Noncoagulating Milk Research Articles

A comprehensive study on milk composition and coagulation properties from six endangered native Norwegian cattle breeds

Six cattle breeds native to Norway, have for almost half a century been at risk of extinction. Due to their small population sizes, they have hardly been improved by breeding for many decades. Still, the endangered breeds represent a source of genetic diversity with special milk qualities compared to the modern breed, Norwegian red (NRF). This study reports for the first time a detailed overview of their milk composition. Milk from seven native breeds, in total 200 individuals, were included in the study. Rare genetic variants of αs1-and αs2-casein, and β-casein A1 and κ-casein B were more prevalent in milk form the endangered breeds compared to NRF. Moreover, milk from these six breeds showed better renneting properties and lower incidences of non-coagulating milk, compared to the NRF milk, which showed better acid coagulation properties. This study shows the potential for native breeds in small-scale production of high-quality rennet cheeses.

Identification of the coagulation properties of Chinese Holstein bovine milk: Effects of milk compositions, milk protein polymorphism, and phosphorylation levels on milk coagulation ability

Milk coagulation ability plays critical roles in cheese production. To assess the effects of milk composition, protein polymorphisms, and phosphorylation levels on milk coagulation properties, milk samples were collected from 3625 Chinese Holstein cows and milk was pooled based on their coagulation properties. The results showed that good coagulating milk had shorter rennet coagulation time and higher gel firmness with tighter connections within the formed gel. Multiple factors were observed to differ among milk with different coagulation ability. For example, lower milk pH, higher amounts of proteins and casein, were related to good coagulation properties. The salt distributions also influenced milk coagulation ability. Especially the calcium content has a large influence on milk coagulation. This may be due to its influence on the aggregation of paracasein micelles in the secondary phase of rennet coagulation. Protein polymorphisms and phosphorylation degrees were found being higher in non-coagulating milk. The proteomics results showed that lower amounts of αS1-casein may result in non-coagulation. Differences of milk fat globule membrane proteins were also observed among milk samples with different coagulation ability, possibly being related to milk protein and fat synthesis, in turn influencing the coagulation process. In addition, Ser76 of αS2-CN was found being highly phosphorylated in non-coagulating milk which may be related to its binding with other caseins during the second phase of rennet coagulation. Of these factors, salt distribution, mainly calcium and magnesium, may be the most important factor affecting casein structures and thereby milk coagulation. Importantly, these factors can affect each other while forming the cheese matrix, resulting in a complex relation with milk coagulation.

Phenotypic and genetic characterization of the occurrence of noncoagulating milk in dairy sheep

Milk coagulation ability is of central importance for the sheep dairy industry because almost all sheep milk is destined for cheese processing. The occurrence of milk with impaired coagulation properties is an obstacle to cheese processing and, in turn, to the profitability of the dairy companies. In this work, we investigated the causes of noncoagulation of sheep milk; specifically, we studied the effect of milk physicochemical properties on milk coagulation status [coagulating and noncoagulating (NC) milk samples, which do or do not coagulate within 30 min, respectively], and whether mid-infrared spectroscopy (MIR) could be used to assess variability in coagulation status. We also investigated the genetic background of milk coagulation ability. Individual milk samples were collected from 996 Sarda ewes farmed in 47 flocks located in Sardinia (Italy). Considered traits were daily milk yield, milk composition traits, and milk coagulation properties (rennet coagulation time, curd firming time, and curd firmness), and MIR spectra were acquired. About 9% of samples did not coagulate within 30 min. A logistic regression approach was used to test the effect of milk-related traits on milk coagulation status. A principal component (PC) analysis was carried out on the milk MIR spectra, and PC scores were then used as covariates in a logistic regression model to assess their relationship with milk coagulation status. Results of the present work demonstrated that the probability of having NC samples increases as milk contents of proteins and chlorides and somatic cell score increase. The analysis of PC extracted from milk spectra that influenced coagulation status highlighted key regions associated with lactose and protein concentrations, and others not associated with routinely collected milk composition traits. These results suggest that the occurrence of NC is mostly related to damage of the epithelium secretory mammary cells, which occurs with the advancement of a lactation or due to unhealthy mammary gland status. Genetic analysis of milk coagulation status and of the extracted PC confirmed the genetic background of the milk coagulability of sheep milk.

Multivariate and Genome-Wide Analysis of Mid-Infrared Spectra of Non-Coagulating Milk of Sarda Sheep Breed

Milk coagulation ability is crucial for the dairy sheep industry since the whole amount of milk is processed into cheese. Non-coagulating milk (NCM) is defined as milk not forming a curd within the testing time. In sheep milk, it has been reported in literature that up to 20% of milk is NCM. Although the clotting properties of individual milk have been widely studied, little attention has been given to NCM and genomic dissection of this trait. Mid-infrared (MIR) spectra can be exploited both to predict cheese-making aptitude and to discriminate between coagulating milk and NCM. The main goals of this work were (i) to assess the predictivity of MIR spectra for NCM classification and (ii) to conduct a genome-wide association study on coagulation ability. Milk samples from 949 Sarda ewes genotyped and phenotyped for milk coagulation properties (MCPs) served as the training dataset. The validation dataset included 662 ewes. Three classical MCPs were measured: rennet coagulation time (RCT), curd firmness (a30), and curd firming time (k20). Moreover, MIR spectra were acquired and stored in the region between 925.92 and 5,011.54 cm−1. The probability of a sample to be NCM was modeled by step-wise logistic regression on milk spectral information (LR-W), logistic regression on principal component (LR-PC), and canonical discriminant analysis of spectral wave number (DA-W). About 9% of the samples did not coagulate at 30 min. The use of LR-W gave a poorer classification of NCM. The use of LR-PC improved the percentage of correct assignment (45 ± 9%). The DA-W method allows us to reach 75.1 ± 10.3 and 76.5 ± 18.4% of correct assignments of the inner and external validation datasets, respectively. As far as GWA of NCM, 458 SNP associations and 45 candidate genes were detected. The genes retrieved from public databases were mostly linked to mammary gland metabolism, udder health status, and a milk compound also known to affect the ability of milk to coagulate. In particular, the potential involvement of CAPNs deserves further investigation.

Genetic parameters for noncoagulating milk, milk coagulation properties, and detailed milk composition in Swedish Red Dairy Cattle

The rennet-induced coagulation ability of milk is important in cheese production. For Swedish Red Dairy Cattle (RDC), this ability is reduced because of a high prevalence of noncoagulating (NC) milk. In this study, we simultaneously combined genetic parameters for NC milk, milk coagulation properties, milk composition, physical traits, and milk protein composition. Our aim was to estimate heritability and genetic and phenotypic correlations for NC milk and 24 traits (milk coagulation properties, milk composition, physical traits, and milk protein composition). Phenotypes and ∼7,000 SNP genotypes were available for all 600 Swedish RDC. The genotypes were imputed from ∼7,000 SNP to 50,000 SNP. Variance components and genetic parameters were estimated with an animal model. In Swedish RDC, a moderate heritability estimate of 0.28 was found for NC milk. For the other 24 traits, heritability estimates ranged from 0.12 to 0.77 (standard errors from 0.08 to 0.18). A total of 300 phenotypic and genetic correlations were estimated. For phenotypic and genetic correlations, 172 and 95 were significant, respectively. In general, most traits showing significant genetic correlations also showed significant phenotypic correlations. In this study, phenotypic and genetic correlations with NC milk suggest that many correlations between traits exist, making it difficult to predict the real consequences on the composition of milk, if selective breeding is applied on NC milk. We speculate that some of these consequences may lead to changes in the composition of milk, most likely affecting its physical and organoleptic properties. However, our results suggest that κ-casein could be used as an indicator trait to predict the occurrence of NC milk at the herd level.

Effects of milk proteins and posttranslational modifications on noncoagulating milk from Swedish Red dairy cattle

Milk that does not coagulate after rennet addition, also called noncoagulating (NC) milk, is unwanted in cheese production due to prolonged processing time. Amounts of whey and casein proteins, genetic variants, as well as posttranslational modifications (PTM) of proteins are all contributing factors in rennet-induced coagulation of milk. In this study, we conducted a wide-ranging investigation of milk proteins in milk samples from 616 Swedish Red dairy cattle using liquid chromatography-high resolution mass spectrometry. Relative concentration of proteins, genetic variants, and PTM were compared between NC milk and coagulating milk. The PTM investigated were phosphorylation of caseins and glycosylation of κ-casein. Several genetic variants and PTM were found, including rare phosphorylation variants of the αS-caseins. Genetic variants were found to effect the expressed amount of different proteins. Further, the effect of protein amounts and PTM on a binary NC milk trait was modeled using a generalized linear model. The model showed that NC milk significantly correlated with higher relative concentrations of α-lactalbumin and β-casein and lower relative concentrations of β-lactoglobulin and κ-casein. Regarding PTM of caseins, an effect on NC milk from a lower relative concentration of αS1-casein with 8 phosphate groups were found, even though an effect from total relative concentration of αS1-casein was not found. This study has provided insights into protein variants and PTM important for NC milk to improve this undesirable property.

An investigation of the enzymatic cleavage of κ-casein in non-coagulating milk

Non-coagulating milk is unwanted in cheese production because it impairs chymosin-induced coagulation properties in bulk milk. Milk samples were analysed to investigate the coagulation process in non-coagulating milk for comparison with milk samples that have a high coagulation ability. This was done by measuring two peptides after chymosin cleavage, namely para-κ-casein and caseinomacropeptide, in all the milk samples using capillary electrophoresis. The results showed that cleavage of κ-casein into para-κ-casein and caseinomacropeptide occurred in both coagulation groups, suggesting that the aggregation stage is the cause of non-coagulating milk. Non-coagulating milk had lower content of para-κ-casein after chymosin addition compared with coagulating milk, which might be the result of a lower content of available κ-casein. Furthermore, this study indicates that there are different mechanisms that explain good coagulation ability and lack of coagulation ability of milk. The results can be useful in understanding the potential chemical mechanisms behind non-coagulating milk.

Characterisation of non-coagulating milk and effects of milk composition and physical properties on rennet-induced coagulation in Swedish Red Dairy Cattle

Non-coagulating milk is a serious problem in the cheese industry, since it decreases cheese yield, resulting in decreased economic output. This study evaluated rennet-induced coagulation properties and composition of milk from individual Swedish Red Dairy Cattle. Milk samples from 679 individual cows were rheologically evaluated, of which 18.1% of the cows produced non-coagulating milk and 18.9% produced poor-coagulating milk. This resulted in 37% of the milk samples being non-optimal in cheese production, which is an alarmingly high figure. A comparison between non-coagulating and coagulating milk showed a significantly lower calcium content and less free Ca2+ in non-coagulating milk. The results provide more information about non- and poor-coagulating milk and will be further used to understand the genetic background of non-coagulating milk and breed against this undesired milk property.

Comparison of milk protein composition and rennet coagulation properties in native Swedish dairy cow breeds and high-yielding Swedish Red cows

Recent studies have reported a very high frequency of noncoagulating milk in Swedish Red cows. The underlying factors are not fully understood. In this study, we explored rennet-induced coagulation properties and relative protein profiles in milk from native Swedish Mountain and Swedish Red Polled cows and compared them with a subset of noncoagulating (NC) and well-coagulating (WC) milk samples from modern Swedish Red cows. The native breeds displayed a very low prevalence of NC milk and superior milk coagulation properties compared with Swedish Red cows. The predominant variants in both native breeds were αS1-casein (αS1-CN) B, β-CN A2 and β-lactoglobulin (β-LG) B. For κ-CN, the B variant was predominant in the Swedish Mountain cows, whereas the A variant was the most frequent in the Swedish Red Polled. The native breeds displayed similar protein composition, but varied in content of αS1-CN with 9 phosphorylated serines (9P) form. Within the Swedish Mountain cows, we observed a strong inverse correlation between the relative concentration of κ-CN and micelle size and a positive correlation between ionic calcium and gel firmness. For comparison, we investigated a subset of 29 NC and 28 WC milk samples, representing the extremes with regard to coagulation properties based on an initial screening of 395 Swedish Red cows. In Swedish Red, NC milk properties were found to be related to higher frequencies of β-CN A2, κ-CN E and A variants, as well as β-LG B, and the predominant composite genotype of β- and κ-CN in the NC group was A2A2/AA. Generally, the A2A2/AA composite genotype was related to lower relative concentrations of κ-CN isoforms and higher relative concentrations of αS1-, αS2-, and β-CN. Compared with the group of WC milk samples, NC milk contained a higher fraction of αS2-CN and α-lactalbumin (α-LA) but a lower fraction of αS1-CN 9P. In conclusion, milk from native Swedish breeds has good characteristics for cheese milk, which could be exploited in niche dairy products. In milk from Swedish Mountain cows, levels of ionic calcium seemed to be more important for rennet-induced gel firmness than variation in the relative protein profile. In Swedish Red, lower protein content as well as higher fraction of αS2-CN and lower fraction of αS1-CN 9P were related to NC milk. Further, a decrease in the frequency of the composite β-κ-CN genotype A2A2/AA through selective breeding could have a positive effect on milk coagulation properties.

Cow milk coagulation: process description, variation factors and evaluation methodologies. A review

Introduction. For dairy producers who want to transform their milk, the ability of milk to coagulate is an important parameter. It makes it possible to transform milk into cheese. Therefore, it is necessary to understand the coagulation process and the techniques to measure it in order to achieve the best transformation performance. The objective of this review is to describe the milk coagulation process, the factors influencing it and the methods for measuring the coagulation of milk at lab level. Literature. The processing of milk into cheese involves three steps: coagulation, dewatering and refining. Coagulation is a key step which involves the use of rennet and depends on several parameters (pH, calcium content, temperature, etc.). Some milks never coagulate. To measure the coagulation ability of milk and identify different parameters in milk coagulation properties, the Formagraph, the computerized renneting meter and the Optigraph have been developed (reference methods). Equations have been developed using infrared spectrometry to predict the parameters obtained by the reference methods. Conclusions. The milk coagulation mechanism is known. However, the issue of non-coagulating milk persists and represents a real challenge in terms of yield. The use of infrared is a faster alternative to reference methods that measure the coagulation properties of milk, but still requires an improvement in prediction equations.

Protein heterogeneity of bovine β-casein in Danish dairy breeds and association of rare β-casein F with milk coagulation properties

ABSTRACTA proteomic approach was applied to characterize genetic variation and relative protein content of β-casein (β-CN) in milk from two minor native dairy breeds in Denmark; Red Danish 1970 and Jutland cows in comparison to the major dairy breeds; Danish Holstein and Danish Jersey. Genetic β-CN variants were related to the relative concentration of β-CN. Furthermore, a very high frequency of variant F in the native breeds was found. This was remarkable as this variant is only found in a very low frequency in the major Danish breeds. Novel associations were found between β-CN variant F and milk coagulation properties in the native breeds, which is an important finding for understanding the genetic background for non- and poor coagulating milk and potential exploitation of β-CN variants in selective breeding programs. Furthermore, in Red Danish 1970 a very high prevalence of non-coagulating milk was found (18%).

Identification of QTL on Chromosome 18 Associated with Non-Coagulating Milk in Swedish Red Cows.

Non-coagulating (NC) milk, defined as milk not coagulating within 40 min after rennet-addition, can have a negative influence on cheese production. Its prevalence is estimated at 18% in the Swedish Red (SR) cow population. Our study aimed at identifying genomic regions and causal variants associated with NC milk in SR cows, by doing a GWAS using 777k SNP genotypes and using imputed sequences to fine map the most promising genomic region. Phenotypes were available from 382 SR cows belonging to 21 herds in the south of Sweden, from which individual morning milk was sampled. NC milk was treated as a binary trait, receiving a score of one in case of non-coagulation within 40 min. For all 382 SR cows, 777k SNP genotypes were available as well as the combined genotypes of the genetic variants of αs1-β-κ-caseins. In addition, whole–genome sequences from the 1000 Bull Genome Consortium (Run 3) were available for 429 animals of 15 different breeds. From these sequences, 33 sequences belonged to SR and Finish Ayrshire bulls with a large impact in the SR cow population. Single-marker analyses were run in ASReml using an animal model. After fitting the casein loci, 14 associations at −Log10(P-value) > 6 identified a promising region located on BTA18. We imputed sequences to the 382 genotyped SR cows using Beagle 4 for half of BTA18, and ran a region-wide association study with imputed sequences. In a seven mega base-pairs region on BTA18, our strongest association with NC milk explained almost 34% of the genetic variation in NC milk. Since it is possible that multiple QTL are in strong LD in this region, 59 haplotypes were built, genetically differentiated by means of a phylogenetic tree, and tested in phenotype-genotype association studies. Haplotype analyses support the existence of one QTL underlying NC milk in SR cows. A candidate gene of interest is the VPS35 gene, for which one of our strongest association is an intron SNP in this gene. The VPS35 gene belongs to the mammary gene sets of pre-parturient and of lactating cows.

Modeling of coagulation, curd firming, and syneresis of milk from Sarda ewes

This study investigated the modeling of curd-firming (CF) over time (CFt) of sheep milk. Milk samples from 1,121 Sarda ewes from 23 flocks were analyzed for coagulation properties. Lactodynamographic analyses were conducted for up to 60min, and 240 CF individual observations from each sample were recorded. Individual sample CFt equation parameters (RCTeq, rennet coagulation time; CFP, asymptotic potential value of curd firmness; kCF, curd-firming instant rate constant; and kSR, curd syneresis instant rate constant) were estimated, and the derived traits (CFmax, the point at which CFt attained its maximum level, and tmax, the time at which CFmax was attained) were calculated. The incidence of noncoagulating milk samples was 0.4%. The iterative estimation procedure applied to the individual coagulation data showed a small number of not-converged samples (4.4%), which had late coagulation and an almost linear pattern of the ascending part of the CFt curve that caused a high value of CFP, a low value of kCF, and a high value of kSR. Converged samples were classified on the basis of their CFt curves into no-kSR (18.0%), low-kSR (72.6%), and high-kSR (4.5%). A CFt that was growing continuously because of the lack of the syneresis process characterized the no-kSR samples. The high-kSR samples had a much larger CFP, a smaller kCF, and an anticipation of tmax, whereas the low-kSR samples had a fast kCF and a slower kSR. The part of the average CFt curves that showed an increase was similar among the 3 different syneretic groups, whereas the part that decreased was different because of the expulsion of whey from the curd. The traditional milk coagulation properties recorded within 30min were not able to detect any appreciable differences among the 4 groups of coagulating samples, which could lead to a large underestimation of the maximum CF of all samples (if predicted by a30), with the exception of the no-kSR samples. Large individual variability was found and was likely caused by the effects of the dairy system, such as flock size (on CFmax, tmax, and % ewes with no-kSR milk), flock within flock size (representing 11 to 43% of total variance for % ewes with no-kSR milk and CFmax, respectively), days in milk (on all model parameters and CFmax), parity (on RCTeq, kSR, and CFmax), daily milk yield (on RCTeq and CFmax), and position of the individual pendulum that significantly affected model parameters and derived traits. In conclusion, the results showed that the modeling of coagulation, curd-firming, and syneresis is a suitable tool to achieve a deeper interpretation of the coagulation and curd-firming processes of sheep milk and also to study curd syneresis.

On effects of subclinical mastitis and stage of lactation on milk quality in goats

Bulk milk is the mixture of all the milked udders in a given herd. Nowadays, about 15–40% of the udders in most herds are intramammary infected by different bacteria species, mainly coagulase negative staphylococci. The presences of bacteria in the lumen of the mammary gland induce impairment of milk quality and increase the number of somatic cells. A positive relationship between % casein (casein/total protein) and curd firmness (CF) and negative relationship between lactose, or somatic cell count (SCC) and CF are associated with bacterial infection and with late lactation milk, and therefore with reduction in cheese yield and quality. On the other hand, in milk of goats with intramammary infection, the correlation between the levels of fat, protein, casein and curd yield is minor compared to milk of uninfected animals. Thus, gross milk composition is an insufficient predictor of milk quality for cheese production, since a high percent of the bulk milk originates from subclinically infected glands. Research carried out in the past few years highlighted the effectiveness of lactose as a predictor of milk quality. The correlation between lactose and CF was higher than that for % casein and SCC. Lactose concentration of ≤4% is associated with non-coagulating milk and therefore, such milk is unsuitable for making cheese, but still meets the criterion for consumption as pasteurized milk. A model that describes the simultaneous and close association between reduction in lactose concentration and milk yield on the one hand and reductions in lactose concentration and milk quality on the other hand is presented. The physiological and biochemical basis for deterioration of milk quality in subclinically infected and in late lactation animals is reviewed and suggestions to improve the quality of milk produced by farmers and acquired by dairies are presented.

Factors influencing chymosin-induced gelation of milk from individual dairy cows: Major effects of casein micelle size and calcium

Optimisation of cheese yield is crucial for cheese production; a previous study showed large variations in chymosin-induced coagulation in milk from the second most common Swedish dairy breed, Swedish Red. In the present study, the effect of gross composition, protein composition, total and ionic calcium content, phosphorous content and casein micelle size on chymosin-induced gelation was determined in milk from 98 Swedish Red cows. The study showed that protein content and total calcium content, ionic calcium concentration and casein micelle size were the most important factors explaining the variation of gelation properties in this sample set. Non-coagulating milk was suggested to have lower ionic and total calcium content as well as lower relative concentrations of β-lactoglobulin than coagulating milk. The lower total calcium content in non-coagulating milk poses a problem as the difference was, theoretically, four times larger than the amount of calcium that is normally added in cheese processing.

Genetic parameters for rennet- and acid-induced coagulation properties in milk from Swedish Red dairy cows

Milk coagulation is an important processing trait, being the basis for production of both cheese and fermented products. There is interest in including technological properties of these products in the breeding goal for dairy cattle. The aim of the present study was therefore to estimate genetic parameters for milk coagulation properties, including both rennet- and acid-induced coagulation, in Swedish Red dairy cattle using genomic relationships. Morning milk samples and blood samples were collected from 395 Swedish Red cows that were selected to be as genetically unrelated as possible. Using a rheometer, milk samples were analyzed for rennet- and acid-induced coagulation properties, including gel strength (G′), coagulation time, and yield stress (YS). In addition to the technological traits, milk composition was analyzed. A binary trait was created to reflect that milk samples that had not coagulated 40min after rennet addition were considered noncoagulating milk. The cows were genotyped by using the Illumina BovineHD BeadChip (Illumina Inc., San Diego, CA). Almost 600,000 markers remained after quality control and were used to construct a matrix of genomic relationships among the cows. Multivariate models including fixed effects of herd, lactation stage, and parity were fitted using the ASReml software to obtain estimates of heritabilities and genetic and phenotypic correlations. Heritability estimates (h2) for G′ and YS in rennet and acid gels were found to be high (h2=0.38–0.62) and the genetic correlations between rennet-induced and acid-induced coagulation properties were weak but favorable, with the exception of YSrennet with G′acid and YSacid, both of which were strong. The high heritability (h2=0.45) for milk coagulating ability expressed as a binary trait suggests that noncoagulation could be eliminated through breeding. Additionally, the results indicated that the current breeding objective could increase the frequency of noncoagulating milk and lead to deterioration of acid-induced coagulation through unfavorable genetic associations with protein content (0.38) and milk yield (−0.61 to −0.71), respectively. The outcome of this study suggests that by including more detailed compositional traits genetically associated with milk coagulation or by including milk coagulation properties directly within the breeding goal, it appears possible to breed cows that produce milk better suited for production of cheese and fermented products.

Impact of genetic variants of milk proteins on chymosin-induced gelation properties of milk from individual cows of Swedish Red dairy cattle

Chymosin-induced gelation properties of the milk of around 400 Swedish Red dairy cows was investigated with the aim of identifying genetic protein variants that influence chymosin-induced gelation for optimisation of cheese milk through breeding practices. The variation in chymosin-induced gelation properties was shown to be large in the milk of Swedish Red and there was a high frequency of cows producing non-coagulating milk, 18%. The present study showed that the common composite β-κ-casein genotypes A1A2/AE and A2A2/AA were associated with both poor gelation properties and non-coagulation in the milk of Swedish Red. The present study suggests that if the frequencies of composite genotypes A1A2/AE and A2A2/AA were decreased in the Swedish Red population in favour for A1A1/AA and A1A1/AE, this could have a positive effect on the rennetability of the milk.

Influence of micellar calcium and phosphorus on rennet coagulation properties of cows milk

The main requirement for milk processed in most cheese typologies is its rennet coagulation ability. Despite the increasing number of studies, the causes for abnormal coagulation of milk are not fully understood. The aim of this study was to ascertain relationships between milk characteristics and its rennet coagulation ability, focusing on the influence of calcium (Ca) and phosphorus (P). Ca and P are essential constituents of the micelles. Micellar P can be present as part of colloidal calcium phosphate (inorganic-P) or covalently bound to caseins as phosphate groups (casein-P). Eighty one herd milk samples (SCC<400000cell/ml) were classified as Optimal (8), Suboptimal (39) Poor (29) and Non-coagulating milk (5), according to their rennet coagulation parameters as assessed by lactodynamographic test. Samples were analysed for their chemical composition (basic composition, protein fractions, minerals and salt equilibria), physicochemical parameters (pH and titratable acidity) and rheological properties. Optimal milk was characterised by the highest contents of major constituents, protein fractions and minerals, lowest content of chloride and highest values of titratable acidity. Non-coagulating milk was characterised by the highest values of pH and the lowest of titratable acidity. At micellar level, Optimal milk showed the highest values of colloidal Ca, casein-P and colloidal Mg (g/100g casein), while Non-coagulating milk showed the lowest values. Interestingly, there was no statistical difference regarding the content of colloidal inorganic-P (g/100g casein) between Optimal and Non-coagulating milks. Overall, high mineralisation of the micelle (expressed as g inorganic-P/100g casein) positively affect its rennetability. However, excessive mineralisation could lead to a reduction of the phosphate groups (g casein-P/100g casein) available for curd formation.

Survival analysis as a statistical methodology for analyzing factors that affect milk coagulation time in Holstein-Friesian and Brown Swiss cows

The aim of this study was to propose the survival analysis technique as a statistical approach for the analysis of rennet coagulation time (RCT) able to make use of coagulating and noncoagulating (NC) milk information in order to estimate potential sources of variations that affects RCT. A total of 1,025 Italian Holstein-Friesian cows (HF; progeny of 54 sires) and 1,234 Brown Swiss cows (BS; progeny of 58 sires) reared in 34 and 38 herds, respectively, were milk-sampled once. Rennet coagulation time was analyzed with a semiparametric proportional hazard model (i.e., a Cox model), with the NC samples considered as censored records. Furthermore, a different censoring scenario, with a new end point at 18min, was considered after the rearrangement of the time space originally used for the observation of RCT. The percentage of NC samples was almost 10% for HF and 3.5% for BS cows in in the 31min set, whereas it increased to 44 and 24.9%, respectively, in the 18min set. Estimated hazard ratios indicated that the most important factors affecting the coagulation process were herd, days in milk, casein number, and milk acidity (expressed in terms of titratable acidity) for both HF and BS, whereas the SCS was relevant only for BS. The survival model seems to be particularly suitable for this analysis, as it can properly account for censored and uncensored records and appropriately use all available information. Moreover, this methodology allows us to rearrange the time space used for the observation of RCT and to define alternative traits (i.e., RCT with an end point at 18min). Our restriction of the time space and the increased percentage of censored records did not highlight any substantial differences in terms of the risk of coagulating with respect to the traditional 31min testing time. Although further research is needed to investigate the effect of these sources of variation on cheese yield, our results indicate that casein number, acidity, and SCS may be used as indicator traits for enhancing the technological properties of bovine milk.

The occurrence of noncoagulating milk and the association of bovine milk coagulation properties with genetic variants of the caseins in 3 Scandinavian dairy breeds

Substantial variation in milk coagulation properties has been observed among dairy cows. Consequently, raw milk from individual cows and breeds exhibits distinct coagulation capacities that potentially affect the technological properties and milk processing into cheese. This variation is largely influenced by protein composition, which is in turn affected by underlying genetic polymorphisms in the major milk proteins. In this study, we conducted a large screening on 3 major Scandinavian breeds to resolve the variation in milk coagulation traits and the frequency of milk with impaired coagulation properties (noncoagulation). In total, individual coagulation properties were measured on morning milk collected from 1,299 Danish Holstein (DH), Danish Jersey (DJ), and Swedish Red (SR) cows. The 3 breeds demonstrated notable interbreed differences in coagulation properties, with DJ cows exhibiting superior coagulation compared with the other 2 breeds. In addition, milk samples from 2% of DH and 16% of SR cows were classified as noncoagulating. Furthermore, the cows were genotyped for major genetic variants in the αS1- (CSN1S1), β- (CSN2), and κ-casein (CSN3) genes, revealing distinct differences in variant frequencies among breeds. Allele I of CSN2, which had not formerly been screened in such a high number of cows in these Scandinavian breeds, showed a frequency around 7% in DH and DJ, but was not detected in SR. Genetic polymorphisms were significantly associated with curd firming rate and rennet coagulation time. Thus, CSN1S1 C, CSN2 B, and CSN3 B positively affected milk coagulation, whereas CSN2 A2, in particular, had a negative effect. In addition to the influence of individual casein genes, the effects of CSN1S1-CSN2-CSN3 composite genotypes were also examined, and revealed strong associations in all breeds, which more or less reflected the single gene results. Overall, milk coagulation is under the influence of additive genetic variation. Optimal milk for future cheese production can be ensured by monitoring the frequency of unfavorable variants and thus preventing an increase in the number of cows producing milk with impaired coagulation. Selective breeding for variants associated with superior milk coagulation can potentially increase raw milk quality and cheese yield in all 3 Scandinavian breeds.