Dark Cutters Research Articles

Recovering value from beef carcasses classified as dark cutters by United States Department of Agriculture graders1

Effects of the dark-cutting condition were examined on commercially slaughtered beef carcass sides that were classified into groups exhibiting 1/3, 1/2, and full degrees of the dark-cutting (DEGDC) condition, as evaluated by a USDA-Agricultural Marketing Service grader (n = 20 per group). Twenty-nine muscles of each carcass side were evaluated to determine the ultimate pH and color (L*, a*, and b*). Fourteen beef muscles (biceps femoris, deep pectoral, chuck complexus, gluteus medius, infraspinatus, latissimus dorsi, psoas major, longissimus thoracis, longissimus lumborum, semimembranosus, semitendinosus, triceps brachii long head, tensor fasciae latae, and vastus lateralis) were evaluated using Warner-Bratzler Shear force (WBSF) and a trained sensory panel. The muscle x DEGDC interaction was significant for ultimate pH, L*, a*, and b* values (P < 0.05). When ultimate pH values of individual muscles were compared with the same muscles evaluated in a previous study, the 1/3, 1/2, and full DEGDC had 7, 9, and 5 muscles, respectively, that fell within a computed 95% prediction limit of what would be considered as a normal pH but were more variable as measured by within-class CV. Color values (L*, a*, and b*) of the muscles from dark-cutting carcasses were numerically lower than those from the normal carcasses. A survey designed to determine the ideal color range of beef lean for retail meat merchandisers (n = 34) and food service chefs (n = 33) across the United States resulted in data analyzed using principal components analysis of L*, a*, and b* values for muscles dissected in the study to estimate the true values for dark-cutting carcasses. Muscles that were within an acceptable color value range for food service chefs had the potential to add between $42.29 to $26.44 and $14.71 to $8.11 per side when valued at Choice and Select prices, respectively. Muscles that were within an acceptable color value range had the potential to add between $30.39 to $16.74 and $10.37 to $5.03 per side for retail meat merchandisers when acceptable muscles were valued at Choice and Select prices, respectively. No muscle x DEGDC interactions were detected for WBSF and sensory panel scores (P > 0.05), but differences were detected among muscles (P < 0.05). Several muscles were considered salvageable from the dark-cutting carcasses that were evaluated, and no significant differences in sensory scores or WBSF between DEGDC classes suggested equal sensory expectations for muscles from dark-cutting carcasses.

The impact of lactic acid concentration and sodium chloride on pH, water-holding capacity, and cooked color of injection-enhanced dark-cutting beef

The objectives of this study were to evaluate the effect of enhancement with 0.5%, 1.0%, 1.5%, or 2.0% lactic acid (LA), with or without 0.5% salt (NaCl), on pH, water-holding capacity, and resultant cooked color of dark-cutting (DC) beef. The pH of DC sections treated with LA decreased ( P < 0.05), whereas water-holding capacity (WHC) increased ( P < 0.05) with increasing concentrations of LA. Sensory panelists noted an increase ( P < 0.05) in the degree of doneness (less pink internal color), whereas, a ∗ and chroma values were lower ( P < 0.05), and hue angles were greater ( P < 0.05), indicating the internal color of LA-treated DC sections was less red and appeared more well-done. Also, 630:580 nm reflectance ratios were similar ( P > 0.05) among DC steaks treated with 0.5% and 1.0% LA and normal pH (NDC) steaks, likely caused by an increase ( P < 0.05) in myoglobin denaturation in LA-enhanced DC steaks. These results indicate that the use of LA can reduce postmortem muscle pH and alter the cooked color of DC beef, ultimately resulting in a deletion of the persistent pinking condition.

Effects of Implant Programs on Buller Incidence, Feedlot Performance, and Carcass Characteristics of Yearling Steers

English and English × Continental crossbred steers (272 steers per pen; 4 pens per treatment) were used in a randomized complete block design to determine the effects of terminal implant type (Revalor S® [Hoechst-Roussel Vet, Somerville, NJ] and Component TES™ [Vet Life, Overland Park, KS]; each containing 24mg of estradiol-17β and 120mg of trenbolone acetate) and timing of terminal implant administration (d 1 or 50) on buller incidence, feedlot performance, and carcass characteristics. Steers either received Component TES™ (TES) or Revalor S® (RevS) on d 1 or 36mg of zeranol (Ralgro®; Schering-Plough, Omaha, NE) on d 1 and TES (Ral/TES) or RevS (Ral/RevS) on d 50. Steers receiving TES and RevS were not removed from the home pen on d 50, and all steers were harvested after 144 d. Bullers pulled during the first 50 d were returned to home pens on d 50 and were classified as a repull if removed again as a buller. The incidence of new bullers during the first 50 d did not differ (P=0.14) between steers receiving TES (2.3%), RevS (1.75%), or Ralgro® initially (1.42%; Ral/TES + Ral/RevS). There were fewer new bullers from d 50 to 144 for TES and Ral/TES than for RevS and Ral/RevS (P=0.02; 0.97% vs 1.88%, respectively) and also when steers received a terminal implant on d 1 compared with d 50 (P=0.01; 0.92% vs 1.93%, respectively); however, the overall incidence of new bullers did not differ (P>0.43) among treatments. Neither implant type nor timing influenced repull incidence from d 50 to 144 (P>0.45) or the overall incidence of total (new + repull) bullers (P>0.43). Steer DMI (implant type × timing, P=0.04) was least (P<0.02) for Ral/TES, intermediate for TES, and greatest RevS and Ral/RevS. Live and carcass-adjusted BW gain efficiencies were 2.4% greater (P<0.03) for TES or Ral/TES than for RevS or Ral/ RevS. Final BW, ADG, and hot carcass weight did not differ (P>0.19) among treatments. Steers receiving Ral/TES and Ral/RevS had a greater percentage of dark cutters (P<0.01), more Yield Grade 1 carcasses (P<0.01), and fewer Yield Grade 3 carcasses (P<0.01) than TES or RevS. Administering TES on d 1 or 50 resulted in improved gain efficiency, whereas overall buller incidence was not influenced by terminal implant type or timing. Administering either TES or RevS on d 50 increased the incidence of dark carcasses, resulted in more Yield Grade 1 and fewer Yield Grade 3 carcasses, and influenced when bullers developed but did not influence carcass quality grade distribution or overall buller incidence.

Dark Cutting Incidence in Holstein Friesian, Brown Swiss and Eastern Anatolian Red Cattle Slaughtered Under Turkish Commercial Slaughter Conditions

The aim of this study was to compare the incidence of dark cutting (DC) in Holstein Friesian (HF, n=382), Brown Swiss (BS, n=294) and Eastern Anatolian Red (EAR, n=212) male cattle slaughtered under Turkish commercial slaughter conditions. The importance of some factors (transport distance from farm to abattoir, lairage time, waiting type at abattoir, carcass weight and behaviour prior to slaughter) influencing of normal, moderate DFD and DFD carcass frequency on breed were also evaluated. There was influence of breed on the incidence of dark cutting condition. In HF, BS and EAR, males produced 54, 47 and 68% moderate DFD carcasses; 23, 34 and 25% DFD carcasses, respectively. Normal carcass percentage was lower in EAR (8%) compared to in HF (24%) and BS (19%). The results show that there were apparent differences in behaviour of these breeds prior to slaughter. During slaughter BS and EAR males had more excitable temperament than HF males. The present study also indicated that the incidence of dark cutting was higher for long haul transport and short lairage time. But, we concluded that the main cause of dark cutting of breed was the free waiting of animals at abattoir pens until slaughter under Turkish commercial slaughter conditions.

A dose-response study of melengestrol acetate on feedlot performance and carcass characteristics of beef steers.

The dose response of melengestrol acetate (MGA) on ADG (kg/d) and gain efficiency (gain/DMI, g/kg) was estimated in beef steers fed a finishing diet under commercial feedlot conditions. Melengestrol acetate is not approved for use in steers as a feed additive. The study design was five blocks of four pens (each pen was assigned a dose of MGA) with 166 to 200 steers per pen. Melengestrol acetate was fed to steers at 0 (n = 899, five pens), 0.1 (n = 900, five pens), 0.2 (n = 899, five pens), and 0.4 (n = 900, five pens) mg of MGA/steer daily. Pens within a block were slaughtered on the same day. Blocks 1 through 5 were fed MGA for 123, 122, 116, 124, and 138 d, respectively. The experimental unit was a pen of steers, and blocking was based on source of steers. The ADG was 1.81, 1.85, 1.80, and 1.83 kg/d for steers fed 0, 0.1, 0.2, and 0.4 mg MGA per day, respectively. For ADG, the dose was significant, but neither linear nor quadratic effects were significant. Compared with steers of the control group, ADG was greater for steers fed 0.1 mg MGA (P < 0.01). Feed efficiencies were 170, 173, 171, and 172 g/kg for steers fed 0, 0.1, 0.2, and 0.4 mg MGA/d, respectively; however, no effects of dose (P = 0.19) or linear (P = 0.21) or quadratic (P > 0.60) effects were observed. There was no evidence for either positive or negative effects of MGA on DMI, hot carcass weight, dressing percent, quality grade, yield grade, back fat thickness, marbling score, longissimus muscle area, and incidence of dark cutter carcasses in response to feeding MGA to steers at doses of 0.1, 0.2, and 0.4 mg daily. The incidence of buller behavior (0.43 to 1.11%) was low and did not permit an accurate test of the clinical observations that feeding MGA to steers decreases the occurrence of buller steers. Melengestrol acetate fed to finishing beef steers produced small improvements in growth performance (ADG, 2.2%) at the 0.1 mg MGA dose, but none of the doses examined produced improvement in carcass quality or yield grade measurements.

Review: Androgenic, Estrogenic, and Combination Implants: Production and Meat Quality in Beef

Literature was reviewed to determine the value of using growth implants in cattle with regard to production parameters and carcass merit. The beef industry's need to balance increased growth traits with acceptable carcass quality is of critical concern when evaluating implant strategies. Anabolic implants affect specific muscles by impacting the action of somatotropin and the rates of muscle accretion and turnover. Muscles showing the greatest response are extensor muscles associated with long bones; muscles showing little response to anabolic implants are believed to be at maximum capacity for growth. Implants may also affect the proliferation rate and (or) activation state of satellite cells. The benefits of implants to production of beef cattle have been well documented, with significant documentation of increased growth rates, ADG, and feed efficiency. Implants increase the vigor of feedlot steers by reducing the incidence of certain illnesses and, in combination with gonadotropin-releasing hormone (GnRH) immunization, replace castration for improving meat quality. Anabolic implants result in both beneficial and detrimental effects on meat quality. Implants increase ribeye area but reduce fat deposition and marbling scores. Skeletal maturity is increased by implants. The most severe quality problem from implant use is an increased incidence of dark cutters. Producers need to weigh the benefits and the disadvantages of anabolic implants for use in animal production strategies.

Shade effects on performance, carcass traits, physiology, and behavior of heat-stressed feedlot heifers.

To determine whether shade influences performance, carcass traits, immunology, respiration rate, and behavior of cattle under conditions similar to those in commercial feedlots, we used 168 heifers in 12 soil-surfaced pens. Six pens were shaded with a galvanized steel-roofed shade (approximately 4 m high), allowing for 2.12 m2 of shade/heifer, and six pens served as the unshaded control. Heifers were fed a 90% concentrate diet during the 121-d trial that began in mid-June, performance variables (DMI, BW, ADG, gain:feed) were measured, and dietary concentrations of NEm and NEg calculated from performance data. A blood sample was collected to assess immune measures. Respiration rates and behaviors (feeding, drinking, walking, standing, lying, agonistic, and bulling) also were measured during the study. Carcass data (yield grade, kidney, pelvic, and heart fat, longissimus muscle area, hot carcass weight, quality grade, liver abscess rate, and incidence of dark-cutting beef) were collected at slaughter. Shaded heifers had higher (P < 0.05) DMI, ADG, and final BW than unshaded heifers. The gain:feed ratio and calculated dietary NEm and NEg concentrations did not differ (P > 0.26) between treatments. Most carcass traits did not differ between treatments, but more (P < 0.02) carcasses ofheifers in shaded pens graded USDA Choice than those in unshaded pens, which resulted primarily from the incidence of dark cutters being decreased (P < 0.04) by approximately half in carcasses from shaded compared with unshaded heifers. Respiration rate and percentage of circulating neutrophils were decreased (P < 0.01) for shaded compared with unshaded heifers. The treatment x time of day effect was significant (P < 0.05) for all behavioral measurements. Shaded heifers spent more time laying down (0800, 1200, and 1500, P < 0.05) and less time standing (1200 and 1500, P < 0.05) than unshaded heifers. Agonistic behavior was less (P < 0.05) for shaded than for unshaded heifers at 1900 and 2000, and bulling was less (P < 0.05) for-shaded than unshaded heifers at 2100. Results suggest that shade improved performance and altered behavior by feedlot heifers during the summertime in West Texas.

Treatments for Prevention of Persistent Pinking in Dark‐Cutting Beef Patties

ABSTRACTFood‐grade oxidants and browning agents were compared for prevention of undesirable raw appearance of cooked dark‐cutting (DC) beef patties. DC beef had higher pH (6.6 vs 5.7) and lower 24h oxidation‐reduction potential (–190 vs –108 mV) than controls, with higher cooked yield and cohesiveness, but lower beef flavor intensity scores. DC patties with lactic acid (LA) had acceptable cooked appearance and increased myoglobin (Mb) denaturation during cooking (77%‐LA; 63%‐normal control; 41%‐DC control), but a tangy off‐flavor. Calcium peroxide increased Mb denaturation to 69%, but caused excessive oxidation. Caramel color eliminated undercooked appearance without increasing Mb denaturation, but raw and cooked patties were dark.

Measuring muscle color on beef carcasses using the L*a*b* color space.

Because beef muscle color affects consumers' purchasing decisions, is a factor in determining USDA grades, and has been shown to be useful in sorting carcasses according to palatability, this study was conducted to determine the effects of measurement conditions on L*, a*, and b* values, to determine the relationships among USDA quality grading factors, muscle pH, electrical impedance, and colorimeter readings, and to develop a classification system that could be used to sort beef carcasses with respect to muscle color. Data were collected over 2 d from 145 beef carcasses in a commercial packing plant. The exposed longissimus muscle at the 12th/13th rib was used for all muscle pH, electrical impedance, and colorimeter measurements. A Minolta Chroma Meter CR-310 was used to obtain L*, a*, and b* readings. Bloom time, from 0 to 93 min, had a greater effect on a* and b* readings than on L* readings. The L* values stabilized after approximately 30 min bloom time, and a* and b* values stabilized after 78 min bloom time, but relative differences among carcasses in L*, a*, and b* values did not change after 3 to 12 min bloom time. Days postmortem, cut surface (anterior versus posterior), and within-muscle location (medial vs lateral) did not affect L*, a*, and b* readings (P > .05). Blotting the surface moisture from the longissimus muscle resulted in lower a* readings (P < .05), but did not affect L* and b* readings (P > .05). The L*, a*, and b* values were correlated with lean maturity scores (-.67, -.30, and -.40, respectively), dark cutter discount (-.60, -.76, and -.73, respectively), muscle pH (-.57, -.79, and -.78, respectively), and electrical impedance (-.27, -.21, and -.25, respectively). Two muscle color classification systems, nine classes each, are proposed, one system based on L* and one system based on b*. The main advantage of the L* categorization system over the b* system is that the L* value was less sensitive to bloom time, and the main advantage of the b* categorization system over the L* system is that the b* system was slightly more precise at segregating carcasses based upon corresponding differences in muscle pH. This research provides procedural guidelines for measuring beef muscle color and shows that a colorimeter can effectively aid researchers and graders in assessing beef carcass quality.

Swine and Beef Producer Evaluation of Handling, Transportation, and Other Management Factors

Questionnaires requesting producers to identify management changes were mailed or handed out to 370 swine and 2050 beef producers. The survey response rate was 71 (19%) and 410 (20%) swine and beef, respectively. Respondents evaluated the amount and importance of changes (codes; 0=no change, 1=little change, 2=moderate change, 3=large change, and 4=not sure or not applicable) made to their enterprises in the past 10 yr, and changes intended in the near future. The questions included facilities, nutrition, handling, transport, herd health, biosecurity, and other management factors. In addition, respondents were requested to indicate the effects of these practices on animal stress, causing or preventing injury or mortality, and improving management of the enterprise. The most important changes identified by swine producers in the past were nutrition, herd health, and quality assurance and in the near future, ventilation, herd health, and quality assurance. Beef producers identified breeding management, nutrition, and herd health as most important changes in the past and in the near future breeding management, quality assurance, and nutrition. Loading and trucking ranked low (9th, 7th) for swine and beef, respectively, which indicates producer satisfaction or a lack of information on transportation and the frequency of associated negative factors (dark cutters, porcine stress syndrome, bruising, shrink, death loss). Waste management also ranked low (swine 7th, beef 9th), which was unanticipated, especially when considering Pennsylvania’s new nutrient management laws. Over all, producers expressed concern with animal well-being and contemporary animal issues. This is indicated by past and intended future changes and the importance producers place on critical management factors.

Factors contributing to the incidence of dark cutting beef.

The 1995 National Beef Quality Audit reported that dark cutting beef (dark cutters) cost $6.08 per animal harvested in the United States. Feedlot data were obtained over a 3-yr period from nine commercial feedyards (15,439 pens of cattle; 2,672,223 total cattle). Feedyard, sex, implant treatment, days from final implant to harvest, maximum and minimum daily temperatures, and temperature fluctuations from 2 d before harvest to the day of harvest all contributed (P < .05) to the incidence of dark cutters. Heifers yielded a higher (P < .05) percentage of dark cutters per pen and, when reimplanted a second time with an estrogenic implant, produced greater (P < .05) mean percentages of dark cutters per pen than heifers reimplanted with either androgens or combination (androgen and estrogen) growth promotants. Furthermore, heifers produced higher (P < .05) mean percentages of dark cutters per pen than steers during periods of hot (> 35 degrees C) weather 2 to 1 d before harvest. Steers, when treated with a combination (androgen and estrogen) implant when entering the feedyard and as a reimplant, produced higher (P < .05) mean percentages of dark cutters per pen when compared to other moderate growth-promoting implant strategies. When producers opted to implant steers with estrogenic growth promotants, either as the cattle entered the feedlot or as a final reimplant before harvest, the occurrence of dark cutters was reduced from 9.2 per thousand cattle shipped to 2.0 and .5 per thousand cattle shipped, respectively. Producers that reimplanted heifers before harvest with products that were not primarily estrogenic reduced the occurrence of dark cutters from 10.4/1,000 cattle shipped to 5.2/1,000 cattle shipped when androgen-based growth promotants were used and to 3.5/1,000 cattle shipped when combination (androgen and estrogen) implants were administered. In addition to implant selection, those producers that held cattle on-feed over 100 d past reimplantation reduced the incidence of dark cutters per pen by an average of 38% among heifers and 69% among steers. By reducing the occurrence of dark cutters, there is an opportunity for beef producers to realize large economic savings.

Bos indicus-cross feedlot cattle with excitable temperaments have tougher meat and a higher incidence of borderline dark cutters

Temperament ratings based on a numerical scale (chute score) were assessed during weighing and handling of cattle at a feedlot. Breeds studied included Braford, Red Brangus and Simbrah. Cattle were fed to a constant fat thickness of 9 to 13 mm (target = 11 mm) over the 12th rib as determined by periodic ultrasound measurements. Cattle were slaughtered in a commercial slaughter plant and stunned by captive bolt. Temperament rating had a significant effect on the incidence of borderline dark cutters which were downgraded by a USDA grader ( P = 0.01). Temperament score also had a significant effect on tenderness ( P < 0.001) as evaluated by Warner-Bratzler Shear (WBS) force at day 14 post mortem. The calmest animals which stood still when restrained in a hydraulic squeeze chute had a mean WBS force of 2.86 ± 11 kg and cattle which became highly agitated and struggled violently during restraint averaged 3.63 ± 19 kg. Forty percent of these cattle had WBS force values which were over 3.9 kg which is a threshold value for acceptability in food service establishments. These data show that cattle with the most excitable temperament ratings produce carcasses with tougher meat and a higher incidence of borderline dark cutters than cattle with calm temperament ratings.

The effects of grade, gender, and postmortem treatment on beef. II. Cooking properties and palatability attributes

A total of 196 beef carcasses of two genders (steers and heifers) and four carcass grades were evaluated for the effects of grade (carcass fatness (B1 = 2 to 4 mm subcutaneous fat; A1 = 4 to 10 mm subcutaneous fat; and A2 = 10 to 15 mm subcutaneous fat)) and meat quality (B2 = dark cutters) and gender. These carcasses also received two postmortem treatments (conventional or high voltage electrical stimulation and 3 or 6 d of postmortem aging) to evaluate the interactive effects of postmortem treatments with grade and gender. Cooking properties, palatability attributes, and consumer acceptance ratings were assessed on the longissimus muscle and flavor and texture profiles were obtained from the semitendinosus muscle. Differences attributable to carcass grade in palatability attributes were in agreement with expected differences, based upon differences in carcass fatness. Gender exerted little influence on either cooking or palatability attributes. Carcass grade or fatness appeared to influence the responses in palatability elicited from high voltage electrical stimulation and postmortem aging. Although the minimum fatness required to assure palatable beef could not be determined from the present results, lean B1 carcasses exhibited greater responses to the postmortem electrical stimulation treatment than fatter A2 carcasses. Key words: Beef, palatability, consumer acceptance, cooking properties, grade, gender, stimulation, aging

Carcass traits and the occurrence of dark cutters in pregnant and nonpregnant feedlot heifers1

The objective of this study was to determine whether the occurrence of dark cutters and selected carcass traits differ between pregnant and nonpregnant feedlot heifers. Feedlot heifers (n = 8,292) were identified at slaughter as being either nonpregnant, pregnant with a moderate-sized fetus (midgestation), or pregnant with a large fetus (late gestation). This was based on visual appraisal of a gravid uterus at the evisceration table. After chilling (24 to 72 h), carcass data were collected. Cattle originated from 23 different commercial feedyards located within a 350-km radius of a commercial slaughter facility located in southwest Kansas. Across slaughter lots, the incidence of pregnancy varied from 0 to 25% with an overall mean of 4.74%. Carcass traits of heifers with moderate or large fetuses did not differ (P > .15). Compared with carcasses from nonpregnant heifers, carcasses from pregnant heifers were 4.5 kg lighter (P < .01), had .11 cm more fat thickness (P < .01), and exceeded the number of carcasses that graded Choice or Prime by 6% (P < .01). Carcasses from pregnant heifers had higher maturity scores (P < .01) and there was no incidence of dark cutters (P < .01) compared with a 1.7% incidence of dark cutters in carcasses from nonpregnant heifers. Any economical advantage in the pregnant heifers due to their higher percentage of Choice carcasses and lower incidence of dark cutters may be offset by their increased carcass fat thickness and lower dressing percentage.

Effects of estradiol or an estradiol-trenbolone acetate reimplant scheme and time on feed on performance and carcass traits of finishing steers (1992)

Two hundred eighty-eight predominantly British and British crossbred steers (702 lb) were used in a 2×3 factorially arranged experiment. Main effect factors were reimplant scheme [estradiol (E ) vs estradiol plus 2 trenbolone acetate (E + TBA)] and time on 2 feed (111, 125 or 139 days). The initial slaughter occurred when 65 to 70% of all steers were estimated to grade low Choice. No interactions occurred for any variable measured. Reimplanting 57 days after the initial implant with E + TBA increased overall daily 2 gain 6.9% (P<.003) and feed efficiency 4.9% (P<.005). Feeding steers for an additional 14 or 28 days resulted in linear decreases in overall daily gain (P<.005) and feed efficiency (P<.0004). Reimplanting with E + 2 TBA increased (P<.001) carcass weight but did not reduce marbling score or percent Choice carcasses. Feeding steers for an additional 14 or 28 days resulted in linear increases (P<.0001) in hot carcass weight, ribeye area, adjusted backfat (P<.004), and skeletal maturity (P<.0005). Additional days on feed increased dressing percentage (P<.002) and marbling score (P<.05) curvilinearly and tended (P=.25) to increase the percentage of carcasses grading Choice and Prime. Incidence of dark cutters was higher (P<.05) for E + TBA carcasses, and was very high at the 2 first slaughter date (54 days after reimplantation). Although feeding for an additional 14 or 28 days can result in heavier live and carcass weights, higher dressing percentage, and increased marbling, poor efficiency of gain may create negative feeding margins.

FACTORS INFLUENCING THE COMMERCIAL INCIDENCE OF DARK CUTTING BEEF

Data collected on 170 534 head of Saskatchewan cattle slaughtered over a period of 12 consecutive months were used to evaluate the importance of some factors influencing the incidence of dark cutting (DC) beef (Canada B2 grade based on a visual assessment of muscle color and texture). The variables examined included carcass weight, gender of animal, daily temperature and precipitation, month of slaughter, distance from farm to abattoir, mixing of loads during transportation and slaughter plant. DC beef compared to normal beef was associated with a slightly warmer daily temperature (5.4 vs. 4.8 °C), a lighter carcass weight (283 vs. 286 kg), but was not influenced by daily precipitation. The incidence of DC beef increased as distance between farm and slaughter plant increased (0.78–0.98%), and was higher in loads of cattle that were mixed during transportation than in those loads that originated from the same farm (1.11 vs. 0.79%). Steers recorded a higher frequency of DC beef than heifers (0.99 vs. 0.77%). There were large differences in the frequency of DC beef among slaughter plants after adjustment of the data for the effects of other variables (gender, mixing, trucking distance). Of the six slaughter plants in this study, the frequency of DC beef ranged from 0.27–1.79%. Month of shipment had a significant effect on the incidence of DB beef, with March and April recording the highest frequencies (1.54 and 1.24%), and December the lowest (0.45%). It was concluded that the mixing of loads and the slaughter plant were the two most important predisposing factors for DC beef. Key words: Beef, carcass, stress, dark cutting

Bruising and muscle pH in zebu crossbred and British breed cattle.

Five trials in Queensland compared the bruising of 302 zebu (Bos indicus) crossbred and 254 British breed (B taurus) steers. The pH of the Longissimus dorsi muscle 24 hours post mortem was measured in three of the trials. Breed groups were transported separately to the abattoir in the first four trials and travelled as mixed breed groups in the fifth one. Differences in bruising between breed types were not significant in any trial. Zebu crossbred animals had significantly (P less than 0.05) lower muscle pH values in trials 1 and 3, whereas the difference was not significant in trial 5. There were also fewer dark cutters among the zebu crossbred animals in trials 1, 3 and 5.

PRESLAUGHTER MANAGEMENT AND DARK-CUTTING IN THE CARCASSES OF YOUNG BULLS

One hundred-and-twelve yearling bulls were penned together for at least 3 mo in groups of 7 or 21. They were then shipped 150 km to an abattoir in groups of either 7 or 21, and were either regrouped or not regrouped before shipment. They were held overnight at the abattoir before slaughter. A further seven yearling bulls were shipped and held individually before slaughter. After slaughter, muscle color was appraised by Federal graders. Load size had no significant effect on the incidence of dark-cutting, but regrouping had a dramatic effect (73 vs. 2% dark cutters, P &lt; 0.01). There were no dark cutters among the bulls shipped individually. It is concluded that agonistic encounters among regrouped bulls was a far more important cause of dark-cutting than either load size or exposure to an alien environment.