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Cows from five dairy herds were used to determine persistence of antibiotic residues in colostrum and milk following dry cow therapy. Cows were treated in all quarters at drying off with antibiotics approved for use for nonlactating cows. Antibiotics procaine penicillin G plus dihydrostreptomycin, novobiocin, cloxacillin, or cephapirin were compared with no treatment. Composite colostrum samples were collected from each cow at first milking after parturition. Samples were screened for residues by Delvotest P. Colostrum samples positive by Delvotest also were tested by Bacillus stearothermophilus disc assay. Four of 186 colostrum samples from cows treated with antibiotics at drying off were positive for residues by Delvotest. Only one was confirmed positive by disc assay following heat treatment. All colostrum samples from 48 cows not treated were negative. Samples of first marketable milk also were collected. Over 96% of milk samples from cows treated at drying off and 100% of milk samples from cows not treated were negative for residues by Delvotest. If manufacturer's recommendations are followed, antibiotic residues in colostrum and milk following dry cow therapy with products in our study should not be a significant problem.

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Salmonella strains and Escherichia coli O157:H7 were detected in 17 and 5 small ruminants in Virginia, respectively, of 287 tested. Background microflora interfered with the fecal analysis. The combination of Salmonella enzyme immunoassay (EIA) detection and xylose-lysine-deoxycholate agar isolation was satisfactory. Modifying enrichment to a 1:100 dilution enabled effective E. coli O157:H7 detection by EIA and isolation by sorbitol-MacConkey agar with cefixime-tellurite.Direct plating using selective media was found to be successful in detecting and isolating Salmonella strains and Escherichia coli O157:H7 from stools of diseased humans (8,15,18). However, an enrichment step was necessary for enhancing the detection and isolation of target pathogens when healthy cattle with possibly low levels of shedding were being evaluated (5,6,7,9,17,24). For rapid detection, enzyme immunoassays (EIA) and immunomagnetic separation systems were developed to screen bovine fecal samples before pathogen isolation by plating enriched samples (4, 30). Comments on the methods for detection and isolation of pathogens in animal feces are available (4,16,19,24,27). stated that previous cattle studies may have missed fecal pathogens and misclassified herds as negative due to the use of limitedsensitivity culture methods. Oberst et al. (19) found that current methods for recovering and identifying E. coli O157:H7 from cattle feces are inconsistent and are hindered by their inability to specifically and rapidly detect small numbers of organisms from the complex and variable matrix. Moreover, Tutenel et al. (27) suggested performing more than one E. coli O157 test on fecal samples to avoid underestimating the incidence of E. coli O157 in cattle.Small ruminants, such as sheep and goats, are potential carriers of Salmonella and E. coli O157:H7 (1,11,14,29). Although a difference between the survivals of E. coli O157:H7 bacteria in ovine and bovine manure was noted (13), specific information on the sensitivities of EIA and common plate assays for detecting and isolating these pathogens in feces of small ruminants is limited. The objectives of this study were to screen for the presence of Salmonella and E. coli O157:H7 in the feces of small ruminants by validated EIA protocols for foods and to evaluate the sensitivities of common selective agars for pathogen isolation (8,15,18,21,24).(An abstract of this study was presented at the Ninth Biennial Symposium on Minorities, the Medically Underserved & Cancer in Washington, D.C., in March 2004.) Sample collection. For the microbiological survey, feces were collected from grazing sheep and goats. The animals (with ages ranging from young to mature) were predominately meat breeds raised under forage-based systems with limited concentrate supplementation. For the inoculation study, feces were collected from 20 healthy male sheep at the Virginia State University research farm. The 20 sheep were of breeding age and were provided with high-quality alfalfa hay daily. In all experiments, fecal sample...