Relationship of somatic cells in quarter milk to type of bacteria and production

Staphylococcus aureus intramammary infection affects milk yield and SCC of dairy cows

Staphylococcus aureus (S. aureus) is the most prevalent infectious microorganism affecting dairy cattle worldwide, and its pathogenic characteristics facilitate its spread in dairy herds. S. aureus intramammary infections (IMI) are mainly subclinical, and associated losses can exceed average herd losses where the pathogen is not isolated. However, the extent it affects milk composition at udder and quarter levels is still unknown, and cow composite milk losses may be underestimated due to the dilution effect. The aim of this study was to investigate the effects of S. aureus subclinical mastitis on mammary quarter milk yield and composition. In order to determine the effects of the pathogen on milk yield and composition at quarter level, a pairwise comparison of infected and non-infected mammary quarters (n = 28) from two dairy herds was carried out. Quarters were individually milked, and milk production and composition were assessed. S. aureus has increased somatic cell counts at quarter level; however, no effect of S. aureus IMI on milk lactose, fat, and protein contents was observed. Fat yield from infected quarters decreased, but losses due to the infection caused by S. aureus were not associated with quarter positioning in cows.

Evidence that bovine forebrain embryonic zinc finger-like gene influences immune response associated with mastitis resistance

Mastitis, a mammary gland inflammation in response to bacterial infection, is a major problem in the dairy industry. We found that cows susceptible to mastitis have a three-base insertion in a glycine-coding stretch of the gene for forebrain embryonic zinc finger-like (FEZL), a transcription factor with a role in neuronal development. Mastitis induces FEZL expression in mammary glands, and induced FEZL promotes expression of the axon-attracting molecule semaphorin 5A (SEMA5A) through a GCAG sequence. FEZL also induces SEMA5A expression in susceptible cattle but at a lower level than in resistant cattle. Enhanced SEMA5A induces expression of at least nine genes related to the host's immune response, including TNF-alpha and IL-8. We propose that susceptibility to mastitis results from an impaired immune response due to the lower transcription activity of susceptible FEZL. Our results provide an avenue to select for genetic improvement of resistance to mastitis and suggest that the FEZL-SEMA5A pathway might control both neuronal development and innate immunity.

Potential for improving description of bovine udder health status by combined analysis of milk parameters

The objective of this study was to assess the potential of a stepwise multivariate procedure to quantify cow-level udder health based on eight milk parameters: milk yield, protein percentage, fat percentage, lactose percentage, citrate percentage, somatic cell count (SCC), and two electrical conductivity parameters. The data were collected in one research herd and included 821 cow-level observations. In addition to milk parameters, disease recordings and bacteriology on quarter milk samples every eighth week throughout lactation were included. A multivariate mixed model was applied to the milk parameters in a healthy subset to adjust for the following systematic factors: total mixed ration (TMR) energy density, breed-line combination, parity, stage of lactation, and season. The proportion of variance accounted for by the mixed model ranged from 0.14 to 0.82 depending on milk parameter. The adjustments estimated in the healthy subset were applied to the whole dataset, including observations pertaining to nonhealthy cows. Combined description of the adjusted variation in the milk parameters was performed with a principal component analysis. The first principal component (Prin1) described 30% of the adjusted variation and was interpreted as being the main consequences of mastitis. Finally, cluster analysis based on Prin1 separated the observations into nine clusters, which were strongly associated with udder health in terms of increasing clinical and subclinical mastitis with increasing level of Prin1. It was concluded that a multivariate approach to assess udder health from milk parameters has the potential to substantially improve description of udder health.

Immunity and mastitis. Some new ideas for an old disease

The biggest challenge for host immune defense against mastitis-causing bacteria in dairy cows is to quickly recruit large enough numbers of opsonizing molecules and mature neutrophils into milk such that intramammary pathogens are cleared before they multiply significantly and the inflammatory response gets out of control. Currently, this challenge is best facilitated when established mastitis control procedures are practiced on the farm, including proper hygiene, milking procedures, and regular administration of approved mastitis vaccines. However, mastitis is still a significant problem. New animal functional genomics research is beginning to allow scientists to solve the puzzle of mastitis susceptibility. Results of this type of research offer the hope of giant leaps toward a clear identification of molecular genetic variation and potential gene targets for therapies and immune manipulations that could significantly reduce the risk of clinical mastitis in traditionally susceptible cows.

Herd characteristics and management practices associated with bulk-tank somatic cell counts in herds in official Dairy Herd Improvement Association programs in Ohio

OBJECTIVE

To identify herd characteristics and management practices associated with bulk-tank somatic cell counts (BTSCC) in dairy herds in Ohio enrolled in official Dairy Herd Improvement Association (DHIA) programs.

SAMPLE POPULATION

186 dairies in Ohio.

PROCEDURE

All herds in official DHIA programs in 9 counties were asked to participate. Extensive information regarding herd characteristics and management practices was obtained, using a standardized questionnaire. Bulk-tank milk samples were requested from all participating herds for bacterial culture. Official DHIA test-day records for January 1997 were obtained from all herds enrolled in official DHIA programs in the 9 counties. Potential associations were identified, using multivariable ANOVA.

RESULTS

Participation was 186 of 479 (39%) herds. Streptococcus agalactiae and Mycoplasma spp were not isolated from bulk-tank milk samples. Staphylococcus aureus was isolated from 64 of 172 (37%) of the herds. The BTSCC were inversely associated with peak daily milk production, postmilking teat disinfection, percentage of eligible cows in the herd detected in estrus, and directly related to the extent to which BTSCC was perceived as a herd problem during the preceding 2 years. Type of housing for nonlactating cows and product used for treatment of nonlactating cows also were significantly associated with BTSCC.

CONCLUSIONS AND CLINICAL RELEVANCE

Consideration of herd characteristics and implementation of management practices associated with BTSCC could result in increased milk yield and production of milk with lower BTSCC.

Herd prevalence and incidence of Streptococcus agalactiae in the dairy industry of Prince Edward Island

Herd prevalence and incidence of mastitis caused by Streptococcus agalactiae was determined for dairy cattle on Prince Edward Island during December 1992 and June 1994. For each census, bulk tank milk samples from all dairy herds (n = 452) in the province were tested on two occasions, and the results were interpreted in parallel. The combined sensitivity of the testing protocol was estimated to be 91%. The confirmatory latex agglutination test had previously reported specificities approaching 100%. Therefore, the estimated specificity of the testing protocol was assumed to be 100%. The apparent prevalence of S. agalactiae in December 1992 and in June 1994 was 17.7 and 13.1%, respectively. Based on the characteristics of the test, the estimated true prevalence was 18.9% in December 1992 and 14.4% in June 1994. Infection with S. agalactiae was associated with elevated bulk tank somatic cell count (SCC) and elevated standard plate counts. Economic losses associated with S. agalactiae were attributed to production losses (associated with bulk tank SCC), milk quality penalties (associated with bulk tank SCC and standard plate count), and decreases in milk quality (associated with bulk tank SCC). For herds that had been negative for S. agalactiae in December 1992, evaluation in June 1994 yielded an incidence of new infections of 3.51 per 100 herds per year.

Mastitis in Camelus dromedarius and the somatic cell content of camels' milk

Seven hundred and sixty-three camels from 400 herds of local Sudanese camel breeds were investigated for the prevalence of mastitis, identification of its bacterial causes and determination of the leucocyte contents of camel's milk. One hundred and forty-nine (19.5 per cent) of the 763 camels examined were diagnosed as mastitis cases based on clinical signs. One hundred and fifty-nine (47.3 per cent) of the 336 randomly selected milk samples were reactive in a rapid mastitis test and 16 of the 153 tested samples contained Brucella abortus agglutinating antibodies. Streptococcus, Staphylococcus, Micrococcus and Aerobacter species and Escherichia coli were found to be the main causes of mastitis (in descending order). The leucocyte contents of the 757 milk samples ranged from < 5 x 10(5) to > 7.5 x 10(6) leucocyte ml-1 and 42.8 per cent of the samples contained < 5 x 10(5) cells ml-1. Neither significant correlation between the leucocyte content of milk and isolated bacterial species nor significant variation in leucocyte contents during different stages of lactation were detected.

Selection on somatic cell score to improve resistance to mastitis in the United States

Increased genetic susceptibility to mastitis has accompanied the rapid genetic increase in milk yield, and genetic selection for mastitis resistance should be considered. Somatic cell score is recommended as an indicator trait to achieve genetic improvement for mastitis resistance. Heritability of somatic cell score is around 10%, and genetic correlation between somatic cell score and clinical mastitis is around .6 to .8. Selection for lower somatic cell score is consistent with the goal of maximizing genetic improvement for total economic merit and should be included in breeding programs. National genetic evaluations for somatic cells scores will use the same animal models and methods as are currently used for milk yield traits. Reliabilities of PTA for somatic cell scores will be smaller than for yield traits because of lower heritability and availability of records from fewer cows. Several forms are proposed for reporting genetic evaluations of somatic cells to producers, and advantages and disadvantages are discussed. Using somatic cell scores for breeding decisions would marginally decrease genetic gain for milk yield and increase total economic merit. Optimal selection indexes would slow the rate of increase in mastitis, rather than decrease its incidence.

Factors affecting milk somatic cells and their role in health of the bovine mammary gland

Milk somatic cells play a protective role against infectious disease in the bovine mammary gland. Many genetic and environmental factors affect the number and kinds of leukocytes that account for the vast majority of somatic cells in milk. Neutrophils constitute the vast majority of somatic cells in mammary glands that are infected with mastitis pathogens. The recruitment of neutrophils into the infected mammary gland is a normal part of the cow's defense mechanisms that is very effective for eradicating the majority of infections that occur. For many reasons, milk production and milk quality are negatively impacted by the presence of inflammation in infected glands. Because of the negative effects of high SCC in milk, various approaches are needed to reduce milk SCC. In the future, genetic gains for milk quality and mastitis resistance may be made by removing bulls from breeding programs when their daughters are predisposed to high SCC.

Genetic improvement of mastitis through selection on somatic cell count

Heredity influences both clinical mastitis and somatic cell score. Intramammary infection is the major cause of elevated somatic cell score. A nationwide program of genetic evaluation of dairy cattle for somatic cell score is being developed. Proper selection of artificial insemination sires, considering their genetic merit for both milk production and somatic cell score, will reduce the genetic increase in mastitis susceptibility that accompanies selection for high production.

Analysis of somatic cell count data by a peak evaluation algorithm to determine inflammation events

Increases in SCC are an expression of inflammation events in the udder. Inflammation events are sporadic, of variable amplitude and duration, and can be analyzed by computer programs designed to evaluate pulses of hormone secretion. Baseline values for SCC, which take into account long-term trends, were calculated using the PULSAR peak evaluation algorithm. An inflammation event was defined as an increase of log2(SCC) of at least 1 unit from the preceding data point if the observed value exceeded the baseline value by a threshold value. Incidence rate, duration, and amplitude of inflammation events were calculated. Weekly composite milk SCC from individual cows from two Florida dairy farms were recorded. Data were analyzed for effects of season (summer and fall) and bST in two separate data sets. Incidence rate of inflammation events was higher in summer than in fall (4.31 and 2.91 events per cow x year). In one of two data sets only, duration of inflammation events was longer in cows treated with bST (2.4 +/- .2 vs. 1.6 +/- .2 wk). In contrast, least squares analysis of variance of log2(SCC) did not detect differences due to season or bST. The use of the peak evaluation algorithm led to the detection of seasonal and bST effects on inflammation events in cows.

Effect of milk yield on relationship between bulk milk somatic cell count and prevalence of mastitis

The possible dilution effect of increasing milk yield on bulk milk SCC was studied in a field trial. Data on breed distribution, numbers of cows, average milk yields, average bulk milk SCC, and estimated prevalences of mastitis were available for 15,514 Swedish dairy herds. The overall mean of herd prevalence of mastitis, as estimated by the definition employed, was 26.7%, and the overall mean of the geometric average of bulk milk SCC was 204,000 cells/ml. Correlations between prevalence of mastitis and average bulk milk SCC ranged between .53 and .77, and geometric averages were only marginally more correlated to prevalence of mastitis than were arithmetic averages. The average herd prevalence of mastitis was found to increase, within bulk milk SCC level, as milk production increased. The regression coefficients of average milk yield on bulk milk SCC, estimated conditionally on mastitis prevalence, show that the bulk milk SCC decreased by 11.1% for each increase in the milk yield of 1000 kg of FCM. This implies that part of the decrease in average bulk milk SCC achieved during recent years may be an artifact due to the concurrent increase in milk production.

Milk production and somatic cell count in Michigan dairy herds

The established association between milk production and SCC in dairy cattle is increasingly used to estimate lost production due to mastitis. Such cost estimates are used to make decisions regarding cost effective mastitis prevention and control. It is therefore important to verify the relationship between SCC and milk production using data from different areas of the country and by using different analytical methodology. Our study used the 1985 to 1986 Michigan DHIA data base and analyzed daily milk production records rather than lactation summary records as used in the past. One advantage to our approach was that it did not give equal weight to all lactations, regardless of their duration. Also, it enabled inclusion of cows that had incomplete lactations caused by culling, or had other reasons for removal from the herd. A statistical model was constructed to predict milk production on the basis of herd, cow within herd, stage in lactation, month of calving, lactation, and SCC. The data base contained 397,172 milk test records obtained from Michigan DHIA from 504 Holstein herds in Michigan's lower peninsula. Our final model predicted 78% of the variation in milk production. Prediction of milk loss for each herd was highly correlated (r = .98) with the prediction model adopted by most DHIA organizations. Our model predicted that the mean herd lost a mean of 1.17 kg of milk/cow per d associated with SCC.

Dynamics and significance of coagulase-negative staphylococcal intramammary infections

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

Effects of estradiol benzoate and estrus on N-acetyl-beta-D-glucosaminidase activity and somatic cell concentration in milk

Quarter composite milk samples were obtained from five cows free of intramammary infection throughout an estrous cycle and after injection of corn oil and of estradiol benzoate (1 microgram/kg body weight) in corn oil. Samples were assayed for NAGase activity and somatic cell concentration. Least squares means for the enzyme were 1.46, 1.47, 1.43, and 1.41 natural logarithm nanomoles per minute per milliliter for control, estrus, corn oil, and estradiol benzoate, respectively. Milk somatic cell count means were 2.77, 2.71, 2.92, and 3.10 loge X 10(3) cells/ml. Treatment had no significant effect on enzyme activity or cell counts. Results suggest no adjustment of NAGase or cell count is necessary for stage of estrous cycle. When administered at physiological dosages, exogenous estrogen did not appear to influence either measure.

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.

Effects of teat dipping on intramammary infections by staphylococci other than Staphylococcus aureus

Effects of intramammary infections in herds 1) either not teat dipping or postmilking teat dipping with either 2) linear dodecyl benzene sulfonic acid, 3) chlorhexidine, or 4) iodophor containing products were determined. Duplicate quarter foremilk samples were collected once from all lactating cows in 16 herds, four for each practice. Mean percentage of quarters infected with Staphylococcus species other than Staph. aureus was 11.0 in herds not teat dipping and 7.2 in herds teat dipping. Prevalence of Staphylococcus species intramammary infections in herds teat dipping with linear dodecyl benzene sulfonic acid was comparable to herds not teat dipping and greater than in herds using chlorhexidine and iodophor. The predominant Staphylococcus species in herds not teat dipping was Staph. epidermidis (37.1%). Staphylococcus hyicus constituted 48.5% of total Staphylococcus species intramammary infections in herds teat dipping and 12.4% in herds not teat dipping. Differences were not observed among SCC for quarters infected with different Staphylococcus species. Application of germicidal teat dips appeared to have selectively altered both prevalence and distribution of Staphylococcus species intramammary infections.

Effective use of dairy herd improvement somatic cell counts in mastitis control

The single most important factor affecting somatic cell count in milk is mammary gland infection status. In comparison, all other factors are minor. Consideration needs to be given to diurnal effects on Dairy Herd Improvement a.m.-p.m. sampling schemes. Somatic cell count linear score of 5 (283,000) appears to be a good choice of threshold for mastitis control applications. A greater understanding of the nonbacteriological factors affecting somatic cell count is needed so that relative thresholds could be used to improve the clarity of somatic cell count interpretation. Linear score loss estimates are effective educational tools providing motivation for mastitis control implementation. Infection status or milk loss estimates based on single somatic cell count tests on individual cows are weak. A lactational average linear score on individual cows or linear score compilations across a herd provide credible estimates. Treatment of subclinical mastitis based on somatic cell count levels is not economically beneficial and is not recommended. Usefulness of Dairy Herd Improvement somatic cell count data as a mastitis management tool requires measures of mastitis level, new infection rate, and mastitis pattern within the herd over time.

Relationships between somatic cell counts and milk production

The relationship between Dairy Herd Improvement program test-day milk yield and somatic cell counts in milk was analyzed in 34 dairy herds over 3 yr. Estimates of this relationship were more accurate when somatic cell counts were transformed to natural logarithms rather than actual. For 67,707 observations, test-day milk yield decreased with increasing somatic cell count. The decrease of milk yield for second and later lactations, as somatic cell count increased, was greater than for first lactations. When herds were partitioned according to herd milk production (greater than 7700, 6500 to 7700, and less than 6500 kg/yr), decrease of milk yield was linear with increasing somatic cell counts for herds averaging below 7700 kg milk. Regressions were linear, quadratic, and cubic for both parity groups in herds with high production, over 7700 kg/yr. Quarter samples were composited for each cow and cultured. Percentage of infected cows increased as somatic cell counts increased with greater infection rates above 400 X 10(3).

Traits for sire selection related to udder health and management

Traits related to udder health were discussed: bacteriological measures, clinical frequency, and milk properties (somatic cell count, enzymes, etc.). Bacteriological testing of quarters maximizes information on infection but is impractical on a population scale. Clinical recording is an objective measure but fails to indicate subclinical cases and is not available in most countries. Cell counts are economical to obtain but are highly variable, difficult to interpret, and not sensitive indicators of subclinical infections. Several milk enzymes are possible indicators of tissue damage. Heritabilities are about .2 for cell counts and .1 for other measures, reflecting genetic variation in teat defenses, phagocytosis, or immune response. There appears to be genetic antagonism between cell count and milk yield (positive gentic correlation of .1 to .2) in contrast to the negative phenotypic relationship between milk yield and cell count. A program to select sires whose progeny have lowest cell counts should be formulated carefully; more needs to be known about interpretation of cell count as a defense mechanism. Heightened cell counts decrease the probability of infection upon subsequent challenge with pathogens. Is there heritable variation in cell count of cows before exposure? A combined criterion of cell count, lactose, and enzyme concentration should be studied.

Programmable Calculator Program for Linear Somatic Cell Scores to Estimate Mastitis Yield Losses

A programmable calculator program calculates loss of milk yield in dairy cows based on linear somatic cell count scores. The program displays the distribution of the herd by lactation number and linear score for present and optimal goal situations. Loss of yield is in pounds and dollars by cow and herd. The program estimates optimal milk production and numbers of fewer cows at the goal for mastitis infection.

Physiological and pathological factors influencing bovine immunoglobulin G1 concentration in milk

Bovine immunoglobulin G1 concentration was determined by radial immunodiffusion in 349 milk samples of uninfected quarters, 95 of infected quarters, and 118 blood serum samples from 42 Holstein-Friesian cows taken at days 30, 150, and 270. In lactation, immunoglobulin G1 concentration in milk was not affected by immunoglobulin G1 concentration in blood serum or location of quarters. The immunoglobulin G1 concentrations increased at the end of lactation and in samples collected from cows beyond the third lactation. Uninfected quarters had a mean immunoglobulin G1 concentration of .46 mg/ml. This was less than means from quarters infected by minor or major pathogens. Quarter infection by Staphylococcus aureus resulted in an increase of immunoglobulin G1 concentration in blood serum (9.22 to 11.3 mg/ml). When Corynebacterium bovis was persistent throughout the lactation, immunoglobulin G1 concentration in blood serum was increased (11.26 mg/ml). There was no correlation between somatic cell count and immunoglobulin G1 concentration in uninfected quarters. There was a slight correlation between bovine serum albumin and immunoglobulin G1 concentration in identical quarters (.23). Infection of quarters increased in varying degrees the correlation between immunoglobulin G1 concentration and bovine serum albumin concentration or somatic cell count in milk.

Cost benefit analysis of lactation therapy with somatic cell counts as indications for treatment

Lactating dairy cows (487) from five commercial herds were in a study of benefits from lactation therapy of sub-clinical mastitis. Bacterial isolations and composite milk samples for somatic cell counts were taken from each cow each month for 15 mo. Cows (254) in the experimental group were infused with cephapirin in all quarters for two consecutive milkings if somatic cell counts rose above 400,000 cells/ml; 103 cows were so treated. Stepwise regression showed that lactation number, somatic cell counts, days in milk, and percent quarters infected explained variation in milk production, but treatment group, herd, and season did not. Also, there were no significant differences between production of infected experimental and control cows with high somatic cell counts on test dates after treatment. With the experimental program, there was a net loss of +19.65/cow. Intramammary lactation therapy based on somatic cell counts less than 400,000 cells/ml is not recommended.

Effects of a selective regimen of dry cow therapy on intramammary infection and on antibiotic sensitivity of surviving pathogens

Selective dry cow therapy with 1 million U of procaine penicillin G and 1 g of dihydrostreptomycin in a slow-release base was administered to all quarters of cows currently infected or treated for mastitis in the previous lactation. All other cows in the herd that were dried off during the experimental period were left untreated. Milk samples were cultured for detection of intramammary infection at drying off, 1 wk later (at time of treatment), and after next calving from 227 treated and 143 untreated cows. Isolants were tested for sensitivity to 12 antibiotics including penicillin and streptomycin. Although treatment resulted in clearance of Staphylococcus aureus, Staphylococcus epidermidis, streptococci other than agalactiae, and coliforms from 78, 82, 88, and 87% of infected glands, the net effect on udder health of the herd was a gain of 1.4% in infected quarters. Incidences of new infection in the early dry period (1 wk) were 18.1 and 12.3% among treated and untreated cows. Therapy failed to control new infection in the late dry and peripartum periods; incidence was about 18% of quarters among both long and short dry periods. Among 46 instances of apparent survival of an intramammary pathogen through a treated dry period, 7 of 10 strains previously sensitive to streptomycin became resistant and 8 of 10 strains previously sensitive to penicillin became resistant. The surviving pathogen population was not large enough to be considered a threat to herd udder health in the next lactation.

Physiological and pathological factors influencing bovine serum albumin content of milk

Concentrations of albumin from bovine blood serum were measured by radial immunodiffusion of 480 milk samples. Content in milk was not affected by content in serum, lactation number, or location of quarters. Bovine serum albumin concentrations in milk increased at the end of lactation (270 days) compared to the beginning (30 days) and at midlactation (150 days). Uninfected quarters had a mean concentration of serum albumin of .193 mg/ml. This was less than means for quarters infected by minor pathogens (.242 mg/ml) and by major pathogens (.284 mg/ml). Distributions of concentrations related to infection status, however, overlapped substantially. Somatic cell count was correlated .53 with concentrations of blood serum albumin in milk. About 32% of quarters infected by major pathogens had fewer than 500 x 10(3) cells/ml, whereas 47.5% of them had serum albumin content less than .2 mg/ml. For subclinical infections, concentration of serum albumin markedly increased when somatic cells were more than 1,000 x 10(3) cells/ml.

Lactation stage, parity, and infection affecting somatic cells, electrical conductivity, and serum albumin in milk

Effects of stage of lactation and parity on cell concentration, electrical conductivity, and serum albumin concentration of milk from quarters of known infection status were examined. For quarters free from infection, somatic cell concentration rose from 80 to 160 x 10(3) cells/ml between 35 and infected with Staphylococcus aureus the increase was from 250 to about 1000 x 10(3) cells/ml. As lactation number advanced, there was little change in cell concentration for quarters free from infection, whereas for quarters infected with Staphylococcus aureus, cell concentration rose from approximately 450 x 10(3) cells/ml for first lactation to about 1500 x 10(3) cells/ml for cows in their sixth or more lactations. Trends in electrical conductivity were similar to those for cell concentration, with the main influence on electrical conductivity being Staphylococcus aureus infection. For serum albumin concentration only the effect os stage of lactation was significant. Concentration of serum albumin rose from 150 mg/liter at the beginning of lactation to 280 mg/liter at 215 days postpartum. Effects of stage and number of lactation were minor compared with effects of infection by Staphylococcus aureus.

Variation in Wisconsin Mastitis Test Scores of bucket milk samples and relationship to bacterial infections

Sources of variation in the Wisconsin Mastitis Test were studied in 4739 bucket milk samples from 111 cows in one herd during 103 days. Quarters of cows were classified infected or uninfected through bacteriologic assays of quarter milk samples. Quarters were uninfected in 70.4% of the cow-quarter-days and infected with Staphylococcus aureus and Streptococcus agalactiae in 1.4 and .9% of the quarter samples. Scores of all cow-days averaged 8.5. Wisconsin Mastitis Test scores of cow-days having no pathogens averaged 5.8. Correlation of duplicate samples was .97. Repeatability of monthly tests was .67. Days within month of lactation, month within age group, cow within age, and age differed. Older cows averaged higher Wisconsin Mastitis Test scores. Scores for uninfected cow-days did not differ with age. Scores were higher by 5.5 units in cows with infected quarters than in those with no infected quarters. The increase was greater with S. aureus or S. agalactiae present than with less virulent pathogens. In a cost-utility analysis, Wisconsin Mastitis Test was inefficient in detecting infected cows with a single test.

Economic losses from and the national research program on mastitis in the United States

Scientific papers estimating economic losses from mastitis were reviewed. Reduced milk production from cows with subclinical mastitis was responsible for the largest losses. Losses from mastitis in the United States in 1976 were estimated by usable responses to a survey from 33 states representing 9.5 million cows or 86% of the dairy cow population. Losses of milk yields caused by mastitis were 386 kg/cow per yr and losses of discarded milk 62 kg/cow per yr. Annual losses per cow from mastitis were a) reduced milk production, $81.32; b) discarded milk, $12.88; c) cost of veterinary services, $1.97; d) cost of drugs, !3,86; e) increased labor, $2.28; f) decreased sale value, $5.72; g) increased replacement costs, $9.32; h) total, $117.35. For the 11 million cows in the United States 1976 losses from mastitis were $1.294 billion. Mastitis research was supported publicly at 22 locations under 43 projects. Approximately 24 scientist years were involved and $2.7 million of public funds were expended annually. If economic losses from mastitis were reduced 2% per year for 10 yr by research and expenditures for mastitis research remained the same, the benefit to cost ratio from mastitis research would be approximately 9.6 to 1.