Influence of Staphylococcus aureus strain-type on mammary quarter milk somatic cell count and N-acetyl-beta-D-glucosaminidase activity in cattle from eight dairies

The hypothesis tested was that there are differences in pathogenicity between strains of Staphylococcus aureus that cause bovine mastitis. Mammary quarter milk somatic cell count (SCC) and N-acetyl-beta-D-glucosaminidase (NAGase) activity were used as indicators of the pathogenicity of different strains of S. aureus that infect the bovine udder. Eight commercial dairy herds with a history of S. aureus in bulk tank milk cultures were studied. Initially, composite foremilk samples were collected from all lactating cattle in each herd and cultured for staphylococci. Subsequently, all cows with a coagulase-positive staphylococcal intramammary infection (IMI) at the initial sampling that were still present in the herd of origin had individual mammary quarter foremilk samples collected. Coagulase-positive staphylococcal isolates were confirmed as S. aureus using a commercial biotyping system. Staphylococcus aureus isolates were strain-typed using pulsed-field gel electrophoresis. Mammary quarter milk SCC and N-acetyl-beta-D-glucosaminidase activity were determined for each cow. The difference in mean somatic cell count and mean NAGase activity for mammary quarters infected with the same strain of S. aureus and for uninfected quarters on the same cow was calculated. One-way analysis of variance was used to assess differences between strains within a herd. Overall, no significant differences were found between strains, suggesting that the degree of udder parenchymal injury induced by S. aureus IMI is in general significantly affected by factors other than strain type.     

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.     

L-lactate dehydrogenase and N-acetyl-beta-D-glucosaminidase activities in bovine milk as indicators of non-specific mastitis

Systematic factors affecting the activities of L-lactate dehydrogenase (LDH) and N-acetyl-beta-D-glucosaminidase (NAGase) and somatic cell count (SCC), the association between the activities of LDH and NAGase and SCC with respect to udder health status, and the ability of LDH and NAGase to classify cows in udder health categories for early detection of mastitis were studied. A dataset of records from 74 Danish Holstein, 76 Danish Red and 47 Jersey cows on one research farm was used. Cows were grouped into healthy and clinically mastitic. A healthy cow was defined as having no veterinary treatment and SCC<100,000 cells/ml. A clinically infected cow was one receiving veterinary treatment after showing clinical signs of mastitis and SCC >800,000 cells/ml. Breed, month of production, and days in milk significantly influenced (P<0.001) LDH activity, NAGase activity and SCC in both healthy and clinically mastitic cows. In healthy cows, LDH activity, NAGase activity and SCC started at a high level immediately after calving and decreased to low levels approximately 30-40 d post partum. All the three parameters increased due to clinical mastitis. NAGase activity had numerically higher variation in healthy cows than in clinically mastitic cows (CV=56.2% v. CV=53.5%). The relationship between LDH activity and SCC was stronger in milk from clinically mastitic than from healthy cows (r=0.76 v. r=0.48 and r=0.67 v. r=0.44 for correlation of observed values and residuals, respectively). LDH activity had higher sensitivity than NAGase activity (73-95% v. 35-77%) while specificities were in a similar range (92-99%). Further, sensitivities for LDH activity were more robust to changes in the threshold value than those for NAGase activity. Opportunities for automated, in-line real-time mastitis detection are discussed.     

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.     

Suppression of milk production during endotoxin-induced mastitis.

Healthy, midlactation cows were given intramammary infusions of 10 micrograms of endotoxin in two homolateral quarters. Productive, inflammatory, and systemic responses were studied to investigate the pathophysiological effects of mastitis on lactational performance. Endotoxin suppressed milk yield in all quarters of treated cows. A more severe and prolonged suppression occurred in infused quarters compared with uninfused quarters. The fat percentage of milk from all quarters was increased with a greater increase occurring in infused quarters. The protein composition of milk was elevated, and the lactose concentration was depressed in infused quarters. Mammary inflammation--as measured by milk SCC, NAGase, serum albumin, and lactoferrin--was limited to infused quarters. Changes in milk NAGase closely paralleled changes in milk SCC. Daily feed intake was unaffected, and serum glucose levels did not decline following infusion. The lactose concentration of urine increased rapidly after infusion. Reduction in milk yield in all quarters, but varying changes in milk composition in infused versus uninfused quarters suggest that mastitic hypogalactia is mediated by multiple pathophysiological events and is not solely due to inflammatory damage to the mammary epithelium. Part of the reduced lactational performance may result from escape of milk components from the udder into the circulation.     

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 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.     

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.     

Natural variation in biomarkers indicating mastitis in healthy cows

Dairy herds are expanding and, with increasing numbers of animals in each herd, there is a need for automatic recording of indicators in milk in order to detect mastitis, inflammation of the udder. A number of biomarkers for mastitis have been suggested over the years. Mastitis usually occurs in one of the four udder quarters and since it is now possible to milk each udder quarter separately in automated milking systems, it is important to evaluate the normal variation in the biomarkers at udder quarter level. This study evaluated the normal variations between milkings for some biomarkers in clinically healthy cows, determined by repeated somatic cell count and bacteriological analysis. The biomarkers studied were serum amyloid A (SAA), haptoglobin (Hp), lactate dehydrogenase (LDH), N-acetyl-β-D-glucosaminidase (NAGase) and alkaline phosphatase (AP), parameters that have been suggested as markers for mastitis. Ten cows were monitored on 42 consecutive milking occasions through collection of udder quarter milk samples and representative cow composite milk samples, giving a total of 2100 individual milk samples. Each cow had its individual profile for the concentrations and variations in the parameters analysed. Although there was relatively large variation between cows for the biomarkers analysed, the variation between milkings in clinically healthy quarters within cows was often below 10%. The biomarker with the lowest variation in this study was LDH. The results suggest that comparing quarters within an individual cow can identify deviations from the natural variations between milkings. This could be a valuable tool instead of, or in combination with, a cut-off value for each parameter in order to detect changes in the milk indicating mastitis.     

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

Six Holstein cows with uninfected quarters were quarter machine milked for four consecutive morning milkings. Foremilk, bucket, and stripping fractions were collected for all milkings. For the first three milkings, an additional milk sample was collected 1 h after milking. After the final milking, oxytocin (20 IU) was injected in the tail vein 20 min after milking, and residual milk was collected. All samples were assayed for NAGase activity and somatic cell concentration. Mean NAGase activity for foremilk, bucket, and stripping samples were 1.65, 1.55, and 1.84 loge nmol/min/ml. Hour after milking and residual samples averaged 2.07 and 1.78. Cell counts (loge thousand cells/ml) for foremilk, bucket, and strippings averaged 2.52, 2.91, and 4.30. Hour after and residual samples averaged 4.56 and 5.53. Results suggest that among uninfected cows, foremilk approximates bucket levels of NAGase and cell count.     

Relationship between somatic cell count,individual leukocyte populations and milk components in bovine udder quarter milk

The somatic cell count (SCC) in bovine milk is an indicator of udder health and milk quality. Individual cell populations, i.e., macrophages, lymphocytes and polymorphonuclear neutrophils, were identified and their relationship to milk components such as acute-phase proteins (serum amyloid A (SAA) and α₁-acid glycoprotein), lactic acid and lactoferrin (LF), as well as protein, fat and lactose, were studied in foremilk from separate udder quarters. The whey proteins and peptides were studied using two-dimensional gel electrophoresis, which was shown in the present study to be a useful method of assessing udder health and milk quality. The growth of a starter culture was evaluated using a conductance method as a simulation of fermentation processes relevant for cheese production. The investigation showed that LF, SAA, l-lactate and lactose are reliable indicators of milk quality on udder quarter level. The correlations between SCC, or the individual cell populations, and the potential indicators were highly significant.     

Day-to-day variation in milk yield and milk composition at the udder-quarter level

Automatic in-line measurement of milk composition and milk yield could be a useful tool in management of the dairy herd. Data on milk components and milk yield provide information on milk quality alterations and cow health status but are also useful in planning feeding and breeding. In automatic milking systems, udder quarters are milked individually, enabling analysis and recording at the udder-quarter level. Frequent records of components require knowledge about day-to-day variations. A component with greater day-to-day variation needs more frequent sampling when used as a diagnostic tool and for management decisions. Earlier studies have described the day-to-day variations in milk components for cow composite milk, but with the quarter milking technique and the possible sampling at the udder-quarter level, knowledge about day-to-day variations at the udder-quarter level is needed. In this study, udder-quarter and cow composite milk samples were collected from 42 consecutive milkings of 10 cows during 21 d. Milk yield was recorded and the milk was analyzed for total protein, whey protein, casein, fat, lactose, and somatic cell count. The results showed that the day-to-day variations and mean values for 4 healthy udder quarters within a cow were similar. In addition, different milk components had different levels of day-to-day variation, the least variation being found in lactose (0.9%) and the greatest in fat (7.7%). This suggests that repeated milk sampling and analysis at the udder-quarter level can be used to detect alterations in composition and cow health and would, thus, be helpful in the management of the dairy herd.     

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.     

Milk composition and health status from mammary gland quarters adjacent to glands affected with naturally occurring clinical mastitis

Mammary gland quarters have usually been considered to be anatomically and physiologically independent, but some recent research has indicated more interdependence than previously reported. The objective of this study was to compare milk composition (fat, total protein, lactose, solids-not-fat, and chloride) and health status (somatic cell count, differential leukocyte count, and lactate dehydrogenase) of milk samples from unaffected mammary glands of an udder with a single clinically inflamed quarter to results of milk samples from healthy mammary glands of healthy cows. The study was designed as a prospective case control study with case and control cows matched by parity and days in milk. Cases were defined as cows (n = 59) experiencing clinical mastitis in a single mammary gland, and controls (n = 59) were defined as cows that had not experienced clinical mastitis during the current lactation. Quarter milk samples were collected from all mammary glands adjacent to clinically affected quarters of cases and from the same mammary glands of controls. Samples were used to assess concentration of chloride and lactate dehydrogenase, fat, total protein, solids-not-fat, somatic cell count, and differential leukocyte count. Microbiological analysis was also performed on milk samples obtained from clinically affected mammary glands (n = 59). Logistic regression models were used to assess possible associations among quarter somatic cell count (≥150,000 cells/mL) and quarter type (adjacent to case or control). Multivariate linear models were used to compare milk composition and health status between quarter types. A total of 170 quarters were enrolled per group. Milk obtained from adjacent quarters of cases contained a lesser concentration of total protein, lactose, and solids-not-fat, but had a greater concentration of fat and chloride. The somatic cell count, total leukocyte count, and absolute numbers of neutrophils, lymphocytes, and macrophages were all increased in milk obtained from adjacent quarters of case cows compared with milk obtained from quarters of control cows. The relative proportion of neutrophils was increased, whereas the proportion of macrophages was decreased in milk obtained from cases. Approximately 30% of milk samples obtained from adjacent quarters of cases had a somatic cell count ≥150,000 cells/mL compared with 12% of milk samples obtained from quarters of control cows. The position of the mammary gland was not associated with any outcomes. In conclusion, our results support previous research that indicates the immune response to intramammary infection in a single mammary gland quarter alters milk composition and health status throughout the udder.     

Somatic cell count assessment at the quarter or cow milking level

The aim was to investigate whether on-line somatic cell count (SCC) assessment, when combined with electrical conductivity (EC), should be implemented at the udder quarter or at the cow level. Data were collected from 3 farms with automatic milking systems, resulting in 3,191 quarter milkings used in the analyses. Visual observations of foremilk and quarter milk samples for laboratory SCC analysis were used to define 2 gold standards. One was based on visual observation only and the other was based on a combination of visual observation and SCC (using a reference value of 500,000 cells/mL), which means that a quarter milking must have visually abnormal milk as well as an increased SCC to be categorized positive. On-line SCC assessment took place at the quarter level during the first part of the milking. Composite cow level samples were used for laboratory SCC analysis and to compare the performance of SCC assessment at quarter and cow levels. The EC at the quarter level was measured by in-line sensors of the automatic milking system. Alerts for SCC indicators were calculated based on straightforward reference values. Alerts for EC were based on straightforward reference values, or on interquarter ratios. The latter was calculated by dividing the value of a given quarter by the average value of the 2 lowest quarters of that milking. The EC and SCC indicators were combined with either a Boolean “and” or “or” function. Receiver operating characteristic curves were used to visually present results using different threshold values. Sensitivity, specificity, and success rate at the quarter level and false alert rate per 1,000 cow milkings were used to compare indicators at given sensitivity or specificity levels. Quarter level SCC assessment was superior to cow level assessment (transformed partial area under the curve = 0.70 vs. 0.62) when combined with EC measurement at quarter level. When aiming for the same sensitivity level (e.g., 50%) with all visual abnormal milk as the gold standard, more false alerts were generated with cow level assessment (137 per 1,000 cow milkings) compared with quarter level SCC assessment (75 per 1,000 cow milkings). As a comparison, using EC alone resulted in 292 false alerts per 1,000 cow milkings in the same situation. Therefore, it is concluded that quarter level SCC assessment was superior to cow level assessment when combined with EC measurement at quarter level.     

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.     

Short communication: Use of an ultrafiltration device in gland cistern for continuous sampling of healthy and mastitic quarters of lactating cattle for pharmacokinetic modeling

Pharmacokinetic studies of the drugs in the milk are often limited due to infrequent sampling associated with milking. Alternatively, frequent sample collection with repeated milking may increase drug elimination. The objective of this study was to determine the feasibility of continuously sampling the udder using ultrafiltration. An ultrafiltration probe was placed into the gland cisterns through mammary parenchyma of normal and mastitic quarters of 6 mature mid-lactation Jersey cows with naturally occurring subclinical mastitis. An ultrafiltration probe was secured to the caudal or lateral aspect of the udder depending on the quarter being sampled. The timed interval samples were collected at 0, 2, 4, 6, 8, 12, 18, 24, 28, 32, 36, 48, 60, 72, 84, and 96 h after drug administration. Plasma samples were collected at the same time points. Each cow received 2.2 mg/kg of flunixin intravenously before milking at time 0. All cows were routinely milked by machine every 12 h. Flunixin concentrations in plasma, whole milk, and milk ultrafiltrates were analyzed by use of ultra-high-performance liquid chromatography with mass spectrometric detection. We found no significant effects on the appearance of the milk or the ability to milk the cows after implantation of the ultrafiltration probes. The concentration of flunixin collected from the ultrafiltration probes in the mastitic quarters tended to be greater than that of the healthy quarters. We concluded that collection of ultrafiltration samples from the mammary gland of cows provides a viable means to continuously assess drug concentrations in the milk while continuing to milk the cow normally. This study demonstrates the utility of continuous sampling of milk via ultrafiltration for future pharmacokinetic studies in cattle.     

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.     

Interaction of somatic cell count and quarter milk flow patterns

Milk flow parameters at udder and quarter levels were studied in relation to somatic cell count (SCC) and other risk factors for mastitis (bimodality, duration of decline, and duration of overmilking phase). Thirty-eight Holstein cows in their first to sixth lactations were investigated during 10 mo of lactation. Monthly milk samples were collected for SCC during morning milking. Quarter and udder milk flows were recorded daily. A cow was included if one quarter was found to have an SCC higher than 200 × 10³ cells/mL. A total of 3,262 quarter milk flow curves and 804 udder milk flow curves from 22 cows (6 primiparous and 16 multiparous) were selected and evaluated. Selected data for milk flow profiles in relation to SCC represented 5 consecutive morning milkings around the time of milk sampling (sampling on d 3). A total of 661 milk samples were analyzed. At both the udder and quarter levels milk yield was reduced in groups with increased SCC. Quarters with high SCC (>500 × 10³ cells/mL) had lower peak flow rate and longer overmilking phases compared with quarters with low SCC (<200 × 10³ cells/mL). There was a tendency for a longer duration of the decline phase in quarters with high SCC but no effect was observed at the udder level. There were longer declines in bimodal milk flows at the quarter, but not at the udder, level. Also, quarters with bimodality had longer overmilking phases. The duration of the decline phases at the quarter level influenced all measured parameters except the duration of the increase phase. The quarters with a longer duration of the decline phase (≥80 s) had greater SCC and peak flow rate but had lower milk yield compared with quarters with a shorter duration of the decline phase (<27 s). Duration of the overmilking phase influenced all measured parameters except SCC. We conclude that for good udder health, the duration of the decline phase at the quarter level should be considered for milking parameters and udder preparation before milking.     

Suitability of somatic cell count,electrical conductivity,and lactate dehydrogenase activity in foremilk before versus after alveolar milk ejection for mastitis detection

Mastitis is responsible for substantial economic loss and significant animal welfare concerns for the dairy industry. Sensors that measure electrical conductivity (EC) and enzyme concentrations of lactate dehydrogenase (LDH) are presently used for automatic detection of mastitis. However, EC is not sensitive enough to detect mastitis, and the ability of LDH activity to identify mastitis caused by different pathogens is a potential option that needs to be investigated. This study was conducted to test the following hypotheses: (a) strict foremilk before milk ejection is more informative in detecting mastitis, in general, than foremilk removed after cows were stimulated for milk ejection; and (b) the value of LDH activity as a mastitis indicator depends on the type of pathogen associated with the infection. Milk samples (before afternoon milking) from 48 Holstein-Friesian cows at the University of Sydney's dairy farm (Camden, New South Wales, Australia) with EC > 7.5 mS/cm in any of the 4 quarters were collected over a period of 2 mo. Quarter milk samples (n = 343) from 48 cows were collected manually in the automatic milking rotary in 3 steps: foremilk before (strict foremilk) and after milk ejection, followed by an aseptic sample for bacteriological culture. The EC (mS), LDH (U/L), SCC (cells/mL), and milk protein and fat content (%) of foremilk in both sampling times were compared and used as predictors for gram-positive and gram-negative mastitis. Quarter (n = 515) observations from 44 cows were analyzed using a logistic mixed or linear mixed model, with cow and quarter nested within cow as random effects. Milk from both sampling times was also assessed by producing a receiver operating characteristic (ROC) curve and calculating the area under the curve (AUC) to determine ability to detect mastitis. Overall, EC and LDH were greater and milk protein (%) was lower in strict foremilk than in milk fractions obtained after milk ejection. Data from strict foremilk samples had slightly higher AUC values (0.98 to 0.99 vs. 0.97 to 0.98, respectively) than did the after-ejection milk samples. Although gram-negative coliform mastitis had significantly higher LDH activity than did gram-positive mastitis (6.19 vs. 5.34 log₁₀ U/L), the robustness of this result is questionable due to limited sample size. We concluded that milk samples taken before ejection can influence major mastitis indicators, suggesting that automatic milking system sensors could be modified to monitor milk before ejection for more efficient mastitis detection.