OUR INDUSTRY TODAY
Mastitis Control Practices: Differences Between Herds with High and Low Milk Somatic cell Counts
c.
T. HUTTON, L. K. FOX, and D. D. HANCOCK Department of Veterinary Clinical Medicine and Surgery Washington State University Pullman 99164-6610
and high see herd groups. (Key words: mastitis control. somatic cell count. dairy management)
ABSTRACT
Effects of differences in herd mastitis control management in maintaining low herd average see, was studied. Washington State DHI herds with Holstein cattle and enrolled in the see program (n = 309) were ranked by percentage of cows in their herd with see less :5283.000 cells/mt. "Low herds" (n = 28) were among the 56 herds with the highest percentage of cows with see :5283.000 cells/ml and "high herds" (n = 31) were among the 75 with the lowest percentage of cows with see :5283,000 cells/mt. Herds were visited annually for 2 yr by a technician who collected samples and recorded data. Geometric mean bulk tank see during the year between herd visits was 175,000 and 460.000 cells/ml for low and high herds. Milking time hygiene practices. teat dipping. and dry cow therapy were practiced with equal frequency on low and high herds. Differences in function and maintenance of milking equipment did not discriminate between herd groups. Differences in mastitis control management of low versus high see herds were that managers of excellent control herds more frequently had highest producers milked first and clinical cows milked last; had automatic milking unit detachers; kept moisture content of cow bedding lower; and had workers disinfect teat ends prior to intramammary antibiotic treatment. Managers of low herds were more likely to use computers and attend dairy informational meetings. Results suggest subtle differences in mastitis control strategies differentiate the low
Received June 12. 19&9. Accepted September 25. 1989.
1990 J Dairy Sci 73: 1135-1143
INTRODUCTION
Mastitis, similar to most livestock diseases, is a result of the interaction between the host (cow). pathogen, and the environment. Although much research has been targeted at improvement in host immune defense and characterization of pathogen virulence factors causing mastitis. most of our success in control of mastitis is a result of research on utilization of management factors that reduce pathogen transmission (26). The basic milking time hygiene program designed to reduce pathogen transmission was established approximately 20 yr ago (4). This program included use of single service towels to wash and dry udders. disinfection of hands and milking unit between cow milkings, and teat dipping. Milking time hygiene, maintenance of the milking system and cattle housing facilities. and dry cow therapy constitute a mastitis control program that is recommended today (6).
Although the mastitis control program was developed 20 yr ago, many herd managers (25 to 75%) have not reduced their herds' see to those deemed by milk processors as deserving quality premiums (8. 20). The question as to what control practices have been associated with lower herd average see has been the subject of several studies (3, 7, 13, 18, 23). Two of these were conducted recently (7. 13); the others were done 10 to 20 yr ago. Yet they all indicate that the mastitis control strategies of teat dip and dry cow therapy were the primary factors that could be used to describe the variation in herd Sec. The only other factors that would help explain the variation in herd see were: 1) use of separate towels to dry udders (18), and 2) maintenance of milking system
1135
1136
HUITON ET AL.
efficiency (23). It would seem incongruous that the use of teat dip and dry cow therapy would be the only factors that could explain why some herds have achieved excellent mastitis control and had reduced their see to below the quality premium threshold, since Hueston et al. (13) reported that teat dip and dry cow therapy were a part of the mastitis control programs of more than 80% of dairies surveyed. Because the only factors that were found to describe differences in the herd average sec were teat dip and dry cow therapy, and these factors are commonly used on dairies, we suspect that the aforementioned studies (3, 7, 13, 18, 23) failed to determine some fundamental differences in mastitis control strategies between herds. These previous studies focused only on the practices that were part of a herd's control program, not on how those practices were conducted. The purpose of this study was to determine mastitis control strategies that were more likely associated with herds with good to excellent (herd average sec ~283,OOO cells/ml) as compared with herds with fair to poor control of mastitis (herd geometric average sec >283,000 cells/ml). A key objective of this study was to determine what practices were used and how those practices were conducted. For example, in addition to whether a herd used teat dip, how much of the teat was dipped, method of application, how the teat dip was stored, and the type and concentration of the active ingredient in the dip were also recorded. MATERIALS AND METHODS
All herds with Holstein cattle enrolled in the Washington State DHI Somatic Cell Count Program were ranked by percentage of cows in their herd that had cell counts of less than and equal to 283,000 cells/ml (linear score ~). Rankings were made for the 12-mo period preceding the start of the study. Twenty-eight of the 56 herds with greatest percentage of cows with linear score ~ agreed to participate and were termed "low herds". Thirty-one of the 75 herds with the lowest percentage of cows with linear score ~ agreed to participate and were termed "high herds". A field technician visited each herd annually for 2 yr. During each visit, the owner or operator was interviewed, samples were collected. Journal of Dairy Science Vol. 73.
No.4, 1990
the milking system was analyzed, and the milking procedures were recorded. Topics covered during the interview were: types of records kept and their usage; use of veterinary services, mastitis therapy program, nutrition program, culling practices, labor force, sources of information on dairy cattle management, and cattle housing and its maintenance. Under the topic of record keeping and usage, the following were determined: type of cow identification and age of animal when identification was initiated; type of supplementary record keeping (card file. computer, both, none); type of information recorded on supplemental record keeping system; and frequency of use of records, both DHI and other. As part of the questions on herd health and veterinary services and their usage, the following were addressed: percentage of the herd with metabolic diseases. the percentage of the herd with reproductive diseases, percentage of the herd treated for clinical mastitis, type of herd health program and frequency of veterinary assisiance and visits, and milk quality results. Under the section of mastitis therapy, the following were determined: method of mastitis detection, both subclinical and clinical stages; type and frequency of treatment during lactation and dry periods; method of treatment; and storage of treatment products. Within the area of nutritional information, the following were obtained by interview: vitamin and mineral supplementation and person responsible for ration balancing. Regarding culling practices, the following were reviewed: proportion of herd culled for mastitis per year; proportion of herd culled per year; and type of replacements (proportion homegrown heifers. purchased heifers, purchased cows). Data obtained concerning labor practices were: percentage of work force that was family or hired; education of the work force; number of milkers employed, including relief help; sex of milkers and hours milked per shift; number of shifts per day; interval between milkings; and experience of labor force. Under the topic of cattle housing, the following were assessed: type of calf housing by age group; type and frequency of manure disposal for all cattle; bedding used and frequency of replacement for all cattle; use and management of pasture; feeding system for calves; size of stalls for milking herd; length of time maternity stalls were used; type of housing for lactating and dry cows (free
OUR INDUSTRY TODAY
stall, tie stall, loose, housing, shade structures); grouping of lactating herd; and milking order. The milking system was evaluated according to Appleman (1). The pulsators were graphed using a Boumatic Dectrace Recorder (Dairy Equipment Co., Madison, WI). Pulsator rate, ratio, alternate versus uniform pulsation, and operating vacuum were determined. Vacuum system reserve was determined by blocking regulator function and determining air flow using a Boumatic Airflow Meter (Dairy Equipment Co., Madison, WI). Vacuum system recovery was determined by allowing air to enter the closed system such that the vacuum recorded at the short milk tube was 16.9 KPa less than operating vacuum; the time required for the return to operating vacuum was recorded. Vacuum at the teat end was also measured using the Dectrace Recorder; vacuum was recorded at the shon milk tube during early, middle, and end phases of cow milkings. The type of milking parlor (herringbone, side opening stall, or flat barn) and its design were recorded; milking and pulsator line sizes determined, milking pump motor horsepower recorded, and slope of lines and vacuum reserve tank capacity determined. The condition and frequency of professional milking system evaluation was determined by interview. Details of milking procedures were recorded. The concentration of disinfectant in the teat dip was recorded from the original container. The average length of the teat immersed in the postrnilking teat dip was determined. Teat dip samples were collected and teat dip pH determined. The time between wetting and milking when a sprinkler system was in operation was determined by the average time elapsed between wetting of the udders and placement of the milking units on the mammary glands. The average area of the gland to which a washing solution was applied was determined. Residual moisture remaining on the gland immediately prior to machine application was determined by rolling a preweighed swab over the teats and then reweighing the swab. Concentration of halide disinfectants in the wash and backflush water solutions was determined by using Chemical Test Kits, MH01 and MH05 (West Agro Chemical, Inc., Kansas City, MO). Type of towels used to dry the mammary gland prior to machine applications was observed and recorded. The average time in sec-
1137
onds taken to wash and dry the mammary gland was recorded. The average time in seconds, between cessation of drying the mammary gland, and machine application, was determined. Machine stripping, and length of time if practiced, was determined. Backflush water was collected into a bucket to determine the volume of the water being flushed through the milking unit. The condition of the teat orifices were classified. Classification as outlined by Sieber and Farnsworth (25) were followed as modified. Teat score of I indicated a "normal" teat end and corresponded to I to 3 classifications. Teat score of 2 signified some erosion of the teat end and corresponded to 4 to 6 classifications. A score of 3 indicated an eroded teat end. The Sieber and Farnsworth (25) 7 to 10 classifications was the basis for the score of 3. Bedding, bulk tank milk, and composite foremilk samples were collected for bacterial analysis. Dilutions of bulk tank milk samples, 10-2 , 10-3, and 10-4, were plated on blood agar. Isolates that were identified were: coagulase-positive and coagulase-negative staphylococci; streptococci other than agalactiae, Streptococcus agalactiae; and coliforms (5). Foremilk samples were collected aseptically, and .05 ml of milk was cultured on blood agar. Bacteriologic identification was done as described for bulk tank milk analysis. Milk samples were collected from randomly selected cows. The sample size was determined assuring that a 90% confidence interval of infection prevalence with a width no wider than ± .1 was used. Bedding samples were collected from a representative number of cow stalls and moisture and bacterial content enumerated. Bacteriologic analysis of bedding material was done by procedure of Janzen et al. (16) with modification. Briefly, bedding samples (10 g) were mixed in 100 ml of .01 M sterile phosphatebuffered saline solution (PBSS, pH 7.4), diluted and cultured on differential agars. Differential agars were thallium crystal violet, MacConkey, and phenol red mannitol salt, which were used to enumerate streptococcal, coliform, and staphylococcal colonies, respectively (5). Greater than 250 factors, variables, were analyzed. A more detailed description of variable recording and analysis is given by Hunon (15). Within-group means for all variables were computed, and between-group differences were Journal of Dairy Science Vol. 73.
No.4, 1990
1138
HUlTON ET AL.
TABLE 1. Prevalence of intramammary infections by herd group.l Herd group Pathogen type Coagulase-positive staphylococci Coagulase-negative staphylococci Streptococcus agalactiae Streptococci other than Strep. agalactiae Coliform
Low
High
p2 .05) in low than in high herds (Table 2). Postmilking teat dip was used on a large majority of herds. Although a number of different types of teat dip and different disinfectants in the dip were used, no one type was associated with low herd sec. A majority of herds used a single service towel to clean udders. Approximately 30% did not use single service RESULTS AND DISCUSSION towels to clean udders. It should not be inferred Over 250 variables were examined with re- that a common herd cloth was used in all of spect to their ability to classify low and high these herds; rather, it was observed that most sec herds. For the purpose of brevity, only the often a towel was shared between cows, one results of variables found to discriminate signif- side of the towel to clean each cow. The use of icantly between herd groups and those that did disinfectant in the mammary gland wash water not significantly discriminate between herd and use of milking unit backflush systems were groups but are commonly thought to have a similar between groups. The percentage of major impact on mastitis control, are presented herds where milkers wore synthetic rubber and discussed. A complete analysis and discus- gloves was greater in the low than in the high sion of all variables is in Hutton (15). The group and approached significance (Table 2), mean (± SO) milk production and bulk tank although only a small fraction of either herd sec during the year between herd visits was group used this practice. Prevalence of IMI by 9555 kg/cow (± 880) and 175,000 (± 60,000) other organisms were similar between groups. cells/ml for low sec herds and 7863 kg/cow (± It was estimated from large survey studies 1270) and 460,000 (± 176,000) cellsImi for that 25% of cows had IMI caused by contagious pathogens, S. aureus or Strep. agaJactiae high herds. (9, 28). In this study, 25.3% of the cows in the high group had contagious pathogen 1M! (Table Control of Mastitis at Milking 1). Thus, although high herds were among The only significant difference in the preva- those with the highest sec in Washington lence of intramammary infections major patho- OHI, they appear to be near average in their gens between high and low herd groups was the incidence of contagious mastitis. This, in addipathogen Staphylococcus aureus, as identified tion to the fact that the prevalence of noncontaas coagulase-positive staphylococci. Eight gious mastitis was similar between low and times more cows had Staphylococcus aureus high groups, would support the contention that intramammary injections (IMI) in high than in herds in the high mastitis group were near low herds (Table 1). Thus, it would be expected average in their control of mastitis. that differences in milking time hygiene pracCows with clinical mastitis were milked last tices would exist between herd groups. Howev- in approximately half of the low sec herds as er, none of the milking time hygiene practices, contrasted to only 13% of the high sec herds as recommended (6), were practiced more fre- (Table 2). Milking cows with IMI last has often Jownal of Dairy Science Vol. 73. No.4, 1990
1139
OUR INDUSTRY TODAY
Percentage of herd group utilizing practice pi
Variable
Low
Use of synthetic rubber gloves by milkers Cow milking order Cows with cI inical mastitis milked last Highest producing cows milked first Use of postmilking teat dip Use of single service towels to dry mammary glands Use of predip disinfection Use of disinfectant in wash water Use of between cow milking unit disinfection
18
3
.09
46 43 93 70 29 32 57
13 9 79 74
Mastitis Control Practices: Differences Between Herds with High and Low Milk Somatic cell Counts
c.
T. HUTTON, L. K. FOX, and D. D. HANCOCK Department of Veterinary Clinical Medicine and Surgery Washington State University Pullman 99164-6610
and high see herd groups. (Key words: mastitis control. somatic cell count. dairy management)
ABSTRACT
Effects of differences in herd mastitis control management in maintaining low herd average see, was studied. Washington State DHI herds with Holstein cattle and enrolled in the see program (n = 309) were ranked by percentage of cows in their herd with see less :5283.000 cells/mt. "Low herds" (n = 28) were among the 56 herds with the highest percentage of cows with see :5283.000 cells/ml and "high herds" (n = 31) were among the 75 with the lowest percentage of cows with see :5283,000 cells/mt. Herds were visited annually for 2 yr by a technician who collected samples and recorded data. Geometric mean bulk tank see during the year between herd visits was 175,000 and 460.000 cells/ml for low and high herds. Milking time hygiene practices. teat dipping. and dry cow therapy were practiced with equal frequency on low and high herds. Differences in function and maintenance of milking equipment did not discriminate between herd groups. Differences in mastitis control management of low versus high see herds were that managers of excellent control herds more frequently had highest producers milked first and clinical cows milked last; had automatic milking unit detachers; kept moisture content of cow bedding lower; and had workers disinfect teat ends prior to intramammary antibiotic treatment. Managers of low herds were more likely to use computers and attend dairy informational meetings. Results suggest subtle differences in mastitis control strategies differentiate the low
Received June 12. 19&9. Accepted September 25. 1989.
1990 J Dairy Sci 73: 1135-1143
INTRODUCTION
Mastitis, similar to most livestock diseases, is a result of the interaction between the host (cow). pathogen, and the environment. Although much research has been targeted at improvement in host immune defense and characterization of pathogen virulence factors causing mastitis. most of our success in control of mastitis is a result of research on utilization of management factors that reduce pathogen transmission (26). The basic milking time hygiene program designed to reduce pathogen transmission was established approximately 20 yr ago (4). This program included use of single service towels to wash and dry udders. disinfection of hands and milking unit between cow milkings, and teat dipping. Milking time hygiene, maintenance of the milking system and cattle housing facilities. and dry cow therapy constitute a mastitis control program that is recommended today (6).
Although the mastitis control program was developed 20 yr ago, many herd managers (25 to 75%) have not reduced their herds' see to those deemed by milk processors as deserving quality premiums (8. 20). The question as to what control practices have been associated with lower herd average see has been the subject of several studies (3, 7, 13, 18, 23). Two of these were conducted recently (7. 13); the others were done 10 to 20 yr ago. Yet they all indicate that the mastitis control strategies of teat dip and dry cow therapy were the primary factors that could be used to describe the variation in herd Sec. The only other factors that would help explain the variation in herd see were: 1) use of separate towels to dry udders (18), and 2) maintenance of milking system
1135
1136
HUITON ET AL.
efficiency (23). It would seem incongruous that the use of teat dip and dry cow therapy would be the only factors that could explain why some herds have achieved excellent mastitis control and had reduced their see to below the quality premium threshold, since Hueston et al. (13) reported that teat dip and dry cow therapy were a part of the mastitis control programs of more than 80% of dairies surveyed. Because the only factors that were found to describe differences in the herd average sec were teat dip and dry cow therapy, and these factors are commonly used on dairies, we suspect that the aforementioned studies (3, 7, 13, 18, 23) failed to determine some fundamental differences in mastitis control strategies between herds. These previous studies focused only on the practices that were part of a herd's control program, not on how those practices were conducted. The purpose of this study was to determine mastitis control strategies that were more likely associated with herds with good to excellent (herd average sec ~283,OOO cells/ml) as compared with herds with fair to poor control of mastitis (herd geometric average sec >283,000 cells/ml). A key objective of this study was to determine what practices were used and how those practices were conducted. For example, in addition to whether a herd used teat dip, how much of the teat was dipped, method of application, how the teat dip was stored, and the type and concentration of the active ingredient in the dip were also recorded. MATERIALS AND METHODS
All herds with Holstein cattle enrolled in the Washington State DHI Somatic Cell Count Program were ranked by percentage of cows in their herd that had cell counts of less than and equal to 283,000 cells/ml (linear score ~). Rankings were made for the 12-mo period preceding the start of the study. Twenty-eight of the 56 herds with greatest percentage of cows with linear score ~ agreed to participate and were termed "low herds". Thirty-one of the 75 herds with the lowest percentage of cows with linear score ~ agreed to participate and were termed "high herds". A field technician visited each herd annually for 2 yr. During each visit, the owner or operator was interviewed, samples were collected. Journal of Dairy Science Vol. 73.
No.4, 1990
the milking system was analyzed, and the milking procedures were recorded. Topics covered during the interview were: types of records kept and their usage; use of veterinary services, mastitis therapy program, nutrition program, culling practices, labor force, sources of information on dairy cattle management, and cattle housing and its maintenance. Under the topic of record keeping and usage, the following were determined: type of cow identification and age of animal when identification was initiated; type of supplementary record keeping (card file. computer, both, none); type of information recorded on supplemental record keeping system; and frequency of use of records, both DHI and other. As part of the questions on herd health and veterinary services and their usage, the following were addressed: percentage of the herd with metabolic diseases. the percentage of the herd with reproductive diseases, percentage of the herd treated for clinical mastitis, type of herd health program and frequency of veterinary assisiance and visits, and milk quality results. Under the section of mastitis therapy, the following were determined: method of mastitis detection, both subclinical and clinical stages; type and frequency of treatment during lactation and dry periods; method of treatment; and storage of treatment products. Within the area of nutritional information, the following were obtained by interview: vitamin and mineral supplementation and person responsible for ration balancing. Regarding culling practices, the following were reviewed: proportion of herd culled for mastitis per year; proportion of herd culled per year; and type of replacements (proportion homegrown heifers. purchased heifers, purchased cows). Data obtained concerning labor practices were: percentage of work force that was family or hired; education of the work force; number of milkers employed, including relief help; sex of milkers and hours milked per shift; number of shifts per day; interval between milkings; and experience of labor force. Under the topic of cattle housing, the following were assessed: type of calf housing by age group; type and frequency of manure disposal for all cattle; bedding used and frequency of replacement for all cattle; use and management of pasture; feeding system for calves; size of stalls for milking herd; length of time maternity stalls were used; type of housing for lactating and dry cows (free
OUR INDUSTRY TODAY
stall, tie stall, loose, housing, shade structures); grouping of lactating herd; and milking order. The milking system was evaluated according to Appleman (1). The pulsators were graphed using a Boumatic Dectrace Recorder (Dairy Equipment Co., Madison, WI). Pulsator rate, ratio, alternate versus uniform pulsation, and operating vacuum were determined. Vacuum system reserve was determined by blocking regulator function and determining air flow using a Boumatic Airflow Meter (Dairy Equipment Co., Madison, WI). Vacuum system recovery was determined by allowing air to enter the closed system such that the vacuum recorded at the short milk tube was 16.9 KPa less than operating vacuum; the time required for the return to operating vacuum was recorded. Vacuum at the teat end was also measured using the Dectrace Recorder; vacuum was recorded at the shon milk tube during early, middle, and end phases of cow milkings. The type of milking parlor (herringbone, side opening stall, or flat barn) and its design were recorded; milking and pulsator line sizes determined, milking pump motor horsepower recorded, and slope of lines and vacuum reserve tank capacity determined. The condition and frequency of professional milking system evaluation was determined by interview. Details of milking procedures were recorded. The concentration of disinfectant in the teat dip was recorded from the original container. The average length of the teat immersed in the postrnilking teat dip was determined. Teat dip samples were collected and teat dip pH determined. The time between wetting and milking when a sprinkler system was in operation was determined by the average time elapsed between wetting of the udders and placement of the milking units on the mammary glands. The average area of the gland to which a washing solution was applied was determined. Residual moisture remaining on the gland immediately prior to machine application was determined by rolling a preweighed swab over the teats and then reweighing the swab. Concentration of halide disinfectants in the wash and backflush water solutions was determined by using Chemical Test Kits, MH01 and MH05 (West Agro Chemical, Inc., Kansas City, MO). Type of towels used to dry the mammary gland prior to machine applications was observed and recorded. The average time in sec-
1137
onds taken to wash and dry the mammary gland was recorded. The average time in seconds, between cessation of drying the mammary gland, and machine application, was determined. Machine stripping, and length of time if practiced, was determined. Backflush water was collected into a bucket to determine the volume of the water being flushed through the milking unit. The condition of the teat orifices were classified. Classification as outlined by Sieber and Farnsworth (25) were followed as modified. Teat score of I indicated a "normal" teat end and corresponded to I to 3 classifications. Teat score of 2 signified some erosion of the teat end and corresponded to 4 to 6 classifications. A score of 3 indicated an eroded teat end. The Sieber and Farnsworth (25) 7 to 10 classifications was the basis for the score of 3. Bedding, bulk tank milk, and composite foremilk samples were collected for bacterial analysis. Dilutions of bulk tank milk samples, 10-2 , 10-3, and 10-4, were plated on blood agar. Isolates that were identified were: coagulase-positive and coagulase-negative staphylococci; streptococci other than agalactiae, Streptococcus agalactiae; and coliforms (5). Foremilk samples were collected aseptically, and .05 ml of milk was cultured on blood agar. Bacteriologic identification was done as described for bulk tank milk analysis. Milk samples were collected from randomly selected cows. The sample size was determined assuring that a 90% confidence interval of infection prevalence with a width no wider than ± .1 was used. Bedding samples were collected from a representative number of cow stalls and moisture and bacterial content enumerated. Bacteriologic analysis of bedding material was done by procedure of Janzen et al. (16) with modification. Briefly, bedding samples (10 g) were mixed in 100 ml of .01 M sterile phosphatebuffered saline solution (PBSS, pH 7.4), diluted and cultured on differential agars. Differential agars were thallium crystal violet, MacConkey, and phenol red mannitol salt, which were used to enumerate streptococcal, coliform, and staphylococcal colonies, respectively (5). Greater than 250 factors, variables, were analyzed. A more detailed description of variable recording and analysis is given by Hunon (15). Within-group means for all variables were computed, and between-group differences were Journal of Dairy Science Vol. 73.
No.4, 1990
1138
HUlTON ET AL.
TABLE 1. Prevalence of intramammary infections by herd group.l Herd group Pathogen type Coagulase-positive staphylococci Coagulase-negative staphylococci Streptococcus agalactiae Streptococci other than Strep. agalactiae Coliform
Low
High
p2 .05) in low than in high herds (Table 2). Postmilking teat dip was used on a large majority of herds. Although a number of different types of teat dip and different disinfectants in the dip were used, no one type was associated with low herd sec. A majority of herds used a single service towel to clean udders. Approximately 30% did not use single service RESULTS AND DISCUSSION towels to clean udders. It should not be inferred Over 250 variables were examined with re- that a common herd cloth was used in all of spect to their ability to classify low and high these herds; rather, it was observed that most sec herds. For the purpose of brevity, only the often a towel was shared between cows, one results of variables found to discriminate signif- side of the towel to clean each cow. The use of icantly between herd groups and those that did disinfectant in the mammary gland wash water not significantly discriminate between herd and use of milking unit backflush systems were groups but are commonly thought to have a similar between groups. The percentage of major impact on mastitis control, are presented herds where milkers wore synthetic rubber and discussed. A complete analysis and discus- gloves was greater in the low than in the high sion of all variables is in Hutton (15). The group and approached significance (Table 2), mean (± SO) milk production and bulk tank although only a small fraction of either herd sec during the year between herd visits was group used this practice. Prevalence of IMI by 9555 kg/cow (± 880) and 175,000 (± 60,000) other organisms were similar between groups. cells/ml for low sec herds and 7863 kg/cow (± It was estimated from large survey studies 1270) and 460,000 (± 176,000) cellsImi for that 25% of cows had IMI caused by contagious pathogens, S. aureus or Strep. agaJactiae high herds. (9, 28). In this study, 25.3% of the cows in the high group had contagious pathogen 1M! (Table Control of Mastitis at Milking 1). Thus, although high herds were among The only significant difference in the preva- those with the highest sec in Washington lence of intramammary infections major patho- OHI, they appear to be near average in their gens between high and low herd groups was the incidence of contagious mastitis. This, in addipathogen Staphylococcus aureus, as identified tion to the fact that the prevalence of noncontaas coagulase-positive staphylococci. Eight gious mastitis was similar between low and times more cows had Staphylococcus aureus high groups, would support the contention that intramammary injections (IMI) in high than in herds in the high mastitis group were near low herds (Table 1). Thus, it would be expected average in their control of mastitis. that differences in milking time hygiene pracCows with clinical mastitis were milked last tices would exist between herd groups. Howev- in approximately half of the low sec herds as er, none of the milking time hygiene practices, contrasted to only 13% of the high sec herds as recommended (6), were practiced more fre- (Table 2). Milking cows with IMI last has often Jownal of Dairy Science Vol. 73. No.4, 1990
1139
OUR INDUSTRY TODAY
Percentage of herd group utilizing practice pi
Variable
Low
Use of synthetic rubber gloves by milkers Cow milking order Cows with cI inical mastitis milked last Highest producing cows milked first Use of postmilking teat dip Use of single service towels to dry mammary glands Use of predip disinfection Use of disinfectant in wash water Use of between cow milking unit disinfection
18
3
.09
46 43 93 70 29 32 57
13 9 79 74
