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Skeletal muscle IGF-I and alpha-actin mRNA responses to increased amino acid availability were investigated in young, rapidly growing steers. Four Holstein steers (208 kg BW) were surgically implanted with an abomasal cannula and jugular catheters and allowed 2 wk to recover. Steers were offered hourly a 43:57 forage:concentrate diet at 95% of ad libitum intake supplemented with continuous abomasal infusion of glucose (to replace 12.5% of metabolizable ad libitum energy intake) for 13 d before the start of abomasal infusion of 67 g of casein N/d. Biopsies of the liver and both semimembranosus muscles were removed and frozen in liquid N, and casein infusion was begun. Muscle biopsies were collected at 8, 16, 24, and 48 h, and on d 7 and 14. Nitrogen balance increased from 23.6 to 71.5 g/d (P < .001) within 24 h and remained elevated (mean = 58.4 g/d) during the 14 d of casein infusion. Plasma urea N increased from 4 to 9.5 mg/dL at 24 h and remained unchanged to d 14. Muscle IGF-I mRNA abundance increased to 215% of basal values at 16 h (P < .01), 244% of basal values at 24 h, and 222% of basal values at 48 h after initiation of casein infusion. Values reached a maximum of 274% of basal values on d 7 and then declined to near preinfusion levels on d 14. The IGF-I mRNA abundance was approximately 100 times higher in liver than in skeletal muscle and was not different on d 0 and 14. Although plasma IGF-I concentrations were numerically higher during the first 24 h of abomasal casein infusion, they were not significantly higher during the chronic phase of treatment. Plasma IGF binding protein (BP)-2 concentrations were higher at 16, 24, and 48 h after casein infusion was begun, but IGFBP-3 concentrations were not altered at these sampling times. Neither acute (first 24 h) nor chronic (daily) plasma insulin concentrations were altered by abomasal casein infusion. Plasma somatotropin concentrations were lower (P = .008) at 24 h of casein infusion and beyond. Results suggest that enhanced amino acid availability may modulate skeletal muscle protein synthesis and accretion through an autocrine or paracrine IGF-I influence.

The effect of type of silage offered to beef heifers during the finishing period on aspects of beef quality was determined. In two experiments, a diet based on grass silage (GS) was compared with a diet based on maize silage (MS) or whole-crop wheat silage (WCW). Compared to the GS-based diet, increasing the amount of MS linearly increased fat whiteness while the increase in fat whiteness due to WCW was dependent on the stage of crop maturity at harvesting. There was no effect of diet on muscle colour or on muscle pH measured at 48h post-mortem, drip loss, taste panel traits after 14days ageing or shear force values at 2, 7 or 14days ageing. The alternative silages decreased the n-3 polyunsaturated fatty acid proportion and increased the linoleic:linolenic acid ratio in intramuscular lipid. It is concluded that type of silage affects fat colour and fatty acid composition of muscle but not the other muscle characteristics examined.

Background Differences between cattle production systems can influence the nutritional and sensory characteristics of beef, in particular its fatty acid (FA) composition. As beef products derived from pasture-based systems can demand a higher premium from consumers, there is a need to understand the biological characteristics of pasture produced meat and subsequently to develop methods of authentication for these products. Here, we describe an approach to authentication that focuses on differences in the transcriptomic profile of muscle from animals finished in different systems of production of practical relevance to the Irish beef industry. The objectives of this study were to identify a panel of differentially expressed (DE) genes/networks in the muscle of cattle raised outdoors on pasture compared to animals raised indoors on a concentrate based diet and to subsequently identify an optimum panel which can classify the meat based on a production system. Results A comparison of the muscle transcriptome of outdoor/pasture-fed and Indoor/concentrate-fed cattle resulted in the identification of 26 DE genes. Functional analysis of these genes identified two significant networks (1: Energy Production, Lipid Metabolism, Small Molecule Biochemistry; and 2: Lipid Metabolism, Molecular Transport, Small Molecule Biochemistry), both of which are involved in FA metabolism. The expression of selected up-regulated genes in the outdoor/pasture-fed animals correlated positively with the total n-3 FA content of the muscle. The pathway and network analysis of the DE genes indicate that peroxisome proliferator-activated receptor (PPAR) and FYN/AMPK could be implicit in the regulation of these alterations to the lipid profile. In terms of authentication, the expression profile of three DE genes (ALAD, EIF4EBP1 and NPNT) could almost completely separate the samples based on production system (95 % authentication for animals on pasture-based and 100 % for animals on concentrate- based diet) in this context. Conclusions The majority of DE genes between muscle of the outdoor/pasture-fed and concentrate-fed cattle were related to lipid metabolism and in particular β-oxidation. In this experiment the combined expression profiles of ALAD, EIF4EBP1 and NPNT were optimal in classifying the muscle transcriptome based on production system. Given the overall lack of comparable studies and variable concordance with those that do exist, the use of transcriptomic data in authenticating production systems requires more exploration across a range of contexts and breeds. Electronic supplementary material The online version of this article (doi:10.1186/s12864-016-2851-7) contains supplementary material, which is available to authorized users.