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Intramuscular fat (IMF) can improve meat product quality through its impact on flavour and juiciness. High marbling cuts can command premium prices in some countries and grading systems, but there is substantial cost involved in choosing to grain feed animals in an effort to deposit more IMF. There would be value in developing methods to predict predisposition to ‘marble’ well. Unfortunately, the biological mechanisms underpinning marbling remain a mystery: the key adipocyte cell populations have not been defined, there are no reliable DNA markers, no known (if any) causal mutations and gene expression analyses in the main have tended to characterise increases in expression of end-point fat metabolism proteins such as the fatty acid-binding proteins. To shed light on expression-based markers of marbling potential, we contrasted LD gene expression in high IMF Wagyu cross animals with a low IMF Piedmontese cross at various time points. The expected divergence in the fat metabolism genes FABP4, THRSP, CIDEC and ACACA between the breeds occurs surprisingly late in postnatal development at about 20 months. On the other hand, divergent expression of WISP2, RAI14 and CYP4F2 was discovered in animals at or before 12 months of age, suggesting these genes may have potential as earlier predictors of marbling potential. In line with other researchers, we found intriguing links between IMF development and connective tissue remodelling. WISP2 – a novel adipokine highly expressed and secreted by adipose precursor cells and an inhibitor of the pro-fibrotic connective tissue growth factor – emerges as a particularly attractive candidate. It is relatively upregulated in high marbling Wagyu before admission to feedlotting, somewhere between 7 and 12 months. This difference is subsequently maintained until 25 months, but not thereafter. RAI14, thought to play a role in porcine adipocyte differentiation and with links to retinoic acid metabolism, has an unusual expression profile. Its expression level increases monotonically with postnatal development, and is always higher in Wagyu than Piedmontese. Strong, sustained upregulation of the anti-inflammatory CYP4F2 in Piedmontese is consistent with Wagyu adiposity being a pro-inflammatory state. Application of regulatory impact factor analysis, a network method for identifying causal effector molecules, suggests marbling roles for transcription factors previously implicated in (1) the formation of liposarcoma (unconstrained fatty masses) (YEATS4, MDM2), (2) adipogenesis (CREBL2, SP1, STAT1) and (3) inflammation (ISGF3G, HOXB13, PML). [ABSTRACT FROM PUBLISHER]

To assess the potential for genetic improvement to help meet the increasing demand for high-yielding beef carcasses, the heritability of muscle score (MS) plus genetic and phenotypic correlations with weight and fatness traits were estimated on 1856 yearlings and 2596 weaners born from 1992 to 2012 in a predominantly Angus herd divergently selected for High/Low MS. In 2005, after noting that some cattle were positive for the 821_del11 myostatin mutation that causes muscle hypertrophy, procedures were modified to create a third group (High[sup Het]) of High animals with one copy of this major gene. This allowed the additive genetic effects of MS to be assessed, and also the effect of the 821_del11 mutation. MS traits were found to be highly heritable (h² = 56-63%), with an extremely high estimated genetic correlation of 99% between weaning and yearling MS. Estimated genetic correlations of MS with rib eye muscle area (EMA) in weaners and yearlings adjusted for either age or weight were 53-56%. Genetic correlations of MS with other traits were relatively low: liveweight (yearlings 5%, weaners 20%), rump fat (yearlings -7%, weaners 11%), rib fat (yearlings -17%, weaners -3%). Apart from weaning liveweight, the estimated genetic correlations were not significantly different from zero. MS had smaller estimated genetic correlations with fatness and weight traits than EMA adjusted for age. For yearlings and weaners born from 2010 to 2012, large significant differences were evident in MS of High and Low calves (4.5-point difference for yearlings; 3.4 points for weaners, on a 15-point scale) and significant differences in EMA (yearlings 2.5, weaners 1.5 cm²). In addition, the 821del11 mutation reduced fatness, increased MS by 1.5-1.9 points and increased EMA by 2.8-3.6 cm². With high heritability, low correlations with weight and fatness in weaners/yearlings, plus other research (Cafe et al. 2012, 2014a) showing no detrimental effect on maternal productivity or meat quality, but improvements in dressing percent, retail meat yield, meat : bone ratio and feedlot feed efficiency, the development of an estimated breeding value for MS could help improve the efficiency and profitability of beef production. Muscle score (MS) is highly heritable (56-63%), with an estimated genetic correlation of 99% between weaning and yearling MS. Estimated genetic correlations with eye muscle area are moderate (55%). Estimated breeding values for MS could help make beef production more efficient and profitable, given its favourable relationships with meat yield and feed efficiency without detrimental effects on meat quality or maternal productivity. [ABSTRACT FROM AUTHOR]

A disintegrin and metalloproteinase-12 (ADAM 12) is involved in the regulation of myogenesis and adipogenesis and is of interest as a potential target to manipulate skeletal muscle development and intra-muscular fat (IMF) deposition in cattle to increase beef yield and improve meat quality. The longissimus thoracis muscle (LM) and semitendinosus muscle (STM) from 5 Bos taunts (Angus) and 5 Bos indicus (Brahman) cattle were collected for histological and ADAM 12 gene and protein expression analysis. Myofiber typing was used to determine if ADAM 12 expression patterns related to differences in muscling and IMF deposition, which are influenced by proportions of the different myofiber types. The STM was found to contain a higher proportion of glycolytic myofibers than the LM, which contained a greater proportion of oxidative myofibers (myofiber ratio of glycolytic to more oxdidative types in LM and STM of 1.1 and 3.5, respectively; P < 0.05). AD AMI 2 gene expression, fluorescent immunohistochemical staining for ADAM 12, and image analysis found ADAM 12 to be greater in the LM (P < 0.05). Regression analysis found a strong, positive relationship for the distribution of ADAM 12 against the proportion of type I myofibers (P < 0.05, r² = 0.86). These findings suggest AD AMI 2 is upregulated in muscles with more slow-oxidative myofi-bres, such as the LM, and is linked to type I myofibers in cattle. ADAM12 may be important in the regulation and maintenance slow myofibers in the LM muscle. [ABSTRACT FROM AUTHOR]

Background -- The beef industry in Australia is subject to variable pasture availability and quality. This results in numerous growth path possibilities that may influence growth potential and body and carcass composition of cattle and eating quality of beef. Studies of cattle within pasture-based nutritional systems have failed to demonstrate substantial long-term differences in body or carcass characteristics due to prenatal nutrition and growth or nutrition and growth from birth to weaning. However, severe nutritional restriction from birth to weaning followed by concentrate (high energy) feeding from weaning resulted in increased fatness at the same live and carcass weights compared to cattle well-nourished to weaning. Furthermore, the extent to which growth early in life interacts with genotype to influence long-term outcomes for growth, carcass and beef quality characteristics of cattle has not been investigated. Objective -- To determine the extent to which prenatal and pre-weaning growth influence subsequent growth, composition and meat eating quality of cattle sired by bulls with high muscle (Piedmontese breed) or high intramuscular fat (Wagyu breed) growth capacity. Design -- Piedmontese x Hereford (n = 120) and Wagyu x Hereford (n = 120) calves of low (28.6 kg, n = 120) or high (38.8 kg, n = 120) birth weight were nourished to grow slowly (554 g/d, n = 119) or rapidly (875 g/d, n = 121) to weaning at 7 months of age (total n = 240). They were grown from weaning to feedlot entry at 26 months of age on improved, temperate pasture, then lot-fed a grain-based diet until conclusion of the study at 30 months of age. Outcomes -- Low birth weight calves grew more slowly to weaning and in the feedlot, were 56 kg smaller on average at conclusion of the study, and had similar composition and eating quality characteristics compared to those of high birth weight. Cattle grown slowly to weaning weighed 70 kg less at weaning, grew more rapidly post-weaning but remained 40 kg lighter at conclusion of the study, and were leaner and had similar meat eating quality at 30 months of age compared to those grown rapidly to weaning. Genotype x early-life nutrition interactions were not evident. Conclusions -- Fetal growth retardation resulted in slower subsequent growth and reduced size of cattle, but had little effect on composition and meat eating quality at 30 months of age. In cattle grown slowly to weaning, compensation in weight was incomplete and cattle were leaner with similar meat eating quality at 30 months of age. These findings on consequences of low birth weight for body or carcass composition are consistent with previous research in cattle,1 but in contrast to findings in sheep grown to 20 kg4 or 35 kg5 live weight in which increased fatness was evident following severe foetal growth retardation that resulted in low birth weight. However, our findings are consistent with previous studies in sheep that showed no adverse effects on eating quality due to restricted nutrition during pregnancy, and with previous research in cattle in which nutrition and growth early in life did not adversely affect beef eating quality characteristics. [ABSTRACT FROM AUTHOR]

Associations between temperament, stress physiology, and productivity were studied in yearling Brahman steers (n = 81). Steers differed in calpain system gene marker status; 41 were implanted with a hormonal growth promotant at feedlot entry. Temperament was assessed with repeated measurements of flight speed (FS) and crush score (CS) during 6 mo of backgrounding at pasture and 117 d of grain finishing. Adrenal responsiveness was assessed with ACTH challenge, with plasma samples collected immediately before and 60 min after challenge. Steers with higher FS and CS had higher prechallenge plasma cortisol, glucose, lactate, and nonesterified fatty acid concentrations. The ACTH-induced cortisol response was unrelated to FS or CS, but glucose remained higher after challenge in flightier steers. The hormonal growth promotant reduced adrenal responsiveness; tenderness genotype had no effect. When temperament assessments and cortisol concentrations before and after challenge were combined in a principal components analysis, four vectors accounting for 38%, 25%, 18%, and 9% of the variation were identified. The first vector had significant loadings on temperament and prechallenge cortisol; increasing scores were associated with increased plasma glucose, lactate, and nonesterified fatty acid and with reductions in BW and feedlot growth rates, carcass fatness, and muscle pH. The second vector loaded only on ACTH-induced cortisol response; increased scores related to increased residual feed intake, number of daily feed sessions, and meat marbling score. The third and fourth vectors had different loadings on FS and CS and appeared to identify different aspects of temperament measured by FS or CS. Fewer associations were found between the third or fourth vectors and productivity traits, possibly because of lower variance accounted for by these vectors. In conclusion, temperament was related to prechallenge cortisol but not to ACTH-induced cortisol response. Principal components analysis separated these traits into separate components, which in turn had different relations with productivity traits. The largest component of temperament was described similarly by FS and CS, but there were smaller components that these described differently. There were some temperament-related differences in the metabolic status of the steers which were not related to the variation in cortisol, suggesting involvement of the sympatho-adrenal-medullary axis in these temperament-related effects., (Copyright © 2011 Elsevier Inc. All rights reserved.)

Severe, chronic growth retardation of cattle early in life reduces growth potential, resulting in smaller animals at any given age. Capacity for long-term compensatory growth diminishes as the age of onset of nutritional restriction resulting in prolonged growth retardation declines. Hence, more extreme intrauterine growth retardation can result in slower growth throughout postnatal life. However, within the limits of beef production systems, neither severely restricted growth in utero nor from birth to weaning influences efficiency of nutrient utilisation later in life. Retail yield from cattle severely restricted in growth during pregnancy or from birth to weaning is reduced compared with cattle well grown early in life, when compared at the same age later in life. However, retail yield and carcass composition of low- and high-birth-weight calves are similar at the same carcass weight. At equivalent carcass weights, cattle grown slowly from birth to weaning have carcasses of similar or leaner composition than those grown rapidly. However, if high energy, concentrate feed is provided following severe growth restriction from birth to weaning, then at equivalent weights post-weaning the slowly-grown, small weaners may be fatter than their well-grown counterparts. Restricted prenatal and pre-weaning nutrition and growth do not adversely affect measures of beef quality. Similarly, bovine myofibre characteristics are little affected in the long term by growth in utero or from birth to weaning. Interactions were not evident between prenatal and pre-weaning growth for subsequent growth, efficiency, carcass, yield and beef-quality characteristics, within our pasture-based production systems. Furthermore, interactions between genotype and nutrition early in life, studied using offspring of Piedmontese and Wagyu sired cattle, were not evident for any growth, efficiency, carcass, yield and beef-quality parameters. We propose that within pasture-based production systems for beef cattle, the plasticity of the carcass tissues, particularly of muscle, allows animals that are growth-retarded early in life to attain normal composition at equivalent weights in the long term, albeit at older ages. However, the quality of nutrition during recovery from early life growth retardation may be important in determining the subsequent composition of young, light-weight cattle relative to their heavier counterparts. Finally, it should be emphasised that long-term consequences of more specific and/or acute environmental influences during specific stages of embryonic, foetal and neonatal calf development remain to be determined. This need for further research extends to consequences of nutrition and growth early in life for reproductive capacity.