Bovine skeletal muscle is a tissue of signifi cant value to the beef industry and global economy. Proteomic analyses offer the opportunity to detect molecular mechanisms regulating muscle growth and intramuscular fat accumulation. The current study aimed to investigate differences in protein abundance in skeletal muscle tissue of cattle from two breeds of contrasting maturity (early vs. late maturing), adiposity, and muscle growth potential, namely, Belgian Blue (BB) × Holstein Friesian and Aberdeen Angus (AA) × Holstein Friesian. Twenty AA (n = 10) and BB (n = 10) sired steers, the progeny of sires of either high or low genetic merit, expressed as expected progeny difference for carcass weight (EPD cwt ), and bred through AI, were evaluated as 4 genetic groups, BB-High, BB-Low, AA-High, and AA-Low (n = 5 per treatment). Chemical composition analysis of M. longissimus lumborum showed greater protein and moisture and decreased lipid concentrations for BB-sired compared with AA-sired steers. To investigate the effects of both sire breed and EPD cwt on M. longissimus lumborum, proteomic analysis was performed using 2-dimensional difference gel electrophoresis followed by mass spectrometry. Proteins were identifi ed from their peptide sequences, using the National Center for Biotechnology Information (NCBI) and Swiss-prot databases. Metabolic enzymes involved in glycolysis (glycogen phosphorylase, phosphoglycerate mutase) and the citric acid cycle (aconitase 2, oxoglutarate dehydrogenase) were increased in AA-vs. BB-sired steers. Expression of proteins involved in cell structure, such as myosin light chain isoforms and troponins I and T, were also altered due to sire breed. Furthermore, heat shock protein β-1 and peroxiredoxin 6, involved in cell defense, had increased abundance in muscle of AA-sired relative to BB-sired steers. Protein abundance of glucose-6-phosphate isomerase, enolase-3, and pyruvate kinase was greater in AA-sired animals of High compared with Low EPD cwt . Changes in the expression of these proteins were supported by gene expression analysis using quantitative real-time PCR. This information will aid in our understanding of genetic infl uences controlling muscle growth and fat accumulation and could contribute to future breeding programs to increase lean tissue gain of beef cattle.

General rightsThis document is made available in accordance with publisher policies. Please cite only the published version using the reference above. The effect of feed restriction (99 days) followed by compensatory growth during a 27 200 day re-alimentation period on the colour and sensory characteristics of meat from 28Aberdeen Angus × Holstein-Friesian (AN) and Belgian Blue × Holstein-Friesian (BB) 29 steers was examined. Compensatory growth had no effect on muscle pH and 30 temperature decline, chemical composition, drip loss, fat colour, or juiciness, but 31 increased (p = 0.009) Warner-Bratzler shear force and decreased tenderness (P = 0.08) 32and overall flavour (P = 0.03). Compared to meat from BB steers, meat from AN 33 steers had a higher intramuscular fat concentration and was rated similarly for 34 tenderness, but higher for many of the flavour characteristics examined. While 35 adjustment for intramuscular fat concentration removed some of these differences, 36 genotype-specific flavour differences remained. It is concluded that genotype had 37 greater effects of meat quality that the compensatory growth feeding regime imposed 38 in this study. 39 40 41

The somatotropic axis plays an important role in postnatal growth, development, and differentiation of skeletal muscle. The aim of this study was to examine the effect of sire breed and sire EPD for carcass weight (EPD(cwt)) on the expression of components of the somatotropic axis in LM of beef cattle at slaughter. Crossbred Aberdeen Angus (AA; n = 17) and Belgian Blue (BB; n = 16) steers born to Holstein-Friesian dams and sired by bulls with either high (H) or low (L) EPD(cwt) were used in the study. Thus, there were 4 genetic groups [i.e., BBH (n = 8), BBL (n = 8), AAH (n = 8), and AAL (n = 9)]. Blood samples were collected via jugular venipuncture at regular intervals for analysis of plasma concentrations of IGF-1 and insulin. Total RNA was isolated from LM collected at slaughter, and the mRNA expression of IGF-1, IGF-2, their receptors (IGF-1R; IGF-2R), 6 IGFBP, acid labile subunit (ALS), and GH receptor (GHR) was measured by real-time reverse-transcription quantitative PCR. There was no effect of either sire breed or EPD(cwt) on concentrations of circulating IGF or insulin (P > 0.05). Gene expression of IGF-1R and IGFBP3 was upregulated in AA (P < 0.001) compared with BB, whereas IGF-1 was upregulated in H compared with L animals (P < 0.01). Correlation analysis indicated moderate positive associations between gene expression of IGFBP3 and IGF-1 (r = 0.54; P < 0.001) and IGF-1R (r = 0.48; P < 0.01). In addition, correlation analysis revealed that mRNA expression of IGFBP3 was moderately negatively associated with LM area per kilogram of carcass weight (r = -0.40; P < 0.05). Greater gene expression of IGF-1 and reduced transcript abundance of IGFBP3 in muscle may have a role in increased muscle growth potential in steers during the finishing period. These data will contribute to a better understanding of the molecular control of muscle growth at a tissue level in cattle.

To compare gene expression among bovine tissues, large bovine RNA-seq datasets were used, comprising 280 samples from 10 different bovine tissues (uterine endometrium, granulosa cells, theca cells, cervix, embryos, leucocytes, liver, hypothalamus, pituitary, muscle) and generating 260 Gbases of data. Twin approaches were used: an information-theoretic analysis of the existing annotated transcriptome to identify the most tissue-specific genes and a de-novo transcriptome annotation to evaluate general features of the transcription landscape. Expression was detected for 97% of the Ensembl transcriptome with at least one read in one sample and between 28% and 66% at a level of 10 tags per million (TPM) or greater in individual tissues. Over 95% of genes exhibited some level of tissue-specific gene expression. This was mostly due to different levels of expression in different tissues rather than exclusive expression in a single tissue. Less than 1% of annotated genes exhibited a highly restricted tissue-specific expression profile and approximately 2% exhibited classic housekeeping profiles. In conclusion, it is the combined effects of the variable expression of large numbers of genes (73%-93% of the genome) and the specific expression of a small number of genes (<1% of the transcriptome) that contribute to determining the outcome of the function of individual tissues.

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