Association of plasma microRNA expression with age, genetic background and functional traits in dairy cattle

Abstract A number of blood circulating microRNAs (miRNAs) are proven disease biomarkers and have been associated with ageing and longevity in multiple species. However, the role of circulating miRNAs in livestock species has not been fully studied. We hypothesise that plasma miRNA expression profiles are affected by age and genetic background, and associated with health and production traits in dairy cattle. Using PCR arrays, we assessed 306 plasma miRNAs for effects of age (calves vs mature cows) and genetic background (control vs select lines) in 18 animals. We identified miRNAs which were significantly affected by age (26 miRNAs) and genetic line (5 miRNAs). Using RT-qPCR in a larger cow population (n = 73) we successfully validated array data for 12 age-related miRNAs, one genetic line-related miRNA, and utilised expression data to associate their levels in circulation with functional traits in these animals. Plasma miRNA levels were associated with telomere length (ageing/longevity indicator), milk production and composition, milk somatic cell count (mastitis indicator), fertility, lameness, and blood metabolites linked with body energy balance and metabolic stress. In conclusion, circulating miRNAs could provide useful selection markers for dairy cows to help improve health, welfare and production performance

Effect of Flow History on the Structure of a Non-Polar Polymer/Clay Nanocomposite Model System

International audienceThe effect of flow history on the linear and non-linear viscoelastic properties of non-polar polymer nanocomposites (PNCs) has been investigated by means of a suitable model system based on a Newtonian matrix. The structural recovery of this model suspension after cessation of different pre-shear rates was monitored by measuring its linear viscoelastic properties while its structural evolution under shear flow was followed by using stepwise changes in shear rate including flow reversal measurements. To assess the kinetics of the structural evolution at rest and under flow, empirical relations of stretched exponential form were used. It is shown that for different pre-shear rates, different equilibrium structures were reached at rest but with a similar kinetics of recovery. As a result, the low frequency behaviour was typical of solid-like or weak gel material, strongly dependent on the flow history. After any given shear rate under steady state, only one reversible equilibrium structure was reached after a kinetics that was dependent on the pre-shear history. Finally, typical flow reversal responses as observed for PNCs are reported and interpreted in light of the microstructure evolution under flow

Structural analysis of non-aqueous layered silicate suspensions subjected to shear flow

International audienceNon-aqueous layered silicate suspensions exhibit a complex rheological behavior due to a multiple length scale structure, which is sensitive to flow and flow history. In the present work, the nature of flow-induced non-equilibrium and metastable structures in non-aqueous layered silicate suspensions based on natural and organo-modified sodium montmorillonites was examined using rheometry and confocal laser scanning microscopy (CLSM). The scaling behavior of their linear and non-linear viscoelastic properties was investigated. Based on fractal scaling theories, the scaling laws of the solid-like properties were ascribed to the presence of space-filling percolating networks consisting of clusters with a mass-fractal dimensionality, Df∼2. CLSM allowed us to detect the formation of aggregates under flow and to characterize their microscopic length scale. The shear-rate dependency of the microstructure characteristic length scale was attributed to a reversible shear-induced aggregation process. Upon cessation of flow, the observed thixotropic behavior of these suspensions was inferred from the CLSM observations to stem from local rearrangements at the nano-scale

Anisotropy of nonaqueous layered silicate suspensions subjected to shear flow

International audienceNonaqueous layered silicate suspensions have a complex rheological behavior due to the presence of a microstructure on multiple length scales, which is sensitive to flow and flow history. In the present work, the flow-induced orientation and anisotropy of the nonequilibrium metastable structures in nonaqueous layered silicate suspensions has been studied using a combination of light scattering, scattering dichroism, and advanced rheometric measurements, including two dimensional small amplitude oscillatory shear ?2D-SAOS? flow experiments. The nature of the structures during flow was mainly studied by means of small angle light scattering patterns. Linear dichroism measurements in the vorticity and velocity gradient directions were used to assess the microstructural anisotropy. The changes observed in the vorticity plane developed in the same range of shear rate as the shear-thinning behavior of the suspensions. Scattering dichroism was used to demonstrate that the flow-induced anisotropy was locked in upon cessation of flow. To verify that this also leads to an anisotropy of the rheological properties, the linear viscoelastic moduli were measured using ?2D-SAOS? experiments. This new technique proved to be particularly sensitive to the anisotropic nature of the metastable microstructure of organoclay suspensions. Both the flow-induced orientation and larger scale microstructural rearrangements are shown to contribute to the transient rheological response of the nonaqueous layered silicate suspensions

X-ray scattering measurements of particle orientation in a sheared polymer/clay dispersion

International audienceWe report steady and transient measurements of particle orientation in a clay dispersion subjected to shear flow. An organically modified clay is dispersed in a Newtonian polymer matrix at a volume fraction of 0.02, using methods previously reported by Mobuchon et al. (Rheol Acta 46: 1045, 2007). In accord with prior studies, mechanical rheometry shows yield stress-like behavior in steady shear, while time dependent growth of modulus is observed following flow cessation. Measurements of flow-induced orientation in the flow-gradient plane of simple shear flow using small-angle and wide-angle X-ray scattering (SAXS and WAXS) are reported. Both SAXS and WAXS reveal increasing particle orientation as shear rate is increased. Partial relaxation of nanoparticle orientation upon flow cessation is well correlated with time-dependent changes in complex modulus. SAXS and WAXS data provide qualitatively similar results; however, some quantitative differences are attributed to differences in the length scales probed by these techniques