Udder health in dairy cattle: association with milk composition, cheese-making traits, and blood serum proteins

The main objective of this PhD thesis was to study the association between udder health [focusing on subclinical cases of bovine mastitis identified by somatic cell count (SCC) and bacteriological analyses] and several milk quality and technological traits related to the cheese-making process, and blood serum proteins, as possible immune response indicators. To achieve our goal, the work was splitted in 4 chapters. Two datasets were used: for the 1st chapter, milk samples from 1,271 Brown Swiss cows from 85 herds were used. In the subsequent 3 chapters, milk and blood samples were collected from 1,508 dairy specialized and dual-purpose cows of 6 different breeds (Holstein Friesian, Brown Swiss, Jersey, Simmental, Rendena and Grey Alpine) housed in 41 multi-breed herds. The aim of the 1st chapter was to determine the effects of very low to very high SCC on milk yield, composition, coagulation properties [including traditional milk coagulation properties (MCP) and new curd firming model parameters (CFt)], cheese yield (CY) and recovery of milk nutrients in the curd (REC) at the individual cow level. The objective of the 2nd chapter was to investigate the association between blood serum proteins [i.e., total protein, albumin, globulin and the ratio of albumin-to-globulin (A:G)] and milk SCC. Since several factors should be considered to appropriately interpret serum proteins concentration in blood, we explored the effect of herd productivity (defined according to the average net energy of milk yielded daily by the cows), breed, and individual cow factors (i.e., stage of lactation and parity) on blood traits. In chapters 3 and 4, pathogen-specific information was included in the analysis to gain a better understanding of the specific changes in the traits previously investigated. Subclinical cases of mastitis were confirmed by bacteriological analysis and multiplex-PCR assays. In particular, in the 3rd chapter we investigated the association between pathogen-specific cases of subclinical mastitis and several milk quality and technological traits (i.e., milk yield, composition, detailed protein profile, coagulation properties and cheese-related traits). Based on the results of the 2nd chapter, the 4th chapter studied the association between pathogen-specific cases of subclinical mastitis and blood serum proteins, that in chapter 2 showed a correlation with SCC in milk. Results of chapter 1 confirmed the negative effect of high SCC on milk yield, composition, MCP, CFt, CY and REC traits. As somatic cell score (SCS) increased, a linear loss of milk production and variations in milk composition (e.g., casein-to-protein ratio, lactose and pH) were observed. These changes decreased the quality and clotting ability of the processed milk, which showed a slower coagulation time and a weaker curd firmness. This, in turn, affected the cheese processing (as confirmed by reductions in the CY and the recovery of milk nutrients in the curd). Our findings showed nonlinear trends for some milk traits with respect to SCS, highlighting the negative effect of very low SCC on some milk technological traits. Our 2nd chapter showed that cows in high producing herds had greater serum albumin concentrations. Breed differences in serum protein profile could be associated with individual genetic variation and could also be explained by the different selective breeding programs to which breeds have been subjected. Changes in blood serum proteins were observed throughout the entire lactation and according to the parity order. Linear relationships between blood serum proteins and SCS confirmed the importance of SCC as an indicator of mammary gland inflammation. Moreover, our results highlighted the potential use of blood serum proteins as indicators of immune response of the mammary gland to infections and their analysis represents a possible initial screening test to identify animals which need further clinical investigations. Such non-genetic factors affecting variation in blood serum proteins should also be considered in future genetics/genomics investigations. Results of the 3rd chapter revealed that compared with normal milk, all culture-positive samples and culture-negative samples with medium to high SCC presented significant variations in the casein-to-protein ratio and lactose content. Given that no differences were observed comparing milk infected by contagious, environmental and opportunistic pathogens, our findings suggested an effect of inflammation rather than infection. The greatest impairment in milk yield and composition, clotting ability and cheese production was observed for milk samples with the highest SCC (i.e., culture-positive samples where contagious pathogens were recovered, and culture-negative samples with high SCC), revealing a discrepancy between inflammatory status and bacteriological results, and thus confirming the important role of SCC as udder health indicator. Culture-negative samples with high SCC were possibly undergoing a strong inflammatory response and pathogens could not be isolated because engulfed by macrophages. In the 4th chapter, culture-negative samples with high milk SCC, which we hypothesized to be infected by contagious bacteria engulfed by neutrophils, and milk samples infected by contagious and environmental bacteria were associated with greater globulin content (and lower A:G) in blood. In accordance with the results in chapter 3 for milk traits, variation in blood serum proteins seemed to be associated with inflammation rather than infection, as globulin significantly increased in the blood of cows whose milk samples had the highest SCC, independently from intramammary infection pathogens

Short communication: Genetic aspects of milk differential somatic cell count in Holstein cows: A preliminary analysis

The aim of the present study was to assess genetic variation and heritability of a novel indicator of udder health, milk differential somatic cell count (DSCC), which represents the percentage of neutrophils plus lymphocytes in the total somatic cell count (SCC). Furthermore, we estimated genetic and phenotypic correlations of DSCC with other milk traits routinely measured in Italian Holstein cows. Besides DSCC, test-day data included milk yield, composition traits (i.e., fat, protein, casein, and lactose percentages), pH, milk urea nitrogen, and SCC. After editing, the final data set included 10,709 test-day records of 5,142 cows in 299 herds. Mean of DSCC was 62.07%, which means that macrophages were approximately 38% of total SCC. Comparing our results with the literature offered compelling evidence of the importance of acquiring information about the proportion of the different cell types in milk to better define the udder health status. In addition, our analysis revealed, for the first time, that DSCC is a heritable trait, and heritability (0.08 ± 0.02) was higher than that of traditional somatic cell score (0.04 ± 0.02). Nevertheless, heritability of DSCC is still low compared with milk yield and quality traits. Single-trait analysis within parity showed that DSCC was less heritable in primiparous than in multiparous cows, whereas bivariate analysis confirmed that DSCC and somatic cell score were 2 different traits, as their genetic and phenotypic correlations differed from unity. From a genetic point of view, the DSCC was positively weakly associated with milk yield, lactose percentage, and milk urea nitrogen, and negatively associated with pH. Our findings contributed to the understanding of the genetic background of DSCC and are a precursor to the potential use of DSCC in breeding programs to enhance cow resistance to mastitis. However, further research is needed to determine the weight this novel trait should receive in a selection program aimed to reduce udder health problems

Short communication: Genetic aspects of milk urea nitrogen and new indicators of nitrogen efficiency in dairy cows.

Milk urea nitrogen (MUN), a trait routinely measured in the national milk recording system, is a useful indicator of nitrogen utilization efficiency of dairy cows, and selection for MUN and MUN-derived traits could be a valid strategy to produce better animals with regard to efficiency of nitrogen utilization. Therefore, the aim of the present study was to explore the genetic aspects of MUN and new potential indicators of nitrogen efficiency, namely ratios of protein to MUN, casein to MUN, and whey protein to MUN, in the Italian Brown Swiss population. A total of 153,175 test-day records of 10,827 cows in 500 herds were used for genetic analysis. Variance components and heritability of the investigated traits were estimated using single-trait repeatability animal models, whereas genetic and phenotypic correlations between the traits were estimated through bivariate repeatability animal models, including fixed effects of herd-test-date, stage of lactation, parity, calving year, and calving season, and the random effects of additive genetic animal, cow permanent environment, and the residual. Heritability estimates for MUN (0.20 ± 0.01) and the 3 new indicators of nitrogen utilization efficiency (0.15 ± 0.01 for protein-to-MUN and casein-to-MUN ratios, and 0.12 ± 0.01 for ratio of whey protein to MUN) suggested that additive genetic variation exists for these traits, and thus there is potential to select for greater organic nitrogen and lower inorganic nitrogen in milk. Genetic association between MUN and the 3 ratios was high (-0.87 ± 0.01) but not unity, suggesting that ratios could provide some further information beyond that provided by MUN with regard to efficiency of nitrogen utilization. Genetic trend of the investigated traits by year of birth of Brown Swiss sires showed how the selection applied in the last 30 yr has led to an increase of both quantity and quality of milk, and a decrease of somatic cell score and MUN. The inclusion of MUN in breeding programs could speed up the process of increasing organic nitrogen such as protein, which is useful for cheese-making, and reducing inorganic nitrogen (MUN) in milk

Variation in blood serum proteins and association with somatic cell count in dairy cattle from multi-breed herds

Blood serum proteins are significant indicators of animal health. Nevertheless, several factors should be considered to appropriately interpret their concentrations in blood. Therefore, the objectives of this study were (1) to assess the effect of herd productivity, breed, age and stage of lactation on serum proteins and (2) to investigate association between serum proteins and somatic cell count (SCC) in dairy cattle. Milk and blood samples were collected from 1508 cows of six different breeds (Holstein Friesian, Brown Swiss, Jersey, Simmental, Rendena and Alpine Grey) that were housed in 41 multi-breed herds. Milk samples were analyzed for composition and SCC, while blood samples were analyzed for serum proteins (i.e.Total protein, albumin, globulin and albumin-To-globulin ratio (A : G)). Herds were classified as low or high production, according to the cow's average daily milk energy yield adjusted for breed, days in milk (DIM) and parity. Data were analyzed using a linear mixed model that included the fixed effects of DIM, parity, SCS, breed, herd productivity and the random effect of the Herd-Test date within productivity level. Cows in high producing herds (characterized also by greater use of concentrates in the diet) had greater serum albumin concentrations. Breed differences were reported for all traits, highlighting a possible genetic mechanism. The specialized breed Jersey and the two dual-purpose local breeds (Alpine Grey and Rendena) had the lowest globulin concentration and greatest A : G. Changes in serum proteins were observed through lactation. Total protein reached the highest concentration during the 4th month of lactation. Blood albumin increased with DIM following a quadratic pattern, while globulin decreased linearly. As a consequence, A : G increased linearly during lactation. Older cows had greater total protein and globulin concentrations, while albumin concentration seemed to be not particularly affected by age. A linear relationship between serum proteins and SCS was observed. High milk SCS was associated with greater total protein and globulin concentrations in blood. The rise in globulin concentration, together with a decrease in albumin concentrations, resulted in a decline in A : G as SCS of milk increased. In conclusion, such non-genetic factors must be considered to appropriately interpret serum proteins as potential animal welfare indicator and their evaluation represents an important first-step for future analysis based on the integration of metabolomics, genetic and genomic information for improving the robustness of dairy cows

Associations between pathogen-specific cases of subclinical mastitis and milk yield, quality, protein composition, and cheese-making traits in dairy cows

The aim of this study was to investigate associations between pathogen-specific cases of subclinical mastitis and milk yield, quality, protein composition, and cheese-making traits. Forty-one multibreed herds were selected for the study, and composite milk samples were collected from 1,508 cows belonging to 3 specialized dairy breeds (Holstein Friesian, Brown Swiss, and Jersey) and 3 dual-purpose breeds of Alpine origin (Simmental, Rendena, and Grey Alpine). Milk composition [i.e., fat, protein, casein, lactose, pH, urea, and somatic cell count (SCC)] was analyzed, and separation of protein fractions was performed by reversed-phase high performance liquid chromatography. Eleven coagulation traits were measured: 5 traditional milk coagulation properties [time from rennet addition to milk gelation (RCT, min), curd-firming rate as the time to a curd firmness (CF) of 20 mm (k20, min), and CF at 30, 45, and 60 min from rennet addition (a30, a45, and a60, mm)], and 6 new curd firming and syneresis traits [potential asymptotical CF at an infinite time (CFP, mm), curd-firming instant rate constant (kCF, % 7 min-1), curd syneresis instant rate constant (kSR, % 7 min-1), modeled RCT (RCTeq, min), maximum CF value (CFmax, mm), and time at CFmax (tmax, min)]. We also measured 3 cheese yield traits, expressing the weights of total fresh curd (%CYCURD), dry matter (%CYSOLIDS), and water (%CYWATER) in the curd as percentages of the weight of the processed milk, and 4 nutrient recovery traits (RECPROTEIN, RECFAT, RECSOLIDS, and RECENERGY), representing the percentage ratio between each nutrient in the curd and milk. Milk samples with SCC > 100,000 cells/mL were subjected to bacteriological examination. All samples were divided into 7 clusters of udder health (UH) status: healthy (cows with milk SCC < 100,000 cells/mL and uncultured); culture-negative samples with low, medium, or high SCC; and culture-positive samples divided into contagious, environmental, and opportunistic intramammary infection (IMI). Data were analyzed using a linear mixed model. Significant variations in the casein to protein ratio and lactose content were observed in all culture-positive samples and in culture-negative samples with medium to high SCC compared to normal milk. No differences were observed among contagious, environmental, and opportunistic pathogens, suggesting an effect of inflammation rather than infection. The greatest impairment in milk quantity and composition, clotting ability, and cheese production was observed in the 2 UH status groups with the highest milk SCC (i.e., contagious IMI and culture-negative samples with high SCC), revealing a discrepancy between the bacteriological results and inflammatory status, and thus confirming the importance of SCC as an indicator of udder health and milk quality

Udder health in dairy cattle: association with milk composition, cheese-making traits, and blood serum proteins

The main objective of this PhD thesis was to study the association between udder health [focusing on subclinical cases of bovine mastitis identified by somatic cell count (SCC) and bacteriological analyses] and several milk quality and technological traits related to the cheese-making process, and blood serum proteins, as possible immune response indicators. To achieve our goal, the work was splitted in 4 chapters. Two datasets were used: for the 1st chapter, milk samples from 1,271 Brown Swiss cows from 85 herds were used. In the subsequent 3 chapters, milk and blood samples were collected from 1,508 dairy specialized and dual-purpose cows of 6 different breeds (Holstein Friesian, Brown Swiss, Jersey, Simmental, Rendena and Grey Alpine) housed in 41 multi-breed herds. The aim of the 1st chapter was to determine the effects of very low to very high SCC on milk yield, composition, coagulation properties [including traditional milk coagulation properties (MCP) and new curd firming model parameters (CFt)], cheese yield (CY) and recovery of milk nutrients in the curd (REC) at the individual cow level. The objective of the 2nd chapter was to investigate the association between blood serum proteins [i.e., total protein, albumin, globulin and the ratio of albumin-to-globulin (A:G)] and milk SCC. Since several factors should be considered to appropriately interpret serum proteins concentration in blood, we explored the effect of herd productivity (defined according to the average net energy of milk yielded daily by the cows), breed, and individual cow factors (i.e., stage of lactation and parity) on blood traits. In chapters 3 and 4, pathogen-specific information was included in the analysis to gain a better understanding of the specific changes in the traits previously investigated. Subclinical cases of mastitis were confirmed by bacteriological analysis and multiplex-PCR assays. In particular, in the 3rd chapter we investigated the association between pathogen-specific cases of subclinical mastitis and several milk quality and technological traits (i.e., milk yield, composition, detailed protein profile, coagulation properties and cheese-related traits). Based on the results of the 2nd chapter, the 4th chapter studied the association between pathogen-specific cases of subclinical mastitis and blood serum proteins, that in chapter 2 showed a correlation with SCC in milk. Results of chapter 1 confirmed the negative effect of high SCC on milk yield, composition, MCP, CFt, CY and REC traits. As somatic cell score (SCS) increased, a linear loss of milk production and variations in milk composition (e.g., casein-to-protein ratio, lactose and pH) were observed. These changes decreased the quality and clotting ability of the processed milk, which showed a slower coagulation time and a weaker curd firmness. This, in turn, affected the cheese processing (as confirmed by reductions in the CY and the recovery of milk nutrients in the curd). Our findings showed nonlinear trends for some milk traits with respect to SCS, highlighting the negative effect of very low SCC on some milk technological traits. Our 2nd chapter showed that cows in high producing herds had greater serum albumin concentrations. Breed differences in serum protein profile could be associated with individual genetic variation and could also be explained by the different selective breeding programs to which breeds have been subjected. Changes in blood serum proteins were observed throughout the entire lactation and according to the parity order. Linear relationships between blood serum proteins and SCS confirmed the importance of SCC as an indicator of mammary gland inflammation. Moreover, our results highlighted the potential use of blood serum proteins as indicators of immune response of the mammary gland to infections and their analysis represents a possible initial screening test to identify animals which need further clinical investigations. Such non-genetic factors affecting variation in blood serum proteins should also be considered in future genetics/genomics investigations. Results of the 3rd chapter revealed that compared with normal milk, all culture-positive samples and culture-negative samples with medium to high SCC presented significant variations in the casein-to-protein ratio and lactose content. Given that no differences were observed comparing milk infected by contagious, environmental and opportunistic pathogens, our findings suggested an effect of inflammation rather than infection. The greatest impairment in milk yield and composition, clotting ability and cheese production was observed for milk samples with the highest SCC (i.e., culture-positive samples where contagious pathogens were recovered, and culture-negative samples with high SCC), revealing a discrepancy between inflammatory status and bacteriological results, and thus confirming the important role of SCC as udder health indicator. Culture-negative samples with high SCC were possibly undergoing a strong inflammatory response and pathogens could not be isolated because engulfed by macrophages. In the 4th chapter, culture-negative samples with high milk SCC, which we hypothesized to be infected by contagious bacteria engulfed by neutrophils, and milk samples infected by contagious and environmental bacteria were associated with greater globulin content (and lower A:G) in blood. In accordance with the results in chapter 3 for milk traits, variation in blood serum proteins seemed to be associated with inflammation rather than infection, as globulin significantly increased in the blood of cows whose milk samples had the highest SCC, independently from intramammary infection pathogens.L’obiettivo principale di questa tesi di dottorato è stato quello di studiare l'associazione tra stato sanitario della mammella [con particolare riferimento a casi subclinici di mastite bovina identificati attraverso conta delle cellule somatiche (SCC) e analisi batteriologica] e una serie di caratteri qualitativi e tecnologici del latte legati al processo di caseificazione, e le proteine del siero, quali possibili indicatori di risposta immunitaria dell’animale. Per raggiungere tale obiettivo, il lavoro è stato suddiviso in 4 capitoli. Due diversi datasets sono stati utilizzati: nel 1° capitolo sono stati utilizzati campioni di latte raccolti da 1,271 bovine di razza Bruna provenienti da 85 allevamenti. Nei successivi 3 capitoli, i campioni di latte e di sangue sono stati raccolti da 1,508 bovine da latte e a doppia attitudine di 6 diverse razze (Frisona, Bruna, Jersey, Pezzata Rossa, Rendena e Grigio Alpina) provenienti da 41 allevamenti multi-razza. Nel 1° capitolo di questa tesi sono stati analizzati, a livello individuale, gli effetti di un contenuto variabile di SCC nel latte (da molto basso a molto alto) sulla produzione di latte, la composizione chimica, le proprietà di coagulazione [includendo le proprietà di coagulazione tradizionali (MCP) e nuovi parametri modellizzati di consistenza della cagliata (CFt)], la resa casearia (CY) e il recupero di nutrienti nella cagliata (REC). Lo scopo del 2° capitolo è stato quello di studiare l'associazione tra proteine del siero [proteine totali, albumina, globulina e il rapporto tra albumina e globulina (A:G)] e SCC nel latte. Tuttavia, per interpretare in modo appropriato la concentrazione delle proteine nel sangue, devono essere presi in considerazione diversi fattori. Pertanto, è stato valutato l'effetto del livello produttivo dell’allevamento (definito sulla base dell'energia netta del latte prodotta in media giornalmente dalle bovine), della razza, dello stadio di lattazione e dell’ordine di parto sulle proteine ematiche. Nei capitoli 3 e 4, sono state incluse nelle analisi informazioni a livello patogeno-specifico allo scopo di acquisire una migliore comprensione dei cambiamenti precedentemente osservati nei caratteri tecnologici e di qualità del latte e nei parametri ematici esaminati. I casi subclinici di mastite sono stati confermati attraverso analisi batteriologica e saggi PCR in multiplex. In particolare, l'obiettivo del 3° capitolo è stato quello di studiare l'associazione tra i casi di mastite subclinica a livello patogeno-specifico e i diversi caratteri qualitativi e tecnologici del latte (produzione, composizione chimica, profilo proteico dettagliato, proprietà di coagulazione e caratteri legati al processo di caseificazione). Sulla base dei risultati ottenuti nel capitolo 2, nel 4° capitolo è stata valutata l'associazione tra i casi di mastite subclinica a livello patogeno-specifico e le proteine del siero, che nel capitolo 2 erano risultate correlate alle SCC nel latte. I risultati ottenuti nel capitolo 1 hanno confermato l'effetto negativo di un alto contenuto di SCC sulla produzione di latte, la composizione e i caratteri MCP, CFt, CY e REC. All’aumentare del punteggio di cellule somatiche (SCS), sono state osservate una diminuzione lineare della quantità di latte prodotto e alcune variazioni nella composizione (in particolare nel rapporto tra caseina e proteina, nel contenuto di lattosio e nel pH). Questi cambiamenti hanno causato una riduzione della qualità e dell’attitudine casearia del latte trasformato, caratterizzato da una coagulazione più lenta e una ridotta consistenza del coagulo. Di conseguenza, tali variazioni hanno avuto ripercussioni negative sul processo di caseificazione, ovvero ridotta resa in formaggio e minor recupero di nutrienti nella cagliata. I risultati ottenuti hanno inoltre evidenziato andamenti non lineari per alcuni caratteri del latte rispetto ad SCS, mettendo in evidenza l'effetto negativo di un contenuto molto basso di SCC su alcuni caratteri tecnologici del latte. Nel 2° capitolo è stato dimostrato che le bovine allevate in allevamenti ad alta produttività presentavano una maggiore concentrazione di albumina sierica. Le differenze nel profilo proteico osservate tra le diverse razze potrebbero essere associate alla variazione genetica individuale e ai diversi programmi di selezione a cui tali razze sono state sottoposte. Variazioni del contenuto di proteine ematiche sono state riportate all’avanzare della lattazione e a seconda dell’ordine di parto. Le relazioni lineari tra proteine del siero e SCS hanno confermato l'importanza delle SCC come indicatore di infiammazione della mammella. I risultati ottenuti hanno evidenziato inoltre il potenziale uso delle proteine del siero come indicatori di risposta immunitaria della ghiandola mammaria alle infezioni e la loro analisi rappresenta un possibile test iniziale di screening per identificare animali che hanno bisogno di ulteriori indagini cliniche. Tali fonti di variazione non-genetiche delle proteine del siero dovrebbero essere prese in considerazione anche in future analisi genetiche e genomiche. I risultati del 3° capitolo hanno mostrato che, rispetto al latte di bovine sane, tutti i campioni di latte risultati positivi all’esame batteriologico e i campioni che non hanno evidenziato crescita batterica ma con un contenuto medio-alto di SCC presentavano significative variazioni nel rapporto tra caseina e proteina, nonchè nel contenuto di lattosio. Poiché non sono state osservate differenze significative confrontando latte infetto da patogeni contagiosi, ambientali e opportunisti, i risultati ottenuti hanno evidenziato un deterioramento del latte dovuto alla risposta infiammatoria dell’animale piuttosto che all'infezione stessa. Un peggioramento più pronunciato per quanto riguarda produzione e composizione chimica del latte, attitudine alla coagulazione e resa in formaggio è stato osservato per i campioni di latte con il più alto contenuto di SCC (ovvero i campioni infettati da patogeni contagiosi e i campioni risultati negativi all’esame batteriologico ma con un alto contenuto di SCC). Questo ha rivelato una discrepanza tra stato infiammatorio e risultati batteriologici, confermando così il ruolo importante delle SCC quale indicatore dello stato di salute della mammella. É possibile che, nei campioni risultati negativi all’esame batteriologico ma con un alto contenuto di SCC, una risposta infiammatoria intensa abbia impedito l’isolamento degli agenti patogeni in quanto internalizzati dai macrofagi. Nel capitolo 4, i campioni che non hanno evidenziato crescita batterica ma con un alto contenuto di SCC, che abbiamo ipotizzato essere infettati da batteri contagiosi internalizzati dai neutrofili, e i campioni di latte infettati da batteri contagiosi e ambientali sono risultati associati a un maggior contenuto di globulina (e a un valore inferiore del rapporto A:G) nel sangue. In accordo con i risultati relativi ai caratteri del latte ottenuti nel capitolo 3, la variazione del profilo proteico del sangue sembra essere associata al processo infiammatorio piuttosto che all'infezione. Infatti è stata osservata una concentrazione elevata di globulina nel sangue di bovine il cui latte presentava un contenuto elevato di SCC, indipendentemente dal tipo di patogeno causa di infezione.

Implementation of SCC breeding values in Italian Jersey breed

In the framework of the LATTeco project, ANAFIJ (Associazione Nazionale Allevatori della Razza Frisona e Jersey Italiana) has been working on improving animal welfare, biodiversity and sustainability. Focusing on animal welfare, ANAFIJ has implemented a genetic evaluation for somatic cell count (SCC) in the Italian Jersey population. The aim of this study is to describe this implementation which became official in December 2020. It is expected that breeding values for SCC will help farmers to produce a progeny more resistant to mastitis, with a consequent reduction of veterinary costs and a valorisation of milk in quality payment systems. The dataset included 284,904 records of SCC collected on 19,305 cows belonging to 774 herds during the official test day milk recording program. Data ranged from 2005 to 2016. Means of SCC and somatic cell score (SCS), calculated as 3+log2(SCC/100), were 277.47\ub1677.43 cells/\ub5L and 3.14\ub11.76. Bulls\u2019 breeding values were estimated using a repeatability animal model which included the fixed effects of parity (first, second and third lactation), the season of calving (4 classes, 3 months each), days in milk (10 classes of 30-d each, ranged from 4 to 305 d), and herd-test-day (26,866 records) as a contemporary group. The random effects were an additive genetic animal, permanent environment and the residual. Breeding values for 187 bulls with a minimum of 10 daughters in at least 10 herds were estimated and they were referred to ANAFIJ genetic base, which is updated every 5 years and at the moment of the study, included animals born between 2010 and 2015. Somatic cell score was standardised to mean 100 and standard deviation 5. Breeding values reliability averaged 0.80\ub10.13 and the mean of daughters\u2019 phenotype for SCC was equal to 275.41\ub192.81 cells/\ub5L. Bulls were divided into 3 groups according to their breeding values for SCS: as expected, bulls with higher ebvs had lower mean SCC; while a decrease in ebvs was associated with increased SCC. In January 2021, the new breeding value was submitted to Interbull for the test-run routine to validate it; this will allow ANAFIJ to have an international result for the SCC breeding value of the Italian Jersey population

Genetic Parameters of Bovine Milk Fatty Acid Profile, Yield, Composition, Total and Differential Somatic Cell Count

The growing interest of consumers for milk and dairy products of high nutritional value has pushed researchers to evaluate the feasibility of including fatty acids (FA) in selection programs to modify milk fat profile and improve its nutritional quality. Therefore, the aim of this study was to estimate genetic parameters of FA profile predicted by mid-infrared spectroscopy, milk yield, composition, and total and differential somatic cell count. Edited data included 35,331 test-day records of 25,407 Italian Holstein cows from 652 herds. Variance components and heritability were estimated using single-trait repeatability animal models, whereas bivariate repeatability animal models were used to estimate genetic and phenotypic correlations between traits, including the fixed effects of stage of lactation, parity, and herd-test-date, and the random effects of additive genetic animal, cow permanent environment and the residual. Heritabilities and genetic correlations obtained in the present study reflected both the origins of FA (extracted from the blood or synthesized de novo by the mammary gland) and their grouping according to saturation or chain length. In addition, correlations among FA groups were in line with correlation among individual FA. Moderate negative genetic correlations between FA and milk yield and moderate to strong positive correlations with fat, protein, and casein percentages suggest that actual selection programs are currently affecting all FA groups, not only the desired ones (e.g., polyunsaturated FA). The absence of association with differential somatic cell count and the weak association with somatic cell score indicate that selection on FA profile would not affect selection on resistance to mastitis and vice versa. In conclusion, our findings suggest that genetic selection on FA content is feasible, as FA are variable and moderately heritable. Nevertheless, in the light of correlations with other milk traits estimated in this study, a clear breeding goal should first be established