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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.
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.
Milk is a heterogeneous fluid in which the colloidal phase is homogeneously dispersed in the aqueous phase. Calcium is partitioned between the colloidal and aqueous phases and is in complex electrochemical equilibrium with several major milk components. In human and bovine milk, calcium is mainly distributed between the aqueous and casein micelle in the colloidal phases (Holt & Jenness, 1984; Neville et al. 1994). Caseins form a complex micelle structure that contains approximately 25000 phosphorylated monomers that react with calcium phosphate complexes in the milk to bind 20–40 mole calcium per mole casein (Holt & Jenness, 1984; Neville et al. 1994). Thus, the distribution of calcium between the colloidal and aqueous phases appears to be governed by the level of casein in the milk (Holt & Jenness, 1984; Neville et al. 1994). In human milk, the casein level is low; ∼25% of calcium is associated with casein, whereas in cows and goats the corresponding figure is higher at ∼65%. In rats, casein levels are among the highest in mammals and 95% of calcium is associated with casein (Neville et al. 1994). In the aqueous phase, calcium is divided among ionic calcium (Ca2+), calcium citrate and calcium phosphate. Calcium citrate and calcium phosphate constitute most of the aqueous calcium in bovine milk in contrast to less than 50% in human milk (Holt & Jenness, 1984; Neville et al. 1994). As the concentration of Ca2+ in milk appears to be essential in preserving the integrity of the mammary tight junctions during lactation (Neville & Peaker, 1981), it is important to follow its concentration precisely in mammary secretions in different stages of the reproduction cycle.
We found previously that the current recommendations for Na+,
K+, and Cl−
contents in the diet do not meet the needs of lactating cows. The responses
cows receiving a ration with increased amounts of Na+,
K+, and Cl− (E cows) were
compared with those of cows consuming the same ration with a fixed concentration
of these ions (C cows) between weeks 2 and 8 post partum (PP). Milk, protein,
lactose yields, and dry matter intake between weeks 2 and 4 PP were higher
than in C cows. These differences did not occur between weeks 4 and 8 PP,
because of a higher incidence of PP complications in E cows. A greater
plasma insulin-like growth factor-1 concentration in E than in C animals
weeks 2 and 3 PP was consistent with the milk responses. A reduction in
concentration in E cows in weeks 2 and 3 PP was a consequence of their
requirements being satisfied as a result of their enhanced Na+
intake. A subsequent
elevation in aldosterone concentration in E animals was probably related
moderate excess in K+
intake. This increase in aldosterone explains the urinary
potassium loss that was detected at week 6 PP. The absence of differences
E and C cows in plasma renin activity was consistent with an absence of
in urine volume and with the apparent utilization of the enhanced ion intake
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