<OL> <LI> Determine prevalence of Salmonella and MDR Salmonella in dairy calves (1 to 60 d of age) fed pasteurized or non-pasteurized waste-milk. <LI> Determine if waste-milk pasteurization influences Salmonella prevalence in older animals (6-, 12-, and 24-month-old heifers) and overall farm prevalence (to include lactating and dry cows), including MDR Salmonella. <LI> Examine waste-milk (pasteurized and non-pasteurized) for: a) Salmonella; b) Antibiotic residues; and c) Generic microbial population. <LI> Evaluate and compare antimicrobial efficacy of antibiotic residues in pasteurized and non-pasteurized waste-milk (if residues present). <LI> Compare commensal bacterial populations and gastrointestinal ecology of calves fed pasteurized and non-pasteurized waste-milk.
Approach: This research will be conducted in collaboration with multiple large commercial dairies in the southwestern United States. The majority of these dairies have been sampled previously and found to have a high incidence of cattle shedding Salmonella. Two regions with a high concentration of dairy cattle will be selected (southwestern NM and west Texas/eastern NM). Cattle on these dairies are housed and managed similarly and will be selected for inclusion in the study on the basis that they utilize waste-milk as their primary source of feed for newborn calves. One-half of the sampled dairies will pasteurize waste-milk prior to calf feeding and have used this method for at least six months. Eight dairies will be enrolled in the study, four from each region, two of which pasteurize their waste-milk. Sixty fecal samples will be collected from each of the following groups of cattle on each farm: hutch calves, 6-month-old heifers, 12-month-old heifers, 24-month-old heifers, and lactating cows (approx. 150 DIM). Thirty head of dry cows will also be sampled on each farm. Freshly voided fecal pats free of contamination will be collected in sterile palpation sleeves and cultured as described below. Multiple waste-milk samples from each farm will also be collected (before and after pasteurization on those farms employing pasteurization) for evaluation.