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Background The A2 β-casein milk variant has gained interest due to potential health benefits, which has contributed to the rise of A2A2 genotypes within dairy herds. Although the A1 to A2 amino acid substitution in β-casein does not directly regulate gene expression, selective breeding for the A2A2 genotype may have indirect transcriptomic consequences in the mammary gland. Results In this study, we investigated whether the A1A1 and A2A2 β-casein genotypes are associated with differential mRNA isoform expression in bovine milk fat globules (MFG) using RNA-Sequencing technology (RNA-Seq). A total of 619 million paired-end reads from 14 MFG cDNA libraries were analysed. In total, 3,454 DE mRNA isoforms were identified (FDR < 0.05, |FC|> 2), of which 823 were mRNA isoforms with annotated associated genes, 2,067 were mRNA isoforms with annotated associated genes but novel transcript lengths and 586 were novel mRNA isoforms with non-annotated associated genes. Functional analysis of the 2,954 DE mRNA isoforms with annotated gene names revealed 523 enriched metabolic pathways ( p  < 0.05). Among these pathways, patterns consistent with mitochondrial dysfunction and reduced mitochondrial fatty acid β-oxidation were observed in A2A2 cows, together with indications of reduced mitochondrial biogenesis and altered mitochondrial RNA degradation, suggesting adjustments in cellular energy metabolism. Additionally, differences in isoforms related to ER-Golgi communication, vesicle trafficking and protein folding pointed to subtle modifications in secretory pathway dynamics. Regarding lipid metabolism, A2A2 cows showed signs of increased fatty acid uptake but reduced capacity for de novo synthesis of fatty acids, triglyceride and cholesterol synthesis, as well as for lipid droplet formation. Conclusions These findings suggest that the A2A2 genotype would be associated with isoform level changes likely driven by alternative splicing events. Further functional validation will be necessary to assess the biological relevance of the observed differences and their potential implications for genetic selection for the A2 β-casein variant.

This study examined the effect of linseed and algae on growth and carcass parameters, adipocyte cellularity, fatty acid profile and meat quality and gene expression in subcutaneous and intramuscular adipose tissues (AT) in lambs. After weaning, 33 lambs were fed three diets up to 26.7 ± 0.3 kg: Control diet (barley and soybean); L diet (barley, soybean and 10% linseed) and L-A diet (barley, soybean, 5% linseed and 3.89% algae). Lambs fed L-A diet showed lower average daily gain and greater slaughter age compared to Control and L (P < 0.001). Carcass traits were not affected by L and L-A diets, but a trend towards greater adipocyte diameter was observed in L and L-A in the subcutaneous AT (P = 0.057). Adding either linseed or linseed and algae increased α-linolenic acid and eicosapentaenoic acid contents in both AT (P < 0.001); however, docosahexaenoic acid was increased by L-A (P < 0.001). The n-6/n-3 ratio decreased in L and L-A (P < 0.001). Algae had adverse effects on meat quality, with greater lipid oxidation and reduced ratings for odor and flavor. The expression of lipogenic genes was downregulated in the subcutaneous AT (P < 0.05): acetyl-CoA carboxylase 1 (ACACA) in L and L-A and lipoprotein lipase (LPL) and stearoyl-CoA desaturase (SCD) in L-A. Fatty acid desaturase 1 (FADS1), fatty acid desaturase 2 (FADS2) and fatty acid elongase 5 (ELOVL5) were unaffected. In the subcutaneous AT, supplementing either L or L-A increased peroxisome proliferator-activated receptor gamma (PPARG) and CAAT-enhancer binding protein alpha (CEBPA) (P < 0.05), although it had no effect on sterol regulatory element-binding factor 1 (SREBF1). In the intramuscular AT, expression of ACACA, SCD, FADS1 and FADS2 decreased in L and L-A (P < 0.001) and LPL in L (P < 0.01), but PPARG, CEBPA and SREBF1 were unaffected.

Background Standard procedures for milk sample collection for transcriptome analysis use ice as preservation method, which can affect the RNA stability and requires immediate sample processing. These problems would be eased if the milk samples could be snap-frozen in liquid nitrogen. This study describes the applicability of a new method for milk sample collection and subsequent RNA extraction from milk fat globules, determining whether the quality, integrity and quantity of the RNA extracts met the minimum requirements for downstream RNA-seq. Results The quality of the extracts measured by A 260/280 ratio and the Integrity and Quality (IQ) values obtained fulfilled the reference values of 1.9 - 2.1 ( P1  < 0.05 and P2  < 0.05) and ≥ 9 ( P  < 0.05), respectively. However, the RNA Integrity Number (RIN), based on rRNA 18S and 28S analysis, was 3.59 ( P  > 0.05) and failed to meet the RIN ≥ 7 benchmark for RNA-seq ( P  > 0.05). Milk fat globules contain low molecular-weight RNA fragments and minimal 18S and 28S rRNA, suggesting low RIN values were inherent to sample type. Likewise, the RNA concentration from milk fat globules were generally low (120.43 ± 22.27 ng/µL, 102.87 ± 15.64 ng/µL and 109.43 ± 22.69 ng/µL, measured by Nanodrop, Qubit HS and QuanTI Ribogreen, respectively). Nevertheless, RNA-seq yielded 52.7 million paired-end reads per sample. The raw reads passed all quality control parameters having the same sequence-read lengths (151 bp), 100% base-coverage, 49% GC base content, and base quality scores of 36, enabling successful transcriptome profiling. Moreover, milk proteins were identified as the most abundant transcripts in MFG in the analysis of the most expressed genes, indicating that the sequenced reads would accurately reflect the transcriptome of this milk fraction. Conclusions Milk preservation in liquid nitrogen is a suitable sample collection method that overcomes the limitations of immediate sample processing required if ice is used. Thus, this procedure, together with the subsequent RNA isolation from milk fat globules and its sequencing by RNA-seq, would provide a practical and a non-invasive method for measuring the mammary epithelial cell transcriptome, improving the feasibility of conducting studies related to mammary gland and lactation physiology.

The protein fraction of β-casein may play a key role in the manifestation of a new intolerance: milk protein intolerance. The most common forms of β-casein among dairy cattle breeds are A1 and A2 β-casein. During gastrointestinal digestion of A1 β-casein, an opioid called peptide β-casomorphin-7 (BCM-7) is more frequently released, which can lead to adverse health outcomes. For that reason, novel products labelled as “A2 milk” or “A1-free dairy products” have appeared on the market. In this context, a bibliometric analysis on A2 β-casein research was carried out through the Web of Science (WoS) database. The main objective of this work was to provide an overview of the state of the art in the field of β-casein A2 by analyzing the number of publications per year, trends in thematic content, the most frequently used terms, and the most important institutions and countries in the field. This bibliometric study showed that a greater effort is needed to determine the possible implications of this novel product for human health and the market.

This review was funded by Ministry of Science, Innovation and Universities of Spain (Grant numbers: INIA RTA2017–00008-C02–01 and − 02), and the Technology Transfer Operation of the Rural Development Program of Catalonia 2014–2020 (Government of Catalonia and the European Regional Development Funds, Grant code 01.02.01).

This study aimed to assess the influence of ageing on the volatile compounds, as well as odour and flavour attributes of lamb meat from the Navarra breed. Twenty-one male lambs were fed a commercial concentrate diet after weaning and were harvested at 101 ± 6.5 days of age. From the Longissimus thoracis, 26 volatile compounds were identified, with hexanal, 2-propanone, and nonanal the most abundant (57.17% relative percentage abundance, RPA). The effect of ageing (1 vs. 4 d) was observed (p < 0.05) in six compounds: 1,4-dimethylbenzene decreased with ageing, while tridecane, 3-methylbutanal, 2-heptanone, 3-octanone, and 1-octen-3-ol increased. In general, ageing was linked to a decrease in livery and bloody flavour, bloody odour and ethanal, and an increase in pentane, hexanal, and heptanal, which are usually associated with fresh green grass and fat descriptors. Consequently, ageing lamb from the Navarra breed for four days might have a positive effect on meat sensory odour and flavour quality.

Dietary recommendations by health authorities have been advising of the importance of diminishing saturated fatty acids (SFA) consumption and replacing them by polyunsaturated fatty acids (PUFA), particularly omega-3. Therefore, there have been efforts to enhance food fatty acid profiles, helping them to meet human nutritional recommendations. Ruminant meat is the major dietary conjugated linoleic acid (CLA) source, but it also contains SFA at relatively high proportions, deriving from ruminal biohydrogenation of PUFA. Additionally, lipid metabolism in ruminants may differ from other species. Recent research has aimed to modify the fatty acid profile of meat, and other animal products. This review summarizes dietary strategies based on the n-3 PUFA supplementation of ruminant diets and their effects on meat fatty acid composition. Additionally, the role of n-3 PUFA in adipose tissue (AT) development and in the expression of key genes involved in adipogenesis and lipid metabolism is discussed. It has been demonstrated that linseed supplementation leads to an increase in alpha-linolenic acid (ALA) and eicosapentaenoic acid (EPA), but not in docosahexaenoic acid (DHA), whilst fish oil and algae increase DHA content. Dietary PUFA can alter AT adiposity and modulate lipid metabolism genes expression, although further research is required to clarify the underlying mechanism.

The amount and distribution of subcutaneous fat is an important factor affecting beef carcass quality. The degree of fatness is determined by visual assessments scored on a scale of five fatness levels (the SEUROP system). New technologies such as the image analysis method have been developed and applied in an effort to enhance the accuracy and objectivity of this classification system. In this study, 50 young bulls were slaughtered (570 ± 52.5 kg) and after slaughter the carcasses were weighed (360 ± 33.1 kg) and a SEUROP system fatness score assigned. A digital picture of the outer surface of the left side of the carcass was taken and the area of fat cover (fat area) was measured using an image analysis system. Commercial cutting of the carcasses was performed 24 h post-mortem. The fat trimmed away on cutting (cutting fat) was weighed. A regression analysis was carried out for the carcass cutting fat (y-axis) on the carcass fat area (x-axis) to establish the accuracy of the image analysis system. A greater accuracy was obtained by the image analysis (R2 = 0.72; p < 0.001) than from the visual fatness scores (R2 = 0.66; p < 0.001). These results show the image analysis to be more accurate than the visual assessment system for predicting beef carcass fatness.

Feed supplementation withα-linolenic acid (ALA) and linoleic acid (LA) increases their content in muscle, ALA increases n-3 polyunsaturated fatty acids and decrease n-6/n-3 ratio in muscle, and LA increases rumenic acid. However, high LA supplementation may have negative effects on lambs' lipid oxidative stability of meat. When the sources of ALA and LA are fed as fresh forage, the negative effects are counterbalanced by the presence of other bioactive compounds, as vitamin E (mainlyα-tocopherol) and polyphenols, which delay the lipid oxidation in meat. There is a wide consensus on the capability of vitamin E delaying lipid oxidation on lamb meat, and its feed content should be adjusted to the length of supplementation. A high dietary inclusion of proanthocyanidins, phenolic compounds and terpenes reduce the lipid oxidation in muscle and may improve the shelf life of meat, probably as a result of a combined effect with dietary vitamin E. However, the recommended dietary inclusion levels depend on the polyphenol type and concentration and antioxidant capacity of the feedstuffs, which cannot be compared easily because no routine analytical grading methods are yet available. Unless phenolic compounds content in dietary ingredients/supplements for lambs are reported, no specific association with animal physiology responses may be established.

Open Access funding provided by Universidad Pública de Navarra. This research was funded by the Public University of Navarre within the framework of Young Researcher Projects 2022 and by the Department of University, Innovation, and Digital Transformation of the Government of Navarre, grant number 0011-1408-2022-000024 (RES 95E/2022 of May 17).