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The dark, firm and dry (DFD) or dark-cutting condition causes large losses to both the cattle feedlot and meat industry due to its unattractive, dark red colour and its limited shelf life. Dark-cutting, is a direct consequence of low muscle glycogen at slaughter and results in a lack of normal acidification of meat during rigor development causing high pH (>5.8). Glycogen breakdown in muscle may be rapidly triggered by increased circulating adrenaline or by strenuous muscular activity. Several other factors have also been found to lead to the DFD condition in cattle. The aims of this investigation were to determine the incidence of DFD in cattle slaughtered at a South African abattoir and to identify potential causative factors of this syndrome. It was furthermore also important to evaluate the sensory attributes, microbiological quality and hence, shelf life of DFD meat. The incidence of DFD carcasses, based on pH measurements (threshold ~ 5.8) within I h post mortem on 22 178 cattle in the M. longissimus dorsi, was 11.8%. The estimated overall incidence measured over a 5 -day period, testing only cattle supplied by the four main feedlots, was 7.83% (N= 5 659), measuring pH 24 (~5.8), confirmed by colour grades (values of 7 or 8 were classified as DFD). The incidence of dark-cutting beef, also seemed to be feedlot related with the highest being 12.37% and the lowest 1.75%. It is suspected that the incidence of DFD carcasses is higher in extremely hot or cold weather or large fluctuations, and should decrease during the months with milder temperatures. Transport distances did not affect the DFD incidence. In experiment 2, cattle from Feedlot C, transported over a short distance (45 km) had a higher incidence of DFD (9%) than those of Feedlot A (1.7%), transported over the longer distance of 290 km. Long holding periods in the holding pens at the abattoir (>24 h and even as high as 54 h), appeared not to have a significant influence on the occurrence of DFD. There was no correlation between bruised carcasses and DFD carcasses (the respective means of bruising were 6.7% and 3%, and respective mean incidences of DFD were 1.7% and 9%). Using Scheffe's test to compare the effect of gender on the incidence of DFD, significantly more bulls and steers were affected by dark-cutting than heifers (P< 0.0001). Mounting behaviour among young bulls, and social regrouping of steers during the pre-slaughter period, have been shown to increase the incidence of dark-cutting. Avoidance of mixing unfamiliar bulls and steers during transport and holding periods has been recommended to minimise stress. The low incidence of dark-cutters (P > 0.05) in heifers could possibly indicate a non-¬oestrus situation in the majority of the heifers, since a significant association between the presence of oestrus and DFD was shown previously by other researchers. The effect of gender on the incidence of dark-cutting, related to feedlot, was also significant. Higher incidences of DFD were found with steers of Feedlots B, C and 0 (14.5%, 11.6% and 13.7% respectively) than in Feedlot A (1.9%). The lowest overall incidence of dark-cutters was found in Feedlot A (1.7%). It appeared as if the breed type of the cattle had an effect on the dark-cutting beef. The Bos indicus (Brahman-type) animals had a significant effect (P< 0.001), on the colour of the beef when compared with European breeds. Cattle of two feedlots, fasted for periods of 40 hand 60 h, showed that a shorter fasting period had a significant effect (P < 0.001) on the pH. It appeared as if pre-slaughter stress, induced dark-cutting more readily in fasted than in fed cattle. Fasting also inhibited muscle glycogen re-synthesis during recovery of stress. The effect of pre-slaughter handling on the blood composition and muscle glycogen content of cattle of three different feedlots was studied. After transport (phase 1), the glycogen depletion was significant for all three feedlots (P < 0.05). Further glycogen depletion was found after slaughter (phase 2) (P < 0.01). The hematocrit increased after transport, which indicated that animals of Feedlot B (P < 0.0001) experienced stress. During the second phase, a significant decrease in hematocrit for Feedlot B was observed (P < 0.05). For Feedlot A, a non-significant increase was found in phase 1, with a significant (P < 0.05) increase in phase 2. The hematocrit of cattle of Feedlot C, however, showed a significant decrease during both phases. The blood glucose concentration for all three feedlots increased during phase 1, but was not significant. However, the blood glucose concentrations for all three feedlots increased significantly during phase 2 which probably indicated that the animals experienced stress during this period. The increase in creatine kinase was significant (P < 0.01) during both phases 1 and 2 for Feedlot A. Fluctuations were found in the creatine kinase concentrations of Feedlot C. Feedlot B, however, showed a significant decrease in the creatine kinase concentrations. Free fatty acid concentrations for all feedlots increased linearly over the different stages. The high free fatty acid concentrations in blood samples of phase 2, of Feedlots Band C confirmed that these animals experienced stress, especially from the period being held in the pens to after slaughter (P < 0.01 for both). The free fatty acid concentration, appear to be the best blood parameter to relate to meat quality. The DFD incidence during this experiment, for Feedlots Band C, is 35%. For Feedlot A, with the lowest DFD incidence (16%), the increase of free fatty acid concentration was not significant. Although the effect of growth promoters was not tested, the use of beta-agonists as growth promoters may increase the incidence of dark-cutting meat unless a sufficient withdrawal period before slaughter is observed. Feedlots A and C implanted Revelor in 9 month old cattle, while Feedlot B implanted both Synovex S (at 6 weeks) and Revelor (at 4 months). Consumer sensory evaluations indicated that the general appearance (P < 0.05), colour (P < 0.001) and acceptability (P < 0.01) of raw normal steak were preferred significantly to those of raw DFD steak. Twice as many panellists preferred the raw normal steak than raw DFD because of the more attractive red colour, compared to the almost black colour of raw DFD steak. The hedonic ratings of the sensory attributes of fried normal steak versus fried DFD steak were non-significant for all attributes, although it was expected that consumers would find the DFD steak more tender and less flavoursome than normal steak. DFD meat samples (N= 84) were tested over a 7-week period for total aerobic count, Pseudomonas, coliforms and Eschericia coli. Normal beef samples were expected to be acceptable, both on microbiological grounds and sensory evaluations until at least the seventh week. Microbiological spoilage of vacuum-packaged DFD meat took place during the second week and deterioration was more evident during the fourth week, due to the presence of cheesy odours. During the fifth week, green discolouration of the meat was observed. / Dissertation (MSc Agric (Food Science))--University of Pretoria, 2007. / Food Science / unrestricted

The cholesterol content (mg/100 g wet tissue) of the longissimus dorsi muscle and the subcutaneous adipose tissue of "Country Natural Beef" and regularly produced beef was determined by a spectrophotometric method. Proximate analysis (moisture, fat and protein contents) of both types of beef was also determined. Country Natural Beef (natural beef) is produced without the use of hormones or antibiotic feed additives and with a feedlot-finishing period of 50-85 days versus 120-150 days for the regularly produced beef. Samples of natural beef were taken from the 12th rib of the right side of each carcass (N = 20) at 48 hr post mortem. They were vacuum packaged, frozen and stored at -20°C until analyzed. An equal number of regular beef (control) samples were obtained from a local food market. The proximate analysis results show that the mean moisture and protein contents of the natural beef muscle (74.15% and 22.31%, respectively) were significantly (P<0.001 and P<0.01, respectively) higher than those of the control (71.56% and 21.02%, respectively). Conversely, the mean muscle fat content of the natural beef (2.92%) was significantly (P<0.01) lower than that of the control (6.19%). For the adipose tissue, both moisture and fat contents of the natural beef (11.21% and 83.40%, respectively) were lower, but not significantly (P>0.05), than those of the control beef (12.57% and 84.76%, respectively). Data of this study show that the difference between mean muscle cholesterol content of the natural beef (56.91 mg/100 g) and the control beef (56.49 mg/100 g) was not statistically significant (P>0.05). However, the cholesterol content of the adipose tissue of the natural beef (106.75 mg/100 g) was significantly (P<0.01) lower than that of the control beef (113.08 mg/100 g). The adipose tissue was found to contain nearly twice as much cholesterol as the muscle tissue (overall mean values of 109.9 and 56.7 mg/100 g, respectively). Even though the natural beef had an average intramuscular fat content of 3% versus 6% for the control beef, the mean cholesterol content of the natural beef muscle was almost identical to that for the control. Although a reduction of feedlot-finishing days reduced the intramuscular fat deposition in the natural beef, it did not influence muscle cholesterol content. / Graduation date: 1988

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Call number: LD2668 .T4 1984 P44 / Master of Science

The National Beef Quality Audit – 2011 assessed the current status of quality and consistency of fed steers and heifers. Beef carcasses (n = 9,802), representing approximately 10 percent of each production lot in 28 beef processing facilities, were selected randomly for the survey. Carcass evaluation for the cooler assessment of this study revealed these traits and frequencies: steer (63.5%), heifer (36.4%), cow (0.1%), and bullock (0.03%) sex classes; dark-cutters (3.2%); blood splash (0.3%); yellow fat (0.1%); calloused ribeye (0.05%); A (92.8%), B (6.0%), and C or greater (1.2%) overall maturities; native (88.3%), dairy-type (9.9%), and Bos indicus (1.8%) estimated breed types; and United States (97.7%), Mexico (1.8%), and Canada (0.5%) country of origin. Certified or marketing program frequencies were age and source verified (10.7%), ≤ A40 (10.0%), Certified Angus Beef (9.3%), top Choice (4.1%), natural (0.6%), and Non-Hormone Treated Cattle (0.5%), and there were no organic programs observed. Mean USDA YG traits were USDA YG (2.9), HCW (374.0 kg), AFT (1.3 cm), LM area (88.8 cm2), and KPH (2.3%); Frequencies of USDA YG distributions were YG 1 (12.4%), YG 2 (41.0%), YG 3 (36.3%), YG 4 (8.6%), and YG 5 (1.6%). Mean USDA QG traits were USDA QG (Select93), marbling score (Small40), overall maturity (A59), lean maturity (A54), skeletal maturity (A62). Frequencies of USDA QG distributions were Prime (2.1%), Choice (58.9%), Select (32.6%), and Standard or less (6.3%). Marbling score distribution was Slightly Abundant or greater (2.3%), Moderate (5.0%), Modest (17.3%), Small (39.7%), Slight (34.6%), and Traces or less (1.1%). Carcasses with QG of Select or greater and YG of 3 or numerically less represented 85.1% of the sample. This is the fifth benchmark study measuring targeted carcass characteristics, and information from this survey will continue to help drive progress in the beef industry. Results will be used in extension and educational programs as teaching tools to inform beef producers and industry professionals of the current state of the U.S. beef industry.

Studies on the enzymology of fat foramtion in beef cattle may lead to the development of a marker for predicting the propensity of these animals to deposit intramuscular (i.m.) fat. Diacylglycerol acyltransferse (DFAT, EC 2.3.1.20) catalyzes the acylation of sn-1,2-diacylglycerol to form triacylglycerol (TAG). This thesis has focused on evaluating DGAT as a potential marker for predicting i.m. fat deposition in cattle and on characterization of the enzyme in three tissue types involved in TAG biosynthesis. Microsomes were isolated from subcutaneous (s.c.) adipose, i.m. adipose and muscle tissue of Wagyu crossbred cattle displaying a wide range of i.m. fat content (marbling). One aspect of this thesis focused on the relationship between total lipid present in meat samples from the pars costalis diaphragmatis (p.c.d.) and DGAT activity from s.c. adipose tissue, i.m. adipose tissue and muscle tissue of the p.c.d. Intramuscular adipose tissue DGAT activity exhibited a negative correlation with % TAG per gram wet weight p.c.d. (r=-.547;P<.01). There was, however, a positive correlation (r=.735;P<.001) between DGAT activity per unit wet weight i.m. adipose tissue and muscle DGAT activity per unit wet weight suggesting these two depots are coordinated in terms of TAG biosynthetic capacity. The second aspect of the thesis exmained the characteristics of microsomal DGAT from the three tissue types. Microsomes from several animals were combined and were used for enzymological studies of DGAT in an attempt to define possible differences in enzymatic properties among the three tissue types. Diacylglycerol acyltransferase from s.c. adipose tissue in the presence of 15 mM MgCl2 exhibited an enhanced preference for substrates containing oleoyl moieties relative to the other two tissue types. Diacylglycerol acyltransferase from s.c. adipose tissue alos differed slightly in sensitivity to N-ethylmaleimide and stability when compared to the other two tissues, muscle and i.m. adipose tissue. Collectively, these results suggested that either a different isoform of DGAT is expressed in s.c. adipose tissue as compared to i.m. adipose and muscle tissue, or that the endoplasmic reticulum micro-environments are sufficiently different to account for the depot specific properties of DGAT in bovine. The data presented in this thesis suggested that DGAT was not a suitable marker for the deposition of i.m. fat in mature cattle. Perhaps an examination of i.m. fat deposition in less mature animals will yield stronger, positive correlations between DGAT activity and the amount of i.m. fat present. / xvi, 109 leaves : ill. ; 28 cm.

The objective of the study was to determine the effects of pre-slaughter conditions and anima-l related factors on bruising, creatine kinase (CK) and beef quality. Three hundred and twenty one cattle from three breeds (108 Bonsmara, 130 Beefmaster and 83 Brahman) were used in this study. The animals were grouped according to age categories as follows; Group 1(16months), Group 2 (18months) and Group 3 (24 months). Blood samples for CK determination were collected at exsanguisation using disposable vacutainer tubes. The Muscularis longisimus thoracis et lumborum (LTL) muscle was used to determine beef colour (L,* a* and b*) and ultimate pH. Significant P (<0.05) breed effects were observed on bruising score and CK levels with Bonsmara breed having the highest percentage (80 percent) of bruising score and higher CK (705.3±80.57) values. The higher CK levels were also in winter season. The effect of breed, sex and age at slaughter on meat quality (pHu, L*, a*, b*) was also observed. There were positive correlations between distance travelled and meat quality, while there was no relationship observed between CK and distance travelled. Therefore, it was concluded that animal related factors had an effect on meat quality and CK levels.

Understanding Beef Quality Development and Different Feeding Regimes Jordan Christie Wicks ABSTRACT Consumption of beef is expected to increase as the world approaches nearly 9 billion inhabitants by the year 2050, adding unprecedented challenges to the future beef industry. Even so, maintaining quality will still be of utmost importance for producers for two reasons. First, the majority of US cattle are sold on the "grid", which offers both premiums and financial penalties based on quality grades. Second, consumers demand quality. Herein, we explored alternative, cost-saving feeding strategies that impact muscle biochemistry and ultimate meat quality in an effort to determine the most feasible management responses during times of sporadic markets. Our results show that reducing feed inputs from intensive feeding (grain-finished) regimes to maintenance diets of forage or grain up to 60 d had minimal effect on metabolic properties of muscle, thus preserving both quality and yield grades. Specifically, muscle metabolism remained largely unchanged, as indicated by lack of significance in oxidative and glycolytic proteins such as succinate dehydrogenase (SDH), citrate synthase (CS), lactate dehydrogenase (LDH), and phosphofructokinase-1 (PFK-1). Additionally, because maintenance rations were fed, we found no difference in non-esterified fatty acid (NEFA) concentration, or O-linked- β-N-acetylglucosamine (O-GlcNAc) protein abundance suggesting a longer or more aggressive feeding approach may be required to evoke such nutrient based muscle and quality differences. Because quality is important and is a factor for optimal pricing at market, intensive feeding practices are often needed to meet such standards. Still, as the cost of feeding increases, producers struggle to balance quality and profitability. To that end, we evaluated carcass quality of cattle subjected to a reduction of time on feed by 30 d, and found quality, yield and color were similar to that of cattle intensively fed for 120 days. Although, little differences were noted between indicators of postmortem metabolism, short-fed (SF) cattle showed a trend for greater adenosine monophosphate deaminase 1 (AMPD1), and significant difference in the expression of myosin heavy chain isoform (MyHC) IIX suggesting muscle of SF cattle is transiting away from that of grass-fed (CON) cattle. Even so, SF cattle proved to have similar color and quality to cattle fed for 120 days, or more traditionally fed. While we failed to detect differences in muscle between days on feed compared to that of CON (grass-fed), we observed differences in quality and yield between long fed and grass-fed cattle. These data suggest variances in quality may be a result of underlying mechanisms yet to be explained. Therefore, we explored the hallmark biomarkers credited for beef quality development. Despite significant differences in quality and yield grades, data resulted in no differences in myoglobin, oxidative or glycolytic proteins, or calpain-1 and calpastatin between varying phases of growth. However, based on our complementary transcriptomics data, we found linear trends in gene expression related to adipogenesis and muscle hypertrophy, implying these differences may simply be a result of growth rather than muscle function. When taken together, our data suggests severe nutrient restrictions may be required to evoke such a shift in muscle that leads to exacerbated differences in quality. A greater understanding of those mechanisms that drive meat quality development from a conventional grain feeding perspective may prove impactful for the future of our industry. / Doctor of Philosophy / As the demand for beef continues to increase, so does the demand for quality. Generally, consumers prefer beef that is bright-cherry red, possess adequate marbling, and offers a tender bite when consumed. These quality attributes are influenced by many factors, however plane of nutrition, or more simply nutrient energy source (grass vs grain) have shown to play a rather impactful role in quality development. Therefore, high-energy intensive feeding systems (feedlot) have been widely adopted by the US beef industry as a means of producing beef. Even so, the cost of gain for cattle is steadily increasing making profitability challenging from a producer standpoint. Therefore, the aim of this dissertation was to investigate low-input feeding strategies and the influence they have on beef quality. First, we tested nutrient availability's effect on muscle plasticity of mature market ready steers. Our results show that reducing feed inputs from intensive feeding (grain-finished) regimes to maintenance diets of forage or grain up to 60 d had minimal effect on metabolic properties of muscle, thus preserving both quality and yield grades. Next, we challenged varying degrees and plane of nutrition on finishing steers to better understand the extent to which intensive feeding has on ultimate beef quality. To that end, we evaluated carcass quality of cattle subjected to a reduction of time on feed by 30 d, and found quality, yield and color were similar to that of cattle intensively fed for 120 days. Although, little differences were noted between hallmark indicators of muscle fiber type, Short-fed (90 d) cattle proved to be transiting away from that of grass-fed (CON) cattle, aligning closer to consumer expectations of quality. Taken together, our data suggest variances in quality may be a result of underlying mechanisms yet to be explained. Therefore, we explored the hallmark biomarkers credited for beef quality development. Despite significant differences in quality and yield grades, data resulted in no differences in myoglobin, oxidative or glycolytic proteins, or calpain-1 and calpastatin between varying phases of growth. However, based on our complementary transcriptomics data, we found linear trends in gene expression related to adipogenesis and muscle hypertrophy, implying these differences may simply be a result of growth rather than muscle function. In conclusion, our data suggests severe nutrient restrictions may be required to evoke such a shift in muscle that leads to exacerbated differences in quality. A greater understanding of those mechanisms that drive meat quality development from a conventional grain feeding perspective may prove impactful for the future of our industry.