-Relationships between Quarter Milk Cell Count (QMCC) and Tank Milk Cell Count (TMCC) with milk biochemical and technological parameters in milk and dairy products were investigated. All parameters measured were affected by the increase of TMCC and QMCC between 0 and 600 000 cells/mL. The variable effect of lactation stage which is different for different authors, is discussed. The three mechanisms, measured during the inflammation of the udder, implicated in the modification of milk quality are described (a decrease in synthesis, a decrease in the milk barrier permeability and an increase in proteolytic activities). The direct effect of plasmin in caseinolysis is well known; the specific role of the increase of somatic cells (especially PMN) in the modification of milk quality is described. Several specific proteolytic activities of PMN are described and the impact of these activities on caseinolysis is evaluated. Two hypothetical mechanisms of caseinolysis by PMN are suggested and a synthetic scheme of the role of plasmin, bacteria and somatic cells in caseinolysis is discussed. caseinolysis / mastitis / milk / PMN proteases / SCC

The water intake of 41 lactating dairy cows managed according to current dairy farm practices was individually and continuously monitored to 1) investigate drinking behavior and 2) determine factors affecting water intake. The cows were housed in a free-stall barn and fed once daily with a corn silage and concentrate-based total mixed ration (48% dry matter content; 20.6 +/- 3.3 kg/d of dry matter intake). Cows were milked twice daily, with a yield of 26.5 +/- 5.9 kg/d. The daily free water intake (FWI) was 83.6 +/- 17.1 L, achieved during 7.3 +/- 2.8 drinking bouts. The drinking bout water intake was 12.9 +/- 5.0 L. Almost three-fourths of the FWI occurred during working hours (0600 to 1900 h). Consumption peaks corresponded to feeding and milking times. More than one quarter of the daily FWI was met during the 2 h after each milking. About 75% of the present cows visited the watering point at least once during the 2 h after the evening milking. It is probable that drinking behavior evolved with lactation, but further studies are required to identify the relationship between lactation stage and drinking behavior. The most relevant factors affecting the daily FWI of lactating cows were best combined according to the following predictive equation: (R(2) = 0.45; n = 41 cows, n = 1,837): FWI, L/d = 1.53 x dry matter intake (kg/d) + 1.33 x milk yield (kg/d) + 0.89 x dry matter content (%) + 0.57 x minimum temperature ( degrees C) - 0.30 x rainfall (mm/d) - 25.65. The results obtained using these equations were in agreement with the equations developed by other researchers.

Eighty-six samples of quarter milk from 31 cows, the mean SCC of which exceeded 400,000 cells/ml, were analyzed for SCC, chloride content, pH, clotting time, total N, soluble N, casein N, proteose-peptone content, plasmin activity, and amount of free NH2 groups, parameters that are related to the udder health condition and to the deterioration of the protein quality. Analysis of the milk from each quarter separately improved the correlations considerably compared with analyses of samples from all 4 quarters mixed together. Measurement of free NH2 groups, using the 2, 4, 6-trinitrobenzene sulfonic acid, was not appropriate for estimating the extent of protein deterioration in milk samples with different SCC. Unlike SCC, the proteolysis index, plasmin activity, and the proteose-peptone content were highly correlated themselves and with most of the parameters related to proteolysis in milk. Proteolysis occurred in milk samples with SCC as low as 250,000 cells/ml. The quality of milk protein decreased unavoidably during lactation, regardless of SCC.

Experimental mastitis has been induced by the lipopolysaccharide (LPS) of Escherichia coli on six dairy cows in order to study the mechanisms involved in milk endogenous proteolysis during the inflammatory process. Variations in somatic cell count (SCC), plasmin activity, and total casein (CN) content were measured, and proteose-peptone content and the percentage of pH 4.6 insoluble peptides including gamma-CN have been considered as indicators of endogenous proteolysis. Furthermore, polymorphonuclear neutrophils (PMN) maturity has been evaluated by optical microscopy, and proteolysis by PMN proteinases has been studied at neutral and acidic pH in order to establish a link between caseinolysis, proteinase class, and PMN maturation. Two peaks of proteose-peptones content have been noticed for the six cows. First peak could be explained by both plasmin activity and SCC, while second peak was concomitant with a low plasmin activity but a SCC remaining high. The second peak of proteose-peptones content confirmed the role of cellular proteases in milk caseinolysis. Casein breakdown by cellular proteases was confirmed by SDS-PAGE electrophoresis, and a link between neutral proteinases activity and immature PMN recruitment was shown. Acidic proteinases activity was effective with mature PMN and during the recovery phase.

This work consisted of the intramammary infections (IMI) of 8 heifers by high doses of Escherichia coli to study both the proteolytic activity in milk and the resulting peptides. Therefore, a milking kinetic has been followed, and several parameters have been studied, such as proteose peptones (PP) fraction (quantitative and qualitative changes), plasmin activity (PA), milk somatic cell count (SCC), and bacterial count. A qualitative study of milk proteins and PP was performed by sodium dodecyl sulfate-PAGE, and the peptides recovered in PP during the acute phase of inflammation were amino-terminal micro-sequenced. A BSA increase in milk over time supported the hypothesis of an increase in the permeability of the epithelial barrier. A significant increase in PP content, considered to be an indicator of proteolysis, was observed from postinfusion hours (PIH) 12 to 48. Both the E. coli bacterial count and the SCC increased from PIH 3 to 216. Plasmin activity was increased noticeably from PIH 15 to 24. The respective increases in SCC, bacterial count, and PA suggest their involvement in a global mechanism responsible for the increase in proteolysis in milk after E. coli challenge. Somatic cell count and E. coli may be involved from PIH 3 to 216, and PA involvement might be highlighted during the maximum proteolysis, from PIH 15 to 24. A qualitative study of PP fraction by electrophoresis revealed the apparition of 5 peptide bands: P1 and P2 previously recovered during the lipopolysaccharide challenge, and E1 (27.0 kDa), E2 (15.5 kDa), and E3 (9.0 kDa) were specific to E. coli challenge; E1, E2, and E3 contained casein fragments. The roles played by leukocytes and E. coli are discussed. 2923Abbreviation key: PA = plasmin activity, PIH = postinfusion hour, PMN = polymorphonuclear neutrophils, PP = proteose peptones, t-PA = tissue plasminogen activator, u-PA = urokinase-type plasminogen activator.