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Intramammary infection (IMI), comprises a group of costly diseases affecting dairy animals worldwide. Many dairy parlours are equipped with on-line computerised data acquisition systems designed to detect IMI. However, the data collected is related to the cow level, therefore the contribution of infected glands to the recorded parameters may be over estimated. The present study aimed at evaluating the influence of single gland IMI by different bacteria specieson the cow's overall milk quality. A total of 130 cows were tested 239 times; 79 cows were tested once and the others were examined 2–8 times. All of the analysed data refer to the number of tests performed, taking into account the repeated testing of the same cows. Of the cows tested ~50% were free of infection in all 4 glands and the others were infected in one gland with different coagulase negative staphylococci (CNS), Streptococcus dysgalactiae, or were post infected with Escherichia coli (PIEc), i.e., free of bacterial infection at the time of sampling but 1–2 months after clinical infection by E. coli. Overall, infection with bacteria had significant effects on somatic cell count (SCC) and lactose concentration. Examining each bacterium reveals that the major influence on those parameters was the sharp decrease in lactose in the PIEc and curd firmness in PIEc and Strep. Individual gland milk production decreased ~20% in Strep. dysgalactiae- and ~50% in PIEc-infected glands with respect to glands with no bacterial findings. Significant differences were found in lactose, SCC, rennet clotting time and curd firmness in the milk of infected glands and among those, these parameters were significantly higher in Strep. dysgalactiae and PIEc than in CNS infected cows. The current results using quarter-milking reinforces the importance of accurate IMI detection in relation to economic and welfare factors, and moreover, emphasises the need for technical sensing and constant reporting to the farmer about changes in the milk quality of every animal.
The assumption, that metabolites derived from the activity of the mammary gland epithelial cells reflect changes in milk secretion and its coagulation properties, was tested in dairy cows. The experiment included cows with uninfected udders and cows with one of the glands infected by different bacteria specie. Analysis were carried at the cow level (including all four glands), or at the gland level. High and significant correlations among the concentrations of lactose, glucose, glucose-6-posphate, milk related respiratory index (the ratio between the concentrations of citrate/lactate+malate in milk) and milk-derived glycolytic index (the ratio between glucose-6-phosphate and glucose in milk) and milk clotting parameters were found. The physiological basis for these relations and their ability to predict the deterioration in milk quality in subclinically infected glands and in glands previously clinically infected with Escherichia coli are discussed.
Real-time analysis of milk coagulation properties as performed by the AfiLab™ milk spectrometer introduces new opportunities for the dairy industry. The study evaluated the performance of the AfiLab™ in a milking parlor of a commercial farm to provide real-time analysis of milk-clotting parameters –Afi-CF for cheese manufacture and determine its repeatability in time for individual cows. The AfiLab™ in a parlor, equipped with two parallel milk lines, enables to divert the milk on-line into two bulk milk tanks (A and B). Three commercial dairy herds of 220 to 320 Israeli Holstein cows producing ∼11 500 l during 305 days were selected for the study. The Afi-CF repeatability during time was found significant (P < 0.001) for cows. The statistic model succeeded in explaining 83.5% of the variance between Afi-CF and cows, and no significant variance was found between the mean weekly repeated recordings. Days in milk and log somatic cell count (SCC) had no significant effect. Fat, protein and lactose significantly affected Afi-CF and the empirical van Slyke equation. Real-time simulations were performed for different cutoff levels of coagulation properties where the milk of high Afi-CF cutoff value was channeled to tank A and the lower into tank B. The simulations showed that milk coagulation properties of an individual cow are not uniform, as most cows contributed milk to both tanks. Proportions of the individual cow's milk in each tank depended on the selected Afi-CF cutoff. The assessment of the major causative factors of a cow producing low-quality milk for cheese production was evaluated for the group that produced the low 10% quality milk. The largest number of cows in those groups at the three farms was found to be cows with post-intramammary infection with Escherichia coli and subclinical infections with streptococci or coagulase-negative staphylococci (∼30%), although the SCC of these cows was not significantly different. Early time in lactation together with high milk yield >50 l/day, and late in lactation together with low milk yield<15 l/day and estrous (0 to 5 days) were also important influencing factors for low-quality milk. However, ∼50% of the tested variables did not explain any of the factors responsible for the cow producing milk in the low – 10% Afi-CF.
The aims of this study were to test the assumption that tissue-type plasminogen activator (t-PA) and plasminogen (PG) are closely associated with the casein micelle and form a functional complex that rules casein degradation. This assumption was essentially verified for bovine milk under conditions wherein the plasmin system was activated by treatment with casein hydrolysate. It was also shown that urokinase-type PA (u-PA), the second type of plasminogen activator present in milk, was not involved in casein degradation. In agreement with previous studies, we show that treatment with casein hydrolysate precipitously reduced mammary secretion, disrupted the tight junction integrity (increase in Na+ and decrease in K+ concentrations), induced hydrolysis of casein, and activated various elements of the innate and acquired immune system. In the present study, we have identified t-PA as the principal PA, which is responsible for the conversion of PG to plasmin. It was found that t-PA and plasminogen are present in freshly secreted milk (less than 10 min from its secretion), suggesting that they are secreted as a complex by the mammary gland epithelial cells. Further research is needed to provide the direct evidence to verify this concept.
Although there has been little study of the origin of intramammary infection (IMI) in goats, a common view is that most bacterial infection in goats occurs during milking. In the present study, the dynamics of occurrence of udder infection during and between lactations in three Anglo-Nubian goat farms in Israel was monitored. Coagulase-negative staphylococci were the predominant bacteria in the IMIs. We found that about 15% of the yearling does were already infected with bacteria when they joined the flock, whereas about 8% of the goats that dried-off returned with new IMIs. Moreover, virtually none of the goats acquired infection during lactation. Thus, our study showed that the aetiology of IMI in goats is very similar to that in dairy cows. A preventive treatment during the dry period should, therefore, be considered as an effective means of reducing the current rate of bacterial infections in goats.
The study was aimed at identifying the pathogens causing subclinical udder infections in representative Israeli dairy goat herds and determining their effect on milk quality. Five hundred goats in ten flocks of various breeds and crossbreeds were surveyed. Of the 500 goats, 13·4% were in their first lactation, 36·4% were in their second lactation and 50·2% were in their third or higher lactation. Percentages of udder halves with subclinical intramammary infection in the flocks ranged from 35 to 71%. The effect of the bacteriological infection on somatic cells count (SCC) was significant (P<0·001). Various species of coagulase-negative staphylococci (CNS), mainly Staphylococcus caprae and Staphylococcus epidermidis, were the main pathogens in infected udder halves. Lactation number did not significantly influence either infection rate of udder halves or SCC, although the percentage of udder halves with no bacteriological findings was higher at the first lactation than at the third lactation. Milk composition (fat, protein and lactose) varied among flocks, with lower mean total protein in uninfected halves than in infected ones and higher lactose in uninfected than infected halves.
Clarification of whey by microfiltration (MF) can be achieved after appropriate pretreatment of the feed. A control pretreatment consists of a physicochemical process comprising increased ionic calcium and pH accompanied by heat (50 °C, 15 min) to cause aggregation of complex lipid–calcium phosphate particles, which are then separated by MF. This pretreatment process was modified by increasing the temperature to 55 °C and by maintaining the pH constant during heat treatment. This modification resulted in larger calcium phosphate particles and a lower content of soluble calcium and phosphate ions. As a consequence, a longer period of MF operation, better whey clarification and lower calcium and phosphate content of the filtrate were achieved. This suggests that a loosely structured deposit was formed on the membrane surface which was less resistant to filtration than that resulting from the control pretreatment. During MF, it was necessary to avoid zones of high shear in the retentate compartment that might cause physical alteration of the aggregates.
Whey clarification can be achieved by using a lipid aggregation step followed by microfiltration. The results from using an M5 Carbosep membrane to ultrafilter defatted sweet whey at pH values in the range 8·0–1·5 furnished understanding of the fouling process so that fouling may be minimized. The conventional method of aggregation, allowing the pH to decrease naturally, has been compared with a modified aggregation process in which the pH was maintained constant. These two methods differed significantly in their influence on the subsequent ultrafiltration (UF), with respect to the UF hydraulic characteristics, i.e. reversible, irreversible and overall fouling resistance. Optimal UF performance was obtained at a pH equal to or slightly higher than the aggregation pH (7·5) owing to the limited fouling contribution of proteins and calcium phosphates. The modified process permitted UF at fluxes in the range 50–115 1 h-1 m-2, with moderate transraembrane pressure, even with a protein content two to five times higher than that of regular whey.
Cleaning of inorganic membranes after ultrafiltration (UF) of skim milk has been assessed using hydraulic, physicochemical and spectroscopic (i.r. and X-ray photoelectron spectroscopy) measurements. A cleaning sequence using hypochlorite alone or hypochlorite followed by HNO3 restored the membrane hydraulic resistance, in contrast to cleaning with HNO3 alone. When using NaOH, addition of Ca complexants (EDTA, gluconate, tripolyphosphate) and surfactants was required to obtain similar results. Three types of criteria (hydraulic, kinetic, chemical) are available to assess the effect of the sequestrant and surfactant types. In all the cases studied, traces of protein and Ca were detected on and within the membrane after cleaning. Nevertheless, it was concluded that it is possible to develop a single-step alkaline product to clean inorganic milk UF membranes if suitable surfactants and Ca sequestrants are included in its formula.
A mathematical model for chymosin action on casein micelles is presented in a two-stage equation which results in a single curve demonstrating the lag time from enzyme addition to the end of coagulum firming. The model uses the Michaelis–Menten enzyme kinetics equation for the first reaction followed by an nth order reaction for the casein micelles agglomeration stage. The computer output using these equations shows that lag time is elongated as enzyme concentration is lowered. Regression analysis of time of gelation against l/E0 shows good correlation. Viscosity of the milk drops at the beginning of the κ-casein hydrolysis and increases thereafter, when the coagulum is being formed.
A new technique is described for the microfiltration of cheese brine. Soft cheese brine with viable counts/ml of up to 1·2 × 106 bacteria and 2·2 × 104 yeasts and moulds was filtered using a pleated tangential flow filtration cartridge of 0·2 εm pore size membrane. This filtration resulted in a 3–4 orders of magnitude reduction of bacteria and the complete rejection of yeast and mould from the permeate. Hard cheese brine with similar bacterial loads was treated with a 1·2 εm pore size membrane cartridge and the resulting permeate contained 2–3 orders of magnitude fewer bacteria and no yeasts or moulds. Flux decline during the filtration was a function of the number of microorganisms and the amount of N in the brine. A cleaning procedure using enzyme and acid washes was established in order to prolong membrane performance.
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