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Summary

A clinical field trial was undertaken to determine the influence of an intramammary device (imd) on environmental mastitis and production. On 4 central California dairies, 200 Holstein first-lactation cows were randomly assigned to 2 groups. Cows in the treatment group were fitted with an imd, and cows in the control group were not. The incidence of clinical mastitis for the 2 groups was determined during the study period. Bacteriologic monitoring at intervals over 2 lactations (lactation 2 and through 60 days of lactation 3) was used to determine the incidence of subclinical infection. In addition, data were collected to determine whether the groups differed in milk production, butterfat production, postmilking and test-day somatic cell counts, and reproductive efficiency. Total milk production and butterfat production over the 2 lactation periods did not vary significantly between the groups. Also, the groups did not differ in calving-to-conception interval, duration of lactation, calving interval, and calving-to-first service interval. Cows with imd were significantly less likely to develop clinical mastitis (5% vs 13%) than control cows. The imd did not appear to affect subclinical infection rates (minor pathogens only) except at day 300 of lactation 2 and at day 10 of lactation 3, when prevalence was greater in the cows with imd. The minor pathogens were predominately (80%) coagulase-negative staphylococci. It was unusual to have coagulase-negative staphylococci in the same quarter at 2 consecutive samplings, prompting the speculation that during lactation, the duration of coagulase-negative staphylococci infection is short (resolves without intervention). However, new infections developed in other quarters, thus maintaining a consistent quarter prevalence throughout the lactation. The imd induced a significant increase in postmilking somatic cell count, compared with results from control cows, and test-day somatic cell count had a more modest increase in cows with imd, compared with previous studies.

Free access
in Journal of the American Veterinary Medical Association

Objective

To determine associations between subclinical Mycobacterium paratuberculosis infection and milk production, milk components, and somatic cell counts of dairy cattle.

Design

Cross-sectional epidemiologic survey.

Animals

23 dairy herds in Wisconsin containing 1,653 adult cows were studied. The herds had above average milk production and a history of bovine paratuberculosis in the herd within the previous 12 months.

Procedure

All adult cows in the herds were tested for paratuberculosis by use of an absorbed ELISA. Milk yield, fat, protein, and somatic cell count data were retrieved electronically from Dairy Herd Improvement Association records.

Results

147 ELISA-positive and 1,506 ELISA-negative cows were identified. ELISA-positive cows had a mature-equivalent milk production of 376 kg (829 lb)/lactation less than that for ELISA-negative herdmates. Significant difference was not found in lactation average percentages of fat and protein, or somatic cell count linear score. When comparing ELISA-positive and -negative cow's current mature equivalent milk with all previous lactations, significant difference was found only from the immediate-preceding lactation. When this difference was examined by parity group, significant difference was confined to cows in the second lactation.

Clinical Implications

Subclinical paratuberculosis infections, as determined by ELISA, are associated with a 4% reduction in milk yield and add to the already substantial costs of clinical M paratuberculosis infection in the dairy industry. (J Am Vet Med Assoc 1996;208:1872-1876)

Free access
in Journal of the American Veterinary Medical Association

Objective

To use an on-farm recording form to quantify the effect of specific management practices on apparent prevalence of Mycobacterium paratuberculosis in dairy cattle herds.

Design

Epidemiologic survey.

Animals

26 commercial Wisconsin dairy farms.

Procedures

An instrument was developed on the basis of literature review and expert interviews to quantify on-farm management practices associated with increased apparent prevalence of M paratuberculosis. On-farm visits were conducted to assess how specific management practices were conducted. Apparent prevalence of M paratuberculosis infection was measured for all animals > 20 months old on all farms, using a commercial ELISA. Regression analysis was used to identify management variables that were significantly associated with apparent prevalence of M paratuberculosis.

Results

Regression analysis (R 2 = 0.90) identified that high scores for environmental conditions, newborn calf care, grower calf care, bred heifer care, and manure handling were significantly associated with M paratuberculosis apparent prevalence in Wisconsin dairy herds.

Clinical Implications

Environmental conditions, newborn calf care, grower calf management, bred heifer management, and manure handling factors may serve as a prioritized checklist for instructing owners and managers where to place emphasis in changing management practices to limit M paratuberculosis prevalence. Likewise, the factors identified as having low association with apparent prevalence may be de-emphasized in control programs, allowing dairy managers to focus time and finances on more effective components of an M paratuberculosis control program. (J Am Vet Med Assoc 1996;208:1877-1881)

Free access
in Journal of the American Veterinary Medical Association