Whole body insulin responsiveness is higher in beef steers selected for increased muscling

The effects of chromium propionate supplementation to yearling steers in a commercial feedyard on growth performance, carcass characteristics, and health

British crossbred steers (n = 3,072; initial body weight [BW] = 358 ± 37 kg) were used to evaluate the effects of chromium propionate supplementation to yearling steers in a commercial feedyard on growth performance, carcass characteristics, and health. Steers were blocked by initial BW; pens were assigned randomly to one of two dietary treatments within block. Treatments, replicated in 15 pens per treatment with 75 to 135 heads per pen, included 1) control, 0 mg supplemental Cr/kg dietary dry matter (DM) (CTL); 2) 0.50 mg supplemental Cr/kg diet DM (chromium propionate; KemTRACE Chromium 0.4%, Kemin Industries, Des Moines, IA) (chromium propionate, CR). Final BW (638 vs. 641 kg), average daily gain (1.81 vs. 1.82 kg), DM intake (11.02 vs. 11.02 kg), and gain efficiency (0.164 vs. 0.165) did not differ between CTL and CR, respectively (P ≥ 0.75). No differences among treatments for hot carcass weight (407 vs. 408 kg, CTL and CR, respectively), dressing percentage, longissimus muscle area, or yield grade were observed (P ≥ 0.15). Twelfth-rib fat thickness tended (P = 0.10) to be greater for CR vs. CTL (1.55 vs. 1.29 cm, respectively). A trend (P = 0.10) for marbling score to be higher for CR vs. CTL was detected (452 vs. 440, respectively). Distribution of quality grade was similar between CR and CTL; 1.52% of carcasses graded prime (P = 0.68), and 87.2% of carcasses graded choice (P = 0.68). Respiratory morbidity was low (1.93%) and not different among treatments (P = 0.20); likewise, there was no difference in respiratory treatment rates between treatments (P ≥ 0.18). Supplementing Cr to high-performing yearling steers did not alter growth performance, carcass characteristics, or health outcomes.

Are muscle fiber types different between normal and dark-cutting beef?

Muscle fiber (MF) characteristics of Longissimus thoracis (LT) muscles from heifer (n = 11) and steer (n = 12) carcasses graded Canada AA (AA, normal, n = 4/sex) or dark-cutting (Canada B4) were examined and related to beef quality. Atypical (AB4, pH < 5.9, n = 4/sex) and typical (TB4, pH > 5.9, n = 3 and 4 for heifers and steers, respectively) dark-cutting carcasses were represented. Muscle fiber type proportions did not differ between AA, AB4 and TB4 muscles, although type I and IIB muscle fiber diameters were greater in TB4 than in AA LT. That AB4 muscle fiber proportions were not different from AA and TB4 muscles suggests that the increased MF diameter of TB4 muscle was due to water retained by muscle proteins at high ultimate pH, as evidenced by decreased cooking loss. Dark-cutting was therefore unrelated to muscle fiber proportions, and increased Type I and IIB diameters in dark cutting LT were likely driven by elevated intramuscular ultimate pH.

Administration of low and high doses of heparin causes changes in plasma non-esterified fatty acid concentration in merino and terminal sired lambs

Context The anticoagulant properties of heparin have led to the routine use of heparinised saline flushes to prevent thrombus formation and to prolong the patency of indwelling cannulas. However, limited work exists on very low-dose heparin used to retain cannula patency for the purpose of repeated blood sampling for metabolic studies. Of particular interest is whether low-dose heparin will cause increases in plasma non-esterified fatty acid (NEFA) concentration. This is most relevant in metabolic studies involving repeated sampling, as this may erroneously elevate apparent plasma NEFA concentrations. Aims The objective of the present study was to evaluate the impacts of low- and high-dose heparin administration on plasma NEFA response in lambs. Methods In total, 14 merino (3 female, 4 wether) and terminal (4 female, 3 wether) sired lambs were selected from the Katanning, Western Australia, site of the Meat and Livestock Australia genetic resource flock All lambs were subjected to the following three treatments: low heparin (0.25 mL, 250 IU), high heparin (1 mL, 1000 IU) or control (1 mL of 0.9% NaCl saline), with each challenge being randomly allocated over 1.5 days. Blood samples were collected at the following time points: –30, –15, –10, –5, 0, 2.5, 5, 10, 15, 20, 30, 45, 60, 90, 120, 125 and 130 min relative to the administration of the challenge (Time 0) and tested for NEFA concentration. A derived exponential function was fitted to the raw data, enabling the plasma NEFA concentration response curve to be modelled at different time pointspre- and post-challenge, using the area under curve (AUC), maximum concentration and return to basal concentration, to quantify the NEFA response. Results Heparin-challenge dose had a significant (P &lt; 0.01) impact on peak NEFA response at 10 min following challenge administration (NEFA AUC10), with the values after high-heparin challenge (1.03 ± 0.086 mmol/L per 10 min) being ~25% higher (P &lt; 0.05) than those after the low-heparin challenge (0.78 ± 0.086 mmol/L per 10 min). The NEFA AUC10 values with low-dose heparin and high-dose heparin were 0.76 units and 1.02 units higher than those with the saline treatment (0.02 ± 0.086 mmol/L per 10 min; P &lt; 0.01). Heparin-challenge dose also had a significant impact on the maximum NEFA concentration (P &lt; 0.05). The high-heparin challenge (0.32 ± 0.057 mmol/L) had 20% higher maximum NEFA concentrations than the low-heparin challenge (0.26 ± 0.057 mmol/L). Both high and low heparin-challenge groups had maximum NEFA concentrations that were 72% and 36% higher respectively, than for the saline-challenge (0.19 ± 0.057 mmol/L) group. NEFA returned to basal concentrations by 60 min for both challenges, although the high heparin-challenge group demonstrated a slower rate of return (P &lt; 0.05). Conclusions High and low doses of heparin caused an increase in plasma NEFA response as measured by AUC10 and maximum NEFA concentration, but returned to basal concentrations within 1 h. Implications Results indicated that heparin as an anticoagulant should be avoided where frequent blood samples are required within intervals of less than 1 h. However, for repeated sampling at intervals greater than 1 h, judicious flushing with heparinised saline is unlikely to have an impact on plasma NEFA concentrations.

Genetics of Marbling in Wagyu Revealed by the Melting Temperature of Intramuscular and Subcutaneous Lipids

Extreme marbling or intramuscular deposition of lipid is associated with Wagyu breeds and is therefore assumed to be largely inherited. However, even within 100% full blood Wagyu prepared under standard conditions, there is unpredictable scatter of the degree of marbling. Here, we evaluate melting temperature (T_m) of intramuscular fat as an alternative to visual scores of marbling. We show that “long fed” Wagyu generally has T_m below body temperature but with a considerable range under standardized conditions. Individual sires have a major impact indicating that the variation is genetic rather than environmental or random error. In order to measure differences of lower marbling breeds and at shorter feeding periods, we have compared T_m in subcutaneous fat samples from over the striploin. Supplementary feeding for 100 to 150 days leads to a rapid decrease in T_m of 50% Red Wagyu (Akaushi) : 50% European crosses, when compared to 100% European. This improvement indicates that the genetic effect of Wagyu is useful, predictable, and highly penetrant. Contemporaneous DNA extraction does not affect the measurement of T_m. Thus, provenance can be traced and substitution can be eliminated in a simple and cost-effective manner.

Ruminant glycogen metabolism

The biochemistry of glycogen metabolism is well characterised, having been extensively studied in laboratory rodents and humans, and from this stems the bulk of our knowledge regarding the metabolism of glycogen in ruminants. With respect to intermediary metabolism, the key tissues include the liver and muscle. The liver glycogen depot plays a central role in intermediary metabolism, storing and mobilising glycogen during the fed and fasted metabolic states, with these responses modulated during pregnancy, lactation, and exercise. Alternatively, the muscle glycogen depot is particularly important for local energy homeostasis, and is likely to be less important as a key post-prandial sink for blood glucose given the reduced absorption of glucose from the gut in ruminant animals. Yet similar to the liver, this depot is also in a constant state of turnover, with the muscle glycogen concentration at any point in time a reflection of the rates of glycogen synthesis and degradation. Muscle glycogen metabolism attracts particular attention given its importance for post-mortem acidification of muscle tissue, with a shortage at slaughter leading to dark cutting meat. Simplistically the concentration of muscle glycogen at slaughter is a function of two key factors, the on-farm starting levels of glycogen minus the amount depleted during the pre-slaughter phase. On-farm concentrations of muscle glycogen are largely a reflection of metabolisable energy intake driving increased rates of muscle glycogen synthesis. Compared with simple-stomached species the rate of glycogen synthesis within ruminants is relatively low. Yet there also appears to be differences between sheep and cattle when fed diets of similar metabolisable energy, with cattle repleting muscle glycogen more slowly after depletion through exercise. While metabolisable energy intake is the key driver, genetic and age-related factors have also been shown to influence glycogen repletion. The amount of muscle glycogen depleted during the pre-slaughter phase is largely associated with stress and adrenaline release, and several recent studies have characterised the importance of factors such as exercise, age and genetics which modulate this stress response. This paper presents a summary of recent experiments in both cattle and sheep that highlight current developments in the understanding of this trait.

Beef carcasses with larger eye muscle areas, lower ossification scores and improved nutrition have a lower incidence of dark cutting

This study evaluated the effect of eye muscle area (EMA), ossification, carcass weight, marbling and rib fat depth on the incidence of dark cutting (pH(u)>5.7) using routinely collected Meat Standards Australia (MSA) data. Data was obtained from 204,072 carcasses at a Western Australian processor between 2002 and 2008. Binomial data of pH(u) compliance was analysed using a logit model in a Bayesian framework. Increasing eye muscle area from 40 to 80 cm², increased pH(u) compliance by around 14% (P<0.001) in carcasses less than 350 kg. As carcass weight increased from 150 kg to 220 kg, compliance increased by 13% (P<0.001) and younger cattle with lower ossification were also 7% more compliant (P<0.001). As rib fat depth increased from 0 to 20mm, pH(u) compliance increased by around 10% (P<0.001) yet marbling had no effect on dark cutting. Increasing musculature and growth combined with good nutrition will minimise dark cutting beef in Australia.