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.

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.

Pasture-finishing of bison improves animal metabolic health and potential health-promoting compounds in meat

BACKGROUND

With rising concerns regarding the effects of red meat on human and environmental health, a growing number of livestock producers are exploring ways to improve production systems. A promising avenue includes agro-ecological practices such as rotational grazing of locally adapted ruminants. Additionally, growing consumer interest in pasture-finished meat (i.e., grass-fed) has raised questions about its nutritional composition. Thus, the goal of this study was to determine the impact of two common finishing systems in North American bison-pasture-finished or pen-finished on concentrates for 146 d-on metabolomic, lipidomic, and fatty acid profiles of striploins (M. longissimus lumborum).

RESULTS

Six hundred and seventy-one (671) out of 1570 profiled compounds (43%) differed between pasture- and pen-finished conditions (n = 20 animals per group) (all, P < 0.05). Relative to pasture-finished animals, the muscle of pen-finished animals displayed elevated glucose metabolites (~ 1.6-fold), triglycerides (~ 2-fold), markers of oxidative stress (~ 1.5-fold), and proteolysis (~ 1.2-fold). In contrast, pasture-finished animals displayed improved mitochondrial (~ 1.3-fold higher levels of various Krebs cycle metabolites) and carnitine metabolism (~ 3-fold higher levels of long-chain acyl carnitines) (all P < 0.05). Pasture-finishing also concentrated higher levels of phenolics (~ 2.3-fold), alpha-tocopherol (~ 5.8-fold), carotene (~ 2.0-fold), and very long-chain fatty acids (~ 1.3-fold) in their meat, while having lower levels of a common advanced lipoxidation (4-hydroxy-nonenal-glutathione; ~ 2-fold) and glycation end-product (N6-carboxymethyllysine; ~ 1.7-fold) (all P < 0.05). In contrast, vitamins B₅, B₆, and C, gamma/beta-tocopherol, and three phenolics commonly found in alfalfa were ~ 2.5-fold higher in pen-finished animals (all P < 0.05); suggesting some concentrate feeding, or grazing plants rich in those compounds, may be beneficial.

CONCLUSIONS

Pasture-finishing (i.e., grass-fed) broadly improves bison metabolic health and accumulates additional potential health-promoting compounds in their meat compared to concentrate finishing in confinement (i.e., pen-finished). Our data, however, does not indicate that meat from pen-finished bison is therefore unhealthy. The studied bison meat-irrespective of finishing practice-contained favorable omega 6:3 ratios (< 3.2), and amino acid and vitamin profiles. Our study represents one of the deepest meat profiling studies to date (> 1500 unique compounds), having revealed previously unrecognized differences in animal metabolic health and nutritional composition because of finishing mode. Whether observed nutritional differences have an appreciable effect on human health remains to be determined.

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.

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.

Product yield and color of fresh beef transported at different refrigerated temperatures

The objective of this study was to determine the impact of environmental temperature during striploin and sirloin transport on moisture loss, color, and tenderness. Cases of striploins (n = 24) and sirloins (n = 24) were alternately placed on two pallets. Each pallet was placed on a refrigerated truck pre-chilled to -2.2°C (-2.2FT) or 3.3°C (3.3FT) and product was transported for 12 h prior to arriving at the South Dakota State University Meat Laboratory. One subprimal was subset from each case for further analysis. Subprimal purge loss was measured prior to fabrication into eight 2.54cm steaks. Steaks were overwrapped and packaged in modified atmosphere packaging prior to a second transport. Four steaks from each subprimal were placed on one of two pallets. Each pallet was placed on a pre-chilled refrigerated truck set at -2.2°C or 3.3°C. The steaks were transported for 12 h prior to returning to the Meat Laboratory. Steaks were utilized for the evaluation of color, cook loss, purge loss, and Warner-Bratzler shear force (WBSF). Subprimal purge loss was increased for 3.3FT sirloins compared to -2.2FT (P = 0.0362). L* values for -2.2FT strip steaks were increased (P &lt; 0.0001) and purge loss decreased (P = 0.0188) compared to 3.3FT steaks. L* values and fresh steak purge loss for 3.3FT sirloins were increased (P = 0.0356 and P = 0.0460 respectively) compared to -2.2FT steaks. These data indicate varied responses to temperature differences based on subprimal. Thus, a universal recommendation for all meat products could not be made and further investigation into the impacts of transportation temperatures on various meat products is vital to optimization of the meat supply chain.

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.

Maternal Nutrition and Meat Quality of Progeny

The concept of fetal programming is based on the idea that nutritional status and environmental conditions encountered by the dam during pregnancy can have lifetime impacts on her offspring. These changes in the gestational environment have been shown to influence fetal development and subsequent growth performance, carcass composition, and meat quality characteristics. Beef fetuses can be particularly prone to experiencing variations in the maternal environment during development owing to a relatively long duration of pregnancy potentially exposing the dam to environmental temperature stress and/or seasonal conditions that can compromise feed quality or quantity. If feed is limited or forage conditions are poor, a maternal deficiency in protein and/or energy can occur as well as fluctuations in body condition of the dam. As a result, the fetus may receive inadequate levels of nutrients, potentially altering fetal development. There are critical windows of development during each stage of gestation in which various tissues, organs, and metabolic systems may be impacted. Skeletal muscle and adipose tissue are particularly vulnerable to alterations in the gestational environment because of their low priority for nutrients relative to vital organs and systems during development. The timing and severity of the environmental event or stressor as well as the ability of the dam to buffer negative effects to the fetus will dictate the developmental response. Much of the current research is focused on the influence of specific nutrients and timing of nutritional treatments on offspring carcass composition and meat quality, with the goal of informing strategies that will ultimately allow for the use of maternal nutritional management as a tool to optimize performance and meat quality of offspring.

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.

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.

South Dakota State University Beef 2020 increases participant knowledge of the beef industry1

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 &lt; 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 &lt; 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.

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 (NE_g) 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.

Influence of maternal protein restriction in primiparous heifers during mid- and/or late-gestation on meat quality and fatty acid profile of progeny

The objective of this study was to evaluate the influence of metabolizable protein (MP) restriction in mid- and/or late-gestation on meat quality characteristics of progeny. Heifers were assigned to 2 levels of dietary protein (control [CON], 102% of MP requirements; or restricted [RES], 80% of MP requirements) at 2 stages of gestation (mid-gestation [MID] and late-gestation [LATE]) in a Balaam's Design crossover treatment structure resulting in 4 treatment combinations (CON-CON, CON-RES, RES-CON, RES-RES). A carryover effect of MID MP treatment on LATE CON indicated CON-CON steaks were more tender (P < .001) than RES CON. Mid-gestation restriction resulted in progeny with increased (P < .05) carcass water, soft tissue moisture, and decreased soft tissue fat percentage compared with progeny from dams receiving MID CON. Reduced maternal MP also differentially influenced the fatty acid profiles of progeny. Results suggest it is possible for progeny to overcome a moderate gestational MP restriction with minimal impacts on carcass composition or meat characteristics.

Effect of nursing-calf implant timing on growth performance and carcass characteristics

The objective of this study was to compare pre- and postweaning growth performance, carcass characteristics, and meat quality attributes of calves that did not receive an implant or were implanted early or late in the nursing period. Crossbred steer calves ( = 135) were stratified by birth date and birth weight and randomly assigned to the following implant treatments: control (CON; no preweaning implant), 58 d (EARLY; 36 mg zeranol, administered at an average of 58 ± 13 d of age), and 121 d (LATE; 36 mg zeranol, administered at an average 121 ± 13 d of age). After weaning, steers were blocked by initial feed yard BW to 15 pens (5 pens/treatment and 9 steers/pen). All steers were implanted on d 21 after arrival at the feed yard and again on d 108 of finishing. Steer BW and ultrasound assessment of rib eye area (uREA), rib fat thickness (uRFT), and percent intramuscular fat (uIMF) were collected when implants were administered, at weaning, and on harvest day. Carcass measurements included HCW, rib eye area (REA), 12th-rib fat thickness (FT), and marbling score. Objective color (L*, a*, and b*) was recorded, and a 3.8-cm strip loin section was removed from both sides of each carcass and portioned into 2.54-cm steaks that were aged for 3 or 14 d for analysis of cook loss and Warner-Bratzler shear force (WBSF). The remaining portion of each sample was used for analysis of moisture and crude fat. Steer BW, ADG, and G:F did not differ among treatments ( > 0.05). Steers implanted in the EARLY treatment had a greater ( < 0.05) cumulative DMI than CON but were not different from steers implanted in the LATE treatment. Ultrasound REA and uRFT (averaged across all collection days) did not differ ( > 0.05); however, steers on the CON treatment had a greater ( ≤ 0.05) percent uIMF than EARLY implanted steers, whereas steers receiving the LATE implant were intermediate and not different from the other treatments. Hot carcass weight, REA, FT, USDA yield grade, marbling score, and objective color did not differ ( > 0.05) among treatments. The proportion of steers in each USDA yield and quality grade was similar ( > 0.05) among treatments, and no differences were detected for total carcass value or price per 45.4 kg (hundredweight; > 0.05). Treatment did not influence ( > 0.05) percent cook loss, crude fat, moisture, or WBSF. In conclusion, administering a nursing implant, regardless of timing, did not influence live performance, carcass characteristics, or meat quality of steers fed in this study.

The influence of maternal energy status during midgestation on beef offspring carcass characteristics and meat quality

Research has suggested that maternal undernutrition may cause the development of a thrifty phenotype in the offspring, potentially resulting in greater adiposity and reduced muscle mass. These alterations in adipose and muscle development could have lasting impacts on offspring growth, carcass characteristics, and meat quality. However, limited research exists evaluating the impact of maternal energy status on these economically important traits of the offspring. Therefore, the objective of this study was to determine the influence of maternal energy status during midgestation on offspring carcass characteristics and meat quality. To alter maternal energy status, cows either grazed dormant, winter range (positive energy status [PES]) or were fed in a drylot at 80% of the energy requirements for BW maintenance (negative energy status [NES]) during a mean period of 102 ± 10.9 to 193 ± 10.9 d of gestation. Changes in BCS, BW, LM area (LMA), and 12th rib backfat were measured throughout midgestation. At the end of midgestation, cows in the NES group had a reduction (P ≤ 0.05) in BCS, BW, LMA, and 12th rib backfat when compared with PES dams. Cows and calves were managed similarly after midgestation through weaning and calves were managed and fed a common diet through the receiving, backgrounding, and finishing phases in the feedlot. Calves were harvested after 208 d in the feedlot, carcass characteristics were recorded, and strip loins were recovered for analysis of objective color and Warner-Bratzler shear force (WBSF). Maternal energy status had no influence on offspring HCW, dressing percent, LMA, percent KPH, marbling score, percent intramuscular fat, objective color, or WBSF (P > 0.10). Progeny of NES cows tended to have improvements in 12th rib backfat and USDA yield grade (P < 0.10). Greater ratio of marbling score to 12th rib fat thickness and ratio of percent intramuscular fat to 12th rib fat thickness (P < 0.05) were discovered in progeny from cows experiencing a NES during midgestation. These results suggest that maternal energy status during midgestation may impact fat deposition in intramuscular and subcutaneous fat depots without impacting muscle mass.

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-β, 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.

Oral flecainide pharmacokinetics in patients with impaired renal function

The pharmacokinetics of flecainide acetate were studied in 20 patients with varying degrees of renal impairment following a single oral dose. The patients were divided into two groups, on the basis of renal creatinine clearance (CLCR), for statistical and kinetic analysis. Patients with a CLCR between 4 and 41 mL/min/m2 were designated group 1 and those below 4 mL/min/m2 or unmeasurable because of lack of urine output were designated group 2. In both groups peak plasma flecainide concentrations, time to peak concentrations, and apparent volume of distribution (Vd) were similar to those reported in healthy subjects with normal renal function. The mean flecainide plasma elimination half-lives from both groups 1 and 2 were longer than those previously reported by several investigators in normal subjects. Nine patients in group 1 and seven patients in group 2 had half-lives within the range reported in healthy subjects. Therefore, CLCR alone is not a good predictor of plasma elimination half-life following a single oral dose of flecainide. Although renal clearance of flecainide is significantly reduced in end-stage renal disease (ESRD), total plasma clearance of flecainide (CLflec) was not reduced to the same degree, although there was a significant, modest correlation with CLCR. Less than 1% of the administered oral dose of flecainide was removed during hemodialysis. The relationship between dosage and plasma elimination half-life in patients with ESRD needs further study to evaluate possible dose-dependent kinetics.

Neurologic outcome and blood glucose levels during out-of-hospital cardiopulmonary resuscitation

We examined the interrelations of outcome, time elapsed during cardiopulmonary resuscitation (CPR), and blood glucose levels drawn from 83 patients with out-of-hospital cardiac arrest. Levels rose significantly during CPR. Although slope and intercept of regression lines differed for those dying in the field and those admitted, regression lines were similar for those who awoke and never awoke after admission. These results suggest that the previously reported association between poor neurologic recovery and high blood glucose level on admission after cardiac arrest is best explained by prolonged CPR, leading to both higher rise of blood glucose and worse neurologic outcome.

Ketoconazole kinetics in chronic peritoneal dialysis

The kinetics of oral ketoconazole in serum and peritoneal fluid were studied in six patients with renal failure receiving peritoneal dialysis. A dose of 400 mg ketoconazole resulted in a maximum blood concentration of 2.3 +/- 1.7 microgram/ml (mean +/- SD), which occurred 3.3 +/- 1.6 hours after dosing. The serum t1/2 was 2.4 +/- 0.8 hours. Peritoneal clearance values were less than 1 ml/min, and peritoneal penetration reached 3.4% of the serum concentration by 5 hours. Protein binding studies were also performed. Compared with healthy controls, patients receiving peritoneal dialysis have significantly less ketoconazole serum protein binding. Fifty to eighty percent of the drug is protein bound in the peritoneal fluid, and the unbound concentration is in the same range as that in the serum of healthy individuals with "therapeutic" total ketoconazole levels of 1 to 2 micrograms/ml.

Synergism at clinically attainable concentrations of aminoglycoside and beta-lactam antibiotics

We evaluated the in vitro synergistic activity at clinically attainable concentrations of combinations of aminoglycoside and beta-lactam antibiotics against 30 gentamicin-resistant clinical isolates of gram-negative bacilli. All 56 pairs of 4 aminoglycosides and 14 beta-lactams were evaluated. Combinations with amikacin demonstrated inhibitory synergistic activity in 29% of the assays, as compared with 22% for netilmicin (P = 0.018), 17% for gentamicin (P less than 0.001), and 13% for tobramycin (P less than 0.001). Among the beta-lactams, combinations with cefoperazone, ceftriaxone, or cefpiramide (SM-1652) demonstrated inhibitory synergistic activity most often (39, 38, and 35% of the assays, respectively) and with ceforanide, cefsulodin, and imipenem least often (less than or equal to 8% each). The most active combination was amikacin and ceftriaxone, with which 67% of the assays demonstrated inhibitory synergism. Isolates with high-level resistance to either antibiotic in a combination were unlikely to be inhibited synergistically by the combination. Further, combinations generally demonstrated little synergistic activity against isolates highly susceptible to beta-lactams.

Cefonicid kinetics in subjects with normal and impaired renal function

Cefonicid is a cephalosporin with a longer t1/2 than currently available cephalosporins. Cefonicid kinetics after an intravenous dose of 7.5 mg/kg were followed in four groups of subjects: group 1, four subjects with normal creatinine clearance (Clcr greater than 80 ml/min); group II, seven subjects with mild renal insufficiency (Clcr 50 to 80 ml/min); group III, five subjects with moderate to severe renal impairment (Clcr 8 to 49 ml/min); and group IV, five subjects with end-stage renal disease who were receiving maintenance hemodialysis (Clcr less than 8 ml/ml). Cefonicid volume of distribution ranged from 6.9% to 17.6% body weight but was not related to Clcr. Elimination t1/2 was 4.6 +/- 0.7 hr in group 1,6.0 +/- 2.7 hr in group II, 25.6 +/- 14.0 hr in group III, and 65.3 +/- 43.6 hr in group IV. There was a strong correlation between plasma cefonicid clearance and Clcr. Nonrenal clearance did not change with decreasing Clcr. Hemodialysis clearance calculated from plasma concentrations and recovery in dialysate was 2.5 +/- 0.9 ml/min. These kinetic parameters were used to formulate dosage regimens for patients with renal impairment.

Pharmacokinetics of ceftizoxime in patients undergoing continuous ambulatory peritoneal dialysis

The pharmacokinetics of ceftizoxime were studied in 12 patients on continuous ambulatory peritoneal dialysis. After a 3-g intravenous dose, the steady-state volume of distribution was 0.23 +/- 0.05 liter kg-1, with an elimination half-life of 9.7 +/- 5.1 h. The peritoneal clearance of ceftizoxime (2.8 +/- 0.7 ml min-1) contributed modestly to the overall serum clearance of the drug (17.1 +/- 7.4 ml min-1) and was greater than the renal clearance (0.8 +/- 0.8 ml min-1). The peritoneal concentration rose to 91 +/- 29 micrograms ml-1 at 6 h, which was 0.61 +/- 0.17 of the serum concentration. A 3-g intravenous dose of ceftizoxime given every 48 h would result in adequate activity against most susceptible organisms, but more frequent dosing may be necessary for less susceptible organisms.

Gentamicin and tobramycin Kinetics

Eighty-two hospitalized adult patients were randomized to treatment with gentamicin or tobramycin. Serum levels were compared to computer-derived mathematically predicted levels to evaluate predictability of gentamicin and tobramycin serum levels. When comparable dosages were used mean peak gentamicin levels (4.87 micrograms/ml) did not differ from those after tobramycin (4.31 micrograms/ml). Seventy-three percent of patients had peak levels after gentamicin greater than 4.0 micrograms/ml compared to 46% after tobramycin. Factors purported to influence predictability of aminoglycoside serum levels were examined. In 46 of 74 patients whose actual body weight was 10 to 35 kg less than estimated ideal body weight levels after both drugs were lower than predicted. Serum levels were also lower than predicted in 7 of 11 patients with ascites, 6 of 7 patients receiving carbenicillin therapy, and 17 of 29 patients who had pneumonia. Neither hematocrit nor temperature appeared to influence predictability of serum levels. A comparison of methods used to obtain computer-derived predicted levels showed that ideal body weight provided the most accurate prediction. Differences between predicted and measured levels were established when calculations were based on actual body weight (P = 0.009) or on surface area (P = 0.003 for peak and 0.023 for trough levels).

Effect of hemodialysis on the pharmacokinetics of theophylline in chronic renal failure

We studied theophylline elimination in 8 patients with chronic renal failure to determine the effect of hemodialysis on the pharmacokinetics of theophylline. Each subject was studied twice, once on a nondialysis day and again during dialysis. Total body theophylline clearance on the nondialysis day was similar to that reported for patients with normal renal function (57.4 +/- 27.2 ml/kg/h). Hemodialysis accelerated theophylline elimination and shortened serum theophylline half-life in all patients (nondialysis t 1/2 = 7.3 h +/- 2.3 vs. dialysis t 1/2 = 2.7 +/- 0.9 h, p less than 0.01). Dialysis clearance averaged 59.7 +/- 16.4 ml/kg/h with a fraction of drug removed of 0.4 liters in 4 h. Guidelines for theophylline management during hemodialysis are suggested.

Sotalol kinetics in renal insufficiency

Kinetics of sotalol, a beta adrenoceptor blocker, was studied in 20 patients with varying renal function. In subjects with creatinine clearance (Clcr) greater than or equal to 39 ml/min/m2, sotalol plasma clearance (x +/- SD) was 71 +/- 31 ml/min/m2, elimination half-life (t 1/2) was 8.1 +/- 3.4 hr, and renal clearance was 46 +/- 26 ml/min/m2. In patients with moderate renal impairment (Clcr = 8 to 38 ml/min/m2) elimination t 1/2 rose to 24.2 +/- 7.5 hr, and plasma clearance fell to 24 +/- 7 ml/min/m2. In patients receiving dialysis, elimination t 1/2 rose to 33.9 +/- 27.1 hr. Elimination t 1/2 during hemodialysis was 5.8 +/- 2.1 hr and was associated with a 56.7 +/- 21% reduction in plasma levels.

Randomized prospective evaluation of cimetidine and antacid control of gastric pH in the critically ill

One hundred forty-four critically ill patients admitted to an intensive care setting were randomly assigned to cimetidine or antacid treatament groups. Gastric pH was monitored hourly. One hundred twenty-three (85%) patients demonstrated a fall in pH to less than 4 and were considered to require prophylaxis. Prophylaxis was considered adequate if the measured pH could then be maintained at greater than or equal to 4. Fifty-eight patients received antacids alone, the average requirement being 41 cc/hour. Sixty-five patients received cimetidine. Seventeen (26%) of the cimetidine prophylaxis patients failed to raise their pH and were than placed on hourly administration of antacid with successful elevations of pH to greater than or equal to 4 in all cases on an average supplementary dose of 53 cc/hour. Risk factors, including sepsis, hypotension, head injury, respiratory failure, degree of trauma, and age, were not statistically different in the two treated groups. Using these same criteria, responders to cimetidine could not be differentiated from nonresponders. All patients were protected from significant stress bleeding while on this study. Significant complications of either treatment were minimal. Antacids offered consistent protection against gastric acidity and were 100% effective. A routine schedule of 300 mg every six hours of cimetidine was effective in only 47% of patients, and the maximum dose of cimetidine was effective in only 74% of patients. Hourly measurement of intragastric pH is required for monitoring the response to prophylaxis of stress bleeding in severely ill patients.

Pharmacological and in vitro evaluation of cyclacillin: assessment as potential single-dose therapy for treatment of Neisseria gonorrhoeae infection

The pharmacokinetic properties of cyclacillin administered as a 3.0-g oral dose, with and without progenecid, have been studied and correlated with in vitro activity of the drug against 109 isolates of Neisseria gonorrhoeae. By 8 h after dosage, levels of cyclacillin in serum declined below the minimal inhibitory concentration and the inferior antibacterial activity of cyclacillin (compared with that of amipicillin) suggest that cyclacillin is not a promising alternative to ampicillin for single-dose treatment of gonorrhea.

Cefadroxil kinetics in patients with renal insufficiency

Kinetic parameters and bioavailability of cefadroxil were studied in 20 subjects with differing renal function as measured by endogenous creatinine clearance (CCr). Two subjects were on hemodialysis. After an overnight fast, each subject ingested two 500-mg capsules of cefadroxil. The peak serum concentration was variable (12 to 57 mg/L) and correlated inversely with the CCr. All but one patient had maximum absorption within 4 hr of ingestion and in most patients the peak was reached within the 2-hr sample. Urinary recovery within 48 hr was 45% to 106% when CCr greater than 8 ml/min. Even in patients with the most severe renal failure (CCr less than 10 ml/min), urine concentrations of cefadroxil were adequate to treat susceptible bacteria. The rate of oral absorption ka, was not affected by the state of renal function and was 0.76 +/- 0.50 hr-1. The apparent distribution volume (V d ext) was 0.28 +/- 0.09 L/kg. The plasma elimination rate was dependent on CCr wih a small fraction of drug being removed by nonrenal routes. Except in advanced renal failure, tubular secretion was present since renal clearance of cefadroxil exceeded CCr. The data suggest that little drug accumulation will occur with the usual 8- to 12-hr dosing schedule except when the CCr is less than 25 ml/min.

Effects of probenecid on furosemide kinetics and natriuresis in man

Furosemide kinetics were studied in 4 normal subjects after single intravenous injections (1 mg/kg). One experiment was done after pretreatment with probenecid. The apparent volume of furosemide distribution was unchanged after probenecid (10.9 L). The mean plasma clearance fell from 155 to 85 ml/min and the mean plasma t1/2 rose from 36 to 61 min. Renal clearance of furosemide fell below 50% of control after probenecid, but the kidney remained the main route of its excretion (75% of the dose appeared in the urine). In another experiment in 4 subjects an infusion of furosemide was sustained following a loading dose to maintain a constant plasma level. After a control period, probenecid was given orally. This resulted in a decrease in renal excretion of furosemide with a simultaneous rise in its plasma concentration. Despite the rising plasma furosemide concentration, however, there was a diminution in both urine flow and the excreted fraction of filtered sodium, which suggested some reduction of diuretic action. In doses commonly used, probenecid reduces renal elimination of furosemide in man with only a mild impairment of its diuretic activity. This suggests that furosemide is eliminated predominantly by way of proximal tubular secretion and that tubular rather than plasma concentration is the main determinant of its diuretic effect.

Pharmacokinetics of amikacin in patients with normal or impaired renal function: radioenzymatic acetylation assay

The acetylating radioenzymatic assay was used for determination of levels of amikacin in serum and urine. Because of an inhibitor present in various amounts in urine, assay of amikacin in urine by this method requires added internal standards and thus is less precise than the assay in serum. Determination of the rate of plasma clearance, half-life, and volume of distribution of amikacin in 10 patients with normal renal function, four patients undergoing dialysis, and five patients with end-stage renal diseases have shown a relation of half-life (t1/2 in hr) to rate of clearance of serum creatinine (Cer) of t1/2 = 3 X Cer, the same relation as found for kanamycin and gentamicin. The apparent steady-state volume of distribution of amikacin in patients with diminished renal function is slightly, but not significantly, larger than that in normal patients; the values were 0.28 +/- 0.10 and 0.21 +/- 0.10, respectively. In normal patients, 87% of the drug is excreted by the kidney.

Assay of flucytosine and furosemide by high-pressure liquid chromatography

A high-pressure liquid chromatographic method for the analysis of flucytosine and furosemide concentrations in biological fluid is described. The separations were carried out on a pellicular cation-exchange resin eluted with an ammonium phosphate buffer. Detection of elution peaks was by UV absorption at 280 nm and fluorescence monitoring. Advantages of the method are specificity, minimal preanalysis sample workup, and small sample size.

Furosemide Concentrations in Serum and Urine, and Its Binding by Serum Proteins as Measured Fluorometrically

We describe a modification of the fluorometric method of Häussler and Hajdú [Arzneim. Forsch. 14, 704 and 709 (1964)] for assay of furosemide in either serum or urine. A 1-ml sample, acidified to pH 2, is extracted with 5 ml of diethyl ether; 4 ml of the ether is back-extracted into 1 ml of phosphate buffer (pH 7.0, 0.1 mol/liter), and finally acidified with 1 ml of dilute HCl (0.6 mol/liter). A procedure for estimating blanks in urine was derived to correct for dilution caused by diuresis. Internal standards are used, and the "effective" extraction ratio is used to correct for the effects of quenching and extraction differences. In equilibrium, 93% of the drug is bound to serum proteins; 65% is tightly bound. Erythrocytes contain less than 5% of the drug. Quantum yield of fluorescence at pH 1 is 0.0496 for furosemide and is 0.0163 for 4-chloro-5-sulfamoylanthranilic acid. Furosemide fluorescence diminishes with increasing pH, while that of 4-chloro-5-sulfamoylanthranilic acid (a degradation product) increases.