Udder quarter milk composition at different levels of somatic cell count in cow composite milk

Automatic milking systems have made possible the separation of high- and low-quality milk at the udder quarter level during the milking process. The aim of this study was to investigate the composition and yield of milk from individual udder quarters to determine whether deteriorated milk composition occurs in udders that are assumed to be healthy and whether quarters with high-quality milk are found in udders with high milk somatic cell count (SCC). Milk samples were collected on one occasion from 90 cows at udder quarter level and cow composite level. The milk was analyzed for content of total protein, whey protein, casein, fat, lactose, citric acid and SCC; milk yield was registered. The cows were divided into three groups depending on the SCC of their composite milk. Cows in group 1, cow composite SCC < 100 000 cells/ml, were assumed to have healthy udders. However, instances of increased SCC and decreased milk quality were discovered in one or more udder quarters of approximately 30% of the group. Cows in group 2, cow composite SCC of 100 000 to 300 000 cells/ml, and group 3, cow composite SCC > 300 000 cells/ml, were assumed to have affected udders. However, the majority of these cows had one or more udder quarters in which increased SCC and deteriorated milk quality were not detected. Calculations of bulk-tank milk values, when separation of milk from affected udder quarters was performed, indicate that SCC changes to a much greater degree compared to the other milk components. These results show that milk from affected udder quarters suffers compositional changes, but calculations of simulated separation indicate that the compositional changes in bulk-tank milk are small. The effect of separation of milk from individual udder quarters on bulk-tank milk needs to be further studied.     

Economic impact of clinical mastitis in a dairy herd assessed by stochastic simulation using different methods to model yield losses

The main aim of the present study was to examine the economic consequences of a reduction in the incidence of clinical mastitis (CM) at herd level under current Swedish farming conditions. A second objective was to ask whether the estimated cost of CM alters depending upon whether the model reflects the fact that in different stages of lactation, CM gives rise to different yield-loss patterns or postulates just one type of yield-loss pattern irrespective of when, during lactation, CM occurs. A dynamic and stochastic simulation model, SimHerd, was used to study the effects of CM in a herd with 150 cows (9000 kg of energy-corrected milk per cow-year). Four herd types, defined by production level and reproductive performance, were modelled to investigate possible interactions between herd type and response to a reduction in the risk of CM. Technical and economic results, given the initial incidence of CM (25.6 per 100 cow-years), were studied together with the consequences of reducing the initial risk of CM by 50% and 90% throughout lactation and the consequences of reducing the initial risk by 50% and 90% before peak yield. A conventional way of modelling yield losses - i.e. one employing a single yield-loss pattern irrespective of when, during the lactation period, the cow develops CM - was compared with a new modelling strategy in which CM was assumed to affect production differently depending on its lactational timing. The effect of the choice of reference level when estimating yield losses was investigated by comparing the results obtained using the potential yield of mastitic cows, had they not developed CM, with those obtained using the yield of non-mastitic cows. The yearly maximum avoidable cost of CM at herd level was estimated at €14 504, corresponding to 6.9% of the net return given the initial incidence of CM. Expressed per cow-year, the maximum avoidable cost was €97. The cost per case of CM was estimated at €428. Herd types all responded in a similar manner to the reduced relative risk of CM. There were no major differences in the results obtained using the new and the conventional modelling strategy, with the exception of the cost per case of CM. Similarities between the results obtained using the two methods were particularly evident when the mastitic cows' own yield level, had they not developed CM, was used as the reference for production in healthy cows when yield losses were estimated. It was concluded that the conventional way of modelling yield losses is adequate and should, for the foreseeable future, be used in decision support systems.     

Genetic analysis for mastitis resistance and milk somatic cell score in French Lacaune dairy sheep

Genetic analysis for mastitis resistance was studied from two data sets. Firstly, risk factors for different mastitis traits, i.e. culling due to clinical or chronic mastitis and subclinical mastitis predicted from somatic cell count (SCC), were explored using data from 957 first lactation Lacaune ewes of an experimental INRA flock composed of two divergent lines for milk yield. Secondly, genetic parameters for SCC were estimated from 5 272 first lactation Lacaune ewes recorded among 38 flocks, using an animal model. In the experimental flock, the frequency of culling due to clinical mastitis (5%) was lower than that of subclinical mastitis (10%) predicted from SCC. Predicted subclinical mastitis was unfavourably associated with the milk yield level. Such an antagonism was not detected for clinical mastitis, which could result, to some extent, from its low frequency or from the limited amount of data. In practice, however, selection for mastitis resistance could be limited in a first approach to selection against subclinical mastitis using SCC. The heritability estimate of SCC was 0.15 for the lactation mean trait and varied from 0.04 to 0.12 from the first to the fifth test-day. The genetic correlation between lactation SCC and milk yield was slightly positive (0.15) but showed a strong evolution during lactation, i.e. from favourable (-0.48) to antagonistic (0.27). On a lactation basis, our results suggest that selection for mastitis resistance based on SCC is feasible. Patterns for genetic parameters within first lactation, however, require further confirmation and investigation.     

Evaluation of quality changes in udder quarter milk from cows with low-to-moderate somatic cell counts

Much emphasis has been put on evaluating alterations in milk composition caused by clinical and subclinical mastitis. However, little is known about changes in milk composition during subclinical mastitis in individual udder quarters with a low-to-moderate increase in milk somatic cell count (SCC). This information is needed to decide whether milk from individual udder quarters with a moderate-to-high increase in milk SCC should be separated or not. The aim of this study was to determine how milk composition in separate udder quarters is affected when cow composite milk has low or moderately increased SCC levels. Udder quarter and cow composite milk samples were collected from 17 cows on one occasion. Milk yield was registered and samples were analyzed for SCC, fat, total protein, whey proteins, lactose, citric acid, non-protein nitrogen (NPN), lactoferrin, protein profile, free fatty acids (FFAs), lactate dehydrogenase (LDH), proteolysis, sodium and potassium. Bacteriological samples were collected twice from all four quarters of all cows. The cows were divided into three groups depending on their SCC at udder quarter level. The first group comprised healthy cows with four udder quarters with low SCC, <50 000 cells/ml; composition was equal when opposite rear and front quarters were compared. In the second and the third groups, cows had one udder quarter with 101 000 cells/ml < SCC < 600 000 cells/ml and SCC > 700 000 cells/ml, respectively. The remaining udder quarters of these cows had low SCC (<100 000 cells/ml). Despite the relatively low average cow composite SCC = 100 000 cells/ml of Group 2, milk from affected udder quarters exhibited lower casein number, content of lactose and β-casein (β-CN), while the content of whey protein, sodium, LDH and α-lactoalbumin (α-la) were higher compared to healthy opposite quarters. In addition to these changes, milk from affected udder quarters in Group 3 also exhibited lower values of potassium and αs1-casein (αs1-CN) and higher values of lactoferrin when compared to milk from opposite healthy quarters. This indicates that even when the SCC in cow composite milk is low, there might exist individual quarters for which milk composition is changed and milk quality impaired.     

Economic weights of somatic cell score in dairy sheep

The economic weights for somatic cell score (SCS) have been calculated using profit functions. Economic data were collected in the Latxa breed. Three aspects have been considered: bulk tank milk payment, veterinary treatments due to high SCS, and culling. All of them are non-linear profit functions. Milk payment is based on the sum of the log-normal distributions of somatic cell count, and veterinary treatments on the probability of subclinical mastitis, which is inferred when individual SCS surpass some threshold. Both functions lead to non-standard distributions. The derivatives of the profit function were computed numerically. Culling was computed by assuming that a conceptual trait culled by mastitis (CBM) is genetically correlated to SCS. The economic weight considers the increase in the breeding value of CBM correlated to an increase in the breeding value of SCS, assuming genetic correlations ranging from 0 to 0.9. The relevance of the economic weights for selection purposes was checked by the estimation of genetic gains for milk yield and SCS under several scenarios of genetic parameters and economic weights. The overall economic weights for SCS range from − 2.6 to − 9.5 € per point of SCS, with an average of − 4 € per point of SCS, depending on the expected average SCS of the flock. The economic weight is higher around the thresholds for payment policies. Economic weights did not change greatly with other assumptions. The estimated genetic gains with economic weights of 0.83 € per l of milk yield and − 4 € per point of SCS, assuming a genetic correlation of − 0.30, were 3.85 l and − 0.031 SCS per year, with an associated increase in profit of 3.32 €. This represents a very small increase in profit (about 1%) relative to selecting only for milk yield. Other situations (increased economic weights, different genetic correlations) produced similar genetic gains and changes in profit. A desired-gains index reduced the increase in profit by 3%, although it could be greater depending on the genetic parameters. It is concluded that the inclusion of SCS in dairy sheep breeding programs is of low economic relevance and recommended only if recording is inexpensive or for animal welfare concerns.     

Carryover of aflatoxin from feed to milk in dairy cows with low or high somatic cell counts

Aflatoxin M1 (AFM1) residues in milk are regulated in many parts of the world and can cost dairy farmers significantly due to lost milk sales. Additionally, due to the carcinogenicity of this compound contaminated milk can be a major public health concern. Thirty-four lactating dairy cows were utilised to investigate the relationship between somatic cell counts (SCC), milk yield and conversion of dietary aflatoxin B1 (AFB1) into milk AFM1 (carryover (CO)). The AFM1 in milk increased as soon as the first milking after animal ingestion with a pattern of increment up to the observed plateau (between 7th and 12th days of AFB1 ingestion). There was a significant (P < 0.01) effect of the milk yield whereas no effect could be attributed to the SCC levels or to the milk yield × SCC interaction. Similarly, the main effect of milk yield was also observed (P < 0.01) on the total amount of AFM1 excreted during the ingestion period. Although the plasma concentration of gamma-glutamyl transferase was significantly affected by aflatoxin administration, levels of this liver enzyme were within the normal range for lactating dairy cows. The current data suggest that milk yield is the major factor affecting the total excretion of AFM1 and that SCC as an indicator of mammary gland permeability was not related to an increase in AFM1 CO.     

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.     

The effect of out-wintering pad design on dirtiness score, somatic cell score and mastitis incidence in dairy cows

This study aimed to compare three woodchip out-wintering pad (OWP) designs, and indoor cubicle housing with regard to cow dirtiness scores during the winter housing period, and udder health during both the winter period and the following lactation, for spring-calving dairy cows. The treatments were: an uncovered (UP) and covered (CP) OWP with a concrete feed apron; an uncovered OWP with self-feed silage pit provided directly on the woodchips (SP); and indoor cubicle housing (IC). Data were compared during 2 years: year 1 was a case study while year 2 was an experimental study. In year 1, treatments were UP (space allowance = 12 m2/cow), CP (6 m2/cow) and IC. In year 2, all three OWP designs (12 m2/cow) were compared with IC. Animals were assigned to treatments at the end of lactation in the autumn, and remained there while dry until calving the following spring. Subsequently, all cows were at pasture during lactation. Outcome measures for analysis were cow dirtiness score, somatic cell score (SCS) and incidence of clinical mastitis during the dry period and during lactation. Quarter milk samples were also taken at drying off, calving and 3 weeks post partum both years, and at approximately 113 days in milk in year 2. Samples were analysed for presence of mastitis-causing agents and SCS was determined. Sub-clinical mastitis was diagnosed when cows had an SCS greater than 200 000, or California mastitis test greater than 1 in at least one quarter. In year 1, cows in CP were dirtier than cows in the other two treatments. These animals also had the highest SCS during lactation and tended to have more mastitis-causing agents isolated from quarter milk samples. In year 2, when all cows were stocked at the same density, cows in the sheltered OWP (i.e. CP) had similar dirtiness scores to cows in cubicles and significantly lower dirtiness scores than cows in the unsheltered OWP designs, i.e. UP and SP. However, there were no effects on SCS or quarter sample results. Cleaning of OWP's stocked at 12 m2/cow reduced cow dirtiness scores. However, cleaning of CP in year 1 when cows were stocked at 6 m2/cow had no effect on dirtiness scores. We conclude that dry cows stocked at 12 m2/cow on OWP's are unlikely to have udder health problems in the subsequent lactation. Furthermore, provision of shelter and cleaning of the woodchips are management factors that help to keep cows clean on OWP's.     

Estimation of economic values and financial losses associated with clinical mastitis and somatic cell score in Holstein dairy cattle

The objective of this study was to develop a method for calculating economic values of clinical mastitis (CM) and somatic cell score (SCS) for inclusion in a dairy cattle breeding goal in the context of a country where farm production and economic data are scarce. In order to calculate the costs and derive economic values for SCS, a new model, 'milk collection method', has been developed and was compared with the Meijering model with individual and average SCS distributions. For the population, estimated economic values using the milk collection method were 1.3 and 2.4 times higher than those of Meijering method with average and individual SCS, respectively. The milk collection method needs no assumptions about normality of the distribution of SCS and because of a lack of normality in Iranian data for SCS, the Meijering method resulted in economic values that were biased downwards. Failing to account for the fact that milk price penalties for SCS are applied at milk collection rather than individual cow level resulted in a further large downward bias in the economic value of SCS. When the distribution of data is unknown or difficult to approximate or when a transformation to normality is not straightforward, the milk collection method would be preferable. Inclusion of SCS and CM in the breeding goal for Iranian dairy cattle is justified based on these results. The model to calculate mastitis costs proposed here could be used to estimate economic values for CM in other developing countries where farm production and economic data are generally poor.     

Survey of yeast mastitis in dairy herds of small-type farms in the Lublin region,Poland

The purpose of this study was to isolate fungi from the quarter milk of cow udders in 9 dairy farms. The samples were collected between May 1996 and April 2000 in the Lublin region. Six hundred and four milk samples collected from the quarters of 172 cows with clinical and subclinical mastitis were examined. Milk samples were plated as soon as possible on blood agar (BA), Mac Conkey agar, aesculin-tallium acetate-crystal violet blood agar, and Sabouraud agar with chloramphenicol and gentamicin. Fifty eight (9.6%) of the samples were positive for fungi. All of the fungal isolates were yeasts of the genera Candida, Rhodotorula and Trichosporon. We also isolated Streptococcus agalactiae (4.9%), Str. spp.(6.4%), Staphylococcus aureus (10.4%), coagulase-negative staphylococci-CNS (36.6%), Escherichia coli (3.5%), other microorganisms (2.6%) and no growth (25.8%). This revised version was published online in June 2006 with corrections to the Cover Date.     

Relationships between milk mid-IR predicted gastro-enteric methane production and the technical and financial performance of commercial dairy herds

Considering economic and environmental issues is important in ensuring the sustainability of dairy farms. The objective of this study was to investigate univariate relationships between lactating dairy cow gastro-enteric methane (CH₄) production predicted from milk mid-IR (MIR) spectra and technico-economic variables by the use of large scale and on-farm data. A total of 525 697 individual CH₄ predictions from milk MIR spectra (MIR-CH₄ (g/day)) of milk samples collected on 206 farms during the Walloon milk recording scheme were used to create a MIR-CH₄ prediction for each herd and year (HYMIR-CH₄). These predictions were merged with dairy herd accounting data. This allowed a simultaneous study of HYMIR-CH₄ and 42 technical and economic variables for 1024 herd and year records from 2007 to 2014. Pearson correlation coefficients (r) were used to assess significant relationships (P<0.05). Low HYMIR-CH₄ was significantly associated with, amongst others, lower fat and protein corrected milk (FPCM) yield (r=0.18), lower milk fat and protein content (r=0.38 and 0.33, respectively), lower quantity of milk produced from forages (r=0.12) and suboptimal reproduction and health performance (e.g. longer calving interval (r=−0.21) and higher culling rate (r=−0.15)). Concerning economic results, low HYMIR-CH₄ was significantly associated with lower gross margin per cow (r=0.19) and per litre FPCM (r=0.09). To conclude, this study suggested that low lactating dairy cow gastro-enteric CH₄ production tended to be associated with more extensive or suboptimal management practices, which could lead to lower profitability. The observed low correlations suggest complex interactions between variables due to the use of on-farm data with large variability in technical and management practices.     

Relationship between somatic cell count and bacterial pathogens in goat milk

The study aimed at evaluation of total count and pattern of somatic cells, as well as lactose content in relation to the type of bacterial pathogens in goat milk. The study was conducted on 66 Polish White Improved and Polish Fawn Improved dairy goats. A total of 487 milk samples were taken from day 30th, 60th and 200th of lactation for three years. The milk samples were divided into four groups: group 1 – containing no pathogens, group 2 – with minor pathogens up to 1000 CFU/mL such as coagulase-negative staphylococci (CNS), alpha-haemolytic streptococci, Enterococcus spp., Corynebacterium spp., group 3 – with minor pathogens (CNS) above 1 × 10³ CFU/mL of milk and group 4 – with major pathogens such as Streptococcus agalactiae, Staphylococcus intermedius and Staphylococcus aureus.In the majority of milk samples (64.9%) no pathogens were observed. The CNS were isolated from 25.3%, while the major pathogens were from 9.8% of milk samples. Both the major pathogens and high numbers of minor pathogens influenced the total somatic cell count (SCC) and lactose content. The percentage of leukocytes in the total somatic cells amounted to about 50% in the milk samples, which contained a high number of CNS or major pathogens. In the remaining samples this value reached only about 35%. Close relationship occurred between the presence of bacterial pathogens and total SCC, percentage of all leukocytes and their subpopulations in milk. The percentage of eosinophils and neutrophils in the total SCC were dramatically higher (p ≤ 0.0016) in samples of group 4 as compared to groups 1, 2 and 3. The percentage of monocytes was the highest in milk samples containing large numbers of minor pathogens. No relationship was found between the type of isolated bacterial pathogen and the percentage of lymphocytes in milk. In most samples, the presence of bacterial pathogens in goat milk led to the increase of the total SCC. However, the microbiological analysis showed that the bacterial pathogens were presented in about 20% of milk samples containing low SCC (below 1 × 10⁶/mL).     

First large-scale isolation of Prototheca zopfii from milk produced by dairy herds in Italy

A total of 1045 milk samples collected from infected and non infected quarters of 269 cows were investigated. This study showed that 4.7% of samples possessed cells of Prototheca spp. (10⁶cells/ml). The presence of other pathogenic microorganisms was also monitored. Prototheca spp. isolates were classified on the basis of current taxonomic guidelines and identified as P. zopfii. Susceptibility tests carried out in vitro by using 25 antibiotic compounds revealed that the strains of P. zopfii. were susceptible only to nystatin and amphotericin B (58 and 33% of total strains, respectively). The present study represents the first large-scale investigation carried out in Italy on the isolation of this achlorophyllous yeast-like microalga in milk samples produced by dairy herds.     

Relationships among somatic cell count, California mastitis test, impedance and bacteriological status of milk in goats and sheep in early lactation

The objectives of this trial were to evaluate and compare the test characteristics of a number of indirect tests of bacteriological status of the milk from goats and sheep and to assess the affect of varying levels of prevalence of infection on the performance of those tests.The somatic cell count, California mastitis test (CMT) score, electrical impedance and the bacteriological status of 220 and 262 milk samples from the glands of lactating dairy goats and sheep, respectively, were determined. The sensitivity and specificity of indirect tests in predicting the bacteriological status were compared by analyzing the areas under the receiver operating characteristic curve and calculating the likelihood ratio at various cut-off values.Bacteria were isolated from 17.7 and 4.6% of glands from goats and sheep, respectively. Somatic cell count was a better predictor of bacteriological status than either the CMT score or impedance in both goats and sheep. However, knowledge of the CMT score in both sheep and goats and the impedance in goats increases the likelihood of predicting the presence of a bacterial pathogen compared to no testing at all (P<0.05). Knowledge of the age and days postpartum of the animals at the time of testing did not increase the probability that infection status could be predicted. Variation in cut-off levels to predict infection status reported in the literature may be due to variation in the prevalence of infection in the populations studied. Use of likelihood ratio allows comparison of tests over a range of prevalence’s as likelihood ratios are independent of prevalence. The prevalence of infection within a herd should be considered when selecting a cut-off value for indirect testing for the presence of bacteria in milk of small ruminants.     

Changes in milk performance and hepatic metabolism in mid-lactating dairy goats after being fed a high concentrate diet for 10 weeks

Feeding a high concentrate (HC) diet is a widely used strategy for supporting high milk yields, yet it may cause certain metabolic disorders. This study aimed to investigate the changes in milk production and hepatic metabolism in goats fed different proportions of concentrate in the diet for 10 weeks. In total, 12 mid-lactating goats were randomly assigned to an HC diet (65% concentrate of dry matter, n=6) or a low concentrate (LC) diet (35% concentrate of dry matter, n=6). Compared with LC, HC goats produced greater amounts of volatile fatty acids and produced more milk and milk lactose, fat and protein (P<0.01). HC goats showed a greater concentration of ATP, NAD, plasma non-esterified fatty acids and hepatic triglycerides than LC goats (P<0.05). Real-time PCR results showed that messenger RNA (mRNA) expression of gluconeogenic genes, namely, glucose-6-phosphatase, pyruvate carboxylase and phosphoenolpyruvate carboxykinase were significantly up-regulated and accompanied greater gluconeogenic enzyme activities in the liver of HC goats. Moreover, the expression of hepatic lipogenic genes including sterol regulatory element-binding protein 1c, fatty acid synthase and diacylglycerol acyltransferase mRNA was also up-regulated by the HC diet (P<0.05). HC goats had greater hepatic phosphorylation of AMP-activated protein kinase than LC (P<0.05). Furthermore, histone-3-lysine-27-acetylation contributed to this elevation of gluconeogenic gene expression. These results indicate that lactating goats fed an HC diet for 10 weeks produced more milk, which was associated with up-regulated gene expression and enzyme activities involved in hepatic gluconeogenesis and lipogenesis.     

Polymorphisms in bovine immune genes and their associations with somatic cell count and milk production in dairy cattle

Background

Chromosome rearrangements are an important part of the speciation process in many taxa. The study of chromosome evolution in bivalves is hampered by the absence of clear chromosomal banding patterns and the similarity in both chromosome size and morphology. For this reason, obtaining good chromosome markers is essential for reliable karyotypic comparisons. To begin this task, the chromosomes of the mussels Brachidontes puniceus and B. rodriguezi were studied by means of fluorochrome staining and fluorescent in situ hybridization (FISH).

Results

Brachidontes puniceus and B. rodriguezi both have 2n = 32 chromosomes but differing karyotype composition. Vertebrate-type telomeric sequences appear at both ends of every single chromosome. B. puniceus presents a single terminal major rRNA gene cluster on a chromosome pair while B. rodriguezi shows two. Both mussels present two 5S rDNA and two core histone gene clusters intercalary located on the long arms of two chromosome pairs. Double and triple-FISH experiments demonstrated that one of the 5S rDNA and one of the major rDNA clusters appear on the same chromosome pair in B. rodriguezi but not in B. puniceus. On the other hand, the second 5S rDNA cluster is located in one of the chromosome pairs also bearing one of the core histone gene clusters in the two mussel species.

Conclusion

Knowledge of the chromosomal distribution of these sequences in the two species of Brachidontes is a first step in the understanding of the role of chromosome changes on bivalve evolution.     

Apoptosis and necrosis of polymorphonuclear leukocytes in goat milk with high and low somatic cell counts

The purpose of the present trial was to compare the percentages of necrotic and apoptotic polymorphonuclear leukocytes (PMNL) in goat milk with low and high somatic cell count (SCC). Twenty eight milk samples were collected from 20 lactating goats, determined to be negative in bacteriological examination, and divided in three groups, according to their SCC: samples with SCC lower than 500 × 10³ cells/mL; between 500 and 1500 × 10³ cells/mL; and higher than 1500 × 10³ cells/mL. SCC was performed in an automatic somatic cell counter. Apoptosis and necrosis were quantified using dual-color flow cytometry with fluorescein labeled annexin-V and propidium iodide (PI). Results of the present study showed a significant positive correlation between the percentage of the viable PMNL and milk SCC (r = 0.495, P = 0.008), as well as a significant negative correlation between apoptotic PMNL and milk SCC (r = −0.486, P = 0.009). Results also pointed out lower PMNL viability rates due to higher apoptosis rates in milk samples with SCC lower than 5 × 10⁵ cells/mL.     

Effect of including genetic progress in milk yield on evaluating the use of sexed semen and other reproduction strategies in a dairy herd

The objective of this study was to explore the importance of including genetic progress in milk yield when evaluating different reproductive strategies in a dairy herd by simulation modeling. The model used in this study was SimHerd V, a dynamic and mechanistic Monte Carlo simulation model of a dairy herd including young stock. A daily increasing trend describing genetic milk yield potential of the sire population was included in the model. The inaccuracy of assuming that replacement heifers have the same (milk yield) potential as the cows present in the herd was hereby dealt with. Improving estrus detection rate from 0.45 to 0.80 increased gross margin (GM) per cow-year by €20 when genetic progress was not included in the model. When genetic progress was included in the model, then the same improvement in estrus detection decreased the GM per cow-year by €7.4. This reduced effect was explained by a lower replacement rate in consequence of the improved estrus detection and thereby a slower genetic progress in the herd. There was a reduced effect of including genetic progress on GM when surplus heifers were sold selectively based on breeding values. Repeated insemination with sexed semen on the superior half of all heifers reduced GM by €8 per cow-year when genetic progress was not included and increased the GM by €16 per cow-year when genetic progress was included in the model. Including genetic progress reduced the losses caused by lower conception and estrus detection rates and had a minimal effect with regard to postponing first insemination. This study has proven that it is important to include genetic progress in decisions on reproduction strategies in a dairy herd.     

奶牛MHC基因多态性及其与经济性状关系的研究进展

本文简述了奶牛 MHC基因的结构、位置、分类、多态性的一般特性,并且介绍了 MHC基因与生产性状、乳房炎等一些经济性状的关系。     

Response of milk fat concentration and yield to nutrient supply in dairy cows

Dietary changes alter dairy cow milk fat concentration (MFC) and yield (MFY) through modifications in the supply of nutrients, which act as precursors or inhibitors of mammary fat synthesis. The current models used to formulate dairy cow diets cannot predict changes in milk fat. The knowledge of the effects of the nutrients on milk fat would help to progress toward this prediction. To this end, we quantified and compared the milk fat responses to variations in the supply of seven nutrients derived from digestion: volatile fatty acids, glucose, proteins, long-chain fatty acids (LCFA) and t10,c12-conjugated linoleic acid (CLA). A database was compiled from studies involving digestive infusions of these nutrients in dairy cows. It included 147 comparisons between a nutrient infusion and a control treatment. The nutrient infusions were limited to the range of physiological variations to mimic nutrient changes after dietary modifications. We established models for the response of MFC, MFY and milk fatty acid (FA) composition to the supply of each nutrient. MFC and MFY responses to the nutrients were significant and linear, except for the MFC response to glucose that was curvilinear. The nutrients differed in their effects on MFC and MFY: acetate, butyrate and LCFA increased MFC and MFY, whereas propionate, glucose and t10,c12-CLA decreased them. Protein infusions increased MFY and decreased MFC because of an increase in milk yield. The effects of numerous interfering factors related to animals, diets or experimental conditions were tested on the residuals of the response models. The responses of milk FA percentages are also provided. When adjusted to the in vivo variations in the nutrients observed after dietary changes, the effects of the different nutrients were moderate. Finally, this study showed that several of these nutrients could contribute to the changes in milk fat production and composition observed after dietary changes. This is a first step toward predicting milk fat response to changes in nutrient supply.