Effect of fatty acid composition on the volatile compounds of pasteurized milk during low-temperature storage.

The change in milk fat during storage greatly influences its flavor. This study investigates the effect of fatty acid composition on milk flavor by analyzing volatile compounds in pasteurized whole milk (PWM) and pasteurized skim milk (PSM) during storage at 4 °C. 33 types of volatile compounds were detected and the content of ketones was highest, followed by esters and aldehydes. Based on variable importance in projection and relative odor activity value, 2-hexenal dimer, acetic acid ethyl ester dimer, acetic acid ethyl ester, and butanal were identified as the key differential volatile compounds. These compounds were found in higher concentrations in PWM than in PSM, indicating a close relationship with the changes in the fatty acid composition of milk fat. Among 11 fatty acids detected in PWM, the content of saturated fatty acids (SFA) and polyunsaturated fatty acids (PUFA) decreased by 0.69 % and 49.1 %, respectively, while the content of monounsaturated fatty acids increased by 46.8 % during 15 days storage, which suggests that the oxidation of SFA and PUFA contributed more to the volatile compound formation. Correlation analysis between fatty acid composition and volatile compounds found that fatty acid C18:2 and C16:0 were strongly associated for 2-hexenal, acetic acid ethyl ester, and butanal. These fatty acids were mainly derived from neutral lipids or phospholipids. These findings provide a new perspective for the formation pathway of milk flavor.

Associations between Dietary Fatty Acid Profile and Milk Fat Production and Fatty Acid Composition in Dairy Cows: A Meta-Analysis.

This meta-analysis aimed to investigate the effect of dietary fatty acid (FA) profile on milk fat production and FA profile in dairy cows. The study also aimed to develop prediction models using a meta-regression approach. The database included 217 peer-reviewed articles on lactating dairy cows (n = 12,892), consisting of 515 treatment means. Effect size was assessed using the raw mean differences between diets with supplementary lipid sources and those without. Subgroup analyses were employed to assess heterogeneity. Diets rich in saturated FA (SFA) increased milk fat production and proportion, while reducing de novo FA in milk. Diets high in monounsaturated FA and polyunsaturated FA decreased mixed FA in milk. Most lipid-supplemented diets increase preformed FA in milk, except those rich in SFA. Prediction models were developed using meta-regression. Key predictors of milk fat production included neutral detergent fiber (NDF), dietary myristic acid, and milk production. Milk fat proportion was best predicted by dietary unsaturated FA, NDF, and forage. De novo FA in milk was predicted by dry matter intake (DMI) and dietary FA, while preformed FA was predicted by DMI, dietary oleic and linoleic acids. In conclusion, this study emphasizes the importance of the dietary FA profile in evaluating the effects of lipids on milk fat production and FA profile. Accurate and precise predictions of milk fat production, proportion, and FA profile can be achieved by considering cow production and dietary characteristics.

Effect of Maternal Diet and Milk Lipid Composition on the Infant Gut and Maternal Milk Microbiomes.

Inter-subject variability in human milk microbiome is well known; however, its origins and possible relationship to the mother's diet are still debated. We investigated associations between maternal nutrition, milk fatty acids composition and microbiomes in mother-infant dyads. Breast milk and infant fecal samples were collected across three time points (one week, one month and three months postpartum) from 22 mother-infant pairs. Food frequency questionnaires for the months of pregnancy and three months postpartum were collected. Milk fatty acids were analyzed by GC-MS and the microbiome in breast milk and infant feces was determined by 16S rRNA sequencing. Statistical interactions were computed using Spearman's method and corrected for multiple comparisons. We found significant negative correlation between Streptococcus relative abundance in maternal milk and intake of unsaturated fatty acids and folic acid at one month postpartum. At three months postpartum, vitamin B-12 consumption was significantly associated with a single operational taxonomic unit belonging to Streptococcus. Comparison between milk microbiome and lipid composition showed, one-month postpartum, significant negative correlation between Streptococcus relative abundance and the abundance of oleic acid. Additional correlations were detected between Staphylococcus hominis and two medium-chain saturated fatty acids. Our results reinforce the hypothesis that maternal nutrition may affect milk microbiome.

Combined use of milk infrared spectra and genotypes can improve prediction of milk fat composition.

It has been shown that milk infrared (IR) spectroscopy can be used to predict detailed milk fat composition. In addition, polymorphisms with substantial effects on milk fat composition have been identified. In this study, we investigated the combined use of milk IR spectroscopy and genotypes of dairy cows on the accuracy of predicting milk fat composition. Milk fat composition data based on gas chromatography and milk IR spectra were available for 1,456 Dutch Holstein Friesian cows. In addition, genotypes for the diacylglycerol acyltransferase 1 (DGAT1) K232A and stearoyl-CoA desaturase 1 (SCD1) A293V polymorphisms and a SNP located in an intron of the fatty acid synthase (FASN) gene were available. Adding SCD1 genotypes to the milk IR spectra resulted in a considerable improvement of the prediction accuracy for the unsaturated fatty acids C10:1, C12:1, C14:1 cis-9, and C16:1 cis-9 and their corresponding unsaturation indices. Adding DGAT1 genotypes to the milk IR spectra resulted in an improvement of the prediction accuracy for C16:1 cis-9 and C16 index. Adding genotypes of the FASN SNP to the IR spectra did not improve prediction of milk fat composition. This study demonstrated the potential of combining milk IR spectra with genotypic information from 3 polymorphisms to predict milk fat composition. We hypothesize that prediction accuracy of milk fat composition can be further improved by combining milk IR spectra with genomic breeding values.

Genome-Wide Association Study for Milk Fatty Acids in Holstein Cattle Accounting for the DGAT1 Gene Effect.

The identification of genomic regions and candidate genes associated with milk fatty acids contributes to better understand the underlying biology of these traits and enables breeders to modify milk fat composition through genetic selection. The main objectives of this study were: (1) to perform genome-wide association analyses for five groups of milk fatty acids in Holstein cattle using a high-density (777K) SNP panel; and (2) to compare the results of GWAS accounting (or not) for the DGAT1 gene effect as a covariate in the statistical model. The five groups of milk fatty acids analyzed were: (1) saturated (SFA); (2) unsaturated (UFA); (3) short-chain (SCFA); (4) medium-chain (MCFA); and (5) long-chain (LCFA) fatty acids. When DGAT1 was not fitted as a covariate in the model, significant SNPs and candidate genes were identified on BTA5, BTA6, BTA14, BTA16, and BTA19. When fitting the DGAT1 gene in the model, only the MGST1 and PLBD1 genes were identified. Thus, this study suggests that the DGAT1 gene accounts for most of the variability in milk fatty acid composition and the PLBD1 and MGST1 genes are important additional candidate genes in Holstein cattle.

Identification of genetic associations of ECHS1 gene with milk fatty acid traits in dairy cattle.

Our previous genome-wide association study identified 83 genome-wide significant SNPs and 20 novel promising candidate genes for milk fatty acids in Chinese Holstein. Among them, the enoyl-CoA hydratase, short chain 1 (ECHS1) and enoyl-CoA hydratase and 3-hydroxyacyl CoA dehydrogenase (EHHADH) genes were located near two SNPs and one SNP respectively, and they play important roles in fatty acid metabolism pathways. We herein validated whether the two genes have genetic effects on milk fatty acid traits in dairy cattle. By re-sequencing the full-length coding region, partially adjacent introns and 3000 bp up/downstream flanking sequences, we identified 12 SNPs in ECHS1: two in exons, four in the 3' flanking region and six in introns. The g.25858322C>T SNP results in an amino acid replacement from leucine to phenylalanine and changes the secondary structure of the ECHS1 protein, and single-locus association analysis showed that it was significantly associated with three milk fatty acids (P = 0.0002-0.0013). The remaining 11 SNPs were found to be significantly associated with at least one milk fatty acid (P = <0.0001-0.0040). Also, we found that two haplotype blocks, consisting of nine and two SNPs respectively, were significantly associated with eight milk fatty acids (P = <0.0001-0.0125). However, none of polymorphisms was observed in the EHHADH gene. In conclusion, our findings are the first to indicate that the ECHS1 gene has a significant genetic impact on long-chain unsaturated and medium-chain saturated fatty acid traits in dairy cattle, although the biological mechanism is still undetermined and requires further in-depth validation.

Invited review: Roles of dietary n-3 fatty acids in performance, milk fat composition, and reproductive and immune systems in dairy cattle.

Mammals can synthesize all of the fatty acids (FA) necessary for proper health and functioning with the exception of FA in the n-3 (omega-3) and n-6 (omega-6) families of polyunsaturated fatty acids (PUFA), which should be supplied in the diet. The PUFA are the predominant type of lipid in dairy cattle diets; however, common feedstuffs are rich in n-6 FA, whereas the supply of n-3 FA in the intensive dairy industry is mainly limited to flaxseed and fish oils. The n-3 FA are involved in many biological systems and processes, and therefore their dietary supplementation is of special interest in dairy cattle. Furthermore, because milk, milk products, and meat are among the most important and widely used components in traditional and modern human diets, enrichment of these food products with n-3 FA is of special importance. The purpose of this review is to provide a comprehensive description of different aspects and outcomes involved in dietary n-3 FA supplementation in dairy cattle. I provide an inclusive review of the effects of n-3 FA on milk and milk solids and the FA profile in milk fat upon feeding a variety of flaxseed products or fish oil. Selective uptake of n-3 FA has been demonstrated in the ovary compartments, as well as in bull sperm and in the unborn calf through the placenta. Incorporation of these unique FA into the reproductive system influences many processes and exerts some positive effects on fertility. In addition, beneficial effects of feeding n-3 FA on the reproductive system of females and males can be achieved with supplementation of α-linolenic acid from flaxseed or from eicosapentaenoic and docosahexaenoic acids from fish oil. This work provides a broad perspective and demonstrates the importance and potential of n-3 FA dietary supplementation in dairy cattle on the animal itself, as well as its secondary effects, which are associated with human nutrition and health.

Fine-mapping of BTA17 using imputed sequences for associations with de novo synthesized fatty acids in bovine milk.

The aim of this study was to fine-map a genomic region associated with milk fatty acids (FA) on Bos taurus autosome (BTA) 17. This genomic region has been discovered with 50,000 (50k) single nucleotide polymorphisms (SNP) imputed to 777,000 (777k) SNP. In this study, high-density genotypes were imputed to whole-genome sequences level to identify candidate gene(s) associated with milk FA composition on BTA17. Phenotypes and genotypes were available for 1,640 cows sampled in winter, and for 1,581 cows sampled in summer. Phenotypes consisted of gas chromatography measurements in winter and in summer milk samples of 6 individual FA and the indicator of de novo synthesis, C6:0-C14:0. Genotypes consisted of imputed 777k SNP, and 89 sequenced ancestors of the population of genotyped cows. In addition, 450 whole-genome sequences from the 1,000 Bull Genome Consortium were available. Using 495 Holstein-Friesian sequences as a reference population, the 777k SNP genotypes of the cows were imputed to sequence level. We then applied single-variant analyses with an animal model, and identified thousands of significant associations with C6:0, C8:0, C10:0, C12:0, C14:0, and C6:0-C14:0. For C8:0 in summer milk samples, the genomic region located between 29 and 34 Mbp on BTA17 revealed a total of 646 significant associations. The most significant associations [-log10(P-value) = 7.82] were 8 SNP in perfect linkage disequilibrium. After fitting one of these 8 SNP as a fixed effect in the model, and re-running the single-variant analyses, no further significant associations were found for any of the 6 FA or C6:0-C14:0. These findings suggest that one polymorphism underlying this QTL on BTA17 influences multiple de novo synthesized milk FA. Thirteen genes in the QTL region were identified and analyzed carefully. Six out of the 8 SNP that showed the strongest associations were located in the La ribonucleoprotein domain family, member 1B (LARP1B) gene, and we suggest LARP1B as a primary candidate gene. Another gene of interest for this QTL region might be PKL4. None of these suggested candidate genes have previously been associated with milk fat synthesis or milk FA composition.

Effect of forage conservation method on plasma lipids, mammary lipogenesis, and milk fatty acid composition in lactating cows fed diets containing a 60:40 forage-to-concentrate ratio.

The effects of forage conservation method on plasma lipids, mammary lipogenesis, and milk fat were examined in 2 complementary experiments. Treatments comprised fresh grass, hay, or untreated (UTS) or formic acid treated silage (FAS) prepared from the same grass sward. Preparation of conserved forages coincided with the collection of samples from cows fed fresh grass. In the first experiment, 5 multiparous Finnish Ayrshire cows (229 d in milk) were used to compare a diet based on fresh grass followed by hay during 2 consecutive 14-d periods, separated by a 5-d transition during which extensively wilted grass was fed. In the second experiment, 5 multiparous Finnish Ayrshire cows (53 d in milk) were assigned to 1 of 2 blocks and allocated treatments according to a replicated 3×3 Latin square design, with 14-d periods to compare hay, UTS, and FAS. Cows received 7 or 9 kg/d of the same concentrate in experiments 1 and 2, respectively. Arterial concentrations of triacylglycerol (TAG) and phospholipid were higher in cows fed fresh grass, UTS, and FAS compared with hay. Nonesterified fatty acid (NEFA) concentrations and the relative abundance of 18:2n-6 and 18:3n-3 in TAG of arterial blood were also higher in cows fed fresh grass than conserved forages. On all diets, TAG was the principle source of fatty acids (FA) for milk fat synthesis, whereas mammary extraction of NEFA was negligible, except during zero-grazing, which was associated with a lower, albeit positive calculated energy balance. Mammary FA uptake was higher and the synthesis of 16:0 lower in cows fed fresh grass than hay. Conservation of grass by drying or ensiling had no influence on mammary extraction of TAG and NEFA, despite an increase in milk fat secretion for silages compared with hay and for FAS than UTS. Relative to hay, milk fat from fresh grass contained lower 12:0, 14:0, and 16:0 and higher S3,R7,R11,15-tetramethyl-16:0, cis-9 18:1, trans-11 18:1, cis-9,trans-11 18:2, 18:2n-6, and 18:3n-3 concentrations. Even though conserved forages altered mammary lipogenesis, differences in milk FA composition were relatively minor, other than a higher enrichment of S3,R7,R11,15-tetramethyl-16:0 in milk from silages compared with hay. In conclusion, differences in milk fat composition on fresh grass relative to conserved forages were associated with a lower energy balance, increased uptake of preformed FA, and decreased synthesis of 16:0 de novo in the mammary glands, in the absence of alterations in stearoyl-coenzyme A desaturase activity.