AS mastitis is associated with leakage of small molecular weight plasma proteins, such as o^-antitrypsin, into milk, this antitrypsin can be used as an indicator of mastitis. A colorimetric procedure was developed for large scale monitoring of milk antitrypsin activity, using microtitration plates and the Multiskan system. The effect of stage of lactation and age of the cow on the antitrypsin concentration and its interrelationship with other mastitis indicators (bovine serum albumin (BSA), somatic cell count) was analysed by computer programs on 1029 cows. Milk antitrypsin activity was high after parturition owing to colostral inhibitors. After the first month of lactation the assay measures only blood-derived antitrypsin and is a good indicator for detecting an increased permeability between blood and milk due to mastitis. Increasing lactation number only slightly affected the antitrypsin and BSA concentrations whereas somatic cell content was markedly affected.Diagnosis of mastitis from milk samples is currently based on somatic cell counts (SCC) and bacteriology. From a practical point of view, neither parameter offers any reasonable potential for large scale screening purposes. The methods of sampling and storage are critical. SCC are influenced by factors other than mastitis (Schalm et al. 1971). The equipment developed for determining SCC has gained a position as the 'classical' method for screening for mastitis, and is based on the infiltration of cells into mastitic milk.One of the main characteristics in any inflammatory response is an alteration of the permeability of the microvasculature. This gives another principle on which mastitis diagnosis could be based. During mastitis, blood proteins leak from the intravascular compartment into milk. These proteins are thought to diffuse from blood to the alveolar space through the separated tight junctions between endothelial and epithelial cells. A sieving effect of the blood/milk barrier is seen by the fact that small molecular weight proteins leak preferentially. Good indicators of inflammation within the mammary gland would appear to be the quantity of serum albumin (BSA) or a 1 -antitrypsin, which belong to the small molecular weight plasma proteins with a mol. wt ~ 70000. The measurement of BSA in milk has been suggested previously as an indicator of mastitis (Schalm et al.
Milk and blood levels of silicon, selenium and the selenoenzyme glutathione peroxidase (GSH-Px) were measured in 20 healthy and 21 mastitic cows. In milk samples from healthy quarters the mean silicon concentration was 0.81 and in affected ones 0.39 ppm. In serum the mean silicon values were 1.63 and 1.02 ppm respectively. The selenium status was not altered but the level of erythrocyte GSH-Px was lowered in mastitic animals. Silicon is known to have marked effects on free radical formation, lipid peroxidation and macrophage activity. Its possible role in infection and inflammation is evaluated. Some of the functions of silicon may resemble those of selenium. The possibility of lowered levels of silicon and of the selenoenzyme in mastitis calls for experimentation with dietary or pharmaceutical supplementation of these trace elements.
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