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Summary

Efforts to reduce the prevalence of Staphylococcus aureus intramammary infection were monitored in 3 Ohio dairy herds. Bacteriologic culturing of milk from all lactating cows in each herd was completed multiple times to identify infected cows and monitor reduction. Partial budgeting techniques were used to determine the economic outcome of the reduction program. Of particular emphasis was the economic impact of culling to maintain or achieve milk quality premium payments on the basis of bulk tank somatic cell counts. The prevalence of S aureus-infected cows was reduced in each herd. Culturing of milk from all lactating cows appeared to be an effective method to identify infected cows. Although numbers were limited, it also appeared that culturing of composite quarter samples was effective as a herd screening test to identify S aureus-infected cows. Bacteriologic culturing had a negative financial impact in all 3 herds. Using partial budgeting to assess the economic impact of the programs, it was determined that 2 herds experienced negative financial impacts as a result of an excess culling rate when compared with a 12-month baseline period prior to the initiation of the project. All herds had increased milk production per cow during the study as measured by the mature-equivalent method. However, when actual production was considered, increased milk production in each herd was not as great as that of other Ohio herds enrolled on Dairy Herd Improvement Association testing programs. Thus, each herd had a slight negative impact in revenues as a result of lower than expected increased production. Two herds received milk quality premiums. Although quality premiums were as great as $70 per cow per year, excess culling costs resulted in a negative net financial impact during the first 2 full years of the project in 1 herd and the first full year of the other herd that received a quality premium. Overall results of this study suggest that although quality premiums may be substantial, excessive culling is expensive, particularly in the short run.

Free access
in Journal of the American Veterinary Medical Association

Summary

A telephone survey was conducted of 50 randomly selected Ohio-licensed veterinarians engaged in dairy practice. The survey's purpose was to determine the extent of mastitis control services offered by practitioners and to assess their utilization of milk somatic cell count (scc) data on individual cows available from the Dairy Herd Improvement Association (DHIA). During the preceding year, 96% (48/50) of practitioners surveyed had performed bacteriologic culture of milk samples. Practitioners were twice as likely to have performed culture on milk from mastitic cows that failed to respond to treatment as they were to have performed culture for purposes of identifying pathogen trends within a herd. Veterinarians in predominantly dairy practices were more likely to have completed bacteriologic examination of milk in their own laboratories than were veterinarians who were engaged in <50% dairy practice (P = 0.016). Most veterinarians (83%) reported that coagulase test results were available or that Staphylococcus aureus was differentiated from other staphylococcal species. Streptococcus agalactiae was not differentiated from other streptococcal species by 35% of practitioners surveyed.

For veterinarians with clients enrolled in the dhia, 91% (43/47) reported looking at, discussing, or otherwise using the dhia records. Eighty-one percent (35/43) of veterinarians who had clients using services from the dhia reported that clients also received individual cow milk scc results. Veterinarians engaged in predominantly dairy practice expressed a greater familiarity with the linear score method of scc reporting than did veterinarians whose practices were <50% dairy (P = 0.085); however, both groups reported a preference for raw scc data. Veterinarian response regarding potential use of dhia scc data was compared with that obtained in a companion survey of Ohio dairy producers. Veterinarians were more likely than producers to consider use of scc from individual cows to select cows for culture and to establish a milking order. Although several results of our survey indicated current high veterinary involvement in mastitis control and dhia record utilization, other trends supported concerns regarding the future of veterinarian involvement in food animal health management.

Free access
in Journal of the American Veterinary Medical Association

Summary:

The association of abnormal uterine discharge with the development of intramammary infection (imi) was studied in 62 multiparous Holstein cows during the nonlactating period and from lactation days 3 through 30. Duplicate milk samples were obtained from each mammary gland at approximately day 30 of the nonlactating period. Milk samples for bacteriologic culture also were obtained from each gland from all cows at the end of the previous lactation, at parturition, and on a minimum of 7 additional dates during the first 30 days of lactation. Beginning after parturition and continuing once weekly for 4 weeks, each cow was examined, using a vaginal speculum to visually estimate the quantity of abnormal uterine discharge in the vagina. Additionally, uterine swab specimens were obtained for aerobic bacteriologic culture. Cows were allotted to groups on the basis of the maximal amount of abnormal uterine discharge observed at any 1 of the 4 examinations. Cows in group 1 had normal discharge or < 30 ml of abnormal discharge; in group 2, ≥ 30 ml of abnormal discharge, observed only on examination by vaginal speculum; and in group 3, ≥ 30 ml of abnormal discharge visible externally. A difference was not detected in the development of new imi in the nonlactating period between cows that subsequently developed uterine discharge and those that did not. Although significant differences were not found, a tendency for lactating cows with abnormal uterine discharge to be at increased risk for developing new imi was observed. Direct associations were not found between aerobic bacterial species isolated from the uterus and species isolated from glands with newly developed imi during lactation. This lack of association indicated that development of imi in lactation was not likely a direct result of teat-end exposure to bacteria originating from the uterus.

Free access
in Journal of the American Veterinary Medical Association

Objective

To determine prevalence of lesions associated with subclinical laminitis in first-lactation Holstein cows during early lactation and pregnant Holstein heifers during late gestation in herds with high milk production.

Design

Cross-sectional study.

Animals

203 cattle in 13 herds.

Procedure

Cattle were placed in lateral recumbency to allow visual examination and photography of their hooves. Claws on a forelimb and hind limb were examined on all cattle. Observable categories of lesions considered to be associated with subclinical laminitis in our study included yellow waxy discoloration of the sole, hemorrhage of the sole, separation of the white line, and erosion of the heel.

Results

Lesions in at least 1 of the categories were found in all herds. Lesions in all categories were found in 11 of 13 herds. Among claws, hemorrhage of the sole was observed most frequently in the lateral claw of the hoof of the hind limb. When days in milk was treated as a covariate, significant (P < 0.01) differences were detected in the prevalence of lesions between herds.

Clinical Implications

Because the prevalence of lesions differed significantly among herds, it is logical to believe that causative factors and corrective measures also may have differed among herds. (J Am Vet Med Assoc 1996;208:1445-1451)

Free access
in Journal of the American Veterinary Medical Association

Abstract

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. (Am J Vet Res 2000;61:1092–1098)

Full access
in American Journal of Veterinary Research

Summary

In vitro transferability of pemcillm. strepiomycin, tetracycline, and erythromycin resistance from coagulase-negative staphylococci to Staphylococcus aureus and among the former species of bovine mammary gland origin was examined by bacterial mating on filters and by mixed-culture matings in broth and in skim milk. One hundred twenty-six (42 each on filter, in broth, and in skim milk) matings were performed among 37 isolates of different Staphylococcus species. Transfer of resistance to penicillin, tetracycline, or erythromycin was not detected. Of 51 matings performed to determine streptomycin-resistance transfer, 9 (3 each on filters, in broth, and skim milk) were successful. Nine strains representing 3 species of coagulase-negative staphylococci were tested as prospective donors of streptomycin resistance. Of these, 2 strains could transfer streptomycin resistance. A double-resistant donor, Shominis, not only transferred its streptomycin resistance to an S chromogenes strain lacking resistance, but also to an S aureus strain already carrying penicillin and tetracycline resistance. The transfer of streptomycin resistance from the donor S hominis, harboring 2 plasmids, to a plasmidless S chromogenes recipient strain was associated with apparent acquisition of the smaller plasmid of the donor by the recipient. The single-resistant donor, S epidermidis 681A, transferred streptomycin resistance to a tetracycline-resistant. S aureus recipient. This strain however failed to transfer its streptomycin resistance to another S aureus, 2 S hyicus, and 1 S xylosus recipient. Frequency of transfer of streptomycin resistance ranged from 1.1 × 10−5 to 1 × 10−4. When transfer of resistance was successful, attempts were made to characterize the transfer process. Conjugation appeared to be the mode of streptomycin-resistance transfer. Transfer of resistance between staphylococci of bovine mammary gland origin appears to be fairly uncommon. However, in view of the limitations of the procedures used, additional in vitro and in vivo work is needed to further assess the role of coagulase-negative staphylococci in dissemination of antibiotic resistance.

Free access
in American Journal of Veterinary Research

Summary

Nine dairy herds (mean size, 149 cows) with bulk-tank milk somatic cell counts of < 300,000 cells/ml and > 80% of cows with Dairy Herd Improvement Association linear somatic cell counts ≤ 4 were selected for study. Each herd was monitored for 12 consecutive months. Duplicate quarter-milk specimens were collected from each cow for bacteriologic culturing at beginning of lactation, cessation of lactation, and at the time of each clinical episode of mastitis. Streptococcus agalactiae was never isolated and Staphylococcus aureus was isolated from < 1% of all quarters. There were 554 episodes of clinical mastitis. During the year of study, the incidence rate of clinical mastitis varied from 15.6 to 63.7% of cows among the 9 herds. Mean costs per cow per year in herd for mastitis prevention were: $10 for paper towels, $3 for nonlactating cow treatment, and $10 for teat disinfectants. Mean cost associated with clinical mastitis was $107/episode. Approximately 84% ($90) of the costs attributed to a clinical episode were associated with decreased milk production and nonsalable milk. Costs of medication and professional veterinary fees per clinical episode varied Significantly among the 9 herds. Three of the herds did not have a veterinarian treat a clinical episode of mastitis during the year of study even though 2 of these herds had the first and third highest incidence rates of clinical mastitis. When calculated on a per cow in herd basis, mean costs of $40/cow/year were attributed to clinical mastitis. Our findings suggest that herds that have effectively controlled mastitis caused by contagious pathogens may still have substantial economic losses as a result of clinical mastitis and that losses and even rates of clinical mastitis may vary considerably among such herds.

Free access
in Journal of the American Veterinary Medical Association