Endotoxin mastitis in cows milked four times daily

As part of a project to identify the pathophysiological cause or causes of mastitic hypogalactia, midlactation cows were infused in two homolateral quarters with 10 micrograms of endotoxin while being milked four times daily to resolve better the temporal changes in mammary synthetic activity during endotoxin mastitis. Milk fat was decreased by the first milking (5 h) postinfusion and then recovered rapidly. In contrast, milk yield and the yields of protein and lactose were not significantly inhibited until the second milking, and these yields recovered slowly thereafter. The decline in milk yield by infused quarters was only 20% greater than the decline by uninfused quarters in this experiment. Mammary inflammation developed rapidly in infused quarters as milk serum albumin concentration was maximal at the first milking. Milk SCC and NAGase were also elevated at this time, and maximal levels occurred at milkings 2 to 4. Increased temperature, increased cortisol, and a mild anorexia were apparent at the first milking only. Endotoxin treatment had no effect on serum prolactin or glucose. These data suggest that the delayed hypogalactia is consequent to the mammary inflammation and systemic responses following endotoxin infusion. The results indicate that different pathophysiological events may inhibit synthesis of the different milk components.     

Reduced lactational performance following intravenous endotoxin administration to dairy cows.

Nonpregnant lactating cows were given 100 micrograms of endotoxin via the jugular vein to determine effects of intravenous endotoxin administration on mammary inflammation and lactational performance. At the first milking (11 h) posttreatment, milk yield was reduced 33%. Milk fat percentage was elevated at this time, but lactose concentration was decreased. Milk yield and composition returned to pretreatment levels within 2 d. Clinical mastitis was not induced by endotoxin treatment, but milk SCC, NAGase, serum albumin, and lactoferrin were increased by 50%. This increase was small compared with increases during mastitis and may have resulted from lower milk volume. These results support the hypothesis that part of the reduced lactational performance during endotoxin mastitis is mediated by systemic pathophysiological responses and indicate that intravenous endotoxin administration may be a useful model to study adverse effects of infectious disease on lactational performance.     

Variation in the composition of selected milk fraction samples from healthy and mastitic quarters, and its significance for mastitis diagnosis

Seven variables--electrical conductivity (EC), somatic cell count (SCC), N-acetyl-beta-D-glucosaminidase (NAGase), lactose, protein, fat and pH--were compared in four quarter milk fractions (MF1: strict foremilk; MF2: first 12-15 ml foremilk; MF3: subsequent 40-45 ml milk; MF4: strippings) and in one cow composite milk sample (CC) per cow. The study used 142 quarters from 37 lactating cows of the German Black Pied breed. To rule out any possible effect due to management, animal physiology and analytical procedures, the collection and processing of milk samples from each cow was repeated for three consecutive days, and the means of 3-d values were used. All variables were affected significantly by milk fraction and udder health. Compared with foremilk, EC, lactose and protein levels in strippings decreased, while SCC, NAGase and fat increased. The pH of foremilk and strippings did not differ significantly in healthy or in mastitic quarters. The difference between MF1 and MF2 was significant for EC in mastitic quarters, and for SCC in healthy quarters only. In general, mastitis resulted in a significant increase in EC, SCC, NAGase and protein but in a decrease in lactose and fat contents of milk in one or more of the milk fractions studied. Comparison of cow composite milk samples from healthy and mastitic cows revealed the significance (P < 0.01) of udder health for EC, SCC and lactose. Of the different parameters that can distinguish between healthy and mastitic quarters or cows, EC could be used to classify 76% of quarters and 73% of cows correctly, while the lactose content permitted correct identification of 81% of quarters and 76% of cows. NAGase and pH could be used to determine the status of 73% and 61% of quarters, respectively. In general, the correlation observed in strippings was higher than in foremilk for almost all the variables studied. Surprisingly, EC, SCC, NAGase and lactose in milk from healthy quarters of mastitic cows (with at least one mastitic quarter) differed significantly (P < 0.05) from those from healthy quarters of cows with all four healthy quarters, indicating an inconsistent effect of mastitic quarters on neighbouring healthy quarters (quarter interdependence).     

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, β-hydroxybutyrate (BHBA), N-acetyl-β-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. β-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.     

Dynamics and significance of coagulase-negative staphylococcal intramammary infections

Cows (n = 139) were sampled within 17 d postpartum and monthly thereafter to examine dynamics of mammary infections and relationships between infection status, milk yield, SCC, NAGase activity, and chloride concentration. Forty-eight and 67% of cows and 19.5 and 30.5% of quarters were infected at first test and lactation end, respectively, with 51% of all infections present at first test. Coagulase-negative staphylococci accounted for 67 and 65% of first test and total infections with 85% persisting to lactation end. Animals with coagulase-negative staphylococci infections had significantly elevated quarter SCC and NAGase activity and a decrease of 821 kg mature equivalent lactation milk production compared with uninfected animals. Clinical cases with no bacterial isolation or major pathogen infections were associated with significant elevations in bucket and quarter milk SCC, NAGase activity, chloride concentration in quarters, and a decrease of 1153 kg mature equivalent lactation milk production as compared with uninfected animals. Correlations between milk production and in SCC and ln NAGase and between ln SCC and ln NAGase were -.15, -.25, and .55 (-.23, -.28, and .41 for first lactation only).     

N-acetyl-beta-D-glucosaminidase activity in whole milk and milk fractions

Experiment 1 was conducted to determine NAGase activity in skim, fat, and cell pellet fractions of foremilk and stripping milk from infection-free quarters. Changes in milk NAGase activity during a 12 h in vitro incubation were also determined. Eight cows, two quarters per cow, were used. One quarter of each cow received an intramammary infusion of oyster glycogen. N-Acetyl-beta-D-glucosaminidase activity was highest in stripping milk and in milk from infused quarters. The percentages of NAGase activity in skim, fat, and cell pellet fractions were 62.6, 22.4, and 12.6. The NAGase activity of milk incubated in vitro did not significantly change over time. Experiment 2 was conducted to determine if neutrophils lost NAGase activity during extravasation into milk. Leukocytosis was induced in infection-free quarters of five cows. The NAGase activities of peripheral neutrophils and milk neutrophils were not significantly different. Results from both studies suggest that the major source of milk NAGase is the mammary epithelial cell and that milk somatic cells contribute less than 15% of the total milk NAGase activity.     

Experimental challenge of bovine mammary glands with Enterococcus faecium during early and late lactation

Mammary glands of early and late lactation cows were challenged with Enterococcus faecium of bovine origin to determine in vivo pathogenicity and milk somatic cell count (SCC) responses. A total of 20 early lactation and 18 late lactation mammary glands were challenged. Two isolates highly adaptive and 2 isolates poorly adaptive for in vitro growth in mammary secretion were used as challenge strains of bacteria. Challenged quarters of early lactation cows were more susceptible to intramammary infection caused by E. faecium than those of late lactation cows. Intramammary challenge with isolates poorly adaptive for in vitro growth in mammary secretions resulted in 94.7% of quarters infected compared with 36.8% of the quarters infused with the isolates highly adaptive for in vitro growth in mammary secretions. Milk from quarters infused with the isolates poorly adaptive for in vitro growth had higher SCC and bacterial counts compared with quarters challenged with the isolates highly adaptive for in vitro growth. A stage of lactation effect within treatment groups was measured when milk SCC were compared between early and late lactation cows. Milk SCC in uninfused (negative control) quarters were lower in early lactation cows compared with late lactation cows. Conversely, in quarters infused with isolates poorly adaptive for in vitro growth, SCC were higher in early lactation cows compared with late lactation cows on d 2, 3, 4, 15, 16, and 17 postchallenge. In quarters infused with isolates highly adaptive for in vitro growth, SCC response did not differ between early and late lactation cows. In vitro growth of E. faecium in mammary secretion was inversely related to in vivo pathogenicity in the mammary glands of early and late lactation cows.     

Effects of Parity,Bacteriological Status,Stage of Lactation,and Dry Period on N-Acetyl-β-D-Glucosaminidase Activity of Milk and Dry Secretion

Quarter foremilk samples from 61 cows were obtained at 1.5, 3, 21, and 35 wk of lactation and at 7 d after drying off. Measurements for each sample were milk SCC, NAGase activity in the milk and ability of milk to promote phagocytosis of Staphylococcus aureus by polymorphonuclear leukocytes. Milk SCC and NAGase were correlated (r = .62). The NAGase in dry cow secretion was 10-fold higher than in milk. Parity differences in NAGase activity were not significant. There were large stage of lactation trends in NAGase: NAGase activity was high in early lactation, decreased in midlactation, and increased in late lactation and in dry secretion. The increase in activity of the enzyme in milk of first parity cows in late lactation was not as great as in milk of second and third lactation cows. N-Acetyl-β-D-glucosaminidase activity of milk from quarters with intramammary infections was higher than that of milk from quarters free of pathogens.     

Associations of udder-health indicators with cow factors and with intramammary infection in dairy cows

The objective of this study was to investigate if and how cow factors and intramammary infection (IMI) are associated with 4 different udder-health indicators in dairy cows as a first step in investigating whether the diagnostic performance of these indicators can be improved. The investigated indicators were somatic cell count (SCC), lactate dehydrogenase (LDH), N-acetyl-β-d-glucosaminidase (NAGase), and alkaline phosphatase (AP) measured in milk. In this cross-sectional study, approximately 1,000 cows from 25 dairy herds were sampled for bacteriology (quarter milk samples) during 3 consecutive days: the day before test milking, at the day of test milking, and at the day after test milking. The whole-udder test milking sample was analyzed for milk composition, SCC, LDH, NAGase, and AP. Cow data (parity, breed, milk yield, percentage of milk fat and protein, milk urea concentration, and days in milk from the sampled test milking) were collected from the Swedish milk-recording scheme. Of the sampled cows 485 were considered IMI negative and were used in multivariable mixed-effect linear regression models to investigate associations between cow factors and the udder-health indicators. A second modeling including all cows, both IMI negative and IMI positive (256 cows), was also performed. The results showed that all udder-health indicators were affected by cow factors but that different cow factors were associated with different indicators. Intramammary-infection status was significantly associated with all udder-health indicators except AP. Parity and milk urea concentration were the only cow factors associated with all indicators in all models. The significant cow factors explained 23% of the variation in SCC and >30% of the variation in LDH, NAGase, and AP in IMI-negative cows, showing that LDH, NAGase, and AP are more affected than SCC by cow factors. The IMI status explained 23% of the variation in SCC in the model with all cows but only 7% of the variation in LDH and 2% of the variation in NAGase, indicating that SCC has the best potential as a diagnostic tool in finding cows with IMI. However, further studies are needed to investigate whether the diagnostic properties of these udder-health indicators will improve with adjustment according to their associations with different cow factors when used as a diagnostic tool for finding cows with IMI.     

Pathological changes in bovine mammary glands following intramammary infusion of recombinant interleukin-2.

Eighteen lactating dairy cows were used to evaluate the physiological response of mammary glands to increasing doses of recombinant bovine interleukin-2. Right front and rear quarters were intramammarily infused with five different doses (.1 to 100 micrograms per quarter) of interleukin-2 as either a single or multiple treatment. Left front and rear quarters were intramammarily infused with a saline placebo and served as within-animal controls. Milk secretion samples for compositional analysis were collected from each quarter prior to infusion and at 12, 24, 36, and 48 h following infusion. Animals were slaughtered by exsanguination immediately following the 48-h sampling period, and mammary gland tissue was obtained for morphometric analysis. No changes in milk composition were observed between control quarters and those infused with up to 10 micrograms of interleukin-2 per quarter, administered as either a single or multiple treatment. Quarters infused with a single 100-micrograms dose of interleukin-2 or three consecutive doses of 25 and 100 micrograms of interleukin-2 had significantly lower lactose concentrations; there was a concomitant increase in bovine serum albumin, pH, and SCC compared with preinfusion concentrations or with control quarters. Morphometric analysis of tissue demonstrated an increase in stroma, a decrease in lumenal area, and a marked increase in the number of infiltrating leukocytes in those quarters infused with the higher doses of interleukin-2. Results suggest that interleukin-2 can be intrammammarily infused at doses as high as 10 micrograms per quarter without adversely affecting milk quality or normal mammary gland function.     

High cortisol concentrations and mediation of the hypogalactia during endotoxin-induced mastitis.

A series of experiments was conducted to define the role of cortisol in the hypogalactia during endotoxin-induced mastitis. In the first experiment, three of six nonmastitic cows were given a continuous infusion of trilostane, a 3 beta-hydroxysteroid dehydrogenase inhibitor that blocks enhanced cortisol synthesis. Trilostane had no effect in these cows. In the second experiment, six midlactation cows were given 10 micrograms of endotoxin in each of two homolateral quarters to induce mastitis. Three of these cows also received trilostane. Increased serum cortisol following endotoxin infusion was blocked by trilostane treatment, whereas serum glucose and rectal temperatures were unaffected. Preventing the cortisol increase failed to reduce hypogalactia in endotoxin-infused or uninfused quarters. Decreases in milk production and increases in measures of mammary inflammation were greater in trilostane-treated cows, indicating that endogenous cortisol may moderate the cow's inflammatory response. In the third experiment, three of six nonmastitic cows were injected intramuscularly with 150 IU of ACTH. Serum cortisol concentration exceeded 70 ng/ml for at least 3 h in cows receiving ACTH. This cortisol concentration, comparable with concentrations found during endotoxin mastitis, did not inhibit milk production. Together, these data demonstrate that the acute cortisol increase does not mediate the hypogalactia associated with endotoxin-induced mastitis.     

Effect of abraded intramammary device on milk yield, tissue damage, and cellular composition

The study was conducted to determine effects of an abraded intramammary device on milk yield, tissue damage, and milk somatic cells during late lactation. Abraded intramammary devices were inserted into diagonally opposed quarters of 20 cows. One group of 11 cows (devices inserted 30 wk of lactation) was quarter machine milked daily for 2 wk before and for 8 wk after insertion. Nine cows had devices inserted within 4 wk postpartum and were quarter milked at 20 and 40 wk of lactation. Aliquots of quarter bucket milk were obtained for determination of milk somatic cells, red blood cells, and NAGase activity. Stripping milk was obtained for milk somatic cell counts. For both groups, there was no significant effect of the abraded intramammary device on NAGase activity. There was a tendency for quarters with devices to produce less milk than control quarters, but the difference was not significant. Milk SCC were significantly elevated in quarter bucket and stripping milk from quarters containing intramammary devices. Red blood cells were higher in quarters containing intramammary devices when compared with controls. Results indicate that abraded intramammary devices increased concentrations of somatic cells and red blood cells in bucket milk, did not damage tissue as measured by NAGase activity, and loss in milk production was nonsignificant.     

The effect of intramammary antibiotic therapy at calving on udder health traits

The effect of intramammary antibiotic therapy at calving on mastitis infection prevalence, linear score milk somatic cell count, and milk NAGase activity, 30 d postpartum, and on milk production, 90 to 120 d postpartum, was tested. Cows (n = 175) were split into treatment and control groups at drying off. All cows received commercial dry cow therapy. At calving, treated cows received commercial lactating cow therapy in all quarters after the first two milkings; control cows were not treated. Composite milk samples were aseptically collected from all cows at drying off, calving, and 30 d postpartum. Udder health traits: linear score milk SCC, NAGase activity, and bacterial content in milk, were determined on all samples. The first three DHI milk weights were recorded for all cows. Treatment and control cows had similar prevalences of intramammary infections during the dry and 30-d postpartum periods. Least squares means of linear score milk SCC and NAGase activities were similar at drying off and calving. Cell count scores were similar between groups; NAGase activities were higher in control cows at 30 d postpartum. Control cows tended to produce more milk postpartum. Results demonstrated no advantage of intramammary therapy at calving in improving milk production or udder health.     

Effect of enterotoxigenic Escherichia coli vaccine on innate immune function of bovine mammary gland infused with lipopolysaccharide

The effects of using an enterotoxigenic Escherichia coli vaccine on innate immune responses following intramammary infusion of lipopolysaccharide (LPS) were investigated in midlactation Holstein-Friesian cows. Seven out of 14 cows were inoculated with E. coli vaccine. Three weeks later, 100μg of LPS dissolved in 10mL of saline was infused into 1 quarter of all cows. Milk was collected every hour from infusion to 12h after infusion, and twice daily (at 0900 and 1600h) for 4d. Blood samples were collected 0, 4, 8, 24, 48, 72, and 96h after infusion. Rectal temperatures and milk yields were measured. The somatic cell count (SCC), lingual antimicrobial peptide concentration, lactoperoxidase (LPO) activity, and lactoferrin (LF) concentration in milk, and haptoglobin concentration in serum were determined. The mean rectal temperature in vaccinated cows was higher than in control cows at 10h. The mean milk yield was decreased significantly in the infused quarter of control cows at 24h compared with pretreatment, but not in vaccinated cows. The mean SCC in milk from vaccinated cows at 12 and 55h was significantly lower than that of control cows. The lingual antimicrobial peptide and LF concentrations were significantly lower at 8h and 55h, respectively, in vaccinated cows than in control cows. The mean antibody titer in the serum against the vaccine at the time of LPS infusion into vaccinated cows was significantly higher than in control cows. These antibody titers were positively correlated with the peak concentrations of LPO and LF in milk following challenge; therefore, cows with a high antibody titer were accompanied by high LPO activity and LF concentration in milk. These results suggest that vaccination suppresses the innate immune reaction after intramammary LPS infusion; however, the elevated antibody titer was unlikely to be responsible for the modification of the innate immune reaction.     

Prediction of mastitis using milk somatic cell count, N-acetyl-beta-D-glucosaminidase, and lactose.

The objectives of this work were 1) to examine the responsiveness of SCC, lactose concentration, and NAGase activity in milk to changes in bacteriological status and 2) to develop models for predicting bacteriological status of mammary glands. Data included 550 cows in 10 commercial herds. Natural logarithm NAGase and log cell count were most responsive to changes in bacterial status. The log NAGase was relatively more effective in identifying major from minor pathogen infections, whereas log SCC was better able to differentiate between infected and uninfected classes. Non-transformed NAGase, SCC, and lactose were considerably less responsive to infection status. Logistic regression of bacterial status on herd, lactation number, milk, log SCC, log NAGase, and stage of lactation was performed. The least significant variables were removed in a stepwise process. Final predictors of infection status were herd, log SCC, and log NAGase. The role of log SCC was to discriminate infection from no infection, whereas log NAGase discriminated major from minor pathogens. The log NAGase, alone or in combination with log SCC, added substantially to the detection power of the model. Chi-square goodness of fit tests found no significant differences between observed and predicted infection probabilities. Substitution of herd averages for log SCC and log NAGase for the herd variables resulted in significant differences between predicted and observed herd infection probabilities.     

Evaluation of milk components during whole lactation in healthy quarters

Several milk components related to immune defences (lysozyme, lactoferrin and gamma-globulins, gamma-G) and to inflammation (somatic cell counts, SCC; N-acetyl-beta-glucosaminidase, NAGase; albumin) were considered. Forty-one quarters and 685 samples of 24 cows were included in the study; among them 534 samples were defined as negative (78.0%), 93 as diseased (13.5%) and 58 (8.5%) as subclinical. The pattern of each milk component in quarters always negative during the follow-up period was evaluated by a mixed model. Statistical analysis showed that days in milk (DIM), age (primiparous, pluriparous), herd and the interaction between herd and days in milk significantly influenced all the markers, with very few exceptions. A subset of samples including the negative quarters before the first outcome of an infection or a subclinical mastitis and the samples from quarters always negative was also selected. The analysis showed that herd, DIM and health status had a significant influence on most markers. Overall, primiparous cows were confirmed to have higher levels of most of the markers than pluriparous cows. The presence of a herd effect on non specific immune defences in fully negative quarters implies that when the mechanisms behind their release are fully elucidated, it might be possible to modulate them. Udder tissues were confirmed as an important source of some immune components, as supported by the inconsistency between SCC mean values and NAGase, lysozyme and lactoferrin values. Overall, quarters with high levels of NAGase, lysozyme and gamma-G, exposed to bacteria, did not develop subclinical mastitis. Hence, invading pathogens could induce the development of subclinical IMI when these components and gammaG are in low concentration.     

N-acetyl-beta-D-glucosaminidase (NAGase) levels in bulk herd milk

N-acetyl-beta-D-glucosaminidase ( NAGase ) levels and somatic cell counts (SCC) were determined monthly for 6 months in the bulk milk of 181 suppliers (1063 samples). A highly significant correlation (r = 0.74; P less than 0.001) was found between supplier's bulk herd milk geometric mean NAGase activity and SCC. Monthly trends which grouped suppliers into various categories defined by different NAGase and SCC thresholds showed that a similar overall pattern was obtained with both SCC and NAGase . However, further analysis indicated that 18% of the bulk milk which had SCC less than 500 X 10(3)/ml had NAGase levels greater than 25 units. Also, 34% of samples with SCC greater than 500 X 10(3)/ml had NAGase levels less than 25 units. Overall, 24% of all samples did not have corresponding NAGase and SCC results. When the bulk milk of 2 commercial dairy herds was tested monthly over 12-18 months whilst the infection status of all quarters in the herds was regularly monitored, those herds with low incidence of mastitis (5% quarters infected) had significantly lower bulk milk SCC and NAGase levels than those with a high incidence of mastitis (22% of quarters infected). This suggests that NAGase measurement on bulk herd milk would be a simple means of monitoring infection status of dairy herds and of rapidly classifying a supplier's milk as being of low, medium or high SCC status. The possible combined use of SCC and NAGase levels in bulk milk monitoring schemes is discussed.     

Relationship between cellular and whey components in buffalo milk

High somatic cell count (SCC) affects milk quality and cheesemaking, resulting in a reduction in cheese yield and quality. In dairy cows, quarter milk samples with > 200,000 cells/ml are considered to have subclinical mastitis, while there is much uncertainty on the corresponding levels of SCC in buffalo milk. In this study 30 lactating water buffaloes were selected and SCC, differential somatic cell counts and several whey components were tested in quarter milk samples to assess the relationship between inflammation markers and milk quality. Overall 236 quarter milk samples were considered. To evaluate the relationship between cellular markers (SCC, polymorphonuclear leucocytes, PMN, and N-Acetyl-beta-glucosaminidase, NAGase) and other milk components, three classes were defined (low, medium and high). Analysis of milk yield showed a significant reduction in the high class of each of the three markers chosen. Overall, the highest class was characterized by significant changes in milk composition and a lower milk quality. The presence of an inflammatory status of the udder was frequent after the first trimester of lactation and in buffaloes with two or more parturitions. This study showed that significant changes in milk components can be observed when SCC are > 400,000 cells/ml, PMN are > 50% and NAGase is > 100 units. These thresholds could be suggested as levels to define udder health status in buffalo cows.     

Effect of storage and separation of milk at udder quarter level on milk composition, proteolysis, and coagulation properties in relation to somatic cell count

Coagulation properties of milk are altered by elevated somatic cell count (SCC), partly due to increased proteolytic and lipolytic activity in the milk and, thereby, degradation of protein and fat during storage. Milk is commonly stored on the farm at cooling conditions for up to 2 d before transport to the dairy for processing. This study evaluated the effects of storage on milk with altered composition due to high SCC and the effects of exclusion of milk from individual udder quarters with high SCC on milk composition, proteolysis, and coagulation properties. Udder-quarter milk and cow-composite milk samples from 13 cows having at least 1 quarter with SCC above 100,000 cells/mL were collected on 1 occasion. In addition, commingled milk from only healthy quarters (<100,000 cells/mL) of each cow was collected, representing a cow sample where milk with elevated SCC was excluded. The milk samples were analyzed for total protein content; protein content in the whey fraction; casein, fat, and lactose contents; SCC; proteolysis; curd yield; coagulation time; and total bacterial count, on the day of sampling and after 2 and 5 d of storage at +4°C. In addition to SCC, duration of storage and total bacterial count had an effect on milk quality. The content of total protein, fat and protein contents in the whey fraction, and curd yield were found to have different storage characteristics depending on the level of SCC at udder-quarter level. The exclusion of milk from udder quarters with elevated SCC decreased the content of total protein and protein content in the whey fraction and increased the content of lactose at cow level. However, the effect of separating milk at udder-quarter level needs to be further studied at bulk tank level to evaluate the effect on overall total milk quality.     

Changes in bovine milk secretion following intramammary infusions of concanavalin A, oyster glycogen, or water

Effects of sterile intramammary infusion of Concanavalin A on milk secretion were contrasted with infusion of oyster glycogen or water. Twenty-four cows were infused intramammary with 100 mg Concanavalin A, oyster glycogen in 20 ml water, or with 20 ml water alone. Concentrations of lactose, somatic cells, immunoglobulins G and A, serum albumin, and activity of N-acetyl-B-D-glucosaminidase were determined in milk. Blood N-acetyl-B-D-glucosaminidase activity and concentrations of blood immunoglobulins G and A and serum albumin were determined. Oyster glycogen and concanavalin A caused inflammation in treated quarters; peak elevations of milk somatic cell counts, serum albumin, immunoglobulin G concentrations, and N-acetyl-B-D-glucosaminidase activity were at 12 to 36 h following treatment. Milk production and lactose concentration were reduced by oyster glycogen and Concanavalin A. Selective indices of relative accumulation of milk immunoglobulins decreased following Concanavalin A and oyster glycogen, whereas the N-acetyl-B-D-glucosaminidase activity selective index generally remained unchanged. Inflammation reduced the selective accumulation of immunoglobulins, and absence of change in the N-acetyl-B-D-glucosaminidase selective index indicated that blood is not a major source of milk N-acetyl-B-D-glucosaminidase.