Frequencies Evaluation of β-Casein Gene Polymorphisms in Dairy Cows Reared in Central Italy

The A1/A2 β-casein genotype of cows, but not their horn status, influences peptide generation during simulated digestion of milk

The effect of the horn status of cows on their milk composition and quality is a controversial research topic. In this study, 128 milk samples from 64 horned and 64 disbudded Brown Swiss and Original Braunvieh cows were collected from alpine farms where both horned and disbudded cows were grazing on mountain pastures. The samples were analyzed for their detailed composition and protein digestion in a simulated in vitro digestion (INFOGEST). To exclude probable influences on digestion, the β-CN genotype with its variants A1 and A2 was also included in the study. The effects of horn status and β-CN genotype were investigated in linear mixed models, which included additional influencing random factors such as Original Braunvieh blood proportion, stage of lactation, and farm. Horn status did not have any effect on milk composition or digestion. In contrast, milk from A1A1 cows showed a different protein digestion than milk of A1A2 and A2A2 cows in the gastric phase, including smaller amounts of β-casomorphin(BCM)21-associated peptides and larger amounts of BCM11-associated peptides. Abundances of BCM7 did not differ between β-CN genotypes. At the end of the intestinal phase, the digested milk of A1A1 and A2A2 β-CN genotypes did not differ.

Health-Related Outcomes and Molecular Methods for the Characterization of A1 and A2 Cow's Milk: Review and Update

A new trend in cow's milk has emerged in the market called type A1 and A2 milk. These products have piqued the interest of both consumers and researchers. Recent studies suggest that A2 milk may have potential health benefits beyond that of A1 milk, which is why researchers are investigating this product further. It is interesting to note that the A1 and A2 milk types have area-specific characteristics compared to breed-specific characteristics. Extensive research has focused on milk derivatives obtained from cow's milk, primarily through in vitro and animal studies. However, few clinical studies have been conducted in humans, and the results have been unsatisfactory. New molecular techniques for identifying A1 and A2 milk may help researchers develop new studies that can clarify certain controversies surrounding A1 milk. It is essential to exercise extreme caution when interpreting the updated literature. It has the potential to spread panic worldwide and have negative economic implications. Therefore, this study aims to investigate the differences between A1 and A2 milk in various research areas and clarify some aspects regarding these two types of milk.

A discussion on A1-free milk: Nuances and comments beyond implications to the health

This chapter provides an overarching view of the multifaceted aspects of milk β-casein, focusing on its genetic variants A1 and A2. The work examines the current landscape of A1-free milk versus regular milk, delving into health considerations, protein detection methods, technological impacts on dairy production, non-bovine protein, and potential avenues for future research. Firstly, it discussed ongoing debates surrounding categorizing milk based on A1 and A2 β-casein variants, highlighting challenges in establishing clear regulatory standards and quality control methods. The chapter also addressed the molecular distinction between A1 and A2 variants at position 67 of the amino acid chain. This trait affects protein conformation, casein micelle properties, and enzymatic susceptibility. Variations in β-casein across animal species are acknowledged, casting doubt on non-bovine claims of "A2-like" milk due to terminology and genetic differences. Lastly, this work explores the burgeoning field of biotechnology in milk production.

Bovine milk β-casein: Structure, properties, isolation, and targeted application of isolated products

β-Casein, an important protein found in bovine milk, has significant potential for application in the food, pharmaceutical, and other related industries. This review first introduces the composition, structure, and functional properties of β-casein. It then reviews the techniques for isolating β-casein. Chemical and enzymatic isolation methods result in inactivity of β-casein and other components in the milk, and it is difficult to control the production conditions, limiting the utilization range of products. Physical technology not only achieves high product purity and activity but also effectively preserves the biological activity of the components. The isolated β-casein needs to be utilized effectively and efficiently for various purity products in order to achieve optimal targeted application. Bovine β-casein, which has a purity higher than or close to that of breast β-casein, can be used in infant formulas. This is achieved by modifying its structure through dephosphorylation, resulting in a formula that closely mimics the composition of breast milk. Bovine β-casein, which is lower in purity than breast β-casein, can be maximized for the preparation of functional peptides and for use as natural carriers. The remaining byproducts can be utilized as food ingredients, emulsifiers, and carriers for encapsulating and delivering active substances. Thus, realizing the intensive processing and utilization of bovine β-casein isolation. This review can promote the industrial production process of β-casein, which is beneficial for the sustainable development of β-casein as a food and material. It also provides valuable insights for the development of other active substances in milk.

Potential status of A1 and A2 variants of bovine beta-casein gene in milk samples of Indian cattle breeds

This study aimed to determine the polymorphism in 7th exon of beta-casein gene (CSN2) gene in seven domestic (Kosali, Tharparkar, Gangatiri, Sahiwal, Gir, Khariar, Motu) and two exotic cattle breeds (Jersey and Holstein-Friesian). Genomic DNA was extracted from 1000 milk samples, and the C > A polymorphism in CSN2 was determined using the tetra-primer amplification refractory mutation system-polymerase chain reaction method. In all Indigenous cattle breeds, the mean frequency of A1A2 and A2A2 genotypes was 0.19 and 0.80, respectively. The A1A1 genotype was absent in all seven domestic cattle breeds. The frequency of the A2A2 genotype was highest in the Gir breed (0.93). However, the Sahiwal, Tharparkar, and Motu breeds also had a higher frequency of A2A2 genotype compared to other breeds. In contrast, Gangatiri breed of India showed lowest frequency of A2A2 genotype. The mean A1 and A2 allele frequency was 0.09 and 0.91, respectively. In exotic breeds, the mean frequencies of the A1A1, A1A2, and A2A2 genotypes were 0.42, 0.55, and 0.03, respectively. Similarly, the mean A1 and A2 allele frequency was 0.69 and 0.31, respectively. This study suggests the high potential of Gir, Sahiwal, Tharparkar, and Motu cattle for A2 milk production since they carry a favorable A2 genotype.

Detection of A2A2 genotype of beta casein protein (CSN2) gene in local, exotic and cross bred cattle in Pakistan

Genetic variants of bovine Beta-casein protein (CSN2) gene especially A1 and A2 are the most important variants in dairy cattle. A1 milk protein is considered as risk factor for different disease and milk intolerance which release Beta-Casomorphin-7 during digestion which is a bioactive opioid but not released from A2 milk protein. This opioid is responsible for several human health problems like Coronary Heart disease, type 1 diabetics, milk intolerance and other neurological disorders. In present study, 360 blood sample were collected from Lohani, Achai, jersey, Holstein Friesian, Achai x jersey, Friesian x Sahiwal and Sahiwal x Friesian from different region of Khyber Pakhtunkhwa (KP) province. The polymerase chain reaction (PCR) amplicons were sequenced for the identification of polymorphism in exon 7 of Beta-casein protein (CSN2) gene. Sequencing analysis explored CSN2 genotype in exon 7 using the Genomic sequence from GenBank (X.71104) g.8101 C > A at codon 67. The allelic and genotypic frequencies of CSN2 gene were analyzed and observed that Holstein Friesian cattle exhibited A1A2 33%, A1A1 50% and A2A2 17%, Jersey cattle show 68% A1A1, 18% A1A2 and 14% A2A2, Sahiwal x Friesian 56% A1A1, 26% A1A2 and 18% A2A2, Jersey × Achai 78% A2A2, 15% A1A2 and 7% A1A1, Achai 100% A2A2 Lohani 100% A2A2. This is a preliminary study, conducted with meager resources, therefore, it is very difficult to make conclusion that which particular breed possess harmful alleles and which breed possess useful alleles of beta-casein gene. Therefore, a comprehensive molecular work is needed to be performed with greater number of samples sequencing.

Worldwide research on the health effects of bovine milk containing A1 and A2 β-casein: Unraveling the current scenario and future trends through bibliometrics and text mining

The possible adverse effect of consuming bovine milk with A1 β-casein (but not with A2 β-casein) on health aspects due to the release of β-casomorphin-7 (BCM-7) is currently under debate. The aim of this study was to perform a bibliometric analysis of studies extracted from Scopus to explore the relationship between BCM-7, A1 or A2 bovine milk with different aspects of health. Over time, several research groups were formed that are no longer active and although some authors have returned to the field of study, they have focused their efforts mainly on conducting reviews that show the same imprecise conclusions due to the few original articles. Research is concentrated in Europe and Asia, where New Zealand, China and Germany are the countries with the most publications, records and citations on the subject, respectively. On the other hand, no country in Africa or South America has scientific production, which opens the possibility of building collaborations between countries and exploring areas that lack scientific studies. Based on conflicting information from primarily in vitro and animal studies, and limited clinical trials with poor designs, A1 milk presents pro-inflammatory and oxidative activity, but the evidence is insufficient to associate its consumption with negative health effects. However, A2 milk may be better tolerated by the digestive system of some individuals, suggesting its possible modulating role in the intestinal microbiota. Stronger scientific evidence is needed to reach a consensus on whether the presence of β-casein A1 can significantly negatively affect health. The information shown will allow a better understanding of the subject and consumers will be able to make their own decisions regarding A1 or A2 milk.

An approach on detection, quantification, technological properties, and trends market of A2 cow milk

The genetic variant A2 β-casein integrates the casein protein group in milk and has been often associated with positive health outcomes. Therefore, this review explores the present understanding of A2 β-casein, including detection methods and the market trends for dairy from A2 milk. Also, the interaction of A2 β-casein with αs₁-casein and κ-casein genotypes was examined in terms of technological impacts on A2 milk. A limited number of preliminary studies has aimed to investigate the sensorial and technological impacts of β-casein variants in milk matrices, for instance, in yogurt and other derivatives. Nevertheless, considering studies carried out so far, it is concluded that the manufacture of dairy products from A2 milk is perfectly feasible, as the products presented slight differences when compared to those derived from traditional milk. In one of the works, sensitive drops in rennet coagulation time and curd firmness values were observed in cheese traits. However, it is relevant to point out that variant A of κ-casein plays a negative role in the coagulation features of milk. Therefore, alterations in the pattern of cheese-making properties are not uniquely related to β-casein variants. Attempts to produce A2 β-casein in laboratory (non-natural source), through biosynthesis, for example, have not been found so far. This knowledge gap offers a promising area for future studies concerning proteins and bioactive peptide production.

Cow's Milk in Human Nutrition and the Emergence of Plant-Based Milk Alternatives

Cow's milk is considered a complete food, providing high-quality protein and essential micronutrients, including vitamins and minerals. For medical reasons or as a lifestyle choice, consumers are replacing cow's milk with plant-based milk alternatives (PBMA); some perceive them as healthier alternatives to cow's milk due to their low saturated fatty acid content and no cholesterol content. However, the nutritional composition of PBMA is quite variable between different types and even within, which makes a comparison with cow's milk a complex issue. Furthermore, the consumption of PBMA has been associated with the development of some diseases in infants and children. Meanwhile, the consumption of cow's milk in human health is a controversial issue since it has been associated with a favorable effect in some diseases (such as obesity, type 2 diabetes, and Alzheimer's) and a negative effect in others (such as prostate cancer risk and Parkinson's disease); while in some diseases, there is no consensus in the cow's milk consumption effect. The aim of this review is to make a nutritional comparison of cow's milk with PBMA and to clarify the potential health issues related to their consumption.

Characterization of the genetic polymorphism linked to the β-casein A1/A2 alleles using different molecular and biochemical methods

The 2 major subvariants of β-casein (A1 and A2), coded by CSN2 gene, have received great interest in the last decade both from the scientific community and the dairy sector due to their influence on milk quality. The consumption of the A1 variant, compared with the A2 variant, has a potential negative effect on human health after its digestion but, at the same time, its presence improves the milk technological properties. The aim of the present study was to compare the best method in terms of time required, costs, and technical engagement for the identification of β-casein A1 and A2 variants (homozygous and heterozygous animals) in milk to offer a reliable service for large-scale screening studies. Two allele-specific PCR procedures, namely RFLP-PCR and amplification refractory mutation system (ARMS-PCR), and one biochemical technique (HPLC) were evaluated and validated through sequencing. Manual and automated DNA extraction protocols from milk somatic cells were also compared. Automated DNA extraction provided better yield and purity. Chromatographic analysis was the most informative and the cheapest method but unsuitable for large-scale studies due to lengthy procedures (45 min per sample). Both allele-specific PCR techniques proved to be fast and reliable for differentiating between A1 and A2 variants but more expensive than HPLC analysis. Specifically, RFLP-PCR was the most expensive and labor-demanding among the evaluated techniques, whereas ARMS-PCR was the fastest while also requiring less technical expertise. Overall, automated extraction of DNA from milk matrix combined with ARMS-PCR is the most suitable technique to provide genetic characterization of the CSN2 gene on a large scale.

Frequency of β-Casein Gene Polymorphisms in Jersey Cows in Western Japan

Simple Summary

Reports presenting survey results for β-casein gene polymorphisms have increased, but none have been about Jersey cows in Asia. This study examined the CSN2 gene variants for 590 Jersey cows in Okayama Prefecture, located in the western region of Japan. Blood samples were collected at eight farms, and nucleotide substitutions were determined by sequencing exon 7 regions of chromosome 6 of the CSN2 gene. Blood biochemical analyses were also performed to clarify if A1A1, A1A2, and A2A2 cows differ in their metabolic profiles. The frequency of the A2 allele found in this study was numerically higher than those reported for Holsteins, crossbreeds, and Mexican and Danish Jerseys. The β-casein genotypes did not affect the metabolism of the major nutrients.

Abstract

This study aimed to investigate β-casein gene polymorphisms in Jersey cows in Japan. Blood samples were collected from 590 cows from eight Jersey farms in Okayama Prefecture, western Japan. Sequence analysis of exon 7 regions in chromosome 6 of the CSN2 gene revealed the genotype and allele frequencies of the β-casein variants. Considering that variant B belongs to the A1 group and variant I to the A2 group, plasma metabolite concentrations were compared among the A1A1, A1A2, and A2A2 group-based genotypes. The most frequent genotype was A2A2 (0.558), followed by A2B (0.190) and A2I (0.103). No variants of A3, F, G, H1, or H2 were found. The frequencies of group-based genotypes were A1A1 (0.032), A1A2 (0.303), and A2A2 (0.665). Although farm-to-farm differences were observed in the plasma concentrations of urea nitrogen, calcium, and phosphorus, no differences were found between the A1A1, A1A2, and A2A2 group-based genotypes; hence, the β-casein genotypes did not affect the metabolism of major nutrients. Owing to the high frequency of the A2 variant, Jersey cows can be considered an attractive breed for marker-assisted selection to create A2A2 herds.

Online trypsin digestion coupled with LC-MS/MS for detecting of A1 and A2 types of β-casein proteins in pasteurized milk using biomarker peptides

Bovine A1-or A2-type β-caseins have attracted a growing interest due to their variation in beta-casomorphin-7 (BCM-7) formation, which may affect health. In the present work, identification and quantification of A1 and A2 types of β-casein proteins at the peptide level was achieved for the first time. An automated and online immobilized trypsin digestion system was employed for high throughput digesting of proteins into peptides. Tryptic peptides were separated and analyzed subsequently by liquid chromatography coupled to mass spectrometry platform. Two specific peptides ranging from the position of 49 to 97 in the peptide chain were selected for the identification and quantification of A1 and A2 β-casein, which covered the different amino acids between them. Synthetic isotopically labeled winged peptides were used for absolute quantification. Compared with traditional in-solution digestion, online digestion shortens digestion times from 2 to 24 h to 4 min. The limits of quantification (LOQ) of A1 and A2 β-casein in pasteurized milk are 0.8 and 2.4 µg/g, respectively. To further demonstrate the applicability of the proposed method, commercial pasteurized milk tests were performed with satisfactory results.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13197-022-05376-6.

Worldwide Research Trends on Milk Containing Only A2 β-Casein: A Bibliometric Study

Simple Summary

A1 β-casein has been correlated with adverse health outcomes, and, as a consequence, milk containing only A2 β-casein has emerged on the market. There has been a relevant increase in publications in this area since 2010. Food Science Technology and Agriculture were the main research areas of this topic. The term β-casomorphin was the most frequently used. The USA, New Zealand, and Australia were the most productive countries, though the most productive research institutions were, in absolute terms, from India, France, and Germany. The majority of the most cited studies that refer to A2 β-casein and health were reviews, and a few clinical trials have also been published.

Abstract

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.

Comparative analysis of allele frequencies for DNA polymorphisms associated with disease and economically important traits in the genomes of Russian and foreign cattle breeds

The genetic makeup of a breed including its genetic differences from other breeds determines its appearance and characteristics, including economically important traits and resistance to pathologies. To date, many loci controlling significant phenotypes have been identified, which is successfully used in the world practice of marker-assisted selection to improve breed properties. The aim of this study was a comparative analysis of frequencies for known causative nucleotide substitutions, insertions and deletions associated with disease and economically important traits in Russian and foreign cattle breeds. As a result, we identified frequencies of these DNA polymorphisms in the populations of Russian cattle breeds, compared them with those of foreign populations of the same breed, as well as other foreign breeds. Our results indicate similarities in frequencies for most of such alleles within breeds (populations of Russian and foreign breeding), as well as the relationship between the causative allele prevalence and the presence of phenotypic traits under the effect. We also found an excess of some undesirable alleles in the Russian cattle populations, which should be paid attention to when designing breeding programs. We found that the alleles increasing fertility in the Hereford breed have a higher frequency in the Russian Hereford population compared to the foreign counterpart. Interestingly, unlike for the European breeds, for Asian Turano-Mongolian Wagyu and Yakut cattle, there was a less clear link between phenotypic traits and frequencies of known causative alleles. Our work points to specific genetic variants that could be used to improve and/or maintain the performance of certain cattle breeds bred in the Russian Federation.

Development of a Microsphere-Based Immunoassay Authenticating A2 Milk and Species Purity in the Milk Production Chain

Processed milk and milk products produced from bovine milk, commonly contain β-casein A1 (βCA1) and β-casein A2 (βCA2). Since the presence of βCA1 is linked to milk intolerance and digestion problems, A2A2 milk, which only contains βCA2, is proposed as a healthier alternative. To support this health claim, the purity of A2A2-milk has to be guaranteed. In the presented study, a multiplex immunoassay, able to distinguish between βCA2 and βCA1, was developed and real-life applicability was shown on raw milk samples from genotyped A1A1, A1A2 and A2A2 cows. Because of its ability to discriminate between βCA2 and βCA1, this newly developed method was able to detect the addition of common bovine A1A2 milk to A2A2 milk, as low as 1%. Besides the detection of A2A2 milk purity, the developed assay can also be implemented as a rapid phenotyping method at dairy farms to replace the more invasive DNA-based screening. Additionally, the developed method was capable of detecting the addition of common bovine milk up to 1% in sheep, goat, buffalo, horse and donkey milk, which conforms to EU recommendations. In conclusion, a newly developed multiplex method capable of reliably detecting the dilution of A2A2 milk of multiple species, with common bovine milk up to 1%, is presented.

Role of CSN2, CSN3, and BLG genes and the polygenic background in the cattle milk protein profile

To devise better selection strategies in dairy cattle breeding programs, a deeper knowledge of the role of the major genes encoding for milk protein fractions is required. The aim of the present study was to assess the effect of the CSN2, CSN3, and BLG genotypes on individual protein fractions (α_S1-CN, α_S2-CN, β-CN, κ-CN, β-LG, α-LA) expressed qualitatively as percentages of total nitrogen content (% N), quantitatively as contents in milk (g/L), and as daily production levels (g/d). Individual milk samples were collected from 1,264 Brown Swiss cows reared in 85 commercial herds in Trento Province (northeast Italy). A total of 989 cows were successfully genotyped using the Illumina Bovine SNP50 v.2 BeadChip (Illumina Inc.), and a genomic relationship matrix was constructed using the 37,519 SNP markers obtained. Milk protein fractions were quantified and the β-CN, κ-CN, and β-LG genetic variants were identified by reversed-phase HPLC (RP-HPLC). All protein fractions were analyzed through a Bayesian multitrait animal model implemented via Gibbs sampling. The effects of days in milk, parity order, and the CSN2, CSN3, and BLG genotypes were assigned flat priors in this model, whereas the effects of herd and animal additive genetic were assigned Gaussian prior distributions, and inverse Wishart distributions were assumed for the respective co-variance matrices. Marginal posterior distributions of the parameters of interest were compared before and after the inclusion of the effects of the 3 major genes in the model. The results showed that a high portion of the genetic variance was controlled by the major genes. This was particularly apparent in the qualitative protein profile, which was found to have a higher heritability than the protein fraction contents in milk and their daily yields. When the genes were included individually in the model, CSN2 was the major gene controlling all the casein fractions except for κ-CN, which was controlled directly by the CSN3 gene. The BLG gene had the most influence on the 2 whey proteins. The genetic correlations showed the major genes had only a small effect on the relationships between the protein fractions, but through comparison of the correlation coefficients of the proteins expressed in different ways they revealed potential mechanisms of regulation and competitive synthesis in the mammary gland. The estimates for the effects of the CSN2 and CSN3 genes on protein profiles showed overexpression of protein synthesis in the presence of the B allele in the genotype. Conversely, the β-LG B variant was associated with a lower concentration of β-LG compared with the β-LG A variant, independently of how the protein fractions were expressed, and it was followed by downregulation (or upregulation in the case of the β-LG B) of all other protein fractions. These results should be borne in mind when seeking to design more efficient selection programs aimed at improving milk quality for the efficiency of dairy industry and the effect of dairy products on human health.

Assessment of A1 and A2 variants in the CNS2 gene of some cattle breeds by using ACRS-PCR method

The aim of this study is to reveal β-casein polymorphism of some cattle breeds and also the potential to produce A2 milk from existing animals and to develop strategies in this area. Therefore, a total of 400 cattle, 100 animals from each breed of Holstein, Brown Swiss, Jersey and Simmental raised commonly in Turkey, were obtained, and C > A polymorphism in 67th amino acid in the 7th exons of β-casein gene was determined by TaqI enzyme with PCR-ACRS method. Blood samples were collected from dairy cattle farms raising Holstein, Brown Swiss and Jersey breeds from Konya province and Simmental breed from Kütahya province in Turkey. A1 and A2 allele frequencies in Holstein, Brown Swiss, Jersey and Simmental cattle breeds were determined as 0.475/0.525, 0.370/0.630, 0.215/0.785 and 0.440/0.560, respectively. The highest A2 allele frequency (0.785) was found in Jersey breed. A1A1 genotypes in Holstein, Brown Swiss, Jersey and Simmental breeds were 0.240, 0.150, 0.030 and 0.160, respectively; A1A2 genotypes were 0.470, 0.440, 0.370 and 0.560, respectively; A2A2 genotypes were determined as 0.290, 0.410, 0.600 and 0.280, respectively. In these breeds, the highest A2A2 genotype frequency was found in Jersey (0.600), the lowest A1A1 genotype frequency (0.030) was found in Jersey and the highest A1A2 genotype frequency (0.560) was found in Simmental. Holstein, Brown Swiss, Simmental and Jersey populations were at the level of Hardy-Weinberg in terms of β-casein gene (p > 0.05). The average H_o, H_e and PIC values were calculated as 0.460, 0.469 and 0.605, respectively. In conclusion, the frequency of commonly reared cattles in Turkey especially Brown Swiss, and Jersey breeds in A2A2 genotype are satisfactory, but it can be said that the use of animals with A2 allele in selection is extremely important for increasing A2 milk producing potential in the future.

Identification and in silico characterization of structural and functional impacts of genetic variants in milk protein genes in the Zebu breeds Guzerat and Gyr

Whole genome sequencing of bovine breeds has allowed identification of genetic variants in milk protein genes. However, functional repercussion of such variants at a molecular level has seldom been investigated. Here, the results of a multistep Bioinformatic analysis for functional characterization of recently identified genetic variants in Brazilian Gyr and Guzerat breeds is described, including predicted effects on the following: (i) evolutionary conserved nucleotide positions/regions; (ii) protein function, stability, and interactions; (iii) splicing, branching, and miRNA binding sites; (iv) promoters and transcription factor binding sites; and (v) collocation with QTL. Seventy-one genetic variants were identified in the caseins (CSN1S1, CSN2, CSN1S2, and CSN3), LALBA, LGB, and LTF genes. Eleven potentially regulatory variants and two missense mutations were identified. LALBA Ile60Val was predicted to affect protein stability and flexibility, by reducing the number the disulfide bonds established. LTF Thr546Asn is predicted to generate steric clashes, which could mildly affect iron coordination. In addition, LALBA Ile60Val and LTF Thr546Asn affect exonic splicing enhancers and silencers. Consequently, both mutations have the potential of affecting immune response at individual level, not only in the mammary gland. Although laborious, this multistep procedure for classifying variants allowed the identification of potentially functional variants for milk protein genes.

First DNA Sequencing in Beninese Indigenous Cattle Breeds Captures New Milk Protein Variants

This study investigated polymorphisms in the milk protein genes CSN1S1, CSN2, CSN1S2, CSN3, LALBA, and LGB, and casein haplotypes in Beninese indigenous cattle. Considering 67 animals, DNA sequencing of the genes' exons, flanking regions and parts of the 5'-upstream regions identified 1058 genetic variants including 731 previously unknown. In addition, four novel milk protein variants were detected, including CSN3K (p.Ala66Val), LALBAF (p.Arg58Trp), LGBB1 (p.Ala134Val) and LGBK (p.Thr92Asnfs*13). CSN3K is caused by a novel SNP (BTA6:85656526C>T, exon 4) whereas LALBAF and LGBB1 are due to rs714688595C>T (exon 1) and rs109625649C>T (exon 4), respectively. Regarding LGBK, a frameshift insertion of one adenine residue at BTA11:103257980 (exon 3) induces a premature translation termination resulting in a 46% reduction of the reference protein sequence. The casein polymorphisms formed five main CSN1S1-CSN2-CSN1S2-CSN3 haplotypes including B-A1-A-B, B-A1-A-A and C-A2-A-B which are predominant in the investigated cattle breeds. Moreover, in silico analyses of polymorphisms within the 5'- and 3'- untranslated regions of all six milk proteins revealed effects on microRNA and transcription factor binding sites. This study suggests a large genetic variation of milk protein genes in Beninese cattle, which should be investigated in further studies for their effects on milk production, including quality and yield traits.

Effect of Protein Genotypes on Physicochemical Properties and Protein Functionality of Bovine Milk: A Review

Milk protein comprises caseins (CNs) and whey proteins, each of which has different genetic variants. Several studies have reported the frequencies of these genetic variants and the effects of variants on milk physicochemical properties and functionality. For example, the C variant and the BC haplotype of αS1-casein (αS1-CN), β-casein (β-CN) B and A1 variants, and κ-casein (κ-CN) B variant, are favourable for rennet coagulation, as well as the B variant of β-lactoglobulin (β-lg). κ-CN is reported to be the only protein influencing acid gel formation, with the AA variant contributing to a firmer acid curd. For heat stability, κ-CN B variant improves the heat resistance of milk at natural pH, and the order of heat stability between phenotypes is BB > AB > AA. The A2 variant of β-CN is more efficient in emulsion formation, but the emulsion stability is lower than the A1 and B variants. Foaming properties of milk with β-lg variant B are better than A, but the differences between β-CN A1 and A2 variants are controversial. Genetic variants of milk proteins also influence milk yield, composition, quality and processability; thus, study of such relationships offers guidance for the selection of targeted genetic variants.

Nonlinear modeling to describe the pattern of 15 milk protein and nonprotein compounds over lactation in dairy cows

The protein profile of milk includes several caseins, whey proteins, and nonprotein nitrogen compounds, which influence milk's value for human nutrition and its cheesemaking properties for the dairy industry. To fill in the gap in current knowledge of the patterns of these individual nitrogenous compounds throughout lactation, we tested the ability of a parametric nonlinear lactation model to describe the pattern of each N compound expressed qualitatively (as % of total milk N), quantitatively (in g/L milk), and as daily yield (in g/d). The lactation model was tested on a data set of detailed milk nitrogenous compound profiles (15 fractions-12 protein traits and 3 nonproteins-for each expression mode: 45 traits) obtained from 1,342 cows reared in 41 multibreed herds. Our model was a modified version of Wilmink's model, often used for describing milk yield during lactation because of its reliability and ease of parameter interpretation from a biological point of view. We allowed the sign of the persistency coefficient (parameter c) that explained the variation in the long-term milk component (parameter a) to be positive or negative. We also allowed the short-term milk component (parameter b) to be positive or negative, and we estimated a specific speed of adaptation parameter (parameter k) for each trait rather than assumed a value a priori, as in the original model (k = 0.05). These 4 parameters were included in a nonlinear mixed model with cow breed and parity order as fixed effects, and herd-date as random. Combinations of the positive and negative signs of the b and c parameters allowed us to identify 4 differently shaped lactation curves, all found among the patterns exhibited by the nitrogenous fractions as follows: the "zenith" curve (with a maximum peak; for milk yield and 10 other N traits), the "nadir" curve (with a minimum point; for 20 traits, including almost all those expressed in g/L of milk), the "downward" curve (continuously decreasing; for 14 traits, including almost all those in g/d), and the "upward" curve (continuously increasing; only for κ-casein, in % N). Direct estimation of the k parameters specific to each trait showed the large variability in the adaptation speed of fresh cows and greatly increased the model's flexibility. The results indicated that nonlinear parametric mathematical models can effectively describe the different and complex patterns exhibited by individual nitrogenous fractions during lactation; therefore, they could be useful tools for interpreting milk composition variations during lactation.

Beneficial Effects of Milk Having A2 β-Casein Protein: Myth or Reality?

Diet has been shown to play an important role in maintaining normal homeostasis in the human body. Milk and milk products are a major component of the Western diet, but their consumption may predispose sensitive individuals to adverse health outcomes. Current literature about milk products recognizes various bioactive components including lactate, whey protein, and β-casein protein. Specifically, cow milk has 2 major subvariants of its β-casein protein, A1 and A2, due to a single nucleotide difference that changes the codon at position 67. Whereas the A2 polymorphism is unlikely to undergo enzymatic cleavage during digestion, the A1 polymorphism is more likely to undergo enzymatic cleavage resulting in the product peptide β-casomorphin-7, a known μ-opioid receptor agonist. The objective of this article is to review the current understanding of the 2 major β-casein subvariants and their effects on various organ systems that may have an impact on the health of an individual. Synthesis of the current existing literature on this topic is relevant given the increased association of milk consumption with adverse effects in susceptible individuals resulting in a rising interest in consuming milk alternatives. We discuss the influence of the β-casein protein on the gastrointestinal system, endocrine system, nervous system, and cardiovascular system as well as its role in antioxidants and methylation. A1 milk consumption has been associated with enhanced inflammatory markers. It has also been reported to have an opioid-like response that can lead to manifestations of clinical symptoms of neurological disorders such as autism spectrum disorder. On the other hand, A2 milk consumption has been associated with beneficial effects and is easier to digest in sensitive individuals. Further research is warranted to investigate the short- and long-term effects of consumption of A1 β-casein in comparison with milk with A2 β-casein proteins.

The Polymorphism in Various Milk Protein Genes in Polish Holstein-Friesian Dairy Cattle

Simple Summary

The aim of the present study was to evaluate the genetic variability within casein alpha S1 (CSN1S1), casein alpha S2 (CSN1S2), beta-casein (CSN2), kappa-casein (CSN3), and progestagen-associated endometrial protein (PAEP) genes. The study was conducted on 1900 Polish Black and White Holstein-Friesian dairy cows that were genotyped using customized EuroGenomics microarrays. Out of investigated 24 genetic variants within four genes coding milk protein, 16 expressed genetic diversity. The fact that many of the investigated Single Nucleotide Polymorphisms (SNPs) were monomorphic may suggest that in the past the reproduction program favored one of these genotypes. Populations of high-yielding cows become more and more even and similar in terms of genotype, which may have an adverse effect in future breeding, therefore, the variability in genetic variants of genes coding milk protein should be monitored.

Abstract

The aim of the present study was to evaluate the genotype and allele frequencies of 24 polymorphisms in casein alpha S1 (CSN1S1), casein alpha S2 (CSN1S2), beta-casein (CSN2), kappa-casein (CSN3), and progestagen-associated endometrial protein (PAEP) genes. The study included 1900 Polish Black and White Holstein-Friesian dairy cows that were subjected to genotyping via microarrays. A total of 24 SNPs (Single Nucleotide Polymorphisms) within tested genes were investigated. Two CSN1S1 SNPs were monomorphic, while allele CSN1S1_3*G in CSN1S1_3 SNP dominated with a frequency of 99.39%. Out of seven CSN2 SNPs, four were polymorphic; however, only for CSN2_3 all three genotypes were detected. Only three out of nine SNPs within CSN3 were monomorphic. Three PAEP SNPs were also found to be polymorphic with heterozygotes being most frequent. Hardy–Weinberg equilibrium (HWE) was observed for eight variants. It was shown that only CSN3_6 was not in HWE. The fact that many of investigated SNPs were monomorphic may suggest that in the past the reproduction program favored one of these genotypes. SNPs that are included in commercially available microarrays should be monitored in relation to changes in their frequencies. If a SNP has turned monomorphic, maybe it should be considered for removal from the microarray.