National Beef Quality Audit-2022: Transportation, mobility, live cattle, and hide assessments to determine producer-related defects that affect animal welfare and the value of market cows and bulls at processing facilities.

The National Beef Quality Audit (NBQA)-2022 serves as a benchmark of the current market cow and bull sectors of the U.S. beef industry and allows comparison to previous audits as a method of monitoring industry progress. From September 2021 through May 2022, livestock trailers (n = 125), live animals (n = 5,430), and post-slaughter hide-on animals (n = 6,674) were surveyed at 20 commercial beef processing facilities across the U.S. Cattle were transported in a variety of trailer types for an average distance of 490.6 km and a mean transport time of 6.3 h. During transit, cattle averaged 2.3 m2 of trailer space per animal indicating sufficient space was provided according to industry guidelines. Of all trailers surveyed, 55.3% transported cattle from an auction barn to a processing facility. When surveyed, 63.6% of all truck drivers reported to be Beef Quality Assurance certified. The majority (77.0%) of cattle were sound when evaluated for mobility. Mean body condition scores (9-point scale) for beef cows and bulls were 3.8 and 4.4, respectively, whereas mean body condition scores (5-point scale) for dairy cows and bulls were 2.3 and 2.6, respectively. Of the cattle surveyed, 45.1% had no visible live animal defects, and 37.9% had only a single defect. Of defects present in cows, 64.6% were attributed to an udder problem. Full udders were observed in 47.5% of all cows. Nearly all cattle were free of visible abscesses and knots (97.9% and 98.2%, respectively). No horns were observed in 89.4% of all cattle surveyed. Beef cattle were predominantly black-hided (68.9% and 67.4% of cows and bulls, respectively). Holstein was the predominant dairy animal observed and accounted for 85.7% of the cows and 98.0% of the bulls. Only 3.1% of all animals had no form of identification. Findings from the NBQA-2022 show improvements within the industry and identify areas that require continued education and research to improve market cow and bull welfare and beef quality.

Influence of Beef Hot Carcass Weight on Sensory Characteristics of Strip Loin, Eye of Round, and Denver Cut Steaks.

The objective of this research was to investigate the influence of beef hot carcass weight (HCW) on consumer sensory attributes. Beef carcasses (n = 116) were selected based on the USDA quality grade and HCW. Lightweight (LW; 296-341 kg), middleweight (MW; 386-432 kg), or heavyweight (HW; 466-524 kg) carcasses with USDA Choice (LC) or USDA Select (SEL) quality grades were used in this study. Carcasses were tracked through fabrication and the semitendinosus, chuck roll, and strip loin were collected and fabricated into eye of round, Denver cut, and strip loin steaks, respectively, for consumer sensory evaluation. USDA Select MW Denver cut steaks had increased overall liking and texture liking scores and were more tender and juicier than the SEL LW steaks (p ≤ 0.02). USDA Select MW strip loin steaks had increased overall and flavor liking scores and were more tender than the SEL LW steaks (p ≤ 0.02). USDA Choice MW eye of round steaks had increased overall, flavor, and texture liking scores and were juicier than the LW eye of round steaks (p ≤ 0.04). The steaks evaluated in this study were differentially impacted by HCW and little to no clear pattern of effects could be determined across cut or quality grade. Additional research is needed to determine the most acceptable HCW from a consumer perspective.

Effects of Zilpaterol Hydrochloride Supplementation on Growth Performance, Carcass Characteristics and Meat Quality for Steers Differing in Breed Type.

To determine the effects of zilpaterol hydrochloride (ZH) on growth performance, carcass characteristics and meat quality for steers differing in breed type, steers with British (B; n = 76) or British × Continental (BC; n = 57) backgrounds were allocated to a randomized incomplete block design with a 2 × 2 treatment structure. Pens within each block × breed type were randomly assigned to either ZH (8.3 mg/kg of DM; fed for 20 d before slaughter, followed by a 3-day withdrawal) or control (CON; 0 mg/kg ZH). Steers were subjected to ultrasound immediately before ZH inclusion and following withdrawal to determine the influence of ZH on changes in longissimus muscle area (LMA), fat thickness and percent intramuscular fat (IMF). Carcass data were collected, and the longissimus lumborum was collected for analysis of tenderness, moisture percentage, crude fat content, collagen content, postmortem proteolysis and sensory attributes. The ZH × breed type interaction did not influence (p > 0.05) the feedlot performance, carcass or meat quality attribute traits evaluated, with the exception of moisture percentage. Responses among breed types were as expected for B vs. BC cattle types. Supplementation with ZH improved (p < 0.05) LMA and yield grade but increased Warner-Bratzler shear force.

Beef color and tenderness response to production systems utilizing additive combinations of growth-promotant technologies.

The objective of this study was to compare the influence of beef production systems using additive combinations of growth-promotant technologies on meat quality. Steer calves (n = 120) were assigned to 1 of 4 treatments: 1) no technology (NT; control), 2) antibiotic treated (ANT; NT plus therapeutic antibiotics, monensin, and tylosin), 3) implant treated (IMP; ANT plus a series of three implants), and 4) beta-agonist treated (BA; IMP plus ractopamine-HCl). Muscle biopsy samples from the longissimus lumborum were extracted from a subset (n = 4 per treatment) of steers to evaluate expression of calpain-1, calpain-2, and calpastatin using real-time RT-PCR. Following carcass chilling, objective color (L*, a*, and b*) was evaluated. The right strip loin was removed from each carcass, portioned into 2.54-cm steaks, and designated to 7, 14, or 21 d postmortem aging periods for analysis of cook loss and Warner-Bratzler shear force (WBSF). The anterior face of each strip loin was used for analysis of crude fat and moisture. Treatment influenced (P < 0.001) L*, a*, and b*. The NT and IMP treatments had greater (P < 0.01) L* values, ANT was intermediate, and BA had the lowest (P < 0.01) L* values. The NT and IMP treatments had higher (P < 0.01) a* and b* values compared with ANT, which were higher (P < 0.01) than BA. Steaks from implanted steers (IMP and BA) tended (P ≤ 0.067) to exhibit higher a* and b* than steaks from nonimplanted steers. Cattle in the NT and ANT treatments produced steaks with increased (P < 0.01) crude fat percentage compared with the IMP and BA treatments, which were similar (P > 0.05). Percent moisture of NT steaks was lower (P < 0.01) than all other treatments, ANT was intermediate, and IMP and BA were similar (P > 0.05) and had the highest (P < 0.01) moisture content. Cook loss tended to be greater (P = 0.088) for implanted steers (IMP and BA) compared to nonimplanted steers (NT and ANT). Steaks from NT and ANT treatments were more tender (P < 0.05) than IMP and BA, which were similar (P > 0.05). Thus, WBSF was lower (P < 0.001) in nonimplanted than implanted steaks. Expression of calpastatin was increased (P ≤ 0.025) in ANT and BA treatments, and there was a tendency for expression of calpain-2 to be increased (P = 0.081) in ANT compared to NT. These results suggest that production systems with limited use of growth promoting technology produced strip loins with more crude fat, less moisture and cook loss, and improved tenderness.

The Effect of Copper and Zinc Sources on Liver Copper and Zinc Concentrations and Performance of Beef Cows and Suckling Calves.

To determine the influence of the source of gestational and postnatal Cu and Zn supplementation on cow and calf performance, cows (n = 287) were assigned to one of the following two treatments: (1) inorganic (INORG) treatment, in which cows were supplemented with 15 mg of Cu (as CuSO4) and 15 mg of Zn (as ZnSO4) per kg of diet DM, or (2) organic (ORG) treatment, in which cows were supplemented with 15 mg of Cu (as Cu proteinate; Bioplex Cu, Alltech, Inc., Nicholasville, KY, USA) and 15 mg of Zn (as Zn proteinate; Bioplex Zn, Alltech, Inc., Nicholasville, KY, USA) per kg of diet DM. The treatments were initiated prior to breeding and continued throughout gestation until weaning. Liver biopsies were collected for analysis of mineral content. Cow body condition score (BCS), body weight (BW), pregnancy data, calf weaning weight (WW), and antibody response of the calves were recorded. The cows receiving the INORG treatment had a greater BW (p < 0.05) and BCS (p < 0.01) at breeding in Year 2, while the cows on the ORG treatment had a greater (p < 0.05) BW at weaning in Year 2. The cows that received the ORG mineral had improved (p < 0.05) conception rates in Year 1. The calves receiving the ORG treatment had heavier (p < 0.05) 205-day adjusted WWs.

Case study: effects of low-stress weaning on calf growth performance and carcass characteristics.

The objective of this study was to compare the influence of two low-stress weaning methods with conventional weaning on post-weaning performance and carcass characteristics of beef steers. Single-sourced steer calves (n = 89) were stratified by body weight (BW) and dam age into three groups in a completely randomized design (n = 29 or 30 steers/treatment): ABRUPT (calves isolated from dams on the day of weaning), FENCE (calves separated from dams via a fence for 7 d prior to completely weaning), and NOSE (nose-flap inserted and calves remained with dams for 7 d prior to completely weaning). At day +7 post-weaning, calves were transported to a commercial feedlot where they received standard step-up and finishing rations typical for a Northern Plains feedlot. BWs were recorded in study day -7 (PreTreat), 0 (Weaning), 7 (PostWean), 26 (Receiving), 175 (Ultrasound), and 238 or 268 (Final), and average daily gains (ADG) were calculated for each time period. Blood samples were collected via coccygeal venipuncture at d -7 (PreTreat), 0 (Weaning), and +7 (PostWean) from a subsample of calves (n = 10 per treatment) and analyzed for haptoglobin (acute-phase stress protein) concentrations using a bovine haptoglobin ELISA kit. On day 175, ultrasound fat thickness and intramuscular fat were determined and utilized to project marketing dates when steers reached 1.27 cm of backfat (day 238 or 268). Carcass measurements were recorded at the time of harvest. The weaning method interacted (P < 0.01) with a time period for ADG and BW. Calf ADG was greater (P < 0.01) in the NOSE treatment during PreTreat to Weaning than ABRUPT or FENCE. In the Weaning to PostWean period, the FENCE calves had greater (P < 0.01) ADG than ABRUPT and NOSE. During the Postwean to Receiving period ADG was greater (P < 0.04) for ABRUPT compared to FENCE and NOSE. Calf ADG was similar (P > 0.05) among treatments for the remainder of the feeding period. Calf BW did not differ among treatments (P > 0.05) at all times of weighing. Haptoglobin was undetectable in all samples except two samples collected on day -7. The weaning method did not influence (P > 0.05) carcass measurements. Collectively these data suggest low-stress weaning methods do not significantly improve post-weaning growth performance or carcass characteristics compared to using conventional methods despite minor, short-term alterations in ADG during the weaning period.

Effects of long-term postgastric infusion of casein or glutamic acid on small intestinal starch digestion and energy balance in cattle.

The objective of this experiment was to evaluate effects of postruminal flows of casein or glutamic acid on small intestinal starch digestion and to quantify changes in energy and nutrient balance. Twenty-four steers (body weight = 179 ± 4 kg) were duodenally infused with raw cornstarch (1.46 ± 0.04 kg/d) and either 413 ± 7.0 g casein/d, 121 ± 3.6 g glutamic acid/d or water (control). Measures of small intestinal starch digestion and nutrient excretion were collected across 4 d after 42 d of infusion and measures of respiration via indirect calorimetry were collected across 2 d after 48 d of infusion. Ileal starch flow was least among calves provided casein, but ileal starch flow was not different between glutamic acid or control. Small intestinal starch digestion tended to be greatest among calves provided casein, least for glutamic acid and intermediate for control. Casein increased ileal flow of ethanol soluble oligosaccharides compared to glutamic acid and control. Large intestinal starch digestion was not different among treatments. By design, N intake was greatest among cattle provided casein, intermediate among calves provided glutamic acid and least for control. Nitrogen retention was greater in response to casein compared to control and glutamic acid. Intake of gross energy from feed was similar across treatments, and gross energy from infusate was greatest for casein, intermediate for glutamic acid and least for control. Variation in gross energy intake from feed resulted in no difference in overall gross energy intake across treatments. Similar to measures of small intestinal starch digestion and N retention, casein increased calories of digestible energy and metabolizable energy, compared to glutamic acid and control, which did not differ. Postruminal infusions did not influence methane production, but heat production was greatest in steers infused with casein, intermediate for steers provided glutamic acid, and least for control. Overall, amounts of energy retained by casein tended to be nearly 34% greater than control, but glutamic acid had no impact on energy balance. Improvement in small intestinal starch digestion in response to casein increased energy and N retained; however, glutamic acid did not influence small intestinal starch digestion and energy or N balance in cattle, which seems to suggest that responses in small intestinal starch digestion to greater postruminal flows of glutamic acid become refractory across greater durations of time.

Small intestinal digestion of starch can provide greater energy from dietary starch in comparison to ruminal fermentation, which can increase performance and improve feed efficiency in cattle fed starch-based diets; however, small intestinal starch digestion in cattle is restricted in comparison to nonruminant animals or to ruminal fermentation of starch. In this experiment, long-term increases in postruminal protein but not glutamic acid increased small intestinal starch digestion, and increases in small intestinal starch digestion resulted in improvements in nitrogen and energy balance. Responses in this study compared to previous reports may suggest effects of increased postgastric flows of glutamic acid in cattle are transient, but that effects of casein are not.

Influence of Maternal Protein Restriction in Primiparous Beef Heifers during Mid- and/or Late-Gestation on Progeny Feedlot Performance and Carcass Characteristics.

This study investigated the impacts of metabolizable protein (MP) restriction in primiparous heifers during mid- and/or late-gestation on progeny performance and carcass characteristics. Heifers were allocated to 12 pens in a randomized complete block design. The factorial treatment structure included two stages of gestation (mid- and late-) and two levels of dietary protein (control (CON); ~101% of MP requirements and restricted (RES); ~80% of MP requirements). Half of the pens on each treatment were randomly reassigned to the other treatment at the end of mid-gestation. Progeny were finished in a GrowSafe feeding system and carcass measurements were collected. Gestation treatment x time interactions indicated that MP restriction negatively influenced heifer body weight (BW), body condition score, and longissimus muscle (LM) area (p < 0.05), but not fat thickness (p > 0.05). Treatment did not affect the feeding period, initial or final BW, dry matter intake, or average daily gain of progeny (p > 0.05). The progeny of dams on the RES treatment in late gestation had a greater LM area (p = 0.04), but not when adjusted on a hot carcass weight basis (p > 0.10). Minimal differences in the animal performance and carcass characteristics suggest that the level of MP restriction imposed during mid- and late-gestation in this study did not have a significant developmental programming effect.

Influence of Maternal Carbohydrate Source (Concentrate-Based vs. Forage-Based) on Growth Performance, Carcass Characteristics, and Meat Quality of Progeny.

The objective of this research was to investigate the influence of maternal prepartum dietary carbohydrate source on growth performance, carcass characteristics, and meat quality of offspring. Angus-based cows were assigned to either a concentrate-based diet or forage-based diet during mid- and late-gestation. A subset of calves was selected for evaluation of progeny performance. Dry matter intake (DMI), body weight (BW), average daily gain (ADG), gain to feed (G:F), and ultrasound measurements (muscle depth, back fat thickness, and intramuscular fat) were assessed during the feeding period. Carcass measurements were recorded, and striploins were collected for Warner-Bratzler shear force (WBSF), trained sensory panel, crude fat determination and fatty acid profile. Maternal dietary treatment did not influence (p > 0.05) offspring BW, DMI, ultrasound measurements, percent moisture, crude fat, WBSF, or consumer sensory responses. The forage treatment tended to have decreased (p = 0.06) 12th rib backfat compared to the concentrate treatment and tended to have lower (p = 0.08) yield grades. The concentrate treatment had increased (p < 0.05) a* and b* values compared to the forage treatment. These data suggest variation in maternal diets applied in this study during mid- and late-gestation has limited influence on progeny performance.

Impact of feeding cover crop forage containing brassicas to steers during backgrounding on live animal performance, carcass characteristics, and meat color1.

Brassica cover crops are an option for producers to incorporate into their cropping system to improve soil health and also provide a feed resource for cattle. While brassica cover crops have been widely used for grazing cows, their use as a backgrounding feedstuff is relatively unknown. The objective of this study was to determine the impact of feeding a brassica cover crop mixture during backgrounding on live animal performance and carcass characteristics. A total of 30 Angus-based steers were assigned to one of two dietary treatments during backgrounding 1) ad libitum access to a diet containing freshly cut brassica cover crop forage (CC) containing radish, turnip, rapeseed, rye grass, and a liquid supplement or 2) common Midwestern dry lot growing diet containing silage, soybean meal, grass hay, and a liquid supplement (CON). Steers were assigned to electronic feed bunks (Insentec RIC, Hokofarm Group; Marknesse, the Netherlands) for collection of individual feed intake. Diets were formulated to be nutritionally similar on a dry matter basis. Steers were paired by weight across treatments and pair fed. Dry matter intake (DMI) was calculated daily for steers in the CC treatment and the following day, CON steers were allowed access to an equal amount of dry matter using the Insentec RIC system. Steers were weighed weekly and backgrounded for 44 days before transitioning to a common finishing diet and weighed every 28 days. Steers were harvested at an estimated average backfat thickness of 1 cm. Standard carcass data were measured and strip loins and shoulder clods were collected. Instrumental and subjective color were measured on ground beef for 8 days and instrumental color was measured on strip steaks for 11 days. Treatment did not influence carcass characteristics, average daily gain, and DMI (P > 0.17). However, CON steers exhibited increased gain to feed ratio (P = 0.02). Additionally, a treatment by day interaction was observed for ground beef discoloration as the CC treatment displayed increased discoloration on days 4, 6, and 7 of case life (P < 0.01). These data indicate that brassicas may be utilized in a backgrounding diet without negatively impacting carcass characteristics but may decrease case life of ground beef.

Evaluation of Bacillus subtilis PB6 on feedlot phase growth performance, efficiency of dietary net energy utilization, and fecal and subiliac lymph node Salmonella prevalence in spring placement yearling beef steers fed in southeastern South Dakota,.

Yearling crossbred beef steers [N = 238; initial shrunk body weight (BW) = 402 ± 31.2 kg] were used to investigate the influence of a Bacillus subtilis probiotic on animal growth performance, efficiency of dietary net energy (NE) utilization, carcass characteristics, and fecal and subiliac lymph node Salmonella prevalence during a 140-d finishing period at the Southeast Research Farm in Beresford, SD. Steers were allotted to 1 of 24 pens (N = 9-10 steers/pen) and assigned to 1 of 2 dietary treatments (12 pens/treatment): no probiotic (CON) or 0.5 g/steer/d of a B. subtilis PB6 probiotic (CLOSTAT500, Kemin Industries, Des Moines, IA; CLO). Bunks were managed according to a slick bunk management approach. Fecal samples were collected on study days 1, 28, 56, 112, and 140 from a subsample of steers from each pen (N = 5 steers/pen) via rectal palpation and composited by pen for the determination of Salmonella prevalence using selective enrichment and culture media. Upon harvest, subiliac lymph nodes were obtained from an equal number of steers from each treatment (collected from every other steer) following evisceration and hide removal. Data were analyzed as a randomized complete block design and pen served as the experimental unit; an α of 0.05 determined significance. Live-basis final BW and average daily gain tended (P ≤ 0.06) to be reduced for CLO. No differences were detected (P ≥ 0.11) between treatments for dry matter intake or gain efficiency. Treatment neither altered the efficiency of dietary NE utilization nor calculated dietary NE content based upon observed performance (P ≥ 0.46). No differences were detected between treatments for any carcass traits (P ≥ 0.15). No Salmonella was recovered in any fecal samples collected on study days 1, 28, or 56. On day 112, steers from CLO had a numerically lower (P = 0.17; 25.0 vs. 8.3%) incidence of fecal Salmonella compared to CON. On study day 140, fecal Salmonella incidence did not differ between treatments (P = 0.34; 0.0 vs. 8.3%) for CON and CLO, respectively. Upon harvest, no Salmonella was recovered in any subiliac lymph nodes. These data indicate that B. subtilis PB6 did not influence feedlot phase growth performance or fecal Salmonella prevalence. Additionally, Salmonella was not observed in the subiliac lymph nodes of any steers upon harvest.

South Dakota State University Beef 2020 increases participant knowledge of the beef industry.

South Dakota State University has developed a hands-on program that addresses the preharvest management factors that influence beef carcass value to aid producers in their management and marketing decisions. The 3-d program includes live cattle and carcass evaluation, beef carcass fabrication, a harvest demonstration, sensory panel, and presentations on topics including live market cattle evaluation, health, and disposition in relation to carcass quality, feeding and management, and value-added beef cuts. To evaluate program effectiveness, data were collected from all programs held between 2013 and 2019. Participants were asked to evaluate their perceived value for each program component, as well as their knowledge of the industry prior to and after completing the program. Upon completion of the 2018 Beef 2020, a focus group of program alumni was assembled to better understand participant experiences, application of the material, and guide future programming. The recommendations of the focus group were implemented during the 2019 program. Component value scores are reported in a box and whisker plot and participant knowledge was evaluated using a paired t-test with significance determined at P < 0.05. Special attention was given to the results of 2019 compared to previous years to determine the efficacy of the program changes. Overall, the average value scores for the sessions all ranked above 8 on a scale of 1-10, indicating a relatively large value to participants. Knowledge of carcass traits, carcass value, and management factors that influence those traits increased after participation in the Beef 2020 program (5.18 vs. 7.67 ± 0.16; P < 0.0001). The use of a focus group was concluded to be an effective means of assessing program value, strengths, and weaknesses. The Beef 2020 program can be used as a model for other Extension professionals to create programs intended to link livestock producers to their end products.

Cattle and carcass performance, and life cycle assessment of production systems utilizing additive combinations of growth promotant technologies.

The objective of this study was to determine the impact of beef production systems utilizing additive combinations of growth promotant technologies on animal and carcass performance and environmental outcomes. Crossbred steer calves (n =120) were stratified by birth date, birth weight, and dam age and assigned randomly to one of four treatments: 1) no technology (NT; control), 2) antibiotic treated (ANT; NT plus therapeutic antibiotics and monensin and tylosin), 3) implant treated (IMP; ANT plus a series of 3 implants, and 4) beta-agonist treated (BA; IMP plus ractopamine-HCl for the last 30 d prior to harvest). Weaned steers were fed in confinement (dry lot) and finished in an individual feeding system to collect performance data. At harvest, standard carcass measures were collected and the United States Department of Agriculture (USDA) Yield Grade and Quality Grade were determined. Information from the cow-calf, growing, and finishing phases were used to simulate production systems using the USDA Integrated Farm System Model, which included a partial life cycle assessment of cattle production for greenhouse gas (GHG) emissions, fossil energy use, water use, and reactive N loss. Body weight in suckling, growing, and finishing phases as well as hot carcass weight was greater (P < 0.05) for steers that received implants (IMP and BA) than non-implanted steers (NT and ANT). The average daily gain was greater (P < 0.05) for steers that received implants (IMP and BA) than non-implanted steers during the suckling and finishing phases, but no difference (P = 0.232) was detected during the growing phase. Dry matter intake and gain:feed were greater (P < 0.05) for steers that received implants than non-implanted steers during the finishing phase. Steers that received implants responded (P < 0.05) with a larger loin muscle area, less kidney pelvic and heart fat, advanced carcass maturity, reduced marbling scores, and a greater percentage of carcasses in the lower third of the USDA Choice grade. This was offset by a lower percentage of USDA Prime grading carcasses compared with steers receiving no implants. Treatments did not influence (P > 0.05) USDA Yield grade. The life cycle assessment revealed that IMP and BA treatments reduced GHG emissions, energy use, water use, and reactive nitrogen loss compared to NT and ANT. These data indicate that growth promoting technologies increase carcass yield while concomitantly reducing carcass quality and environmental impacts.

Effects of rumen-protected long-chain fatty acid supplementation during the finishing phase of beef steers on live performance, carcass characteristics, beef quality, and serum fatty acid profile.

The effect of a rumen-protected long-chain fatty acid (LCFA) supplement on live performance, meat quality, blood serum fatty acid profile, and predicted carcass composition was evaluated in this study. Angus steer calves (n = 99) were fed a low energy diet for 77 d prior to finishing. Prior to study initiation, the steers were separated into 12 pens with eight or nine steers per pen. Steers were transitioned from the low energy forage-based diet to a high concentrate diet containing high moisture ear corn, corn silage, dry rolled corn, soybean meal, and a liquid supplement containing monensin across 21 d. Megalac-R (RPFA) was fed to six pens at 2% of the diet dry matter. Control pens (CON; n = 6) received an additional 2% of diet dry matter as dry rolled corn and soybean meal. The final finishing diet net energy for gain (NEg) was 1.20 and 1.19 mega calories·kg-1 of dry matter (DM) for RPFA and CON treatments, respectively. Steers were weighed every 28 d. Growth performance data including average daily gain (ADG), gain to feed ratio (G:F), and DM intake (DMI) were calculated as both monthly and overall data. After a 147-d finishing phase, steers were transported to a commercial abattoir for slaughter. After a 28-h chilling period, carcass data were obtained by trained personnel. Final live weights were greater (P = 0.01) for RPFA than CON cattle. Overall ADG and overall G:F was increased (P = 0.02; P = 0.01, respectively) for RPFA cattle. Ribeye area, backfat thickness, kidney pelvic heart fat, marbling score, and yield grade did not differ (P > 0.05) between treatments. Predicted percent carcass fat was increased for RPFA cattle (P = 0.05). Conversely, predicted percent carcass protein (P = 0.07) and bone (P = 0.06) tended to be greater for CON cattle. Long-chain fatty acid supplementation during the finishing phase did not increase marbling scores of the steers in this study but did increase final live weight, HCW, and predicted total body fat. These results suggest that RPFA supplementation has the potential to increase adipose tissue development. However, it is likely that animal age during supplementation and duration of supplementation impact the effect RPFAs have on carcass characteristics.

AMP-activated protein kinase signalling pathways are down regulated and skeletal muscle development impaired in fetuses of obese, over-nourished sheep.

Maternal obesity and over-nutrition give rise to both obstetric problems and neonatal morbidity. The objective of this study was to evaluate effects of maternal obesity and over-nutrition on signalling of the AMP-activated protein kinase (AMPK) pathway in fetal skeletal muscle in an obese pregnant sheep model. Non-pregnant ewes were assigned to a control group (Con, fed 100% of NRC nutrient recommendations, n = 7) or obesogenic group (OB, fed 150% of National Research Council (NRC) recommendations, n = 7) diet from 60 days before to 75 days after conception (term 150 days) when fetal semitendinosus skeletal muscle (St) was sampled. OB mothers developed severe obesity accompanied by higher maternal and fetal plasma glucose and insulin levels. In fetal St, activity of phosphoinositide-3 kinase (PI3K) associated with insulin receptor substrate-1 (IRS-1) was attenuated (P < 0.05), in agreement with the increased phophorylation of IRS-1 at serine 1011. Phosphorylation of AMP-activated protein kinase (AMPK) at Thr 172, acetyl-CoA carboxylase at Ser 79, tuberous sclerosis 2 at Thr 1462 and eukaryotic translation initiation factor 4E-binding protein 1 at Thr 37/46 were reduced in OB compared to Con fetal St. No difference in energy status (AMP/ATP ratio) was observed. The expression of protein phosphatase 2C was increased in OB compared to Con fetal St. Plasma tumour necrosis factor alpha (TNFalpha) was increased in OB fetuses indicating an increased inflammatory state. Expression of peroxisome proliferator-activated receptor gamma (PPARgamma) was higher in OB St, indicating enhanced adipogenesis. The glutathione: glutathione disulphide ratio was also lower, showing increased oxidative stress in OB fetal St. In summary, we have demonstrated decreased signalling of the AMPK system in skeletal muscle of fetuses of OB mothers, which may play a role in altered muscle development and development of insulin resistance in the offspring.

Relationship between kinase phosphorylation, muscle fiber typing, and glycogen accumulation in longissimus muscle of beef cattle with high and low intramuscular fat.

The objective of this study was to examine the association of adenosine monophosphate (AMP)-activated protein kinase (AMPK) with glycogen content in bovine muscle and their links with intramuscular fat (IMF) and muscle fiber type composition. Five steers with high intramuscular fat (High IMF, IMF content is 5.71 +/- 0.36%) and five steers with low intramuscular fat (Low IMF, IMF content is 2.09 +/- 0.19%) in the longissimus thoracis muscle (LM) were selected for immunoblotting, glycogen, and myofiber type composition analyses. The glycogen content was higher in Low IMF muscle than in High IMF muscle (1.07 +/- 0.07 versus 0.85 +/- 0.08 g/100 g muscle, P < 0.05). Phosphorylation of the AMPK alpha subunit at Thr 172, which is correlated with its activity, was lower (P < 0.05) in High IMF compared to Low IMF. In agreement with the lower AMPK phosphorylation in High IMF muscle, the phosphorylation of acetyl-CoA carboxylase (ACC) was also lower (P < 0.05) in High IMF muscle than in Low IMF muscle. Glycogen synthase kinase 3 (GSK3) down-regulates glycogen synthesis through phosphorylation of glycogen synthase. The phosphorylation of GSK3 in High IMF was lower (P < 0.05) than that in Low IMF, which should down-regulate glycogen synthase activity and reduce the glycogen content in High IMF beef. Type IIB myosin isoform was absent in beef muscle. No noticeable difference in myosin isoform composition was observed between Low and High IMF muscle. In summary, High IMF cattle had lower LM glycogen levels than low IMF cattle, and AMPK activity was less in High IMF than in Low IMF cattle. The difference in glycogen content between Low and High IMF muscle was not correlated with muscle fiber composition. This data shows that LM lipid and glycogen metabolisms are affected by AMPK activity. Thus, AMPK may be a molecular target to alter IMF and glycogen levels in beef muscle.

Early post-mortem AMP-activated protein kinase (AMPK) activation leads to phosphofructokinase-2 and -1 (PFK-2 and PFK-1) phosphorylation and the development of pale, soft, and exudative (PSE) conditions in porcine longissimus muscle.

Pale, soft, and exudative (PSE) meat has been recognized for decades. Fast glycolysis during early post-mortem stage while the muscle temperature is still high is the cause of PSE meat. To elucidate the molecular mechanism underlying this fast glycolysis in muscle to become PSE meat, post-mortem ATP metabolism, fructose-2,6-diphosphate content, and the activities of AMPK, glycogen phosphorylase, and pyruvate kinase were examined in post-mortem muscle. Earlier and faster post-mortem AMPK activation was responsible for the significantly lower pH and higher lactic acid accumulation (p<0.05) seen in PSE muscle, which resulted in the occurrence of PSE meat. In muscle that became PSE meat, AMPK was activated at 0 h post-mortem and reached maximal activation at 0.5 h post-mortem, whereas AMPK reached maximal activation at 1 h post-mortem in the normal pork loin. Higher fructose-2,6-diphosphate content (p<0.05) was detected in PSE muscle compared to normal muscle at early post-mortem stage. However, no difference in the activities of glycogen phosphorylase and pyruvate kinase, rate-controlling enzymes in glycogenolysis and glycolysis, respectively, was detected between PSE and normal pork loins. Because fructose-2,6-diphosphate is a product of phosphofructokinase-2 (PFK-2), these data suggest that AMPK regulates post-mortem glycolysis through its phosphorylation and activation of PFK-2, which then up-regulates the activity of phosphofructokinase-1 (PFK-1), a key rate-controlling enzyme in glycolysis. Early AMPK activation in PSE muscle is associated with early consumption of ATP, because higher AMP and IMP contents and lower ATP content were detected in PSE meat compared to normal meat. Other mechanisms causing early AMPK activation in PSE meat may exist, which warrants further investigation.