Production effects related to mastitis and mastitis economics in dairy cattle herds

Mastitis is the most prevalent production disease in dairy herds world-wide and is responsible for several production effects. Milk yield and composition can be affected by a more or less severe short-term depression and, in case of no cure, by a long-acting effect, and, sometimes, an overlapping effect to the next lactation. Summary values in the literature for losses of milk production were proposed at 375 kg for a clinical case (5% at the lactation level) and at 0.5 kg per 2-fold increase of crude SCC of a cow. Due to the withdrawal period after treatment, composition changes in milk can almost be neglected in economic calculations. Lethality rate for clinical mastitis is very low on the average, while anticipated culling occurs more frequently after clinical and subclinical mastitis (relative risk between 1.5 and 5.0). The economics of mastitis needs to be addressed at the farm level and, per se, depends on local and regional epidemiological, managerial and economic conditions. To assess the direct economic impact of mastitis, costs (i.e. extra resource use) and losses (i.e. reduced revenues) have to be aggregated. To support decision making for udder health control, it is necessary to use a marginal approach, based on the comparison of the losses avoided and the additional costs of modified plans, compared to the existing ones.

Monitoring udder health and milk quality using somatic cell counts

In this article the use of somatic cell counts for monitoring udder health and milk quality is discussed. Somatic cell count dynamics at quarter, cow, herd and population level are discussed and illustrated with examples. Quarter and cow somatic cell counts directly represent the inflammatory status of the mammary gland. Herd and population somatic cell count are related to the inflammatory process in individual cows but much more reflect the udder health status of the herd and the quality of the raw milk in the herd and the population. Application of monitoring tools in herd health management are illustrated using a case study. Understanding infection dynamics requires precise longitudinal data. Monitoring tools are required to find the areas of risk in the herd. It is inevitable that more complete udder health programs and monitoring systems are to be developed and implemented. These programs are necessarily dynamic and complex. Implementation of complete udder health programs should be accompanied by research efforts to further fine-tune these complete udder health control and monitoring programs.

Mastitis of dairy small ruminants

Staphylococci are the main aetiological agents of small ruminants intramammary infections (IMI), the more frequent isolates being S. aureus in clinical cases and coagulase negative species in subclinical IMI. The clinical IMI, whose annual incidence is usually lower than 5%, mainly occur at the beginning of machine milking and during the first third of lactation. These features constitute small ruminant peculiarities compared to dairy cattle. Small ruminant mastitis is generally a chronic and contagious infection: the primary sources are mammary and cutaneous carriages, and spreading mainly occurs during milking. Somatic cell counts (SCC) represent a valuable tool for prevalence assessment and screening, but predictive values are better in ewes than in goats. Prevention is most often based on milking machine management, sanitation and annual control, and milking technique optimisation. Elimination mainly relies on culling animals exhibiting clinical, chronic and recurrent IMI, and on drying-off intramammary antibiotherapy; this treatment allows a good efficacy and may be used selectively by targeting infected udders only. Heritability values for lactation mean SCC scores are between 0.11 and 0.15. Effective inclusion of ewe's mastitis resistance in the breeding goal has recently been implemented in France following experimental and large scale estimations of genetic parameters for SCC scores.

Indicators of inflammation in the diagnosis of mastitis

Mastitis affects the quality of milk and is a potential health risk for the other cows. In a well managed dairy herd, in addition to clinical mastitis, subclinical mastitis should be efficiently detected. Bacteriological sampling is not feasible as a routine test to identify subclinical mastitis, and indirect tests of mastitis are more suitable for selecting cows with intramammary infections for subsequent bacteriological sampling. Mastitis affects the composition of milk, and the degree of changes depends on the infecting agent and the inflammatory response. Indicators of inflammation in the milk which can be determined using rapid, reliable and easy routine techniques, can be used for the early detection of mastitis. The measuring of the somatic cell count in milk is the standard method, but the analysis technique is problematic for routine use in herds. The most promising parameters for monitoring subclinical mastitis are milk N-acetyl-beta-D-glucosaminidase activity, lactose, and electrical conductivity along with some other indicators such as optical and milk flow measurements, preferably with an inter-quarter evaluation included in the test. Acute phase proteins, haptoglobin and serum amyloid A, are also potential candidates for mastitis monitoring. New mastitis detection systems which can be adapted into on-line use are urgently needed, since dairy units are growing bigger and automatic milking systems are being taken into use.

Survey of the incidence and aetiology of mastitis on dairy farms in England and Wales

A survey of clinical and subclinical mastitis was carried out on 97 dairy farms in England and Wales, selected at random from members of a national milk recording scheme. The farmers were asked to collect aseptic milk samples from five consecutive cases of clinical mastitis and from five quarters with high somatic cell counts using a defined protocol, and they completed a questionnaire that included information on the cows sampled, the herd and the history of mastitis in the herd. The samples were collected throughout the year. The mean incidence of clinical mastitis was 47 cases per 100 cows per year (estimated from historic farm records) and 71 cases per 100 cows per year (estimated from the samples collected). Streptococcus uberis and Escherichia coli were isolated in pure culture from 23.5 per cent and 19.8 per cent, respectively, of the clinical samples; 26.5 per cent of the clinical samples produced no growth. The most common isolates from the samples with high cell counts were coagulase-negative staphylococci (15 per cent), S uberis (14 per cent) and Corynebacterium species (10 per cent). Staphylococcus aureus and coagulase-positive staphylococci together accounted for 10 per cent of the samples with high somatic cell counts; 39 per cent produced no bacterial growth.

Effects of insulin, insulin-like growth factor I, and gonadotropins on bovine granulosa cell proliferation, progesterone production, estradiol production, and(or) insulin-like growth factor I production in vitro

The objectives of the present studies were to determine the effect of insulin, insulin-like growth factor I (IGF-I), testosterone, and FSH on proliferation, progesterone production, and(or) estradiol production of bovine granulosa cells. In addition, existence of IGF-I mRNA in granulosa cells and in vitro IGF-I production by granulosa cells were assessed. Cells from small (1 to 5 mm) and large (> or = 8 mm) follicles were collected from cattle and cultured for either 3 or 4 d. When cells from small follicles were cultured, insulin (.1 to 10 micrograms/mL) and IGF-I (100 to 400 ng/mL) increased (P < .05) cell numbers compared with controls. Insulin alone or IGF-I alone increased (P < .05) progesterone production per cell by severalfold on d 4. In cells from both sizes of follicles, insulin (1 microgram/mL), in the presence of FSH, increased estradiol production per cell. In contrast, IGF-I (100 ng/mL) inhibited estradiol production by cells from small follicles and stimulated estradiol production by cells from large follicles. Insulin-like growth factor II (100 ng/mL) and insulin at higher doses (> or = 5 micrograms/mL) had no effect on estradiol production by cells from small and large follicles. Granulosa cells contained four IGF-I mRNA transcripts and produced IGF-I in vitro. These results support the hypothesis that insulin and IGF-I may have direct local effects on bovine ovarian function, and that these effects are influenced by dose and size of follicle.

Relationship between udder and leg hygiene scores and subclinical mastitis

The objective of this study was to determine the relationship between udder and leg hygiene scores of lactating dairy cattle and measures of subclinical mastitis. Study animals (n = 1250) consisted of lactating dairy cows from eight commercial dairy farms. Herds were enrolled during December 2000 and January 2001 and were visited bimonthly for a total of five visits per herd. Udder and leg hygiene scores were recorded by one person using a four-point scale ranging from one (very clean) to four (very dirty). Udder and leg hygiene scores were compared to bacteriological cultures of milk samples and monthly individual SCC values. Mean hygiene scores were 2.09 and 2.33 for udders and legs, respectively. Udder hygiene scores (UHS) were significantly associated with leg hygiene scores and varied among farms. Linear somatic cell scores increased as udder hygiene score increased. Significant differences in somatic cell scores were observed for all contrasts of udder hygiene score, except between scores of 1 and 2 and of 3 and 4. Linear somatic cell scores were associated with leg hygiene scores, but the only significant contrast was between leg hygiene scores of 2 and 4. There was a significant association between the prevalence of intramammary contagious pathogens and udder hygiene score. The prevalence of intramammary environmental pathogens was significantly associated with udder hygiene score and was 7.7, 10.0, 10.6, and 13.5% for UHS of 1, 2, 3, and 4, respectively. The prevalence of environmental pathogens was not associated with LHS. Cows with udder hygiene scores of 3 and 4 were 1.5 times more likely to have major pathogens isolated from milk samples compared with cows with hygiene scores of 1 and 2.

Genetics of resistance to mastitis in dairy cattle

Genetic variability of mastitis resistance is well established in dairy cattle. Many studies focused on polygenic variation of the trait, by estimating heritabilities and genetic correlation among phenotypic traits related to mastitis such as somatic cell counts and clinical cases. The role of Major Histocompatibility Complex in the susceptibility or resistance to intrammamary infection is also well documented. Finally, development from molecular genome mapping led to accumulating information of quantitative trait loci (QTL) related to mastitis resistance and better understanding of the genetic determinism of the trait. From economic and genetic analyses, and according to welfare and food safety considerations and to breeders and consumer's concern, there is more and more evidence that mastitis should be included in breeding objective of dairy cattle breeds. Many countries have implemented selection for mastitis resistance based on linear decrease of somatic cell counts. Given biological questioning, potential unfavourable consequences for very low cell counts cows are regularly investigated. Improvement of selection accuracy for mastitis resistance is ongoing and includes: advances in modelling, optimal combination of mastitis related traits and associated predictors, such as udder morphology, definition of global breeding objective including production and functional traits, and inclusion of molecular information that is now available from QTL experiments.

Field survey of clinical mastitis in low somatic cell count herds

Nine commercial dairy herds, each with low herd milk somatic cell counts, were monitored for 1 yr to determine prevalence of intramammary infections and rates of clinical mastitis. Staphylococcus species was the bacterial group most frequently isolated from quarters at calving and at drying off. Environmental streptococci and coliform intramammary infections totaled less than 6% of quarters at both calving and at drying off. Staphylococcus aureus were isolated from less than 1% of quarters and Streptococcus agalactiae from 0% of quarters at both calving and drying off. A total of 646 clinical cases of mastitis were diagnosed in 548 quarters of 406 cows. Mean rate of clinical mastitis among herds was .457 clinical cases/305 cow-days. Rates of clinical mastitis ranged among herds from .273 to .748 clinical cases/305 cow-days. Coliforms and bacteriologically negative and environmental streptococci accounted for 82.3% of clinical cases. Rates of clinical mastitis and severity of clinical signs differed among herds, seasons of the year, parity groups, and stages of lactation. Rates of clinical mastitis were highest during summer, in first lactation cows, and during the first 7 d of lactation.

Characterization of equine adipose tissue-derived stromal cells: adipogenic and osteogenic capacity and comparison with bone marrow-derived mesenchymal stromal cells

OBJECTIVE

To characterize equine adipose tissue-derived stromal cell (ASC) frequency and growth characteristics and assess of their adipogenic and osteogenic differentiation potential.

STUDY DESIGN

In vitro experimental study.

ANIMALS

Horses (n=5; aged, 9 months to 5 years).

METHODS

Cell doubling characteristics of ASCs harvested from supragluteal subcutaneous adipose tissue were evaluated over 10 passages. Primary, second (P2), and fourth (P4) passage ASCs were induced under appropriate conditions to undergo adipogenesis and osteogenesis. Limit dilution assays were performed on each passage to determine the frequency of colony-forming units with a fibroblastic (CFU-F) phenotype and the frequency of ASC differentiation into the adipocyte (CFU-Ad) and osteoblast (CFU-Ob) phenotype.

RESULTS

ASC isolates exhibited an average cell-doubling time of 2.1+/-0.9 days during the first 10 cell doublings. Approximately 1 in 2.3+/-0.4 of the total stromal vascular fraction nucleated cells were ASCs, based on the CFU-F assays, and 1 in 3.6+/-1.3 expressed alkaline phosphatase, an osteogenic marker. Primary ASCs differentiated in response to adipogenic (1 in 4.9+/-5.4, CFU-Ad) and osteogenic (1 in <2.44, CFU-Ob) inductive conditions and maintained their differentiation potential during subsequent passages (P2 and P4).

CONCLUSION

The frequency, in vitro growth rate, and adipogenic and osteogenic differentiation potential of equine ASCs show some differences to those documented for ASCs in other mammalian species.

CLINICAL RELEVANCE

Adipose tissue is a potential source of adult stem cells for tissue engineering applications in equine veterinary medicine.

Environmental pathogens and intramammary infection during the dry period

Rate of coliform and streptococcal intramammary infection during the dry period was studied in 168 dry periods. Coliform infection rate was influenced by stage of dry period, parity, and season during which dry periods occurred. Effects of dry cow therapy, immunization, or induced inflammation on coliform infection rate were minimal. Coliform infections originating in the first 50% of the dry period and persisting to lactation were predominantly other than Escherichia coli, whereas the majority originating in the last 50% of the dry period and persisting to lactation were Escherichia coli. Duration of streptococcal infections was greater than coliform infections. Dry cow therapy reduced streptococcal infection rate, and the effect was exerted primarily during the first 25% of the dry period. Effects of parity and season were not significant and likely masked by the positive effects of dry cow therapy. Results support the contention that all quarters of all cows should be dry treated for maximum reduction of new streptococcal infection during the dry period. Results suggest that methods other than conventional dry cow therapy are required for control of coliform infection during the dry period and streptococcal infection during the latter half of the dry period.

Influence of Raw Milk Quality on Fluid Milk Shelf Life

Pasteurized fluid milk shelf life is influenced by raw milk quality. The microbial count and somatic cell count (SCC) determine the load of heat-resistant enzymes in milk. Generally, high levels of psychrotrophic bacteria in raw milk are required to contribute sufficient quantities of heat-stable proteases and lipases to cause breakdown of protein and fat after pasteurization. Sanitation, refrigeration, and the addition of CO2 to milk are used to control both total and psychrotrophic bacteria count. It is not uncommon for total bacterial counts of raw milk to be < 10,000 cfu/mL. In the past, fluid milk processors have not focused much attention on milk SCC. Increased SCC is correlated with increased amounts of heat-stable protease (plasmin) and lipase (lipoprotein lipase) in milk. When starting with raw milk that has a low bacterial count, and in the absence of microbial growth in pasteurized milk, enzymes associated with high SCC will cause protein and fat degradation during refrigerated storage, and produce off-flavors. As the ability to kill, remove, or control microbial growth in pasteurized refrigerated milk continues to improve, the original milk SCC will be the factor limiting the time of refrigerated storage before development of an off-flavor in milk. Most healthy cows in a dairy herd have a milk SCC < 50,000 cell/mL. Bulk tank SCC > 200,000 cell/mL are usually due to the contribution of high SCC milk from a small number of cows in the herd. Technology to identify these cows and keep their milk out of the bulk tank could substantially increase the value of the remaining milk for use in fluid milk processing. To achieve a 60- to 90-d shelf life of refrigerated fluid milk, fluid processors and dairy farmers need to work together to structure economic incentives that allow farmers to produce milk with the SCC needed for extended refrigerated shelf life.

Cell Growth Characteristics and Differentiation Frequency of Adherent Equine Bone Marrow?Derived Mesenchymal Stromal Cells: Adipogenic and Osteogenic Capacity

OBJECTIVES

To characterize equine bone marrow (BM)-derived mesenchymal stem cell (MSC) growth characteristics and frequency as well as their adipogenic and osteogenic differentiation potential.

STUDY DESIGN

In vitro experimental study.

ANIMALS

Foals (n=3, age range, 17-51 days) and young horses (n=5, age range, 9 months to 5 years).

METHODS

Equine MSCs were harvested and isolated from sternal BM aspirates and grown up to passage 10 to determine cell-doubling (CD) characteristics. Limit dilution assays were performed on primary and passaged MSCs to determine the frequency of colony-forming units with a fibroblastic phenotype (CFU-F), and the frequency of MSC differentiation into adipocytes (CFU-Ad) and osteoblasts (CFU-Ob).

RESULTS

Initial MSC isolates had a lag phase with a significantly longer CD time (DT=4.9+/-1.6 days) compared with the average DT (1.4+/-0.22 days) of subsequent MSC passages. Approximately 1 in 4224+/-3265 of the total nucleated BM cells displayed fibroblast colony-forming activity. Primary MSCs differentiated in response to adipogenic and osteogenic inductive conditions and maintained their differentiation potential during subsequent passages.

CONCLUSIONS

The frequency, in vitro growth rate, and adipogenic and osteogenic differentiation potential of foals and young adult horses are similar to those documented for BM MSCs of other mammalian species.

CLINICAL RELEVANCE

The results have direct relevance to the use of BM as a potential source of adult stem cells for tissue engineering applications in equine veterinary medicine.

Adipose tissue growth and cellularity: changes in bovine adipocyte size and number

Forty crossbred steers of similar birth date and fed the same growing-finishing diet were used to study adipocyte changes in six fat depots during growth from 11 to 19 mo of age. Steers were slaughtered at 2-mo intervals. Adipose tissue samples were obtained from kidney, mesenteric and brisket fat and subcutaneous, intermuscular and intramuscular fat from the 10th to 12th rib section. The osmium tetroxide fixation technique was used for determination of cell size and number. Except for three brisket fat samples, distributions of adipocyte diameters from six different fat depots were monophasic during the age range considered in this study. At 17 mo of age, the mean adipocyte diameter, in decreasing order, was: kidney fat greater than mesenteric greater than subcutaneous greater than intermuscular greater than intramuscular greater than brisket fat. Fat deposition during growth to 19 mo of age occurred mainly by hypertrophy of adipocytes. An apparent cell hyperplasia occurred in the intramuscular fat depot from 11 to 15 mo and in the brisket fat depot after 15 mo of age. Based on cellularity characteristics, evidence exists to classify intramuscular and brisket fat depots as late-developing ones. Cell number/gram of intramuscular adipose tissue was a better predictor of marbling score than was fat cell diameter.

Effects of somatic cell count on quality and shelf-life of pasteurized fluid milk

Milk was collected from eight Holstein cows four times before and four times after intramammary infection with Streptococcus agalactiae. Postinfection milk had significantly higher somatic cell count (SCC) (849,000 cells/ml) than preinfection milk (45,000 cells/ml). High SCC raw milk had more lipolysis and proteolysis than low SCC raw milk. Pasteurized, homogenized, 2% fat milks from pre- and postinfection periods were stored at 5 degrees C and analyzed for lipolysis, proteolysis, microbial quality, and sensory attributes at 1, 7, 14, and 21 d post processing. During refrigerated storage, the average rates of free fatty acid increase (i.e., lipolysis) and casein hydrolysis in high SCC milk were, respectively, three and two times faster than those in low SCC milk. In general, standard plate counts, coliform counts, and psychrotrophic bacterial counts of both the high and low SCC milks remained low (<100,000 cfu/ ml) during 5 degrees C storage. Low SCC milk maintained high organoleptic quality for the entire 21-d shelf-life period. However, for high SCC milk, between 14 and 21 d, sensory defects were detected, which resulted in low overall quality ratings. The sensory defects mainly included rancidity and bitterness and were consistent with higher levels of lipolysis and proteolysis. Hence, mastitis adversely affected the quality of pasteurized fluid milk. It is recommended that the fluid milk industry consider implementation of premium quality payment programs for low SCC milks.

Cytokine induction in pulmonary airways of horses with heaves and effect of therapy with inhaled fluticasone propionate

Work in humans and laboratory animals has identified a central role for cytokines and chemokines in development and persistence of lower airway inflammation. The objectives of this study were to determine interleukin (IL)-1 beta, IL-2, IL-4, IL-5, IL-6, IL-8, IL-10, interferon (IFN)-gamma and tumor necrosis factor (TNF)-alpha induction in bronchoalveolar lavage (BAL) of control horses and horses with heaves both during remission and exacerbation of the disease, and to determine the effect of therapy with inhaled fluticasone propionate on the cytokine profile of horses with heaves. IL-1 beta and TNF-alpha mRNA expression was significantly higher in horses with heaves after exposure to moldy hay compared to either values obtained during clinical remission or to healthy controls. IL-8 mRNA expression and protein concentrations were significantly higher in horses with heaves than in controls. Both IL-4 and IFN-gamma mRNA expression was increased at various times in heaves-susceptible horses compared to controls. IL-2, IL-5 and IL-10 mRNA expression was not detected in BAL cells of either group. Therapy with inhaled fluticasone propionate after induction of a severe heaves exacerbation resulted in complete resolution of clinical signs, normalization of pulmonary function tests, and significant decrease in BAL neutrophilia. This was associated with a significant decrease in IL-4 mRNA expression and increase in IFN-gamma/IL-4 ratio in horses with heaves. These results demonstrate the clinical efficacy of inhaled fluticasone propionate for the treatment of heaves and suggest a role for cytokines in the development of lower airway inflammation in heaves-susceptible horses.

Quarter milk somatic cell count in infected dairy cows: a meta-analysis

The aim of this paper was to evaluate the effects associated with intramammary infection (IMI) by a bacterium or a group of bacteria (Staphylococcus aureus, Streptococcus agalactiae, Streptococcus dysgalactiae, Streptococcus uberis, coliforms, Staphylococci other than S. aureus, and Corynebacterium bovis) on the somatic cell count (SCC) in quarter milk of dairy cows. Papers selected for analysis had to provide SCC values associated with the natural infection in quarters by different bacteria. Sampling for measurement of SCC and determination of the infection had to be done on the same day. Only papers published in English or in French after 1971 were considered. Twenty-one papers fulfilled the selection criteria. The animals sampled, the measurement techniques for SCC and the bacteriological identification, as well as the definition of the infection, all differed widely among the selected studies. The meta-analysis method was used to estimate both the mean SCC (arithmetic and geometric) value and the average increase on SCC of each type of infection. The geometric mean SCC in bacteriologically negative quarters was 68 000 c/mL. In case of IMI, the retained SCC was 357 000, 857 000, 547 000, 1 024 000, 1 151 000, 138 000 and 105 000 c/mL in quarters infected by Staphylococcus aureus, Streptococcus agalactiae, Streptococcus dysgalactiae, Streptococcus uberis, coliforms, staphylococci other than S. aureus and Corynebacterium bovis, respectively. The variation factors that could influence these SCC values and the bacteriological results are discussed.

Changes in milk composition as affected by subclinical mastitis in goats

The mechanism of the effects of subclinical mastitis (SM) at the glandular level in dairy goats on milk yield and its composition as expressed in curd yield (Yc) was studied. Twenty-five Israeli goats of various crossbreeds were chosen; one udder half was naturally infected with identified coagulase-negative staphylococci, and the contralateral gland was free of bacteria. The milk yield of the infected halves was significantly lower than that of the uninfected ones. Somatic cell count and N-acetyl-beta-D-glucosaminidase activity were significantly higher in the infected halves. The lactose concentration in the infected glands was significantly lower than that in the uninfected ones, casein concentrations did not differ, and the whey protein and albumin concentrations were significantly higher in the infected glands. Plasmin activity was significantly higher in the infected glands, whereas plasminogen activity was undetectable. Concentrations of Ca2+ did not differ, whereas Ca2+ activity was significantly lower in the infected glands. The proteose peptone concentration was 1.5 times as great in the infected glands as in the uninfected ones. The Yc was significantly lower in the infected halves, and clotting time was significantly longer. The mechanisms of the effects of SM on milk yield and Yc in goats and sheep are discussed and compared.

Sensitivity and specificity of somatic cell count and California Mastitis Test for identifying intramammary infection in early lactation

Associations between values for the somatic cell count (SCC) or the California Mastitis Test (CMT) and intramammary infection (IMI) were studied in 131 dairy cows from three herds during the first 10 d post-calving. Intramammary infection was defined as the presence of one or two bacterial species in one or both quarter milk samples taken within 12 h of calving and at d 3 postcalving. Quarter milk samples identified IMI in 36% of glands. Values for SCC declined at a significantly faster rate over the first 10 d postcalving in non-infected quarters than in infected quarters. The usefulness of quarter milk SCC and CMT for screening was evaluated by calculating the sensitivity and specificity for various threshold values and days postcalving. A SCC threshold of 100,000 cells/ml for quarter samples evaluated on d 5 postcalving had the maximal sensitivity and specificity for detecting IMI. Evaluation of the CMT samples taken on d 3 postcalving using a threshold reaction of greater than zero had the highest sensitivity and specificity for detecting IMI. With this CMT sampling scheme, the sensitivities for detecting IMI with any pathogen, IMI with a major pathogen, and IMI with a minor pathogen were 56.7, 66.7, and 49.5, respectively. The CMT could have a useful role in dairy herd monitoring programs as a screening test to detect fresh cows with IMI caused by major pathogens.

Efficacy of nisin in treatment of clinical mastitis in lactating dairy cows

Nisin is an antimicrobial polypeptide produced by Lactococcus lactis and is believed nontoxic to humans. The objective of this study was to evaluate a nisin-based formulation for the treatment of bovine clinical mastitis in lactating dairy cattle. A total of 92 cows with 107 clinically mastitic quarters were randomly assigned to nisin- (48 cows with 51 quarters) and gentamicin (GM)-treated (44 cows with 56 quarters) groups. In the nisin-treated group, cows received an intramammary infusion of nisin at a dose of 2,500,000 IU; in the GM-treated group, intramammary infusion of GM was administered at a dose of 0.8 g. Results indicated that nisin offered a clinical cure rate similar to GM (90.2 vs. 91.1%) and no difference in bacteriological cure rate than GM-treated group (60.8 vs. 44.6%, respectively). Proportion of the quarters with milk somatic cell counts <500,000 cells/mL was not different in the nisin-treated group (50.0 and 47.8%) compared with the GM-treated group (33.3 and 37.3%) 1 and 2 wk after treatment. Of 17 Staphylococcus aureus isolates, 82.5% were resistant to penicillin, and 35.3% to GM, but none of them to nisin. Nisin therapy eliminated 54.5% (6 of 11) of S. aureus IMI, whereas GM eliminated 33.3% (2 of 6). Nisin in milk (4.5 +/- 0.8 IU/mL) was detected only at 12 h following intramammary infusion, which was much lower than the upper limit (500 mg/mL) allowed as preservative in milk by the China authority. Because of its efficacy in the treatment of bovine clinical mastitis, especially resistant Staph. aureus-caused IMI, as well as its safety in humans, nisin deserves further study to clarify its effects on mastitis caused by different mastitis pathogens on a larger scale.

Characterization of cytokine expression in milk somatic cells during intramammary infections withEscherichia coliorStaphylococcus aureusby real-time PCR

The expression of inflammatory cytokines, including interleukin (IL)-6, IL-8, IL-12, granulocyte macrophage-colony stimulating factor (GM-CSF), tumor necrosis factor (TNF)-alpha, and interferon (IFN)-gamma, by milk somatic cells was characterized by real-time polymerase chain reaction (PCR) in dairy cows experimentally challenged with either E. coli (n = 8) or S. aureus (n = 8). The mRNA abundance of a target gene was calibrated with that of a reference gene (beta-actin) and expressed as fold of induction over the control quarter at each time point. At no single time point did all eight quarters challenged with the same type of bacteria demonstrated increased expression of a target gene and there was large variation among animals at each given time. As a consequence, most tested comparisons were not statistically significant except the peak time points of IL-8 expression (75- and 29- fold in glands challenged with E. coli and S. aureus, respectively). However, the average fold induction of all targeted cytokines was increased in response to both bacterial challenges with the exception of IFN-gamma. The expression of IFN-gamma was only increased in milk somatic cells isolated from E. coli, but not S. aureus, challenged mammary glands. Moreover, upregulated expression of cytokine genes had higher magnitudes and/or faster responses in glands challenged with E. coli in comparison with those challenged with S. aureus. We propose that the compromised upregulation of inflammatory cytokines in S. aureus infected glands may, at least partially, contribute to the chronic course of infection caused by this pathogen. Further research on identifying factors responsible for the differentially expressed cytokine profiles may be fundamental to developing strategies that mitigate the outcome of bovine mastitis.

Tumor necrosis factor-alpha and nitrite/nitrate responses during acute mastitis induced by Escherichia coli infection and endotoxin in dairy cows

Concentrations of tumor necrosis factor-alpha (TNF-alpha) and of NO(x) (sum of nitrite and nitrate as indicators of endogenous nitric oxide production) in milk and blood plasma were measured in three mastitis models in dairy cows in early lactation. Escherichia coli P4:O37 bacteria or endotoxin O111:B4 were administered into both left quarters of 12 and 6 cows, respectively. Six of the E. coli-infected cows were treated with a bactericidal antibiotic (Enrofloxacin; Bayer AG, Leverkusen, Germany) i.v. at 10 hr and subcutaneously (sc) at 30 hr after infection. NO(x) concentrations transiently increased maximally 10- to 11-fold in milk of E. coli-infected quarters with or without antibiotic treatment at 24 hr and after endotoxin administration. NO(x) concentrations did not change in milk of unchallenged quarters and in blood plasma. Increases of NO(x) were proceeded by a transient (96- to 149-fold) rise of milk TNF-alpha concentrations, which in endotoxin-administered quarters was maximal at 6 hr and in infected quarters without or with Enrofloxacin treatment at 10 and 14 hr. In blood plasma TNF-alpha concentrations only moderately increased to peaks in endotoxin-administered cows at 6 hr and in E. coli-infected cows at 14 hr postchallenge. In one severely sick, nontreated E. coli-infected cow milk, TNF-alpha response at 14 hr was excessive and followed by a spectacular rise of NO(x) concentration in milk between 48 and 72 hr. In conclusion, a possible clinical relevance of nitric oxide production associated with a rise of intramammary and systemic TNF-alpha during acute mastitis by E. coli infection and endotoxin in lactating dairy cows is indicated, but could not be inhibited by antibiotic treatment.

Survival of Listeria monocytogenes in milk during high-temperature, short-time pasteurization

Milk from cows inoculated with Listeria monocytogenes was pooled for 2 to 4 days and then heated at 71.7 to 73.9 degrees C for 16.4 s or at 76.4 to 77.8 degrees C for 15.4 s in a high-temperature, short-time plate heat exchanger pasteurization unit. L. monocytogenes was isolated from milk after heat treatment in six of nine pasteurization trials done at 71.7 to 73.9 degrees C and in none of three trials done at 76.4 to 77.8 degrees C. An average of 1.5 to 9.2 L. monocytogenes cells was seen in each milk polymorphonuclear leukocyte before heat treatment in 11 of 12 pasteurization trials. Noticeable degradation of leukocytes with intracellular listeria was detected in unpasteurized milk after 3 days of storage at 4 degrees C, and by 4 days of storage leukocytes had deteriorated to cellular debris, suggesting that holding unpasteurized milk refrigerated for 4 or more days would eliminate a protective effect leukocytes may provide for increasing heat resistance of L. monocytogenes. Results indicate that under the conditions of this study, L. monocytogenes can survive the minimum high-temperature, short-time treatment (71.7 degrees C, 15 s) required by the U.S. Food and Drug Administration for pasteurizing milk.