Effect of incomplete milking on milk production rate and composition with 2 daily milkings

The primary aim of this study was to assess the effects of incomplete milking on milk secretion and milk composition at the quarter level. Twelve cows were enrolled beginning at 5 d in milk and remained on study through 47 d in milk. Half of each contralateral udder was incompletely milked (treatment), detaching the teat cup early to leave approximately 30% of the total milk yield behind. This target milk remaining in the gland was based on weekly calibration milking measurements of quarter total milk yield. Control quarters were milked completely until milk flow had decreased to 0 kg/min based on visual assessment. Harvested milk yield was measured twice daily at each milking, and milk components (fat, protein, lactose, solids nonfat, milk urea nitrogen) and somatic cell count, were measured twice weekly at the quarter level. The experimental unit in this design was the half-udder, and a mixed-model approach was used to assess the main and interactive effects of experiment week and treatment on milk production rate, milk remaining in the gland, and milk composition. The effect of treatment on milk production rate was significant, with the average control half-udder producing 0.97 kg/h and the treatment half-udder 0.73 kg/h. The effect of week on milk production rate and the interaction of week × treatment were also significant. The effect of treatment on milk remaining in the gland was significant, illustrating that an increase in milk remaining in the cisternal compartment had been achieved. We detected a significant decrease in milk lactose percentage in treatment half-udders, and a significant increase in somatic cell count (log₁₀). The increase was relatively small, from a geometric mean of 26,300 cells/mL in control quarters to 48,300 cells/mL in treatment quarters. The decrease in milk production rate in treatment half-udders supports current knowledge about how mammary epithelial cell secretion, proliferation, and apoptosis are modulated by autocrine-paracrine factors.     

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.     

Influence of sampling technique and bedding type on the milk microbiota: Results of a pilot study

The objective of this pilot study was to evaluate the influence of sampling technique and exposure to different bedding types on the milk microbiome of healthy primiparous cows. Primiparous Holstein cows (n = 20) with no history of clinical mastitis or monthly somatic cell counts >150,000 cells/mL were selected for this study. From each enrolled cow, a composite milk sample was aseptically collected from all 4 mammary quarters (individual quarter somatic cell counts <100,000 cells/mL), 1 individual quarter milk sample was collected using conventional aseptic technique, and 2 individual quarter milk samples were collected directly from the gland cistern using a needle and vacuum tube. All milk samples were cultured using standard milk microbiological techniques and DNA was extracted. Extracted DNA was subjected to PCR and next-generation sequencing for microbiota determination. All samples yielded relatively little total DNA. Amplification of PCR was successful in 45, 40, and 83% of composite, conventional, and cisternal samples, respectively. Bacteria were successfully cultured from 35% of composite milk samples but from none of the quarter milk samples collected using conventional or cisternal sampling techniques. Bacterial DNA sequences were assigned to operational taxonomic units (OTU) based on 97% sequence similarity, and bacterial richness and diversity were determined. Most samples were dominated by low-prevalence OTU and of the 4,051 identified OTU, only 14 were prevalent at more than 1% each. These included bacteria typically recovered from environmental sources. Chao richness was greatest in composite samples and was 636, 347, and 356 for composite, conventional quarter, and cisternal milk samples, respectively. Shannon diversity was similar among sample types and ranged from 3.88 (quarter) to 4.17 (composite). Richness and diversity did not differ by bedding type among cisternal samples, but the power of this pilot study was limited due to small sample size. Despite the small sample size, for milk samples collected from the gland cistern, overall bacterial community composition differed among bedding types. These results demonstrate that sampling technique and bedding type may be associated with the microbiota detected in bovine milk, and we suggest that these variables should be considered in designing and reporting studies about the milk microbiota.     

Application of differential inflammatory cell count as a tool to monitor udder health.

A flow cytometric technique called differential inflammatory cell count was standardized by staining bovine peripheral blood leukocytes with a combination of DNA binding dyes SYBR green 1 and propidium iodide in water. Leukocytes were also stained with propidium iodide in detergent to determine total cell count. Differential inflammatory cell count assay was evaluated with individual quarter milk samples from 13 cows. Cows were sampled at weekly intervals for 3 wk and assayed for total cell count, mononuclear leukocyte count, and polymorphonuclear leukocyte count. Simultaneously, milk samples were evaluated by the conventional electronic somatic cell count (SCC) technique. Somatic cell count positively correlated with total cell count (r = 0.9), mononuclear leukocyte count (r = 0.8), and polymorphonuclear leukocyte count (r = 0.89). Quarters with SCC > log10 5.4 had a higher total cell count, mononuclear leukocyte count, and polymorphonuclear leukocyte count and were more often culture positive compared with quarters with SCC < log10 5.4. Quarters that were culture positive on all three test occasions had a higher proportion of polymorphonuclear leukocytes (33 to 49%) compared with quarters that were culture negative on all three test occasions (17 to 25%). The findings of this study suggest that differential inflammatory cell count assay has the potential to evolve as a new technique for evaluation of udder health status.     

Association of anatomical characteristics of teats with quarter-level somatic cell count

Mastitis occurs after bacteria successfully traverse the teat orifice and cause an intramammary infection. Anatomical characteristics of the teat are potential risk factors for infection. The objective of this study was to identify potential associations between anatomical characteristics of teats and quarter-level somatic cell count (QSCC) from cows on larger dairy farms in Wisconsin. Teat dimensions (length and diameter at the teat barrel and apex) were measured, and hyperkeratosis scores were assessed for 3,713 quarters of 959 cows on 9 dairy farms. The SCC of quarter milk samples obtained from those teats was determined. Multivariate models were used to determine associations of teat anatomical characteristics with QSCC. Subclinical mastitis was defined as a quarter milk sample with SCC of >150,000 cells/mL. Teat dimensions and milk components varied among farms. In the group of farms enrolled in this study, prevalence of subclinical mastitis in mammary gland quarters ranged from 13.6 to 28.9%. An interaction of teat apex diameter and quarter position (front or rear) was identified for QSCC. For both front and rear quarters, a tendency existed for narrower teat barrels to be associated with increased QSCC. However, for front quarters only, greater diameter of the teat apex was associated with increased QSCC. Teat shape (square or triangular teats) was not associated with QSCC. Milk samples obtained from teats with hyperkeratosis scores of very rough had greater QSCC compared with milk samples obtained from teats with hyperkeratosis scores of normal, smooth ring, or rough ring.     

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.     

Short communication: Repeated mammary tissue collections during lactation do not alter subsequent milk yield or composition

Mammary biopsy collection (MB) is a valuable approach for studying mammary gland biology, but it is unclear if repeated MB impair the performance of lactating dairy cows. The objective of this trial was to examine the effect of repeated MB during lactation on udder health, dry matter intake (DMI), and lactation performance of lactating dairy cows. Sixty-four multiparous, mid-lactation Holstein cows were enrolled in a 29-wk trial, and 32 cows were randomly selected for repeated MB. The MB and non-MB (NMB) cows had similar parity (2.6 ± 0.9) and days in milk (96.5 ± 56.3 d) at enrollment. All animals were housed in the same barn and managed in the same manner. Cows were milked 3 times daily with milk yield recorded at each milking. Milk composition was measured weekly and DMI recorded daily. Three MB were performed per cow: 1 wk after enrollment and at 15 and 24 wk. The first and third MB were performed on the left rear quarter, whereas the second MB was on the right rear quarter. The MB were performed based on previously described procedures using a rotating stainless steel cannula with a retractable blade connected to a cordless drill, with appropriate sedation and antiseptic treatment after each MB. After MB, udder health, surgical wound healing, and presence of blood in milk were visually examined at each milking. Blood was cleared from milk 3.86 ± 2.0 d after MB. During the experiment, 4 rear quarters of MB cows and 5 rear quarters from NMB cows were diagnosed and treated for clinical mastitis. No differences were observed in DMI, milk yield, somatic cell score, or milk concentration and yields of fat, protein, lactose, and solids-not-fat between MB and NMB. In conclusion, lactating cows recover rapidly from MB, and repeated MB have no long-term effects on DMI, milk yield and composition, or udder health of lactating dairy cows.     

Lipoprotein lipase activity of milk from cows with prolonged subclinical mastitis

The influence of prolonged subclinical mastitis on bovine milk lipoprotein lipase activity was investigated. Nine cows with at least one quarter with prolonged subclinical mastitis and at least one nonmastitic quarter were selected in various stages of lactation. Milk from subclinical quarters had a mean somatic cell count of 5.7 X 10(6) cells/ml while milk from nonmastitic quarters had an average somatic cell count of 9.4 X 10(4) cells/ml. Quarters with a subclinical infection contained the same pathogenic organisms for a minimum of 6 wk. The average milk lipoprotein lipase activity of 108.7 units/ml milk from subclinical quarters was 27.1% higher than the average enzyme activity of 79.2 units/ml milk from nonmastitic quarters. Conditions present in the mammary gland during prolonged subclinical mastitis could lead to increased milk lipoprotein lipase activity in raw milk.     

Effects of local or systemic administration of meloxicam on mammary gland inflammatory responses to lipopolysaccharide-induced mastitis in dairy cows

Nonsteroidal anti-inflammatory drugs (NSAID) are commonly used in combination with antimicrobial mastitis treatments to reduce pain. Little is known about whether meloxicam, an NSAID designed for the preferential inhibition of cyclooxygenase-2 over cyclooxygenase-1, affects the mammary immune response. The objective of this study was to analyze the mammary immune response to intramammary (local) or intravenous (systemic) administration of meloxicam with or without immune activation by lipopolysaccharide (LPS). We challenged 108 quarters of 30 cows with or without a low or high dose of LPS from Escherichia coli (0.1 or 0.2 µg/quarter), with or without meloxicam via intramammary administration (50 mg/quarter) or intravenous injection (0.5 mg/kg of body weight; ~300 mg/cow). Intramammary administration of meloxicam alone did not trigger an acute inflammatory response, verified by unchanged somatic cell count (SCC) and lactate dehydrogenase (LDH), BSA, and IgG concentrations in milk, which are normally augmented during mastitis due to an opening of the blood–milk barrier. Similarly, intramammary meloxicam did not change the mRNA abundance of inflammatory factors in mammary gland tissue. As expected, quarters challenged with either dose of LPS showed increased leukocyte infiltration (SCC); increased LDH, BSA, IgG, Na, and Cl concentrations; and diminished K concentrations in milk. In contrast to our hypothesis, the addition of intramammary or intravenous meloxicam did not reduce these markers of mastitis in milk. Instead, intramammary meloxicam appeared to accelerate the SCC response to LPS, but only at the lower LPS dose. Moreover, the mRNA expression of inflammatory factors in mammary tissue was not modified by the intramammary application of meloxicam compared with the contralateral quarters that were challenged with LPS only. We demonstrated for the first time that intramammary meloxicam at a dose of 50 mg/quarter did not trigger an immune response in the mammary glands of dairy cows. At the doses we used, meloxicam (intramammary or systemic) did not lower inflammatory responses. The intramammary administration of meloxicam seemed to stimulate leukocyte recruitment into the milk in quarters challenged with a low dose of LPS. The integrity of the blood–milk barrier was not protected by meloxicam in LPS-stimulated quarters. This study provides the first indications that meloxicam does not limit the inflammatory response in the mammary gland, although it does not impair the mammary immune system.     

Endoscopic examination and tissue sampling of the bovine teat and udder cistern

The aim of this study was to evaluate the application of an endoscopic technique to investigate the teat and udder cisterns of the bovine mammary gland, and to biopsy tissues within the cisterns. An anesthetic protocol for application in standing animals was designed, using a combination of general and local anesthesia. Individual quarter milk production (QMP), quarter somatic cell count (SCC), and occurrence of new intramammary infection were assessed after application of the technique, and possible applications for biopsies collected were investigated. Bovine teat and gland cistern lining could be visualized and small biopsy samples could be collected. The collected biopsy samples were successfully used in histological-histopathological examination and PCR analysis. To study the impact of endoscopy on QMP, milk SCC, and bacteriology, endoscopic examination of 12 low SCC (<200,000 cells/ mL) quarters was performed in 8 different first- and second-lactation cows. Immediately following endoscopy, 8 quarters received antibiotic treatment, whereas 4 quarters remained untreated. During a 15-d follow-up, no new intramammary infection could be observed in the endoscopically treated quarters. For QMP, no significant interaction between time and treatment could be observed throughout the 15-d follow-up period. Quarter SCC did not differ among treatments (control, endoscopy with antibiotics, and endoscopy without antibiotics). In conclusion, the endoscopic technique is suitable for examination and tissue biopsy collection of the bovine mammary gland cisterns without major interference with QMP and quarter SCC.     

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.     

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.     

Study on the relationship between milk immune factors and Staphylococcus aureus intramammary infections in dairy cows

The distribution of Staphylococcus aureus within herds seems to be related to interactions among the shedding characteristics of the bacteria, their pathogenicity and mammary gland immune status. The aim of the present study was to investigate the relationships between selected mammary gland immune factors and intramammary infections associated with Staph. aureus. Overall, 70 cows from five commercial dairy herds were included in the study and quarter milk samples were assessed using bacteriological and cytological tests. We evaluated differential cell count, lysozyme concentration, N-acetyl-beta-glucosaminidase (NAGase) activity, cell viability and respiratory burst activity in randomly chosen quarter milk samples from each cow. Staph. aureus intramammary infection elicited different responses in the mammary gland immune defences investigated. Polymorphonuclear leucocytes (PMN) as a proportion of total somatic cells in milk, cell viability and NAGase activity were higher in infected quarters, while the proportions of macrophages and lymphocytes, respiratory burst activity and lysozyme levels were lower. Mean values differed among herds, but the differences were not significant. These changes were associated with Staph. aureus infection. The reduced respiratory burst activity together with the increase in the proportion of PMN suggests that both the number and activity of PMN could influence the susceptibility of the mammary gland to pathogens. Indeed, the logistic model adopted suggests that impairment of milk immune factors could be concurrent with the development of an infection.     

The value of the biomarkers cathelicidin,milk amyloid A,and haptoglobin to diagnose and classify clinical and subclinical mastitis

Timely and objective diagnosis and classification of mastitis is crucial to ensure adequate management and therapeutic decisions. Analyzing specific biomarkers in milk could be advantageous compared with subjective or semiquantitative criteria, such as palpation of the udder in clinical mastitis cases or evaluation of somatic cell count using cow side tests (e.g., California Mastitis Test) in subclinical mastitis quarters. The objective of this study was to investigate the diagnostic value of 3 biomarkers; cathelicidin, milk amyloid A, and haptoglobin for the diagnosis of subclinical and clinical mastitis. Furthermore, the suitability of these biomarkers to differentiate between mild, moderate, and severe clinical mastitis and the influence of different pathogens on biomarker levels was tested. A total of 67 healthy cows, 119 cows with subclinical mastitis, and 212 cows with clinical mastitis were enrolled in the study. Although cathelicidin, haptoglobin, and milk amyloid A were measured in all samples from healthy cows and those with subclinical mastitis, haptoglobin, and cathelicidin results were only available from 121 out of 212 cows with clinical mastitis. Milk amyloid A was measured in all samples. In cows with clinical mastitis, the mastitic quarter and a second healthy quarter serving as a healthy in-cow control quarter were sampled. It was possible to differentiate between healthy quarters, quarters with subclinical mastitis, and quarters with clinical mastitis using all 3 biomarkers. Concerning cathelicidin, thresholds were 0.000 [sensitivity (Se) = 0.83, specificity (Sp) = 0.97] and 0.053 (Se = 0.98, Sp = 0.99) for normalized optical density at 450 nm (NOD450) for differentiating between healthy quarters and quarters with subclinical or clinical mastitis, respectively. Thresholds of 1.28 µg/mL (Se = 0.65, Sp = 0.76) and 1.81 µg/mL (Se = 0.77, Sp = 0.83) for milk amyloid A and 3.65 µg/mL (Se = 0.92, Sp = 0.94) and 5.40 µg/mL mL (Se = 0.96, Sp = 0.99) for haptoglobin were calculated, respectively. Healthy in-cow control quarters from cows with CM showed elevated milk amyloid A and haptoglobin levels compared with healthy quarters from healthy cows. Only the level of milk amyloid A was higher in severe clinical mastitis cases compared with mild ones. In contrast to clinical mastitis, cathelicidin and haptoglobin in subclinical mastitis quarters were significantly influenced by different bacteriological results. The measurement of cathelicidin, milk amyloid A, and haptoglobin in milk proved to be a reliable method to detect quarters with subclinical or clinical mastitis.     

Invited review: Selective use of antimicrobials in dairy cattle at drying-off

Administering intramammary antimicrobials to all mammary quarters of dairy cows at drying-off [i.e., blanket dry cow therapy (BDCT)] has been a mainstay of mastitis prevention and control. However, as udder health has considerably improved over recent decades with reductions in intramammary infection prevalence at drying-off and the introduction of teat sealants, BDCT may no longer be necessary on all dairy farms, thereby supporting antimicrobial stewardship efforts. This narrative review summarizes available literature regarding current dry cow therapy practices and associated impacts of selective dry cow therapy (SDCT) on udder health, milk production, economics, antimicrobial use, and antimicrobial resistance. Various methods to identify infections at drying-off that could benefit from antimicrobial treatment are described for selecting cows or mammary quarters for treatment, including utilizing somatic cell count thresholds, pathogen identification, previous clinical mastitis history, or a combination of criteria. Selection methods may be enacted at the herd, cow, or quarter levels. Producers' and veterinarians' motivations for antimicrobial use are discussed. Based on review findings, SDCT can be adopted without negative consequences for udder health and milk production, and concurrent teat sealant use is recommended, especially in udder quarters receiving no intramammary antimicrobials. Furthermore, herd selection should be considered for SDCT implementation in addition to cow or quarter selection, as BDCT may still be temporarily necessary in some herds for optimal mastitis control. Costs and benefits of SDCT vary among herds, whereas impacts on antimicrobial resistance remain unclear. In summary, SDCT is a viable management option for maintaining udder health and milk production while improving antimicrobial stewardship in the dairy industry.     

Heat stress and cow factors affect bacteria shedding pattern from naturally infected mammary gland quarters in dairy cattle

Mastitis-causing pathogens are shed from infected mammary gland quarters and thus contribute to an increased risk of new intramammary infections. The objective of the current study was to investigate the shedding characteristics of various mastitis-causing pathogens and associated animal-specific (somatic cell score and parity) and environmental (heat stress) factors. In a longitudinal study, infected udder quarters were sampled consecutively on 5 dairy farms in Germany. To capture climatic factors, temperature-humidity index (THI) was calculated. In the laboratory analysis, the pathogens and their counts in the milk samples were determined. A generalized linear mixed model with gamma link was used to evaluate the factors influencing pathogen-shedding characteristics. The variables somatic cell count, pathogen, parity, and THI had significant influence on pathogen shedding. Staphylococci were shed in lower values than streptococci. The pathogen shedding from mammary gland quarters with intramammary infections was higher in the first and second lactation than in higher lactations. Exceeding the THI threshold 60 resulted in higher pathogen counts on the same day. This was only caused by the pathogens yeasts and Streptococcus uberis. Possible mechanisms causing differences in pathogen shedding are changes in the counts due to influenced milk quantities, better growth conditions at higher temperatures, or altered immunological reactions. The mechanisms often remain speculative and require further investigation. The study underlines the contribution of cows with high somatic cell counts regarding the transmission of mastitis pathogens within a herd. Furthermore, it becomes clear that heat stress in Germany influences udder health and that prevention measures are useful.     

Factors related to milk loss in quarters with low somatic cell counts

Relationship between milk production and milk composition was studied through comparisons of udder halves within cow. Cows were milked by milking unit for separate quarters of udder. Six trials had six cows per trial. Trial length was 3 d, and milkings were at 12-h intervals. Foremilk samples were taken aseptically for bacterial analysis. Milk weights by quarter were recorded, and samples by quarter were analyzed for concentrations of lactose, somatic cells, and chloride. Milk cell differential counts and N-acetyl-B-D-glucosaminidase activity also were determined. Eighty-four percent of quarter milk samples contained less than 400,000 cells/ml. Differences between right and left udder halves with respect to all measurements were computed. For halves of udders within-cow correlation coefficients for differences between production and log(base 2) somatic cell count, lactose, chloride, bacterial presence, neutrophil percent, lymphocyte percent, macrophage percent, and N-acetyl-B-D-glucosaminidase activity were -.16, .23, -.31, .09, .12, .01, -.14, and -.41. Regression coefficients of milk production (kg) on somatic cell count log(base 2) cells per milliliter, lactose (%), chloride (mg/100 ml), and N-acetyl-B-D-glucosaminidase (nmol/min per ml) were -.12, .57, -.05, and -.46. From negative correlations between production and concentrations of chloride, somatic cells, and N-acetyl-B-D-glucosaminidase activity, differences between udder halves in production may be related to changes of the blood-milk barrier, leukocyte diapedesis, and loss of integrity of secretory cells.     

Factors affecting ability of skim milk to support phagocytosis by bovine polymorphonuclear leukocytes

Milk samples from quarters were collected from 48 Holstein cows at 1.5, 3, 21, and 35 wk postpartum and at 1 wk after drying off. Foremilk samples were obtained for bacteriological examination, somatic cell count of milk, and for assay of phagocytosis. Thirty-two cows in first lactation and 16 in third lactation produced by two criteria of sire selection (high milk versus multiple trait) were studied. In vitro phagocytosis was assayed four times on each original quarter milk sample, yielding 3,840 determinations. Variance components were large for cow-associated variation. Cow, stage X cow, and cow X sample dilution were 18.7, 20.6, and 6.0% of total variance. Phagocytosis was 9% higher in skim milk from third lactations than from first. Phagocytosis was highest in dry period samples, followed by 1.5, 35, 3, and 21-wk postpartum samples. Milk somatic cell count tended to be related more closely to phagocytosis than was current bacteriological status of the quarter. Skim milk from genetically higher producing cows was less conducive to phagocytosis than skim milk from genetically lower producing cows, possibly because of dilution.     

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.