollars, -0.79 dollars, -1.75 dollars, and -2.44 dollars/0.45 kg for the TB, IF, SS, and SV, respectively. Average appearance trait differentials and average palatability trait differentials were correlated significantly with average price differentials. Results indicate the IF and TB were acceptable to consumers as steaks but only at prices lower than the LM.