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

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.

Effect of visual marbling on sensory properties and quality traits of pork loin.

Pork loins (N=53) were selected from a commercial packing plant to determine the influence of subjective marbling score on sensory attributes and eating quality properties. The pork loins were obtained from commercially raised hybrid barrows (average carcass weight=67.7 kg), originating from nine cooperating herds, and fed similar diets throughout the finishing period. Carcass quality measurements, trained sensory panel analyses, fatty acid composition, thiobarbituric acid-reactive substance (TBARS) index, and cholesterol content were assessed and analyzed on the individual pork loins. With an increase in marbling level, there was a corresponding decrease in drip loss (P=0.049) and observed increases in pH (P=0.001), sensory tenderness (P=0.001), and sensory juiciness scores (P=0.017). The most notable results demonstrated that protein concentrations were reduced as marbling levels amplified (P=0.012). The increase in marbling score was observed to be a significant source of variation in polyunsaturated fatty acid (PUFA) concentrations. Linoleic and arachidonic acids decreased in both raw and cooked samples as marbling score increased. The data demonstrated that visual marbling score does have an influence on sensory properties and pork quality.

Establishing an appropriate mode of comparison for measuring the performance of marbling score output from video image analysis beef carcass grading systems.

A beef carcass instrument grading system that improves accuracy and consistency of marbling score (MS) evaluation would have the potential to advance value-based marketing efforts and reduce disparity in quality grading among USDA graders, shifts, and plants. The objectives of this study were to use output data from the Video Image Analysis-Computer Vision System (VIA-CVS, Research Management Systems Inc., Fort Collins, CO) to develop an appropriate method by which performance of video image analysis MS output could be evaluated for accuracy, precision, and repeatability for purposes of seeking official USDA approval for using an instrument in commerce to augment assessment of quality grade, and to use the developed standards to gain approval for VIA-CVS to assist USDA personnel in assigning official beef carcass MS. An initial MS output algorithm was developed (phase I) for the VIA-CVS before 2 separate preliminary instrument evaluation trials (phases II and III) were conducted. During phases II and III, a 3-member panel of USDA expert graders independently assigned MS to 1,068 and 1,242 stationary carcasses, respectively. Mean expert MS was calculated for each carcass. Additionally, a separate 3-member USDA expert panel developed a consensus MS for each carcass in phase III. In phase II, VIA-CVS stationary triple-placement and triple-trigger instrument repeatability values (n = 262 and 260, respectively), measured as the percentage of total variance explained by carcasses, were 99.9 and 99.8%, respectively. In phases II and III, 95% of carcasses were assigned expert MS for which differences between individual expert MS, and for which the consensus MS in phase III only, was < or = 96 MS units. Two differing approaches to simple regression analysis, as well as a separate method-comparability analysis that accommodates error in both dependent and independent variables, were used to assess accuracy and precision of instrument MS predictions vs. mean expert MS. Method-comparability analysis was more appropriate in assessing the bias and precision of instrument MS predictions. Ether-extractable fat percentages (n = 257; phase II) differed among MS (P < 0.05) but were not suitable to predict or validate assigned MS. The performance and reproducibility of expert MS assignment in future evaluations was considered, and an official USDA performance standard was established, to which an instrument must conform to be approved for official on-line MS assessment. The VIA-CVS subsequently was approved to assign MS to carcasses on-line after completion of a 2006 USDA instrument approval trial conducted according to methods developed during completion of this study.

Associations between portion size acceptability of beef cuts and ribeye area of beef carcasses.

Carcasses that do not conform to mainstream specifications (i.e., those with nonconforming ribeye area) may not achieve their full potential value. Research was conducted to evaluate the relationship between beef carcass LM area at the 12th and 13th rib interface (LMA) and portion size acceptability of other muscles in the carcass. Sixty beef carcass sides of varying LMA sizes (between 67.74 and 116.13 cm(2)) were fabricated to generate 14 individual muscle cuts (triceps brachii long head, infraspinatus, chuckeye complexus, pectoralis profundus, longissimus thoracis, latissimus dorsi, gluteus medius, longissimus lumborum, tensor fasciae latae, psoas major, semimembranosus, biceps femoris, semitendinosus, and vastus lateralis). Retail portion size (g/1.27-cm-thick steak) as well as face surface area and dimensions were recorded for each steak cut perpendicular at the midpoint of the longitudinal axis of each muscle. Subsequently, a nationwide survey was conducted with foodservice chefs and retail meat merchandisers to evaluate acceptability of portion sizes and dimensions of individual muscle cuts. Simple linear regression and nonparametric regression analyses were used to evaluate results of the carcass muscle evaluation and survey, respectively. Results demonstrated that LMA did not affect (P < 0.05) retail portion size of 7 of the 14 muscles (chuckeye complexus, pectoralis profundus, psoas major, semimembranosus, tensor fasciae latae, triceps brachii, and vastus lateralis). Similarly, LMA did not affect (P < 0.05) surface area of steak cross-sectional face areas from 7 of the 14 muscles (chuckeye complexus, psoas major, semimembranosus, tensor fasciae latae, infraspinatus, vastus lateralis, and latissimus dorsi). Muscles for which carcass LMA (P < 0.05) was related to portion size or surface area of portion steaks, or both, were included in the survey. Results of the survey demonstrated that portion size for many muscles were still acceptable to retail merchandisers and foodservice chefs, even though carcass LMA was outside the range of commercially acceptable sizes. Results of this study demonstrated that carcass LMA is not an accurate determinant of the size, and subsequent acceptability, of many other muscles of beef in the carcasses, and may not be a good determinant of value of the beef carcass.

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

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.

Dietary thyroxine induces molt in chickens (Gallus gallus domesticus).

Thyroxine increases during a molt in wild and captive birds, and thyroidectomy prevents induction of molt. This trial examined the effect of dietary thyroxine on molt induction molt in chickens (laying hens, 59 weeks of age). In a completely randomized design (n=15 hens/replication; 6 replications/treatment), hens were randomly assigned to either a traditional molting program consisting of feed withdrawal (FWD), or to diets containing 40 mg thyroxine/kg diet (HT), 20 mg thyroxine/kg diet (LT), or 40 mg thyroxine from thyroactive iodinated casein/kg diet (TIC). The molting treatment lasted 7-13 d, until egg production reached 0%. After molt induction, birds had ad libitum access to the same diet, until egg production was re-initiated and maximized ( approximately 56 d). All treatments induced molt, based upon cessation of egg laying and regression of ovary and oviduct. Birds on FWD treatment lost more body weight during the molting period, but gained more after molt compared to thyroxine treatments (P<0.01 for each), although all body weights were similar when egg production was maximized. Data demonstrate that oral thyroxine, in purified or non-purified form, induces a molt and may enhance animal well-being by reducing the need for FWD.