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.

Somatic cell count, electrical conductivity, and serum albumin concentration for detecting bovine mastitis.

Cell concentration, electrical conductivity, and serum albumin concentration of milk were evaluated for predicting infection status of quarters in three herds. Probability of misclassifying quarters was lowest for cell concentration. For discriminating quarters infected with Staphylococcus aureus from quarters free from infection, probability of misclassification for cell concentration ranged from 8 to 20% among herds. For electrical conductivity probability of misclassification ranged between 22 and 32%, whereas for serum albumin the range among herds was from 15 to 48%. Among herds there was also considerable variation of the trait, which minimized the probability of misclassification. Cell concentrations for the three herds were 158, 200, and 251 x 10(3) cells/ml whereas for electrical conductivity counts were 4.6, 5.8, and 6.5 mS/cm. For electrical conductivity and serum albumin comparisons within cow by differences and ratios from different quarters yielded little advantage over absolute estimations. For a single sampling, cell concentration provided the most accurate prediction of quarter infection status. We suggest that 200 x 10(3) cells/ml should be the threshold above which quarters are considered likely to be infected with a major pathogen.

Investigations into falsely elevated somatic cell counts of bulked herd milk.

Bulk milk cell counts obtained by a Coulter Milk Cell Counter were shown to be falsely elevated because of the formation of non-cellular particles (NCP). The NCP, which were detected by the use of a particle size analyser, were removed if the milk samples were heated to 55 degrees C for 15 min before the addition of formalin. A survey of bulk milk supplies in New South Wales showed that NCP occurred in milk from 2% of farms, the counts being falsely elevated by about 200 000 cells/ml. Surveys of milking equipment of farms where the bulk milk had shown this phenomenon demonstrated a relationship between the use of centrifugal milk pumps and the presence of NCP with a much lower prevalence in herds where spit chamber releasers were used. These particles were not air bubbles since air was removed from the milk by heating to 60 degrees C for 15 min, vacuum at 65 mmHg for 15 min or 0.5% v/v octan-2-ol; only the heat treatment removed the NCP.

The detection of mastitis in individual quarters using electrical conductivity or somatic cell concentration.

In this investigation electrical conductivity (EC) and somatic cell concentration (SCC) were compared in 3 herds for their ability to correctly identify the infection status of quarters. For EC, thresholds of 6.0 and 6.8 mS/cm were used and comparisons were made between quarters within each cow. The method of comparison between quarters was the same as that described by the manufacturers of the AHI Mastitis Detector. For SCC a threshold of 500 x 10(3) cells/ml was used. For both EC and SCC considerable variation was found between herds for sensitivity (the proportion of quarters infected with a major pathogen and detected as abnormal), and specificity (the proportion of quarters free from infection and detected as normal). The mean sensitivity and specificity of EC for the three herds was 49% and 79% respectively, whereas for SCC the means were 71% and 81% respectively. The variation in sensitivity and specificity of EC between herds was attributed to differences in the distribution of EC for quarters of similar infection status. It was concluded that these differences in herd EC precluded the use of pre-determined EC thresholds which were applicable for detecting mastitis in all herds.

Relationship of somatic cell count and cell volume analysis of goat's milk to intramammary infection with coagulase-negative staphylococci.

The prevalence of intramammary infection in 4 commercial goat herds was studied in conjunction with electronic somatic cell count and volume analysis determined using a Coutler Counter and volume analyser. Neither streptococci nor mycoplasma were isolated from any half and the prevalence of intramammary infection with Staphylococcus aureus ranged from 0 to 3% between herds. For coagulase-negative staphylococci the range from infected halves was 36-71%. There was no significant difference between the mean total microscopic somatic cell count for halves infected with coagulase-negative staphylococci and those free from infection. A similar trend was observed for electronic somatic cell counts although the mean electronic cell count was greater than the mean total microscopic count on the 2 occasions that they were compared. The correlation coefficients between the 2 cell counting methods were 0.86 and 0.94. Between herds there were significant differences in mean electronic somatic cell count, with herd means ranging from 438 x 103 to 1684 x 103 cells/ml. In 2 of the 4 herds studied, milk samples from halves infected with coagulase-negative staphylococci had a significantly higher prevalence of cell volume distributions with a modal cell volume between 65 mu 3 and 100 mu 3. This was attributed to a higher proportion of polymorphonuclear neutrophils. Use of electronic somatic cell count and cell volume analysis were considered of little value in predicting infection caused by coagulase-negative staphylococci as there was a high proportion of false negative and false positive predictions.

Effect of teat skin disinfection on the rate of infection and interval to infection in cows exposed to high levels of Staphylococcus aureus.

All teats of a herd of lactating cows were contaminated after each milking with Staphylococcus aureus. Two teats of each cow were subsequently dipped in an iodine solution, while the remaining 2 teats were not dipped. For cows with a single infection the interval to infection in dipped and undipped quarters was 64 and 60 d respectively, while for the first infected quarter of cows with multiple infections the interval to infection in dipped and undipped quarters was 50 and 39 d respectively. For the second quarter infected in cows with multiple infections, the period between the first and second infection was 21 and 12 d for dipped and undipped quarters respectively. It is suggested that while teat skin disinfection was effective in reducing the rate of new infection, it had little effect on the process of infection in those quarters becoming infected. The occurrence of an infection in one quarter doubled the rate of infection in the other quarters.

Effect of a disinfectant udder wash and a post-milking teat dip on the bacterial population of the teat end and on the rate of new intramammary infection.

A pre-milking wash disinfectant procedure employing a 2% (w/v) chlorhexidine solution in a detergent basic did not reduce the rate of new intramammary infection in a lactating herd challenged with Staphylococcus aureus. Teat-end swabs showed no significant difference in the number of Staph. aureus isolated from the teat-ends pre-washed with either water, or water and chlorhexidine. In contrast, disinfecting teats after milking with a solution containing 5000 mg available iodine/l significantly reduced the staphylococcal population of the teat-ends and the rate of new intramammary infection, compared with teats not disinfected.

Analysis of somatic cell volume distribution as an aid to the diagnosis mastitis.

Electronic somatic cell counts (ESCC) and relative cell volume distributions (RCVD) in milk samples were obtained simultaneously on a Coulter Counter Model TA and their potential assessed, either singly or in combination, for identifying mastitic quarters and cows in 2 herds. Using log (ESCC) alone the probability P m of misclassifying quarters infected with major pathogens was 6.7% for herd 1 and 18.1% for herd 2. The inclusion of RCVD variables with log (ESCC) did not substantially improve the chance of detecting quarters infected with major pathogens. However, the RCVD variables did improve the chance of identifying quarters infected by major and minor pathogens compared to the use of log (ESCC) alone, the P m figures being reduced by about one third. When testing composite quarter samples, where milk from infected quarters was diluted with that from uninfected quarters, the inclusion of RCVD variables decreased the P m compared to the use of log (ESCC) alone. In hered 1 the improvement was from 26.1 to 3.0%, while in herd 2 the effect was less marked, the P m being reduced from 28.6 to 21.6%. However, as the RCVD assessment is provided simultaneously with ESCC, the additional information is obtained at minimal cost.

Post-milking iodine teat skin disinfectants. I. Bactericidal efficacy.

An iodine teat skin disinfectant tested in lactating cows over a range of concentrations, 100 to 10 000 mg available iodine/l(mgavI/l) was found bactericidally effective against Staphylococcus aureus when containing 1000 mg avI/l or greater. Against Streptococcus dysgalactiae 5000 mg avI/l or greater was bactericidally effective. The addition of glycerine to a disinfectant containing 5000 or 1000 mg avI/l at levels of 225 ml/l and 105 ml/l, respectively, resulted in a reduction in bactericidal efficacy of the disinfectant. Emulsified paraffin added at concentrations of between 50 and 500 ml/l had no effect on the efficacy of the 5000 mg avI/l disinfectant, but the addition of 200 ml/l emulsified paraffin to a 1000 mg avI/l disinfectant significantly reduced its efficiency. Iodine disinfectants containing emulsified paraffin phase separated rapidly during storage, and the bactericidal efficacy of the phases differed significantly and diminished with time.

Post-milking iodine teat skin disinfectants. 2. New intramammary infection rates.

Use of an iodine teat dip containing 5000 mg available iodine/l (mg avI/l) resulted in a significant reduction in the number of new Staphylococcus aureus infections in a lactating herd, while no significant reduction was found with a disinfectant containing only 1000 mg avI/l. When Streptococcus dysgalactiae was used as the challenge organism, the rate of new infection was extremely low, and no reduction in levels of new infection were found with either disinfectant. The pathogenicity of the Str. dysgalactiae strain was high, as 60% of the quarters becoming infected produced clinical symptoms.

Post-milking iodine teat skin disinfectants. 3. Residues.

Teat dipping of lactating cows with either 1000 or 5000 mg available iodine/; (mg avI/;) solution and thoroughly washing and drying of the teats before sampling resulted in levels of 70 and 99 micrograms avI per quarter per milking respectively. Without any pre-milking udder preparation prior to sampling the levels of iodine recorded were 143 and 291 micrograms avI per quarter per milking respectively. Some systemic transfer of iodine from the teat skin to the milk was observed, but the bulk of iodine residue in milk was of direct teat skin origin.

The New South Wales mastitis control program. 1. Field aspects and their effect on clinical and subclinical mastitis.

A mastitis control program based on teat dipping and dry cow therapy was evaluated in 35 herds over a 3 year period. The incidence of subclinical mastitis as detected by the Rapid Mastitis Test (RMT) fell from 34% to 12% quarters positive, a reduction of 65%. Clinical mastitis was reduced from 37 clinical cases per 100 cows in the first 3 month period to 12 clinical cases per 100 cows in the last 3 month period, a reduction of 68%. Variations in response to the program in the reduction of subclinical and clinical mastitis are discussed and the results compared with similar trials conducted overseas. The Modified Whiteside Test was used on bulk milk samples from the control herds and these results were significantly correlated with the prevalence of subclinical mastitis assessed by RMT individual quarters.

The New South Wales mastitis control program. 2. Effect upon bacterial infections.

Bacteriological examinations were made on quarter samples from cows in 35 herds over a 3 year period to monitor the response in a mastitis control program. Initially, Staphylococcus aureus predominated in 32 of the herds and the mean herd prevalence was 26%. The control measures halved this rate but there was considerable variation in response between herds. The decline occurred rapidly and there was a significant reduction (P less than 0.01) by 3 months. Streptococcus agalactiae predominated in 3 herds and the overall infection rate was 4.9%. Control measures eliminated the infection completely from most herds but reinfection occurred in 2 herds. The greatest decline occurred in the first 6 months and was significant (P less than 0.05). The measures had little effect upon Str. uberis and Str. dysgalactiae which remained fairly consistently at low levels. Initially, strains of Staph. aureus resistant to penicillin were dominant in most herds. In a minority of herds strains resistant to streptomycin predominated and in these herds there was a concurrent resistance to penicillin. These patterns did not change greatly over the control period. Resistance by Str. agalactiae to streptomycin occurred in most herds at the start of the program.

Cell volume to aid analysis and technique of somatic cell counts in milk.

In conjunction with a Coulter Counter, somatic cells in milk were sized by electronic analysis. Quarter milk from cows with mastitis had a cell volume peak with a modal cell volume of 102 mu3 while milk from healthy quarters had no peak. Bulk milks with a peak had higher cell counts than milks where there was no peak. Dimensions of peak from bulk milks were the same as from quarter milks. Modal cell volume and cell count varied after milks were fixed with varying concentrations and types of fixative. The concentration of fixative recommended by the International Dairy Federation was sufficient, but only marginally so, and it should be increased.