Quantification of milk yield and composition changes as affected by subclinical mastitis during the current lactation in sheep

The aim of this work was to quantify, on a half-udder basis, the changes in ewe milk yield and composition caused by unilateral subclinical mastitis within the current lactation. Fluctuations due to production level, infection severity, time from the onset of infection, and lactation curves were also studied. Yield and composition of milk from half-udders of unilateral infected ewes were compared between them and with a set of healthy halves using a mixed model. The experiment was completed with a whole-udder approach on the same animals. To test the effect of intramammary infection (IMI) in the 7 wk following the onset of infection, 20 ewes that acquired unilateral subclinical mastitis during lactation and 40 healthy ewes were used. Another group of 20 unilaterally infected ewes from wk 1 of lactation and other 40 healthy ewes were studied to test the effect of IMI on lactational milk yield and composition. The individual milk loss in ewes infected during lactation was 15% for the 7 wk following the onset of infection, and 6.6% more milk was produced by the uninfected half to compensate milk lost by the infected half. Lactational milk yield loss in ewes infected from wk 1 postpartum was 17%. The changes in milk yield were noticed from the week of infection diagnosis. The production level of animals influenced the milk yield changes caused by IMI in such a way that the more productive ewes lost more milk, although these losses were proportional to their production level. On the other hand, infection severity affected milk loss between glands, being more pronounced as somatic cell count increased. A clear decrease of lactose content and casein:protein ratio due to subclinical IMI was observed and it remained throughout the postinfection period. Improving udder health status is necessary to maintain milk production and quality in dairy ewes during lactation.     

The microbiome of Escherichia coli and culture-negative nonsevere clinical mastitis: Characterization and associations with linear score and milk production

Culture-negative and Escherichia coli cases are uncommonly treated in pathogen-based protocols for nonsevere mastitis. High-throughput 16S rRNA sequencing might reveal the presence of other pathogens and can provide information on microbial diversity. The objective was to explore the milk microbiome at the time of the mastitis event (enrollment) and its association with survival in the herd, milk production, and postevent linear score (LS) for cows with clinical mastitis characterized as negative or E. coli by culture. Fifty E. coli-positive and 35 culture-negative samples from cases were enrolled. No cases were treated with antimicrobials. All E. coli-positive quarters were characterized as transient; microbiological culture of samples taken 15 d postmastitis were negative for this organism. However, a difference in α-diversity (Shannon index) was present between enrollment and follow-up samples (3.8 vs. 5.1). When α-diversity was explored for enrollment E. coli samples, no relationship was observed between the Shannon indices of these samples and postmastitis LS. Alpha-diversity of the enrollment samples was lower for E. coli-positive cows that subsequently had greater losses in milk production. This difference was explained by a greater relative abundance of the family Enterobacteriaceae (67.8 vs. 38.4%) for cows that dropped in production. Analysis of composition of the microbiome identified one phylum, Proteobacteria, that differed between E. coli-positive cows that dropped in production and those that did not. Evaluation of β -diversity found no statistical relationship between postmastitis LS and the microbiome. When evaluating α- and β-diversities and composition of the microbiomes for culture-negative quarters, no associations were found for milk production changes and postmastitis LS. Three cows did not remain in the herd, limiting the ability to analyze survival. The findings suggest that a contributing factor to negative outcomes in E. coli-positive cows is relative abundance of this pathogen, and that no single or collective group of bacterial families is associated with milk production changes or postmastitis LS in culture-negative quarters. Although additional studies should be performed, the absence of associations between outcomes explored and microbial profiles in this study suggests that we are not missing opportunities by not treating nonsevere E. coli or culture-negative mastitis cases.     

Mammary pathogens and their relationship to somatic cell count and milk yield losses in dairy ewes

A total of 9592 samples of half udder milk were collected monthly throughout lactation for bacteriological and somatic cell count (SCC) study from 1322 Churra ewe lactations from seven separate flocks enrolled in the recording scheme of the National Association of Spanish Churra Breeders in the Castile-Le6n region of Spain. Statistical analyses were carried out from a mixed model with random factor half udder or ewe for repeated measures. Test of significance of fixed effects of this mixed model showed significant effects of organisms, flock, parity, lactation stage, and birth type on SCC. Special reference must be made to novobiocin-sensitive coagulase-negative staphylococci, which represented more than 50% of the isolates and which elicited SCC geometric means of around 106/ml. In addition, the analysis of 4352 monthly test-day records for milk yield, SCC, and bacteriology showed that the ewes that were uninfected and infected by minor pathogens had the lowest SCC and the highest milk yields, whereas those infected by major pathogens had high SCC and milk yield losses between 8.8 and 10.1% according to the uni- or bilateral character of the infection. Finally, ewes infected by novobiocin-sensitive coagulase-negative staphylococci elicited SCC values similar to those of infections by major pathogens and milk yield losses ranging between those caused by minor and major pathogens. As a result, emphasis should be put on prevention of subclinical mastitis, particularly mastitis caused by novobiocin-sensitive coagulase-negative staphylococci in dairy sheep herds to improve microbiological and hygienic milk quality and to minimize losses in milk yield.     

Proteomic analysis of differentially expressed proteins in bovine milk during experimentally induced Escherichia coli mastitis

The objectives of the current study were to profile changes in protein composition using 2-dimensional gel electrophoresis on whey samples from a group of 8 cows before and 18 h after infection with Escherichia coli and to identify differentially expressed milk proteins by peptide sequencing using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry post source decay. Only proteins present in whey fractions of all 8 cows were sequenced to avoid reporting a protein response unique to only a subset of infected cows. Despite the overwhelming presence of casein and β-lactoglobulin, the low abundance proteins transthyretin, lactadherin, β-2-microglobulin precursor, α-1-acid glycoprotein, and complement C3 precursor could be identified in whey samples from healthy cows. Whey samples at 18 h postinfection were characterized by an abundance of serum albumin, in spots of varying mass and isoelectric point, as well as increased transthyretin and complement C3 precursor levels. Also detected at 18 h postinoculation were the antimicrobial peptides cathelicidin, indolicidin, and bactenecin 5 and 7, and the proteins β-fibrinogen, α-2-HS-glycoprotein, S100-A12, and α-1-antiproteinase. Most notable was the detection of the acute phase protein α-1-acid glycoprotein in mastitic whey samples, a result not previously reported. In contrast to methods used in previous proteomic analyses of bovine milk, the methods used in the current study enabled the rapid identification of milk proteins with minimal sample preparation. Use of a larger sample size than previous analyses also allowed for more robust protein identification. Results indicate that examination of the protein profile of whey samples from cows after inoculation with E. coli could provide a rapid survey of milk protein modulation during coliform mastitis and aid in the identification of biomarkers of this disease.     

Short communication: Toxicokinetics of ochratoxin A in dairy ewes and carryover to milk following a single or long-term ingestion of contaminated feed

Ruminal microbes have the capacity to inactivate ochratoxins, rendering ruminants less sensitive to this fungal contaminant found in cereal feeds. However, ochratoxin A has been reported in milk surveys. The objective of this study was to assess the toxicokinetics, excretion, and transmission into milk of ochratoxin A using doses similar to those of naturally occurring field contaminations. Six Lacaune dairy ewes in late lactation were separated into 2 groups that received a single dose of contaminated wheat containing 5 or 30 μg of ochratoxin A/kg of body weight. After administration, toxicokinetics and excretion were monitored for 48 h. Subsequently, ewes were administered the corresponding toxin dose daily for 24 d followed by a second toxicokinetics and excretion monitoring period for this long-term exposure. The doses used did not affect production or health of ewes. After a single dose, ochratoxin A and its main metabolite, ochratoxin α, were found in blood 1 h postexposure. The maximum blood concentrations of ochratoxin A and α, respectively, were dose dependent and were observed, on average, 6 and 8 h after exposure. Long-term exposure increased the maximum concentration of ochratoxin A detected in blood, whereas ochratoxin α was not affected. In contrast, the time to reach the maximum concentration was reduced to 3 h for both molecules. Ochratoxins, essentially ochratoxin α, were mainly excreted in feces. Ochratoxin A and α were detected in milk at concentrations that were dose dependent but with a low carryover rate (<0.02%). Chronic administration did not increase the concentration of toxin in milk. Even though ochratoxin A can escape ruminal degradation and traces were found in milk of experimentally exposed ewes, the low carryover of ochratoxin A in milk minimizes the risk to consumers.     

Effects of seasonal changes in feeding management under part-time grazing on the evolution of the composition and coagulation properties of raw milk from ewes

Ewe raw milk composition, rennet coagulation parameters, and curd texture were monitored throughout the milk production season in 11 commercial flocks reared under a part-time grazing system. Milking season lasted from February to July. During that period, the diet of the animals shifted from indoor feeding, consisting of concentrate and forage, to an outdoor grazing diet. Lean dry matter, fat, protein, calcium, and magnesium contents increased throughout the milking season, as did rennet coagulation time, curd firmness, and curd resistance to compression. However, lean dry matter, protein content, and curd resistance to compression stabilized when sheep started to graze. Principal component analysis correlated curd resistance to compression and proteins, whereas curd firmness was highly correlated with fat content and minerals. Discriminant analysis distributed milk samples according to the feeding management. Curd firmness, fat, and magnesium turned out to be discriminant variables. Those variables reflected the evolution of the composition and coagulation parameters when fresh pasture prevailed over other feeds in the diet of the flocks. The present study shows that seasonal changes associated with feeding management influence milk technological quality and that milk of good processing quality can be obtained under part-time grazing.     

Effect of wheat middlings-based total mixed ration on milk production and composition responses of lactating dairy ewes

The effect of feeding pelleted total mixed ration (TMR) containing wheat middlings (WM) from durum wheat (Triticum durum Desf. cv. Appulo) as a corn grain substitute on milk yield and composition performance was measured in Comisana × Leccese crossbred lactating ewes. Forty ewes were divided into 2 equal groups and fed 1 of the 2 experimental diets for 18 wk. The control diet contained 255 g of corn/kg of dry matter (DM) as the main starch source, whereas the experimental diet contained 500 g of WM/kg of DM. To evaluate the in vivo digestibility of pelleted TMR, 4 adult rams were placed in metabolic cages and their individual feces and urine were collected. In the performance trial, ewe milk yield was recorded daily and individual milk samples were analyzed weekly for milk composition and to determine milk renneting parameters. The ewes fed both diets showed similar DM, crude protein, and neutral detergent fiber intakes. Digestibility of DM, organic matter, and crude protein of the 2 TMR was similar, but neutral detergent fiber digestibility was higher in the WM diet. In the milking trial, the WM diet increased milk fat percentage and yield but had no effect on milk yield, protein, lactose, and clotting properties compared with the control diet. Our findings indicate that WM can be fed to lactating ewes as an alternative to more traditional concentrate sources such as corn. Feeding 50% of WM in a lactation diet supported milking performance in a manner similar a corn-based diet. Moreover, the results may be applied in countries where corn cultivation is adversely affected by the high cost of production.     

Effect of clinical mastitis on the lactation curve: a mixed model estimation using daily milk weights

The objective of this study was to estimate the milk production losses associated with clinical mastitis using mixed linear models and correlation structures that have not been available previously. Data used included computer-recorded daily milk yields and detailed and accurate recordings of clinical mastitis cases. Two commercial Holstein dairy farms in New York State participated in the study, one with 650 lactating cows and another that began the study with 830 lactating cows and increased to 1120 cows by the end of the study. Cows on both farms were housed in free stall barns and milked 3 times daily in milking parlors. Electrical conductivity was used as a diagnostic aid for clinical mastitis on both farms. Date of clinical onset was recorded for every episode of clinical mastitis as well as for 8 other diseases defined using standardized case definitions (dystocia, milk fever, retained placenta, metritis, ketosis, displaced abomasum, lameness, and cystic ovarian disease) during the study period of October 1, 1999 to July 31, 2001. The mixed linear model for explaining variation in the outcome variable daily milk yield relative to non-mastitic herdmates found the terms for all 9 diseases studied, including clinical mastitis, significant. The model with an autoregressive correlation structure was preferred based on -2 * log likelihood, Akaike's information criterion, and Bayesian information criterion as well as savings in degrees of freedom. Separate analyses were run for first lactation cows and for second-plus lactation cows because their lactation curves were shaped differently. Adjusting for the effects of the other 8 diseases, milk production loss from clinical mastitis during the whole lactation was estimated as approximately 598 kg for second-plus lactation cows. However, cows that contracted mastitis had a daily production advantage of 2.6 kg over their herdmates until they contracted the disease. When compared with this potentially higher milk production, the total loss from clinical mastitis was estimated as 1181 kg.     

Ultra-performance liquid chromatography-quadrupole-time of flight mass spectrometry MSE-based untargeted milk metabolomics in dairy cows with subclinical or clinical mastitis

In this study, a novel metabolomics technique based on ultra-performance liquid chromatography-quadrupole-time of flight mass spectrometry in the MS^E mode was used to investigate the milk metabolomics of healthy, subclinical, and clinical mastitis cows, which were classified based on somatic cell count and presentation of clinical symptoms. Meanwhile, univariate and multivariate statistical analyses were performed to identify the significant differences across the 3 groups. Compared with healthy milk samples, less glucose, d-glycerol-1-phosphate, 4-hydroxyphenyllactate, l-carnitine, sn-glycero-3-phosphocholine, citrate, and hippurate were detected in the clinical mastitic milk samples, whereas less d-glycerol-1-phosphate, benzoic acid, l-carnitine, and cis-aconitate were found in the subclinical mastitic milk samples. Meanwhile, the milk concentration of arginine and Leu-Leu increased in both the clinical and subclinical mastitis groups. Besides, less 4-hydroxyphenyllactate, cis-aconitate, lactose, and oxoglutarate were detected in the clinical than the subclinical mastitic milk samples, whereas the abundance of some oligopeptides (Leu-Ala, Phe-Pro-Ile, Asn-Arg-Ala-Ile, and Val-Phe-Val-Tyr) increased by over 7.95-fold. Our results suggest that significant variations exist across healthy and mastitis cows. The current metabolomics approach will help in better understanding the pathobiology of mastitis, although clinical validation will be required before field application.     

Effects of a mastitis treatment strategy with or without on-farm testing

The etiology of mastitis is crucial information to use antimicrobials prudently for control and treatment. This study aimed to evaluate the effects of mastitis diagnosis and treatment strategies with on-farm testing, on cure, new intramammary infections (IMI), somatic cell count (SCC), and antimicrobial use, compared with farmers' current diagnosis and treatment strategies. The on-farm tests used, CHROMagar Mastitis (CHROMagar, Paris, France) and Minnesota Easy Culture System II Tri-plate (University of Minnesota, St. Paul, MN), both had etiological groups of IMI as result, being gram-positive growth, gram-negative growth, or culture negative. Two randomized controlled trials were conducted on 15 herds: trial 1 prospectively enrolled 155 cows with clinical mastitis, and trial 2 cross-sectionally included 78 cows with subclinical mastitis. In both trials, cows were randomly distributed over 3 equal-sized groups: a test group using CHROMagar, a test group using Minnesota, and a control group not using on-farm tests. Farmers decided whether or not to treat, and which antimicrobial treatment would be applied, using information available on the day of enrollment (control group), complemented with the on-farm test result 1 d after enrollment (both test groups). For clinical mastitis, an antimicrobial treatment was given in 58% of cases that used CHROMagar, in 80% that used Minnesota, and in 86% of the controls. For subclinical mastitis, an antimicrobial treatment was given in 50% of cases that used CHROMagar, in 54% that used Minnesota, and in 4% of the controls. Bacteriological cure rate of clinical mastitis was lowest in the CHROMagar group [odds ratio 0.18 (95%CI 0.03–0.99)] compared with the controls. Using the Minnesota on-farm test for subclinical mastitis diagnosis and treatments resulted in fewer new IMI on d 21 [odds ratio 0.06 (95%CI 0.00–0.74)] compared with the controls. Clinical cure rate, percentage of new IMI, and SCC on d 21 of clinical mastitis were comparable among the groups. Using on-farm tests in farmers' decision-making process resulted in more treatments in accordance with the etiology of mastitis than without on-farm testing. A diagnosis and treatment strategy with on-farm testing is advised in cows with clinical mastitis to enhance prudent antimicrobial use. For subclinical mastitis, however, on-farm testing may lead to an unacceptable increase in use of antimicrobials and thus should not be advised as the common approach.     

Comparative metabolite profiling of raw milk from subclinical and clinical mastitis cows using 1H-NMR combined with chemometric analysis

The objectives of this study were to characterise and compare non-volatile metabolite profiles of raw milk from healthy, subclinical and clinical mastitis cows using a non-targeted proton nuclear magnetic resonance (¹H-NMR) metabolomic approach. A total of 46 metabolites were identified. Multivariate analysis allowed discrimination of milk from healthy and mastitis cows according to their ¹H-NMR metabolite profiles. Significant increases in acetate, formate, lactate, benzoate, hippurate, β-hydroxybutyrate, valerate, alanine, histidine, isoleucine, leucine, N-acetylamino acid, phenylalanine, threonine and valine content were associated with extremely high somatic cell count and clinical mastitis status of the cows. Furthermore, significant rises in hippurate, valerate, N-acetylglucosamine, histidine, isoleucine and leucine content could be used as potential biomarker for indicating subclinical mastitis infection of the udders. Beside the existing biomarkers for diagnosing mastitis in literatures, we found additional candidate metabolites, such as alanine, valerate and N-acetylglucosamine, in correlation with mastitis status of Thai crossbred Holstein dairy cows.     

Invited review: Technical solutions for analysis of milk constituents and abnormal milk

Information about constituents of milk and visual alterations can be used for management support in improving mastitis detection, monitoring fertility and reproduction, and adapting individual diets. Numerous sensors that gather this information are either currently available or in development. Nevertheless, there is still a need to adapt these sensors to special requirements of on-farm utilization such as robustness, calibration and maintenance, costs, operating cycle duration, and high sensitivity and specificity. This paper provides an overview of available sensors, ongoing research, and areas of application for analysis of milk constituents. Currently, the recognition of abnormal milk and the control of udder health is achieved mainly by recording electrical conductivity and changes in milk color. Further indicators of inflammation were recently investigated either to satisfy the high specificity necessary for automatic separation of milk or to create reliable alarm lists. Likewise, milk composition, especially fat:protein ratio, milk urea nitrogen content, and concentration of ketone bodies, provides suitable information about energy and protein supply, roughage fraction in the diet, and metabolic imbalances in dairy cows. In this regard, future prospects are to use frequent on-farm measurements of milk constituents for short-term automatic nutritional management. Finally, measuring progesterone concentration in milk helps farmers detect ovulation, pregnancy, and infertility. Monitoring systems for on-farm or on-line analysis of milk composition are mostly based on infrared spectroscopy, optical methods, biosensors, or sensor arrays. Their calibration and maintenance requirements have to be checked thoroughly before they can be regularly implemented on dairy farms.     

Heritability and genetic correlations of test day milk yield and composition,individual laboratory cheese yield,and somatic cell count for dairy ewes

Genetic parameters for milk yield, contents of fat, total protein, casein and serum protein, individual laboratory cheese yield, and somatic cell counts (SCC) were estimated from 7492 monthly test-day records of 1119 Churra ewes. Estimates were from multivariate REML using analytical gradients (AG-REML) procedures. Except for fat content, estimates for the other routinely recorded traits (milk yield, protein content, and SCC) agreed with those previously obtained in this and other dairy sheep populations. Protein content and composition had the highest heritabilities and repeatabilities. Heritabilities for protein and casein contents were very similar (0.23 and 0.21, respectively), and genetic correlation between the traits was close to unity (0.99). Accordingly, casein content is not advisable as an alternative to protein content as a selection criterion in dairy ewes; it does not have any compelling advantages and costs more to measure. Individual laboratory cheese yield (ILCY) obtained with Churra ewes had a low heritability (0.08), suggesting that potential for selection for this parameter would be possible but is not recommended. All correlations with ILCY were high and positive except for milk yield. A high SCC was accompanied by an increase in serum protein content and involved a loss in milk yield.     

Proteomic analysis of the temporal expression of bovine milk proteins during coliform mastitis and label-free relative quantification

The discovery of biomarkers in milk indicative of local inflammation or disease in the bovine mammary gland has been hindered by the extreme biological complexity of milk, the dynamic range of proteins in the matrix that renders the identification of low-abundance proteins difficult, and the challenges associated with quantifying changes during disease in the abundance of proteins for which no antibody exists. The objectives of the current study were to characterize the temporal expression of milk proteins following Escherichia coli challenge and to evaluate change in relative abundance of identified proteins using a liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) label-free semiquantitative approach. Liquid chromatography-MS/MS conducted on whey from milk samples collected just before infusion with E. coli and at 12, 18, 24, 36, 48, and 60 h following infection resulted in the identification of the high- to medium-abundance proteins α_S1-, α_S2- β-, and κ-caseins and the whey proteins serum albumin, β-lactoglobulin, and α-lactalbumin. Additionally, a select number of lower abundance markers of inflammation were also identified, including lactoferrin, transferrin, apolipoprotein AI, fibrinogen, glycosylation-dependent cell adhesion molecule-1, peptidoglycan recognition receptor protein, and cyclic dodecapeptide-1. Normalized peptide counts for each protein identified were used to evaluate temporal changes in milk proteins following infection. For comparison with relative protein abundance determined using proteomic-based methods, changes in serum albumin, lactoferrin, and transferrin in milk during disease were also measured using ELISA. Label-free, proteomic-based quantification revealed relative changes in milk proteins that corresponded to expression profiles generated by ELISA. The results indicate that label-free LC-MS/MS methods are a viable means of tracking changes in relative protein abundance in milk during disease. Despite the identification of primarily abundant milk proteins, the results indicate that, with further refinement, LC-MS/MS could be used to evaluate temporal changes in proteins related to host response for which no antibody or ELISA currently exists.     

A gas chromatography-mass spectrometry untargeted metabolomics approach to discriminate Fiore Sardo cheese produced from raw or thermized ovine milk

Thermization is a sub-pasteurization heat treatment of cheese milk (at 57–68°C for 15–30 s) aimed to reduce the number of undesirable microbial contaminants with reduced heat damage to the indigenous milk enzymes. In this work, the effects of milk thermization on the compositional parameters, proteolysis indices, free fatty acid levels, and low molecular weight metabolite profiles of ovine cheese were studied. Cheese samples at different ripening stages and produced in 2 different periods of the year were analyzed. While the effects of milk thermization on cheese macro-compositional parameters and free fatty acid levels were not evident due to the predominant effects of milk seasonality and cheese ripening stage, the gas chromatography-mass spectrometry based metabolomics approach of ovine cheese produced from raw and thermized milk highlighted strong differences at the metabolite level. Discriminant analysis applied to gas chromatography-mass spectrometry data provided an excellent classification model where cheese samples were correctly classified as produced from raw or thermized milk. The metabolites that mostly changed due to the thermization process belonged to the classes of free amino acids and saccharides. Gas chromatography-mass spectrometry-based metabolomics has proven to be a valid tool to study the effect of mild heat treatments on the polar metabolite profile in ovine cheese.     

The microbiome of bulk tank milk: Characterization and associations with somatic cell count and bacterial count

Numerous studies have evaluated associations between bacterial groups and milk quality parameters. However, to our knowledge, no research has been published that has analyzed associations between the microbiome and quality parameters of bulk tank milk (BTM). Thus, the aims of this study were to identify the core microbiome of BTM and to examine associations between the microbiome and milk quality parameters. Four hundred seventy-two BTM samples from 19 different dairy farms located in New York State were analyzed by next-generation sequencing and quantitative PCR of the 16S rRNA gene to assess the milk microbiome and measure total bacterial load, respectively. Flow cytometry was used to determine bacterial and somatic cell counts. Heatmaps were constructed and simple linear regressions and response screening analysis were performed. To facilitate data analysis and interpretation of the results, we dichotomized the BTM samples into high (HSCC, >200,000) and low somatic cell count (LSCC, ≤200,000) and into high (HSPC, >3.6) and low log₁₀ SPC (LSPC, ≤3.6). Spoilage-causing, spore-forming, and pathogenic bacteria of importance to the dairy industry were identified in the core microbiome. In addition, the taxa Thermoanaerobacterium and 5–7N15 were identified in the core microbiome; to our knowledge, these genera have not been previously identified in milk samples. Several bacterial genera were encountered in significantly higher relative abundances in the HSCC group when compared with the LSCC group, including Corynebacterium, Streptococcus, Lactobacillus, Coxiella, Arthrobacter, and Lactococcus. Additionally, several bacterial taxa were found in significantly higher relative abundances in the HSPC groups versus the LSPC groups: Acinetobacter, Enterobacteriaceae, Corynebacterium, and Streptococcus. In addition, Streptococcus was highly correlated with HSPC, and this genus was the second most abundant bacterial taxon detected in samples classified as HSCC. Bacterial diversity (Shannon index) was negatively correlated with bacterial load, suggesting that the microbiomes of high-bacterial load BTM samples are dominated by smaller groups of bacterial taxa. In conclusion, the associations described corroborated current knowledge about pathogens and spoilage bacteria in relationship to milk quality, and also indicated that other bacterial taxa should be a focus of further investigations.     

Investigations of milk quality from teats with milk flow disorders

The objective of this study was to investigate the quality of milk from teats with milk flow disorders. Somatic cell count, pathogens, and signs of mastitis (>100,000 cells/ml and pathogens detected) were determined in the milk from all teats of the udder before treatment of the affected teat, as well as 1 and 6 mo later. Teats with milk flow disorders were compared to all of the other teats from the same udder. Before treatment, the SCC from affected teats was 4.3 million higher, the odds of detecting pathogens 6 times higher, and the odds of mastitis 11 times higher than in control teats (when adjusted for other significant explanatory variables). SCC and the risk of mastitis decreased after surgical treatment of the affected teats, whereas the chance of detecting pathogens was not affected. Six months after treatment, the SCC was 1.3 million higher, and the odds of mastitis 6.5 times higher than in control teats. Throughout the study period neither SCC, the odds of detecting pathogens, nor mastitis changed significantly in control teats. It may be concluded from this study that milk quality from teats with milk flow disorders is decreased before treatment and does not reach the milk quality from unaffected teats within 6 mo after treatment.     

Effect of the inclusion of artichoke silage in the ration of lactating ewes on the properties of milk and cheese characteristics during ripening

The effect of including artichoke silage in the rations of dairy ewes on milk characteristics and biochemical changes of ripened cheeses was evaluated. Four groups of lactating ewes were fed rations containing 0, 10, 20, or 30% artichoke silage on a dry matter basis. Bulk milk samples were collected 3 times during the feeding period, and semi-hard cheeses were manufactured and sampled during ripening. Milk composition and cheese yield were not affected by diet. Inclusion of 20 and 30% artichoke silage reduced the firmness of the curds at a level only detected by the Gelograph (Gelograph-NT, Gel-Instrumente, Thalwil, Switzerland) probe. Inclusion of artichoke silage in ewes’ diet decreased fat and total free fatty acids content of these cheeses and increased total free amino acids content. Despite the effect of diet on cheese ripening characteristics, the overall sensory scores for cheeses corresponding to artichoke silage diets were statistically higher than those for the control cheeses.     

Effect of the inclusion of whole citrus in the ration of lactating ewes on the properties of milk and cheese characteristics during ripening

The effect of including citrus fruits (CF) in the rations of dairy ewes on the milk characteristics and biochemical changes of cheeses during ripening was evaluated. For this purpose, 48 lactating ewes (Guirra breed) were divided into 4 homogeneous groups and fed with isoenergetic and isoprotein rations containing CF at 0, 10, 20, and 30% on a dry matter basis in substitution of dry barley and pelleted beet pulp. During the experimental period, 3 batches of bulk milk were collected from each group and semi-hard cheeses were manufactured. Cheeses were sampled at 15, 30, and 60 d of ripening. Milk coagulation parameters and cheese yield were not negatively affected by the inclusion of CF in the ration. Physicochemical composition of cheeses at 60 d showed statistical differences for lower total solids and fat content of 30% CF cheeses. Proteolysis of cheeses measured by water-soluble nitrogen and total free amino acids content was not influenced by the ration. Differences between rations with respect to free fatty acids were significant for medium- and long-chain free fatty acids, and therefore for total content, but differences did not show a trend related to the increase of CF in the diet. The inclusion of CF in the ration of lactating ewes up to levels of 30% did not negatively affect the properties of milk and the biochemical and sensory characteristics of cheeses.