The influence of growth stage on carcass composition and factors associated with marbling development in beef cattle.

Subcutaneous fat and marbling both increase in beef cattle during the feeding phase but are antagonistic in regard to their contribution to beef carcass value. The objective of this study was to determine whether cellular factors associated with marbling development change with growth stage throughout the feeding period and whether they are correlated to marbling relative to carcass composition. Twenty-four steers of known origin with the cytosine and thymine (CT) leptin genotype were allotted to 3 harvest groups. Six steers per harvest group were harvested at the following predetermined points: 35 d on feed (early feeding period, EF), average live weight of 464 kg (middle feeding period, MF), and 1.17-cm 12th-rib subcutaneous fat thickness (late feeding period, LF). Longissmus muscle samples were collected within 30 min postmortem and snap frozen for real-time PCR and Western blot analysis of lipoprotein lipase, adenosine monophosphate-activated protein kinase α (AMPKα), stearoyl-coenzyme A desaturase (SCD), PPARγ, C/EBP-ß, and myostatin. Carcass data were recorded, and LM samples were collected and aged 2, 7, 14, and 21 d postmortem for Warner-Bratzler shear force determination. Carcass composition was estimated by dissection of the 9-10-11 rib section and subsequent proximate analysis of the soft tissue. Intramuscular fat content of the LM increased linearly throughout the feeding period, giving additional support to marbling as an early developing tissue. Expression of AMPKα was found to be downregulated, whereas SCD expression was upregulated in the LF group relative to the first 2 harvest groups. Additionally, SCD and PPARγ were downregulated in the EF group relative to the latter 2 harvest groups. These changes in gene expression resulted in a linear increase in only PPARγ protein abundance, whereas myostatin tended to increase quadratically. A correlation was found between intramuscular fat and PPARγ abundance. This gives further evidence of the importance of adipocyte hyperplasia in increasing marbling. Targeting and increasing PPARγ expression may serve as a mechanism to increase marbling deposition. Last, LF steaks were more tender than MF or EF steaks, indicating improved tenderness with increased days on feed.

Effect of distillers dried grains with solubles and ractopamine (Paylean) on quality and shelf-life of fresh pork and bacon.

Pigs (n = 240) were allotted in a 5 x 2 factorial arrangement with 5 levels of distillers dried grains with solubles (DDGS): 0, 15, 30, 45, and 60%, and 2 ractopamine (RAC) levels: 0 and 5 mg/kg. Four pigs per pen (2 barrows, 2 gilts) closest to pen mean BW were used for meat quality evaluation. Loins (n = 119) were evaluated for objective color; moisture and fat; subjective color, marbling, and firmness; and drip loss. Bellies (n = 119) were evaluated for weight, length, width, thickness, objective fat color, and firmness. Cured bellies were evaluated for pump yield, cook loss, and sliced bacon cook loss. Loin thiobarbituric acid reactive substances (TBARS) were evaluated on enhanced (salt and phosphate) boneless chops held in modified atmosphere (80% O(2)/20% CO(2)) packages for 0, 7, 14, and 21 d. Bacon TBARS were evaluated on sliced bacon held in vacuum packages for 0, 28, 56, and 84 d. Fat samples were collected from each jowl and belly and evaluated for fatty acid profile and iodine value (IV). Increasing DDGS decreased subjective marbling (P = 0.0134) and firmness (P = 0.0235), and increased drip loss (P = 0.0046). Distillers dried grains with solubles did not affect loin pH, subjective or objective color, percent moisture, or percent fat (P > 0.05). The RAC decreased subjective color (P = 0.0239), marbling (P = 0.0445), and a* (P = 0.0355). Increasing DDGS decreased belly weight (P = 0.0155), length (P = 0.0008), thickness (P = 0.0019), and firmness (P = 0.0054); decreased belly fat L* (P = 0.0818); and increased belly cook loss (P = 0.0890). Ractopamine did not affect any belly measurements, and there were no DDGS x RAC interactions (P > 0.05). Distillers dried grains with solubles did not affect loin TBARS at 0, 7, or 14 d. At 21 d, loin TBARS from 30, 45, and 60% DDGS groups were increased compared with 0 and 15% groups (P < 0.05). Ractopamine did not affect (P > 0.05) loin TBARS, and there were no (P > 0.05) DDGS x RAC interactions. Distillers dried grains with solubles and RAC did not affect bacon TBARS (P > 0.05). Increasing DDGS increased belly (P = 0.0207) and jowl (P < 0.0001) IV, and decreased MUFA:PUFA in belly (P < 0.0001) and jowl (P < 0.0001) fat. Ratio of SFA:unsaturated fatty acids decreased in jowl (P = 0.0002) and belly fat (P = 0.2815). Ractopamine did not affect fatty acid profiles or IV, and there were no DDGS x RAC interactions (P > 0.05). Results indicate that increased DDGS have minimal effects on loin quality, but decrease belly quality, bacon processing characteristics, and fat stability. Ractopamine does not negatively affect these characteristics and does not interact with DDGS.

Comparative effects of ractopamine hydrochloride and zilpaterol hydrochloride on growth performance, carcass traits, and longissimus tenderness of finishing steers.

Ractopamine hydrochloride (RAC) and zilpaterol hydrochloride (ZH) are beta-adrenergic agonists that improve growth performance and affect carcass characteristics. The objective of this study was to evaluate the comparative effects of RAC and ZH when fed to beef steers during the last 33 d of the finishing period. Three hundred crossbred beef steers (516 +/- 8 kg) were grouped by BW, BCS, and breed type and randomly assigned to 1 of 3 treatments (10 steers per pen; 10 pens per treatment). Treatments were control (no beta-agonists added), RAC (200 mg of ractopaminexhdx(-1)d(-1), for 33 d), or ZH (75 mg of zilpaterolxanimalx(-1)d(-1), for 30 d, removed 3 d for required withdrawal period). Steers were slaughtered, carcass characteristics were evaluated, and cut-out yields were determined. Both RAC and ZH increased final BW, ADG, feed efficiency (G:F), and HCW compared with controls (P < 0.05). Compared with RAC, ZH decreased ADG, ADFI, and final BW, but increased HCW and dressing percentage (P < 0.05). Carcass yield was not affected by RAC in this experiment, whereas ZH decreased adjusted fat thickness and KPH, increased ribeye area, improved yield grade, and increased cut-out yields, when compared with controls (P < 0.05). Marbling, lean maturity, and skeletal maturity were not different between treatments (P > 0.05). Steaks from RAC steers had greater (P < 0.05) Warner-Bratzler shear force (WBSF) values than steaks from control steers at 3 and 7 d of aging, but did not differ from controls after 14 d of aging. Steaks from ZH steers had greater WBSF values (P < 0.05) than steaks from controls and RAC steaks throughout the 21-d postmortem aging period. Although both beta-adrenergic agonists were effective at improving feedlot performance, RAC showed no negative effect on WBSF after 14 d, whereas WBSF values for ZH steaks were significantly greater than controls after 21 d.

The effect of zilpaterol hydrochloride on meat quality of calf-fed Holstein steers.

The objective of these studies was to evaluate the effects of zilpaterol hydrochloride (ZH), fed for 0, 20, or 30 d, on meat quality attributes of calf-fed Holstein steers. Steers were slaughtered at a commercial facility, and carcasses were selected by HCW to represent the pen mean. Further carcass selection was based on quality grade (Choice and Select) and yield grade. Proximate composition, measures of water holding capacity, and tenderness using Warner-Bratzler shear force after 7, 14, or 21 d postmortem were evaluated on the shoulder clod (triceps brachii), top butt (gluteus medius), and strip loin (longissimus lumborum). Percentage of purge for the 3 subprimals was not different (P > 0.05) among ZH treatments. Steers fed ZH for 20 d or 30 d had decreased (P < 0.05) percentages of fat in the triceps brachii, compared with 0-d ZH. Percentage of fat was less (P < 0.05) in the gluteus medius and longissimus lumborum when steers were fed ZH for 30 d compared with those steers fed ZH for 0 d. Percentage of fat was greater in Choice triceps brachii (P < 0.05) and longissimus lumborum (P < 0.10) compared with Select. Thaw loss was not different (P > 0.05) for any muscle due to ZH treatment. Only longissimus had a greater (P < 0.05) cooking loss with ZH treatment. Cooking loss was not different (P > 0.05) for the gluteus medius or longissimus lumborum due to quality grade or aging day. At each aging day, the 20- and 30-d ZH longissimus lumborum had greater (P < 0.05) shear force values than 0 d; however, 20- and 30-d ZH had a greater absolute change in shear force from 7 to 21 d than that of 0 d ZH. Triceps brachii steaks were less tender (P < 0.05) after ZH treatment, but gluteus medius steaks were not different (P > 0.05). There was no difference (P > 0.05) in shear force due to quality grade. Results illustrate the use of ZH in calf-fed Holstein steers will have minimal effects on purge, thaw, or cooking loss. Percentage of intramuscular fat will decrease, especially when fed for longer durations. Steaks from ZH treated steers were tougher than steaks from control animals at all aging times, but ZH steaks became more tender with postmortem aging.

Contribution of lean, fat, muscle color and degree of doneness to pork and beef species flavor.

Flavor is an important contributor to consumer acceptability of meat, our objective was to characterize the impact of species-specific fat/lean sources, fat level, degree of doneness and muscle color are on pork and beef flavor. Three separate experiments were conducted. Patties were formulated differently for each experiment in order to evaluate the desired variables. Experiment. 1: Flavor from combination patties (same species lean/fat or combination of species lean/fat) was not impacted by degree of doneness (66°C vs. 71°C). Beef flavor was highest in samples made with beef lean, regardless of species fat type. Pork flavor was highest in samples made with pork lean and had higher flavor intensity scores. Experiment. 2: Beef flavor was not increased in all-beef patties formulated with higher fat levels. Pork patties formulated with higher fat content increased pork flavor. Experiment. 3: All-beef and all-pork patties formulated with light or dark lean did not impact flavor in either species.

Carcass, meat quality, and sensory characteristics of heavy body weight pigs fed ractopamine hydrochloride (Paylean).

Carcass characteristics, meat quality traits, and sensory attributes were evaluated in late-finishing barrows and gilts, weighing between 100 to 130 kg of BW, fed 0, 5, or 7.4 mg/kg of ractopamine hydrochloride (RAC) for the final 21 to 28 d before slaughter. Carcass data were collected from carcasses from barrows and gilts (n = 168), and all primal cuts from the right sides of these carcasses were fabricated to calculate primal yields as a percentage of the HCW. Subjective (National Pork Producers Council and Japanese) color, firmness, and marbling scores were determined on the LM of each loin and the semimembranosus muscle (SM) of the ham, whereas the moisture, extractable lipid, Warner-Bratzler shear force (WBSF), and trained sensory evaluations (juiciness, tenderness, and pork flavor) were measured on the LM samples only. Gilts produced heavier (P < 0.05) HCW than barrows, whereas feeding RAC increased (P < 0.05) HCW over pigs fed diets devoid of RAC. Carcasses from gilts also had greater (P < 0.02) primal cut and lean cut (P < 0.01) yields than barrows, and dietary inclusion of 5 mg/kg of RAC increased (P < 0.05) total boneless cut and lean cut yields when compared with carcass from pigs fed 0 or 7.4 mg/kg of RAC. Warner-Bratzler shear forces values were greater (P < 0.05) in the LM of gilts than barrows, but only juiciness scores were greater (P < 0.03) in LM chops from barrows than gilts. The LM from barrows had greater intramuscular lipid (P < 0.001) than the LM from gilts, and even though the LM from pigs fed 5 mg/kg of RAC had greater (P < 0.04) WBSF values than the LM from pigs fed 0 or 7.4 mg/kg of RAC, including RAC in the late-finishing diets for 21 or 28 d did not affect sensory panel rating or percentages of moisture and intramuscular lipid. In summary, addition of RAC in the late-finishing diet improved carcass and primal cut yields when it was fed at 5 and 7.4 mg/kg without altering pork quality traits regardless of whether RAC was fed for 21 or 28 d.

Effect of ractopamine level, gender, and duration of ractopamine on belly and bacon quality traits.

The objective was to determine belly and bacon quality traits in pigs fed ractopamine (RAC) for various durations during finishing. A 2×3×2 factorial arrangement was used with barrows and gilts, fed RAC levels of 0.0, 5.0, or 7.4ppm, for 21 or 28d prior to harvest. Bellies were fabricated and measured for length, thickness, firmness, and processing yields. Once processed, 1.27cm slices were removed at 25%, 50%, and 75% the distance from the blade end, packaged and digitally imaged using a Chem1 Genius(2) Bio Imaging System. Total slice area (TA), total slice length (TL), secondary lean length (SL), secondary lean area (SA), and percent lean area (TA - all lean components=LA) were determined by tracing images in Adobe Photoshop Elements. A composite sample from the three slices was used for proximate analysis to determine moisture and fat composition for each belly. Feeding RAC increased belly yield, TA, TL, SA, and LA (P<0.05), but did not alter moisture or fat composition (P>0.05). Gilts had decreased firmness and higher pump uptakes compared to barrows (P<0.05). Additionally gilts had increased TL, SL, and LA with lower fat and higher moisture content (P<0.05). RAC feeding duration had no significant effect on belly or bacon quality traits (P>0.05), furthermore, no interactions were found to be significant (P>0.05). RAC administration during finishing resulted in improved belly and bacon yields with no negative effects on the quality traits evaluated.