Beef cattle selected for increased muscularity have a reduced muscle response and increased adipose tissue response to adrenaline

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.

Cattle production practices and the incidence of dark cutting beef

The effects of cattle sex, production system, growth promotant use, slaughter season, carcass phenotype, and pre-slaughter cattle management on the incidence of beef carcasses grading Canada B4 (dark cutting) were investigated using two data sets (A, n = 2009, and B, n = 86,408) containing data from cattle that produced Canada Prime, AAA, AA, A, and B4 carcasses. The probability of producing a Canada B4 carcass was greater (P < .0001) for heifers than steers in both data sets, with the likelihood of dark cutting decreasing with increased carcass weight in heifers in data set B. The incidence of dark cutting was increased (P < .0001) in Winter-born calf-fed (WC) and Fall-born calf-fed (FC) heifers. Production system and phenotype appear to interact to influence the incidence of dark cutting.

Feed deprivation in Merino and Terminal sired lambs: (2) the metabolic response under pre-slaughter conditions and impact on meat quality and carcass yield

Under current Australian industry pre-slaughter guidelines, lambs may be off feed for up to 48 h before slaughter. The purpose of this study was to examine what proportion of circulating metabolites at slaughter are due to stress and feed deprivation and if this response differs between Merino and Terminal genotypes. In addition the effect of feed deprivation on carcass weight and meat quality was examined. Jugular blood samples were collected from 88 Merino and Terminal sired lambs at rest and at slaughter following 24, 36 and 48 h of feed deprivation and plasma analysed for glucose, lactate, non-esterified fatty acids (NEFA) and β-hydroxybutyrate (BHOB). From the same carcasses hot carcass weight (HCWT) were measured as well as a suite of meat quality traits measured such as M. longissimus lumborum (loin) and M. semitendinosus pH at 24 h postmortem. Loin samples were also analysed for intramuscular fat content and Warner-Bratzer Shear Force. Merino sired lambs had a higher NEFA response compared to Terminal sired lambs at slaughter after 24, 36 and 48 h of feed deprivation, with NEFA levels up to 35% higher than previously reported in the same animals at rest in animal house conditions, whereas BHOB response to feed deprivation was not affected by sire type (P&gt;0.05) and similar to previously reported at rest. In addition to the metabolic effects, increasing feed deprivation from 36 h was associated with a 3% reduction in HCWT and dressing percentage as well as causing increased ultimate pH in the M. semitendinosus in Merino sired lambs. Findings from this study demonstrate that Merino and Terminal sired lambs differ in their metabolic response to feed deprivation under commercial slaughter conditions. In addition, commercial feed deprivation appears to have a negative effect on ultimate pH and carcass weight and warrants further investigation.

Feed deprivation in Merino and Terminal sired lambs: (1) the metabolic response under resting conditions

The aim of this study was to examine the metabolic response to feed deprivation up to 48 h in low and high yielding lamb genotypes. It was hypothesised that Terminal sired lambs would have decreased plasma glucose and increased plasma non-esterified fatty acids (NEFA) and β-hydroxybutyrate (BHOB) concentrations in response to feed deprivation compared to Merino sired lambs. In addition, it was hypothesised that the metabolic changes due to feed deprivation would also be greater in progeny of sires with breeding values for greater growth, muscling and leanness. Eighty nine lambs (45 ewes, 44 wethers) from Merino dams with Merino or Terminal sires with a range in Australian Sheep Breeding Values (ASBVs) for post-weaning weight (PWT), post-weaning eye muscle depth and post-weaning fat depth (PFAT) were used in this experiment. Blood samples were collected via jugular cannulas every 6 h from time 0 to 48 h of feed deprivation for the determination of plasma glucose, NEFA, BHOB and lactate concentration. From 12 to 48 h of feed deprivation plasma glucose concentration decreased (P &lt; 0.05) by 25% from 4.04 ± 0.032 mmol/l to 3.04 ± 0.032 mmol/l. From 6 h NEFA concentration increased (P &lt; 0.05) from 0.15 ± 0.021 mmol/l by almost 10-fold to 1.34 ± 0.021 mmol/l at 48 h of feed deprivation. Feed deprivation also influenced BHOB concentrations and from 12 to 48 h it increased (P &lt; 0.05) from 0.15 ± 0.010 mmol/l to 0.52 ± 0.010 mmol/l. Merino sired lambs had a 8% greater reduction in glucose and 29% and 10% higher NEFA and BHOB response, respectively, compared to Terminal sired lambs (P &lt; 0.05). In Merino sired lambs, increasing PWT was also associated with an increase in glucose and decline in NEFA and BHOB concentration (P &lt; 0.05). In Terminal sired lambs, increasing PFAT was associated with an increase in glucose and decline in NEFA concentration (P &lt; 0.05). Contrary to the hypothesis, Merino sired lambs showed the greatest metabolic response to fasting especially in regards to fat metabolism.

Association between Loin Ultimate pH and Plasma Indicators of Pre-Slaughter Stressors in Australian Lamb

The purpose of this study was to test if associations exist between plasma indicators of acute and chronic stress and lamb ultimate pH. Blood was collected at exsanguination from 2,877 lambs from the Meat and Livestock Australia Genetic Research flock with a suite of indicators analyzed. Ultimate pH was measured in the loin (M. longissimus lumborum) at 24 h post-slaughter. There was a positive association (P < 0.05) between ultimate pH and plasma glucose and lactate concentrations, which indicates that opportunities exist to reduce variation in ultimate pH by reducing stress in the pre-slaughter period. These effects were small by comparison to production factors, however further understanding of how to best manage lambs in the pre-slaughter period is required to minimize stress and maximize lamb wellbeing and meat quality.

Do extended transport times and rest periods impact on eating quality of beef carcasses?

The experiment tested the effect of four extended transport treatments on sensory and objective meat quality in beef. A total of 343 steers (88 steers from each of three properties and 79 from a fourth property) were allocated to four treatments including a 12 hour transport time (T12), 24 hour transport time (T24), 24 h as 12 hour transport time, a 12 hour rest, with a further 12 hour transport (T12 ~ T12), 36 hour transport treatment (T36). Within property departure times of treatments were staggered to arrive at the abattoir together. There were no significant transport effects (P > .05) on live animal, carcass traits, consumer sensory scores, and objective meat quality of the longissimus lumborum. There was large between property variation in the proportions of carcasses excluded from grading on the basis of low ribfat, high ultimate pH and dark meat color scores. Variation in these traits was not associated with transport treatments and was likely related to variation in on-farm factors.

Responses of body fat mobilization to isoproterenol or epinephrine challenge in adult cows: influence of energy level, breed, and body fatness

The sustainability of livestock production systems facing climatic or economic changes is linked in part to the potential of the female ruminants to adapt to feeding constraints through metabolic and hormonal regulation, notably responses of body fat mobilization, depending on adipose tissue (AT) lipolysis. Our hypothesis was that these responses could change according to genotype (breed) and body fatness. Six fat, nonpregnant, nonlactating Charolais cows, six fat Holstein cows, and six lean Holstein cows were used in a 2 × 2 crossover design with two treatments (underfeeding or overfeeding, at 62% [low] or 128% [high] of maintenance energy requirements [MER], respectively) and two periods. Isoproterenol (ISO, a nonselective β-adrenergic agonist) or epinephrine (EPI, a β- and α2-adrenergic agonist) was injected (6 nmol/kg of lean mass). Blood samples were collected regularly from -20 to 75 min after the injection and then were analyzed for NEFA, glycerol, glucose, and L-lactate. Underfeeding greatly increased (P < 0.001) basal plasma NEFA concentrations (+467%, +264%, and +600% for fat Charolais, fat Holstein, and lean Holstein cows, respectively). For each drug, underfed cows had higher NEFA or glycerol responses to adrenergic challenges than overfed cows. Fat Charolais cows had higher basal plasma NEFA (P < 0.05) concentrations (+64.9%) than fat Holstein cows. The plasma NEFA or glycerol response at 5 min (P < 0.05) was higher for fat Charolais than for fat Holstein cows, whatever the injected drug. Basal plasma lactate concentration and lactate response to ISO or EPI were higher (P < 0.05) for fat Charolais cows than for fat Holstein cows. Fat Holstein cows had higher (P < 0.01) basal glycerol (+18.4%) than lean Holstein cows. This increase could be linked to the increased AT mass. ISO increased more lipolytic responses in fat than in lean Holstein cows, whereas EPI increased more these responses in lean than in fat Holstein cows (drug × fatness interaction), suggesting an increased antilipolytic effect due to α2-AR stimulation in fat cows. Breed had a significant effect on basal and stimulated fat mobilization as well as lactate concentrations, suggesting that the Charolais breed could be more sensitive to stress.

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.

Adipose depots differ in cellularity, adipokines produced, gene expression, and cell systems

The race to manage the health concerns related to excess fat deposition has spawned a proliferation of clinical and basic research efforts to understand variables including dietary uptake, metabolism, and lipid deposition by adipocytes. A full appreciation of these variables must also include a depot-specific understanding of content and location in order to elucidate mechanisms governing cellular development and regulation of fat deposition. Because adipose tissue depots contain various cell types, differences in the cellularity among and within adipose depots are presently being documented to ascertain functional differences. This has led to the possibility of there being, within any one adipose depot, cellular distinctions that essentially result in adipose depots within depots. The papers comprising this issue will underscore numerous differences in cellularity (development, histogenesis, growth, metabolic function, regulation) of different adipose depots. Such information is useful in deciphering adipose depot involvement both in normal physiology and in pathology. Obesity, diabetes, metabolic syndrome, carcass composition of meat animals, performance of elite athletes, physiology/pathophysiology of aging, and numerous other diseases might be altered with a greater understanding of adipose depots and the cells that comprise them-including stem cells-during initial development and subsequent periods of normal/abnormal growth into senescence. Once thought to be dormant and innocuous, the adipocyte is emerging as a dynamic and influential cell and research will continue to identify complex physiologic regulation of processes involved in adipose depot physiology.

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.

Duration of time that beef cattle are fed a high-grain diet affects the recovery from a bout of ruminal acidosis: short-chain fatty acid and lactate absorption, saliva production, and blood metabolites

This study was conducted to determine if the duration of time that beef cattle are fed a high-grain diet affects short-chain fatty acid (SCFA) absorption, saliva production, and blood metabolites before, during, and following an induced bout of ruminal acidosis. Sixteen Angus heifers were assigned to 1 of 4 blocks and within block to 1 of 2 treatments designated as long adapted (LA) or short adapted (SA). Long adapted and SA heifers were fed a backgrounding diet [forage:concentrate (F:C) = 60:40] for 33 and 7 d, respectively, and then transitioned over 20 d to a high-grain diet (F:C = 9:91) with the timing of dietary transition staggered such that the LA and SA heifers were fed the high-grain diet for 34 and 8 d, respectively, before inducing ruminal acidosis. Ruminal acidosis was induced by restricting feed to 50% of DMI:BW for 24 h followed by an intraruminal infusion of ground barley at 10% DMI:BW. Heifers were then given their regular diet allocation 1 h after the intraruminal infusion. Data were collected during an 8 d baseline period (BASE), on the day of the acidosis challenge (CHAL), and during 2 consecutive 8 d recovery periods (REC1 and REC2). When pooled across periods, the fractional rates of propionate (42 vs. 34%/h; P = 0.045) and butyrate (45 vs. 36%/h; P = 0.019) absorption, measured using the isolated and washed reticulorumen technique, were greater for LA than SA heifers. Moreover, overall, LA heifers tended to have greater absolute rates of butyrate absorption (94 vs. 79 mmol/h; P = 0.087) and fractional rates of total SCFA absorption (37 vs. 32%/h; P = 0.100). Treatment × period interactions for lactate absorption (P = 0.024) and serum D-lactate concentration (P = 0.003) were detected with LA heifers having greater D-lactate concentrations during CHAL and greater fractional rates of lactate absorption during REC1 than SA. The absolute and fractional absorption of acetate, propionate, and butyrate increased between REC1 and REC2, with intermediate values for BASE (P ≤ 0.05). Although fractional rates of SCFA absorption were low during REC1, saliva production (P = 0.018) increased between BASE and REC1, with intermediate values for REC2. These results suggest that the duration of time that animals are fed a high-grain diet may increase propionate, butyrate, and lactate absorption, and that cattle may decrease SCFA absorption and increase saliva production shortly after an acute bout of ruminal acidosis.

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.