J. M. Gonzalez

Differential response of cull cow muscles to the hypertrophic actions of ractopamine-hydrogen chloride

Ractopamine-HCl (RAC) is a beta-adrenergic agonist with variable effects on cattle performance and carcass variables. Cull cows fed RAC (200 mg . head(-1) . d(-1)) demonstrate an increased size of type I and II muscle fibers that does not translate into a larger ribeye area. The objective of this study was to examine the dose-dependent effects of RAC on cull cow muscle morphometrics. Eighty-eight cull beef cows representing 2 breed types (n = 44 each) were fed 0, 100, 200, and 300 mg . head(-1) . d(-1) of RAC for the last 28 d of a 54-d feeding period. On d 54, cows were slaughtered, and samples of the LM and semimembranosus muscle (SM) from 16 randomly selected carcasses (n = 4 per treatment) were taken for measurement of beta (2)-adrenergic receptors and type I, IIA, and IIX myosin heavy chain (MyHC) gene expression. Twenty-four hours postmortem, LM, SM, infraspinatus (INF), and vastus lateralis samples from 40 randomly selected carcasses (n = 10 per treatment) were obtained and frozen for immunohistochemical analysis. Muscle fiber cross-sectional area and diameter, MyHC isoform expression, and fiber-associated nuclei numbers were measured. Ractopamine dosage exhibited differential effects on muscle morphometrics and MyHC gene expression. Muscle fiber cross-sectional area and diameter were increased (P < 0.05) by RAC in INF type I and IIA fibers and SM type IIA fibers. Ractopamine increased (P < 0.05) MyHC type IIX mRNA and tended to increase (P < 0.10) beta(2)-adrenergic receptors in the SM; a change in mRNA abundance was not detected for either gene in the LM. Treatment with RAC decreased (P < 0.05) fiber-associated nuclei numbers in the INF, vastus lateralis, and LM but did not affect (P > 0.05) MyHC or beta-adrenergic receptor expression. These results indicate that cull cow feeding programs may consider supplementing RAC as a means of adding value to cuts within the chuck, such as the INF.

Realimentation of nutrient restricted pregnant beef cows supports compensatory fetal muscle growth

Drought and other weather-related disasters impact the amount and quality of grains and forages available to beef cattle. The impact of nutrient restriction at specific gestational timeframes on fetal skeletal muscle growth was examined. Crossbred beef cows were fed to NRC recommendations (CCC) or restricted to 60% of said levels for the first 85 or 140 d of pregnancy followed by realimentation to recommended protein and energy levels (RCC and RRC, respectively). Fetal infraspinatus (INF) morphometrics and gene expression analyses were performed at d 85, 140, and 254 of gestation. Results demonstrate that fetal primary myofibers are larger (P < 0.05) after 85 d of maternal caloric restriction by comparison to controls. Realimentation of pregnant dams at d 85 causes an increase (P < 0.05) in RCC INF cross-sectional area (CSA) by comparison to RRC at d 140 but the fibers remain smaller (P < 0.05) than CCC muscle cells. Returning nutrient load to recommended levels at d 140 of pregnancy increases RRC CSA equivalent to CCC fibers at d 254 (343.4 ± 5.2 and 345.2 ± 5.3 μm(2), respectively). Fetal RRC and CCC muscle fibers are smaller (P < 0.05) than RCC fibers at d 254 suggesting the later experienced compensatory growth. Numbers of Paired box 7 (Pax7) immunopositive cells were fewer (P < 0.05) in the nutrient restricted fetuses at d 85 suggesting a loss of muscle progenitor cells. Moreover, mRNA content for the collagen crosslinking enzymes, lysyl oxidase and bone morphogenetic protein 1, were greater (P < 0.05) in the d 85 nutrient restricted fetal INF than CCC suggesting increased connective tissue cell numbers and/or activity. Because myogenesis is acutely regulated by the IGF, mRNA content of these growth factors and their receptors was examined. Fetal IGF1 mRNA content was lower in the d 85 nutrient restriction fetuses (P < 0.05) by comparison to CCC. Levels of INF IGF2 mRNA were greater (P < 0.05) in d 85 NR fetuses than CCC. Continued nutrient restriction through d 140 resulted in a reduction (P < 0.05) in IGF2 expression by comparison to CCC. No treatment effect on IGF1R or IGF2R mRNA content was noted. In summary, NR for 85 d causes an increase in primary INF fiber size that may be a result of increased IGF2 transcription and Pax7-immunopositive cell fusion. Realimentation of NR beef cows supports compensatory growth of the fetal musculature such that normal muscle fiber size and muscle progenitor numbers are achieved before birth.

Effect of dietary zinc and ractopamine hydrochloride on pork chop muscle fiber type distribution, tenderness, and color characteristics

A total of 320 finishing pigs (PIC 327 × 1050; initially 98 kg) were used to determine the effects of adding Zn to diets containing ractopamine HCl (RAC) on muscle fiber type distribution, fresh chop color, and cooked meat characteristics. Dietary treatments were fed for approximately 35 d and consisted of a corn-soybean meal-based negative control (CON), a positive control diet with 10 mg/kg of RAC (RAC+), and the RAC+ diet plus 75, 150, or 225 mg/kg added Zn from either ZnO or Availa-Zn. Loins randomly selected from each treatment (n = 20) were evaluated using contrasts: CON vs. RAC+, interaction of Zn level × source, Zn level linear and quadratic polynomials, and Zn source. There were no Zn source effects or Zn source × level interactions throughout the study (P > 0.10). Pigs fed RAC+ had increased (P < 0.02) percentage type IIX and a tendency for increased (P = 0.10) percent type IIB muscle fibers. Increasing added Zn decreased (linear, P = 0.01) percentage type IIA and tended to increase (P = 0.09) IIX muscle fibers. On d 1, 2, 3, 4, and 5 of display, pork chops from pigs fed the RAC+ treatment had greater (P < 0.03) L* values compared to the CON. On d 0 and 3 of display, increasing added Zn tended to decrease (quadratic, P = 0.10) L* values and decreased (quadratic, P < 0.03) L* values on d 1, 2, 4, and 5. Pigs fed RAC+ had decreased (P < 0.05) a* values on d 1 and 4 of display and tended to have decreased (P < 0.10) a* values on d 0 and 2 compared to CON pork chops. Pork chops from the RAC+ treatment had a tendency for increased (P < 0.08) oxymyoglobin percentage compared to CON pork chops on d 1, 2, 4, and 5. On d 0, as dietary Zn increased in RAC+ diets, there was a decrease (linear, P < 0.01) in the formation of pork chop surface oxymyoglobin percentage. Metmyoglobin reducing ability (MRA) of pork chops on d 5 was decreased in the RAC+ group. Chops from pigs fed added Zn had increased (quadratic, P < 0.03) MRA on d 3 and 5 of the display period. There was a trend for increased (linear, P = 0.07) cooking loss with increasing Zn in RAC diets and treatments did not affect tenderness as measured by Warner-Bratzler shear force (P > 0.07). In conclusion, RAC+ diets produced chops that were lighter and less red but maintained a greater percentage of surface oxymyoglobin throughout a 5-d simulated retail display. Ractopamine reduced MRA at the end of the display period, but supplementing Zn to RAC diets restored MRA to near CON treatment levels at the end of the display period.

Effect of added zinc in diets with ractopamine hydrochloride on growth performance, carcass characteristics, and ileal mucosal inflammation mRNA expression of finishing pigs

Two experiments were conducted to determine the effects of increasing the dietary Zn content on growth performance, carcass characteristics, plasma Zn, and ileal mucosal inflammation mRNA expression of finishing pigs fed diets containing ractopamine HCl (RAC; Elanco Animal Health, Greenfield, IN). In Exp. 1, 312 pigs (327 × 1050; PIC, Hendersonville, TN; 94 kg BW) were used in a 27-d study. There were 2 pigs per pen and 26 pens per treatment. Treatments included a corn-soybean meal diet (control; 0.66% standardized ileal digestible [SID] Lys); a diet (0.92% SID Lys) with 10 mg/kg RAC; and the RAC diet plus 50, 100, or 150 mg Zn/kg from ZnO or 50 mg Zn/kg from a Zn AA complex (ZnAA; Availa-Zn; Zinpro, Eden Prairie, MN). All diets also contained 83 mg Zn/kg from ZnSO4 in the trace mineral premix. Pigs fed the RAC diet without added Zn had increased (P < 0.05) ADG, G:F, HCW, carcass yield, and loin weight compared with pigs fed the control diet. Increasing Zn from ZnO in diets containing RAC tended to increase (linear, P = 0.067) G:F and loin weight (quadratic, P = 0.064). Pigs fed diets with 50 mg Zn/kg from ZnAA tended to have increased (P = 0.057) ADG compared with pigs fed the RAC diet. In Exp. 2, 320 pigs (327 × 1050; PIC; 98 kg BW) were used in a 35-d study. There were 2 pigs per pen and 20 pens per treatment. Treatments included a control diet (0.66% SID Lys); a diet (0.92% SID Lys) with 10 mg/kg RAC; or the RAC diet plus 75, 150, and 225 mg Zn/kg from ZnO or ZnAA. All diets also contained 55 mg Zn/kg from ZnSO4 from the trace mineral premix. Pigs fed the RAC diet had increased (P < 0.05) ADG, G:F, HCW, loin depth, percentage lean, and liver weight compared with pigs fed the control diet. No Zn level or source effects or level × source interactions were observed for growth performance. A Zn level × source interaction (quadratic, P = 0.007) was observed in liver Zn concentrations. This resulted from liver Zn concentrations plateauing at 150 mg Zn/kg when ZnO was supplemented, while there was a linear increase when using ZnAA. Increasing Zn in diets containing RAC increased (linear, P < 0.05) plasma Zn on d 18 and 32. The expression of IL-1β was increased (P = 0.014) in mucosa of pigs fed the RAC diet compared with those fed the control diet. Expression of IL-1β decreased (linear, P = 0.026) in the mucosa of pigs fed increasing added Zn. In conclusion, adding Zn to diets containing RAC resulted in a trend for improved growth performance of pigs in 1 of 2 experiments. Also, additional Zn increased plasma Zn and reduced IL-1β.

Effects of the Programmed Nutrition Beef Program on meat quality characteristics.

The objective of this study was to examine the effects of alternative finishing strategies on beef steak color and cooked meat characteristics. Beef steers (n = 64 pens; 8 steers/pen) were allocated to a randomized complete block design with a 2 × 2 factorial treatment arrangement and initial body weight serving as the blocking factor. Factor 1 consisted of dietary treatment with cattle either being fed a conventional feedlot diet (CON) or a diet that included Programmed Nutrition Beef Program supplements. Cattle in the Programmed Nutrition (PN) treatments were fed in two-stages: 1) the basal diet with Programmed Nutrition Beef Receiver from d 1 to 20 and the basal diet with Programmed Nutrition Beef Finisher from d 21 to harvest. Factor 2 consisted of the inclusion (EGP+) or absence (EGP-) of an exogenous growth promoting program. Steers in the EGP+ treatments were implanted initially with Component E-S, reimplanted with Component TE-IS, and fed 400 mg · d(-1) · steer(-1) of ractopamine hydrochloride for the final 28 d before harvest. Steers were harvested on d 175 of feeding and 1 strip loin was removed from 2 carcasses selected at random from each pen for transport to Kansas State University. After 14 d of aging, loins were fabricated into 2.54-cm thick steaks for objective and trained sensory panel measurement of cooked meat characteristics and objective color measurements during 7 d retail display. There were no interactions (P > 0.10) between feeding strategy and exogenous growth promotants for all objective measures of color and cooked meat characteristics. Throughout the display period, PN steaks were darker (P = 0.02) than CON steaks, but surface percentages of oxymyoglobin and metmyoglobin and metmyoglobin reducing ability were unaffected by feeding strategy (P > 0.10). Loins and steaks from PN cattle possessed decreased moisture loss during aging and cooking (P < 0.01). Trained sensory panel evaluation of cooked meat revealed a dietary program × growth promotant interaction for myofibrillar tenderness, connective tissue amount, and overall tenderness (P = 0.01). Compared to the CON/EGP- and PN/EGP- treatments, steaks from the CON/EGP+ and PN/EGP+ treatments were evaluated by panelists as being less myofibrillar and overall tender (P < 0.05). The alternative feeding strategies presented in this study can favorably impact water-holding capacity without negatively compromising retail display discoloration.

Equations generated to predict iodine value of pork carcass back, belly, and jowl fat.

Data from existing literature were used to generate equations to predict finishing pig back, belly, and jowl fat iodine values (IV) and an experiment was conducted to evaluate these equations. The final database included 24, 21, and 29 papers for back, belly, and jowl fat IV, respectively. For experiments that changed dietary fatty acid composition, initial (INT) diets were defined as those fed before the change in diet composition and final (FIN) diets were those fed after. The predictor variables tested were divided into 5 groups: 1) diet fat composition (dietary percent C16:1, C18:1, C18:2, C18:3, EFA, unsaturated fatty acids, and IV product) for both INT and FIN diets, 2) day feeding the INT and FIN diets, 3) ME or NE of the INT and FIN diet, 4) live performance criteria (initial BW, final BW, ADG, ADFI, and G:F), and 5) carcass criteria (HCW and backfat thickness). The PROC MIXED procedure of SAS (SAS Inst., Inc., Cary, NC) was used to develop regression equations. Evaluation of models with significant terms was then conducted based on the Bayesian information criterion. The optimum equations to predict back, belly, and jowl fat IV were backfat IV = 84.83 + (6.87 × INT EFA) - (3.90 × FIN EFA) - (0.12 × INT days) - (1.30 × FIN days) - (0.11 × INT EFA × FIN days) + (0.048 × FIN EFA × INT days) + (0.12 × FIN EFA × FIN days) - (0.0060 × FIN NE) + (0.0005 × FIN NE × FIN days) - (0.26 × backfat depth); belly fat IV = 106.16 + (6.21 × INT EFA) - (1.50 × FIN days) - (0.11 × INT EFA × FIN days) - (0.012 × INT NE) + (0.00069 × INT NE × FIN days) - (0.18 × HCW) - (0.25 × backfat depth); and jowl fat IV = 85.50 + (1.08 × INT EFA) + (0.87 × FIN EFA) - (0.014 × INT days) - (0.050 × FIN days) + (0.038 × INT EFA × INT days) + (0.054 × FIN EFA × FIN days) - (0.0066 × INT NE) + (0.071 × INT BW) - (2.19 × ADFI) - (0.29 × backfat depth). Dietary treatments from the evaluation experiment consisted of a corn-soybean meal control diet with no added fat or a 3 × 3 factorial arrangement with main effects of fat source (4% tallow, 4% soybean oil, or a blend of 2% tallow and 2% soybean oil) and feeding duration (d 0 to 42, 42 to 84, or 0 to 84). The back, belly, and jowl fat IV equations tended to overestimate IV when observed IV were less than approximately 65 g/100 g and underestimate belly fat IV when actual IV are greater than approximately 74 g/100 g or when the fat blend was fed from d 0 to 84 or 42 to 84. Overall, with the exceptions noted, the regression equations were an accurate tool for predicting carcass fat quality based on dietary and pig performance factors.

Effect of Brahman genetic influence on collagen enzymatic crosslinking gene expression and meat tenderness.

The objective of the study was to examine the effect of Brahman genetics on collagen enzymatic crosslinking gene expression and meat tenderness. Steers were randomly selected to represent a high percentage Brahman genetics (n = 13), Half-Blood genetics (n = 13), Brangus genetics (n = 13), and a high percentage Angus genetics (n = 13). Muscle samples from the Longissimus lumborum muscle were collected at weaning and harvest and reverse transcription quantitative PCR (qPCR) analysis was conducted to measure the mRNA expression of lysyl oxidase (LOX), bone morphogenetic protein 1 (BMP1), and cystatin C (CYS). Steaks from subject animals were collected at harvest, aged for 14 d and subjected to collagen analysis, Warner-Bratzler Shear Force (WBS) and trained sensory panel analysis (tenderness, juiciness, and connective tissue). Data indicated that Half-Blood and Brahman steers had greater (P<0.05) WBS values and tended to receive decreased (P < 0.06) panel tenderness scores than Angus and Brangus steers. Panelists tended to detect more connective tissue in Brahman and Half-Blood steaks when compared to Angus and Brangus steaks (P < 0.07). Crosslinking gene expression data revealed that at weaning Half-Blood steers had more (P < 0.05) mRNA expression of CYS and LOX than Angus and Brangus steers. At weaning and harvest, all genetic groups had similar mRNA expression of BMP1 (P > 0.10). At harvest, Brangus and Angus steers had greater LOX mRNA expression than Brahman cattle (P < 0.05). Pearsons correlation coefficients indicated that only weaning CYS mRNA expression was correlated to WBS, panel tenderness and connective tissue scores (P < 0.05). Expression of LOX was only correlated to these measures at harvest, and BMP1 was correlated to these traits at both time periods (P < 0.05). These results indicate that collagen crosslinking enzyme activity, as indicated by mRNA levels, early in an animals life may account for some of the variation seen in steak tenderness due to Brahman genetic influence.

Substrate elasticity affects bovine satellite cell activation kinetics in vitro

Satellite cells support efficient postnatal skeletal muscle hypertrophy through fusion into the adjacent muscle fiber. Nuclear contribution allows for maintenance of the fiber myonuclear domain and proficient transcription of myogenic genes. Niche growth factors affect satellite cell biology; however, the interplay between fiber elasticity and microenvironment proteins remains largely unknown. The objective of the experiment was to examine the effects of hepatocyte growth factor (HGF) and surface elasticity on bovine satellite cell (BSC) activation kinetics in vitro. Youngs elastic modulus was calculated for the semimembranosus (SM) and LM muscles of young bulls (5 d; n = 8) and adult cows (27 mo; n = 4) cattle. Results indicate that LM elasticity decreased (P < 0.05) with age; no difference in Youngs modulus for the SM was noted. Bovine satellite cells were seeded atop polyacrylamide bioscaffolds with surface elasticities that mimic young bull and adult cow LM or traditional cultureware. Cells were maintained in low-serum media supplemented with 5 ng/mL HGF or vehicle only for 24 or 48 h. Activation was evaluated by proliferating cell nuclear antigen (PCNA) immunocytochemistry. Results indicate that BSC maintained on rigid surfaces were activated at 24 h and refractive to HGF supplementation. By contrast, fewer (P < 0.05) BSC had exited quiescence after 24 h of culture on surfaces reflective of either young bull (8.1 ± 1.7 kPa) or adult cow (14.6 ± 1.6 kPa) LM. Supplementation with HGF promoted activation of BSC cultured on bioscaffolds as measured by an increase (P < 0.05) in PCNA immunopositive cells. Culture on pliant surfaces affected neither activation kinetics nor numbers of Paired box 7 (Pax7) immunopositive muscle stem cells (P > 0.05). However, with increasing surface elasticity, an increase (P < 0.05) in the numbers of muscle progenitors was observed. These results confirm that biophysical and biochemical signals regulate BSC activation.

Effect of extended postmortem aging and steak location on myofibrillar protein degradation and Warner-Bratzler shear force of beef M. semitendinosus steaks

The objective of this study was to evaluate the effect of steak location and postmortem aging on cooked meat tenderness and myofibrillar protein degradation of steaks from M. semitendinosus (ST). Following harvest and a 6 d chill period, the left ST was removed from carcasses of crossbred feedlot steers ( = 60, average hot carcass weight 427 ± 24 kg). Each ST was fabricated into ten 2.54-cm thick steaks originating from the proximal to distal end of the muscle. Steaks cut adjacent to each other were paired, vacuum packaged, and randomly assigned to 7, 14, 21, 42, or 70 d of aging at 2 ± 1°C. After aging, within each steak pair, steaks were randomly assigned to Warner-Bratzler shear force or myofibrillar proteolysis analysis (calpain activity and desmin and troponin-T degradation). Muscle fiber type and size were also determined at the 2 ends of the muscle. There was no location × d of aging interaction ( = 0.25) for ST steak WBSF. Steak location affected (quadratic, < 0.01) WBSF. As steaks were fabricated from the proximal to distal end, WBSF values decreased toward the middle of the muscle and then increased toward the distal end. Activity of all calpains and myofibrillar protein proteolysis were unaffected by steak location ( > 0.13). Type I, IIA, and IIX muscle fibers were larger at the proximal end of the muscle than the distal end ( < 0.01). Increasing d of aging improved WBSF (quadratic, < 0.01) for the duration of the 70 d postmortem period. As d of aging increased, intact calpain-1 activity decreased (quadratic, < 0.01) with activity detected through 42 d. Day of aging affected autolyzed calpain-1 (linear, < 0.01) and calpain-2 activity (quadratic, < 0.01). Through d 70 of aging, the intensity of intact 55 kDa desmin band decreased (linear, < 0.01), while there was an increase (linear, < 0.01) in the degraded 38 kDa band. Similarly, d of aging increased troponin-T proteolysis, indicated by a decrease (quadratic, < 0.01) in intensity of the intact 40 kDa band and an increase (linear, < 0.01) in the 30 kDa degraded band. Intramuscular WBSF differences are not due to proteolytic activity or myofibrillar degradation and seem related to muscle fiber size. The improvement of ST steak WBSF through 70 d of aging is partly due to continued degradation of desmin and troponin-T. Calpain proteolytic analysis indicates that autolyzed calpain-1 and calpain-2 may be involved in extended postmortem myofibrillar protein proteolysis.

Effect of growth-promoting technologies on Longissimus lumborum muscle fiber morphometrics, collagen solubility, and cooked meat tenderness

The objective of the study was to examine the effect of growth-promoting technologies (GP) on Longissimus lumborum steak tenderness, muscle fiber cross-sectional area (CSA), and collagen solubility. Crossbred feedlot heifers ( = 33; initial BW 464 ± 6 kg) were blocked by BW and assigned to 1 of 3 treatments: no GP (CON; = 11); implant, no zilpaterol hydrochloride (IMP; = 11); implant and zilpaterol hydrochloride (COMBO; = 11). Heifers assigned to receive an implant were administered Component TE-200 on d 0 of the study, and the COMBO group received 8.3 mg/kg DM of zilpaterol hydrochloride for the final 21 d of feeding with a 3 d withdrawal period. Following harvest, strip loins were collected and fabricated into 4 roasts and aged for 3, 14, 21, or 35 d postmortem. Fiber type was determined by immunohistochemistry. After aging, objective tenderness and collagen solubility were measured. There was a treatment × day of aging (DOA) interaction for Warner-Bratzler shear force (WBSF; < 0.01). At d 3 of aging, IMP and COMBO steaks had greater WBSF than CON steaks ( < 0.01). By d 14 of aging, the WBSF of IMP steaks was not different ( = 0.21) than CON steaks, but COMBO steaks had greater shear values than steaks of other treatments ( < 0.02). The COMBO steaks only remained tougher ( = 0.04) than the CON steaks following 35 DOA. Compared to CON muscles, IMP and COMBO type I and IIX muscle fibers were larger ( < 0.03). Treatment, DOA, or the two-way interactions did not impact measures of total and insoluble collagen ( > 0.31). Soluble collagen amount tended to be affected ( 0.06) by a treatment × DOA interaction which was due to COMBO muscle having more soluble collagen than the other 2 treatments on d 21 of aging ( < 0.02). Correlation analysis indicated that type I, IIA, and IIX fiber CSA are positively correlated with WBSF at d 3 and 14 of aging ( < 0.01), but only type IIX fibers are correlated at d 21 and 35 of aging ( < 0.03). At these time periods, total and insoluble collagen became positively correlated with WBSF ( < 0.01). This would indicate that relationship between muscle fiber CSA and WBSF decreases during postmortem aging, while the association between WBSF and collagen characteristics strengthens. The use of GP negatively impacted meat tenderness primarily through increased muscle fiber CSA and not through altering collagen solubility.