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Animal robustness is a complex trait of importance for livestock production systems and genetic selection. Phenotyping is essential for evaluation of the adaptation of different genotypes to changing environments. This study tested an experimental framework to induce marked deviations in the adaptive responses of suckling beef cows and to identify relevant indicators of responses to characterise individual differences in the robustness of cows. The production and metabolic responses of primiparous suckling Charolais cows to two periods of feed restriction (FR, 50% of their net energy requirements) of different durations were monitored. After calving, 13 cows (aged 39 ± 2 months, BW of 680 ± 42 kg at calving) had ad libitum access to a diet composed of hay and supplemented with concentrate to meet their energy and protein requirements. Starting at 54 ± 6 days postcalving, the cows underwent two periods of FR: 4 days of FR (FR4), which was followed by 17 days of ad libitum intake to study the recovery from FR4, and 10 days of FR (FR10), which was followed by 18 days of ad libitum intake to study the recovery from FR10. The milk yield (MY), BW, body condition score and plasma non-esterified fatty acid (NEFA), β-hydroxybutyrate, glucose and urea concentrations were measured before, during and after each FR. Among all measured variables, the MY and NEFA concentrations showed the most significant changes in response to FR. A functional data analysis approach was applied to the MY and NEFA data to model the adaptive responses and extract quantifiable indicators of deviation and recovery. Linear correlations (P < 0.03-0.07) between FR4 and FR10 were found for some indicators describing MY and NEFA levels before and after FR. The overall repeatability of MY and NEFA responses between both FR accounted for 46% based on quartile analysis performed on average responses. Moreover, the variance in both the MY and NEFA variables did not differ significantly between FR4 and FR10, despite a trend for higher variances in FR10. Altogether, (1) the calculated variables derived from the functional data analysis of the time patterns of the MY and NEFA accounted for the differences in the cow responses to FR, and (2) the animal responses appeared to show concordance between FR4 and FR10. In conclusion, short-term FR is a relevant framework for studying productive and metabolic adaptive responses in suckling cows and allows the identification of potential robustness indicators., (Copyright © 2022 The Authors. Published by Elsevier B.V. All rights reserved.)

Some proteins have been revealed as biomarkers for beef tenderness by previous studies. These markers could be used in immunological tests to predict beef tenderness, in living animals as well as in carcasses. It is well known that rearing practices modify the amounts of mRNA and proteins. Therefore, the reliability of protein tests could be affected by livestock and biological effects such as production systems, breed, muscle and animal type. This study analysed the effects of animal and muscle type on 24 proteins. The animals studied were 67 young bulls and 44 steers of the Charolais breed, and muscles were Longissimus thoracis and Semitendinosus. Protein amounts were determined by Dot blot, an immunological technique. Results showed that expressions of 20 proteins were influenced by animal and/or muscle type. These results could lead to modifications and adaptations of prediction tests according to rearing practice, bovine breed and beef cut.

We have recently shown that the expression of the DNAJA1 gene encoding a heat shock protein (Hsp40) is a negative marker of meat tenderness in Charolais bulls. To acquire knowledge on the regulation of DNAJA1 expression, we analysed the abundance of DNAJA1 transcripts and protein during development and according to management factors (e.g. feeding treatments, growth path and stress status) in different bovine muscles during postnatal life. We report here a developmental expression profile for DNAJA1 with decreased levels of transcript and protein during the progression of myogenesis. During postnatal life, we found the highest expression of DNAJA1 in the most oxidative muscles. No effect was detected for dietary treatment (pasture v. maize-based diet), growth path (compensatory growth after a restriction period) or pre-slaughter stress status. Therefore, the genetic background and muscle type could be considered as the main factors regarding the level of DNAJA1. Integration of the knowledge gained from this study should help to predict muscle metabolic properties and the ability of the live animals to give high sensory quality meat.

Myostatin (MSTN), a member of the TGF-β superfamily, is a negative regulator of skeletal muscle mass. We have previously shown that the cell survival/apoptosis pathway is a downstream target of MSTN loss-of-function in mice through the regulation of the expression or abundance of many survival and apoptotic factors. In this study, we used western-blot and quantitative PCR (qPCR) analyses to validate these novel downstream targets of MSTN in double-muscled (DM) cattle v. their controls including 260-day-old foetuses and adult cows from the INRA95 strain. MSTN loss-of-function in DM foetuses and DM cows resulted in a glycolytic shift of the muscles (e.g. upregulation of H-MyBP, PGM1 and SNTA1 and downregulation of H-FABP), activation of cell survival pathway through regulation of some components of the PI3K/Akt pathway (e.g. upregulation of DJ-1 and Gsk-3βser9/Gsk-3βtotal ratio and downregulation of PTEN) and upregulation of cell survival factors translationally controlled tumour protein (14-3-3E, Pink1). We also found a lower abundance of pro-apoptotic transcripts and/or proteins (Caspase-3, caspase-8, caspase-9, BID, ID2 and Daxx) and a higher expression of anti-apoptotic transcripts (Traf2 and Bcl2l2) in DM muscles. All together, these results are in favour of activation of the cell survival pathway and loss of apoptosis pathway within the muscles of DM animals. Alteration of both pathways may increase myonuclear or satellite cell survival, which is crucial for protein synthesis. This could contribute to muscle hypertrophy in DM foetuses and DM cows.

The lean-to-fat ratio, that is, the relative masses of muscle and adipose tissue, is a criterion for the yield and quality of bovine carcasses and meat. This review describes the interactions between muscle and adipose tissue (AT) that may regulate the dynamic balance between the number and size of muscle v. adipose cells. Muscle and adipose tissue in cattle grow by an increase in the number of cells (hyperplasia), mainly during foetal life. The total number of muscle fibres is set by the end of the second trimester of gestation. By contrast, the number of adipocytes is never set. Number of adipocytes increases mainly before birth until 1 year of age, depending on the anatomical location of the adipose tissue. Hyperplasia concerns brown pre-adipocytes during foetal life and white pre-adipocytes from a few weeks after birth. A decrease in the number of secondary myofibres and an increase in adiposity in lambs born from mothers severely underfed during early pregnancy suggest a balance in the commitment of a common progenitor into the myogenic or adipogenic lineages, or a reciprocal regulation of the commitment of two distinct progenitors. The developmental origin of white adipocytes is a subject of debate. Molecular and histological data suggested a possible transdifferentiation of brown into white adipocytes, but this hypothesis has now been challenged by the characterization of distinct precursor cells for brown and white adipocytes in mice. Increased nutrient storage in fully differentiated muscle fibres and adipocytes, resulting in cell enlargement (hypertrophy), is thought to be the main mechanism, whereby muscle and fat masses increase in growing cattle. Competition or prioritization between adipose and muscle cells for the uptake and metabolism of nutrients is suggested, besides the successive waves of growth of muscle v. adipose tissue, by the inhibited or delayed adipose tissue growth in bovine genotypes exhibiting strong muscular development. This competition or prioritization occurs through cellular signalling pathways and the secretion of proteins by adipose tissue (adipokines) and muscle (myokines), putatively regulating their hypertrophy in a reciprocal manner. Further work on the mechanisms underlying cross-talk between brown or white adipocytes and muscle fibres will help to achieve better understanding as a prerequisite to improving the control of body growth and composition in cattle.

Muscle contractile and metabolic characteristics were studied on nine cloned and eight non-cloned (control) heifers. The animals were submitted to repeated biopsies of the semitendinosus (ST) muscle at the ages of 8, 12, 18 and 24 months. The contractile type was determined from the proportion of the different myosin heavy chain (MyHC) isoforms separated by electrophoresis. Glycolytic metabolism was assessed by lactate dehydrogenase (LDH) activity, and oxidative metabolism was assessed by isocitrate dehydrogenase (ICDH), cytochrome-c oxidase (COX) and β-hydroxyacyl-CoA dehydrogenase (HAD) activities. In cloned heifers at 8 months of age, there was a greater proportion of MyHC I (slow oxidative isoform) and MyHC IIa (fast oxido-glycolytic isoform), a lower proportion of MyHC IIx (fast glycolytic isoform), greater COX and HAD activity and a lower LDH/ICDH ratio compared with control heifers. Thus, young cloned heifers had slower muscle types associated with a more oxidative muscular metabolism than control heifers. From 12 months of age onwards, no significant differences were observed between cloned and control heifers. A delay in muscle differentiation and maturation in cloned heifers is hypothesised and discussed.

It is well known that any quantitative (energy and protein levels) and qualitative (nature of the diet, nutrient dynamic) changes in the feeding of animals affect metabolism. Energy expenditure and feed efficiency at the whole-body level, nutrient partitioning between and within tissues and organs and, ultimately, tissue and organ characteristics are the major regulated traits with consequences on the quality of the meat and milk produced. Recent progress in biology has brought to light important biological mechanisms which explain these observations: for instance, regulation by the nutrients of gene expression or of key metabolic enzyme activity, interaction and sometimes cross-regulation or competition between nutrients to provide free energy (ATP) to living cells, indirect action of nutrients through a complex hormonal action, and, particularly in herbivores, interactions between trans-fatty acids produced in the rumen and tissue metabolism. One of the main targets of this nutritional regulation is a modification of tissue insulin sensitivity and hence of insulin action. In addition, the nutritional control of mitochondrial activity (and hence of nutrient catabolism) is another major mechanism by which nutrients may affect body composition and tissue characteristics. These regulations are of great importance in the most metabolically active tissues (the digestive tract and the liver) and may have undesirable (i.e. diabetes and obesity in humans) or desirable consequences (such as the production of fatty liver by ducks and geese, and the production of fatty and hence tasty meat or milk with an adapted fatty acid profile).

The advent of high-throughput DNA sequencing techniques, array technology and protein analysis has increased the efficiency of research in bovine muscle physiology, with the ultimate objective of improving beef quality either by breeding or rearing factors. For genetic purposes, polymorphisms in some key genes have been reported for their association with beef quality traits. The sequencing of the bovine genome has dramatically increased the number of available gene polymorphisms. The association of these new polymorphisms with the variability in beef quality (e.g. tenderness, marbling) for different breeds in different rearing systems will be a very important issue. For rearing purposes, global gene expression profiling at the mRNA or protein level has already shown that previously unsuspected genes may be associated either with muscle development or growth, and may lead to the development of new molecular indicators of tenderness or marbling. Some of these genes are specifically regulated by genetic and nutritional factors or differ between different beef cuts. In recognition of the potential economic benefits of genomics, public institutions in association with the beef industry are developing livestock genomics projects around the world. From the scientific, technical and economical points of view, genomics is thus reshaping research on beef quality.