Variation in N-acetyl-beta-D-glucosaminidase activity and somatic cell count among various milk fractions

Oxytocin Induces Mammary Epithelium Disruption and Could Stimulate Epithelial Cell Exfoliation

Mammary epithelial cells (MEC) are exfoliated from the epithelium into milk, influencing the number of MEC present in the udder. This process is associated with epithelium integrity. The release of oxytocin (OT) induced by milking causes myoepithelial cell contraction, which, in turn, may stimulate MEC exfoliation through mechanical forces. To investigate the role of OT in MEC exfoliation, we inhibited or induced myoepithelial cell contraction by injecting the OT receptor antagonist atosiban (Ato) or a supraphysiological dose of OT, respectively. Eight cows were assigned to 2 treatments during 2 milkings according to a crossover experimental design: Control+OT (cows were first milked to collect standard milk and then received 5 IU of OT to collect residual milk through a second milking) and Ato + OT (cows were injected with Ato (50 μg/kg of body weight) and milked to collect cisternal milk, then received 5 IU of OT to collect alveolar milk through a second milking). Milk MEC were purified to determine their concentration and number in milk. Mammary epithelium integrity was assessed by measuring the kinetics of plasma lactose concentration. Inhibiting myoepithelial cell contraction by Ato injection decreased the number of exfoliated MEC in milk. In contrast, OT injection increased the concentration of MEC in the residual milk and the number of MEC in the alveolar milk. Ato injection reduced plasma lactose concentration, whereas, in both treatments, OT injections increased it. Our results suggested that myoepithelial cell contraction caused by OT could stimulate MEC exfoliation into milk and was associated with epithelium disruption.

Quarter health, milking interval, and sampling time during milking affect the concentration of milk constituents

Eleven Danish Holstein cows were used to examine the effects of quarter health (healthy vs. unhealthy), milking interval (12 vs. 6 h), and sampling time during milking on the concentration of 8 milk constituents [acetone, beta-hydroxybutyrate (BHBA), N-acetyl-beta-D-glucosaminidase (NAGase), somatic cell count (SCC), urea, fat, protein, and lactose]. The selection criterion was that each cow should have 2 or 3 healthy and 1 or 2 unhealthy quarters. Foremilk was collected before attaching the teat cups of the milking machinery, and thereafter, milk samples were collected automatically from each quarter every 45 s during milking. Compared with milk from healthy quarters, milk from unhealthy quarters had a higher concentration of BHBA, NAGase, SCC, and protein during the entire milking, whereas urea was higher in the last part of the milking process. Healthy quarters had a higher content of acetone and lactose during the whole milking, whereas fat was higher in the first part of the milking process. When the cows were milked at the 6-h interval, all milk constituents except lactose and protein were higher during the whole (NAGase, SCC, and urea) or part of the milking (acetone, BHBA, and fat) compared with when cows were milked at the 12-h interval. Lactose was higher in the first part of the milking at the 12-h compared with the 6-h interval, whereas protein was not affected by milking interval. beta-Hydroxybutyrate, NAGase, SCC, and fat increased during the milking process, whereas acetone, urea, protein, and lactose decreased. Foremilk was remarkably different for all constituents, except acetone, and should not be used as a representative milk sample to achieve the true level of a milk constituent. If these milk constituents are to be used in an inline management system, these effects should be taken into account.

Changes in milk protein fraction as affected by subclinical mastitis

From cows that had both healthy quarters and quarters with subclinical mastitis [somatic cell count (SCC) 84,000 vs. 293,000/ml in bucket milk], foremilk, bucket milk, and stripping and residual milks were collected. Young milk was obtained 1.5 h later following a repeated oxytocin injection. Compared with milk from healthy quarters, milk from quarters with subclinical mastitis showed elevated SCC, plasminogen, and protein and had increased activity of n-Acetyl-beta-D-glucosaminidase (NAGase) and plasmin, as well as elevated portions of whey proteins and gamma-casein in the total protein. The SCC and the other mentioned parameters were also higher in the foremilk and the stripping and residual milks compared with bucket milk, independent of the udder health status; however, decreased values were found for total protein. Young milk showed an increase of SCC and n-Acetyl-beta-D-glucosaminidase activity compared with bucket milk. Because of lower levels of total plasmin and gamma-casein, we concluded that this young milk was newly synthesized milk containing some casein degradation products and that proteolysis of casein continued in the udder until the next milking. The n-Acetyl-beta-D-glucosaminidase activity was shown to be a better indicator for subclinical mastitis and correlated better with protein degradation than did SCC.

Variations during lactation in total and differential leukocyte counts, N-acetyl-beta-D-glucosaminidase, antitrypsin and serum albumin in foremilk and residual milk from non-infected quarters in the bovine

Quarter samples of foremilk and residual milk were taken approximately every second week from 2 days post partum (pp) throughout lactation month 9, from 5 dairy cows in their second lactation period. Bacteriologically positive milk samples were excluded. The aim was to study the variation in total and differential leukocyte counts, N-acetyl-beta-D-glucosaminidase (NAGase), antitrypsin (ATR) and serum albumin (BSA) in milk during the lactation period and different stages of oestrous cycle. Also the between milkings variation was studied from lactation month 4 to 9. At 2 days pp, each fraction of milk contained significantly higher numbers of leukocytes and had a higher activity of NAGase and ATR than later in the lactation period. In foremilk the highest content of BSA was also recorded at 2 days pp. From lactation month 2 to 9, stage of lactation had, in general, a slight effect on the variation in the variables measured. The total leukocyte count in residual milk tended to increase as lactation proceeded. The proportion of monocyte-macrophages in foremilk was significantly decreased during the last 4 months. NAGase and BSA in both fractions and ATR in residual milk increased significantly towards the end of the lactation period. From lactation month 4 to 9 the highest recorded ranges of variation between milkings, within quarter and stage of lactation, in the total leukocyte count, proportions of neutrophils, lymphocytes, monocyte-macrophages, NAGase, ATR and BSA in foremilk were 215 x 10(3)/ml, 42%, 34%, 54%, 6.68 units, 0.36 units and 0.14 mg/ml respectively. The corresponding figures in residual milk were higher except for the variation in BSA which was slightly lower in residual milk than in foremilk. In residual milk there was a positive correlation between the proportion of neutrophils and the total leukocyte count, when calculated on data from all cows and the entire experimental period. During the oestrous periods, the proportion of neutrophils in residual milk was higher than during the dioestrous periods. Foremilk and residual milk differed in the total as well as the differential leukocyte counts in all the various stages of lactation, whereas the contents of NAGase, ATR and BSA were equal in both fractions. The exception was 2 days pp when the proportions of lymphocytes were equal in both fractions and BSA-significantly higher in foremilk than in residual milk.

Variation in milk somatic cells of heifers at first calving

To evaluate variation in milk somatic cells, 24 primiparous cows (paired by calving date) were sampled during the first 75 d of lactation. Milk somatic cell counts were lowest at 9 to 10 wk. For differential cell counts in milk, only percentage of macrophages changed significantly during first 75 d (33% at 1 wk, 25% at 6 wk, and 34% at 11 wk). Epithelial cells were identified and ranged from 11 to 20% of total. For milk somatic cell count, variation between cows within pairs sampled contemporaneously was small (3 to 24%). However, variation between cows was much greater for the differential cell counts (46% of total for lymphocytes and 34% for epithelial cells). Of 1021 quarter foremilk samples, 26 were positive for major pathogens, but 326 were positive for various species. Prevalence of bacteria was significantly higher during first 10 d after calving. Rear quarters had significantly higher bacterial presence: 47% for left rear versus 21% for left front and 37% for right rear versus 24% for right front. Total milk somatic cell count after first calving appears to depend primarily on differences in temporary factors and is not a stable characteristic of individual cows. Proportions of the different somatic cell types in milk may vary consistently by cow in early first lactation.

Variation in somatic cell count, California mastitis test, and electrical conductivity among various fractions of ewe's milk

Variation of three estimates of udder inflammation (SCC, California mastitis test, and electrical conductivity) among the foremilk, machine milk, and hand stripping samples were studied. Foremilk and hand stripping milks were taken from each individual teat; machine milk was taken from the entire udder. For this experiment a total of 30 Manchega ewes were subjected to machine milking during the 9th wk of lactation. Samples were taken in duplicate during two milkings on consecutive mornings. Significant differences were observed in the SCC and electrical conductivity, but not in California mastitis test, between foremilk and stripping milk. The stripping fraction had higher SCC (70 +/- 12%) and lower electrical conductivity (difference = .52 +/- .03 mS/cm) than did the foremilk fraction in both healthy and mastitic udders. Machine milk, foremilk, and stripping milk fractions in udders where both halves were healthy were compared. The electrical conductivity values for the machine milk were intermediate and significantly different from conductivity of foremilk and stripping fractions. The log SCC of the machine milk did not differ from that of the foremilk fraction but was significantly less than the stripping milk.