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Biomedical subjects

H D Mercer

Publications and source records attributed to H D Mercer.

At least 37 records · Page 2Linked to original sources
PubMed1976

Herd health status of animals exposed to polybrominated biphenyls (PBB).

The health status of 16 herds of dairly cattle exposed to low levels of polybrominated bipenyl (PBB) was compared with that of 15 control herds. Milk production of the contaminated herds was not significantly changed in 1972, 1973, and 1974 and was not significantly different from that of control herds in the same years. Mortality of adult cows and calves, the percentages of cows culled from the herds because of old age and low production, disease, or sterility, and the general health conditions were similar in the two groups. Serum concentrations of calcium, glucose, and cholesterol in contaminated herds were significantly different from those of the control herds, but the relationship to PBB exposure needs further investigation.

Animal Feed↗
PubMed1976

Persistence of transferable drug resistance in the lactose-fermenting enteric flora of swine following antimicrobial feeding.

Six groups of swine (85 animals) were fed a combination of antimicrobial drugs (sulfamethazine 100 g/ton, chlortetracycline 100 g/ton and penicillin 50 g/ton). After two weeks the antimicronial drugs were removed from the diet of two groups (28 animals). These swine were compared to four groups fed the medicated diet to determine the effect of duration of treatment and degree of animal isolation on the persistence of resistance in lactose-fermenting enteric organisms. The degree of resistance to penicillin, oxytetracycline, dihydrostreptomycin and neomycin as determined by minimum inhibitory concentrations and the incidence of resistant organisms were examined during and after antibiotic feedings. Ninety-two percent or greater of all isolates tested during and after treatment had minimum inhibitory concentrations for oxytetracycline of greater than 100 mug/ml. Thirty-two weeks after cessation of dietary antibiotic, resistance to oxytetracycline and dihydrostreptomycin remained at 100% and 89% respectively. Variation in degree of contact between swine receiving medicated feed and those receiving nonmedicated feed was not sufficient to reduce the incidence of resistance to oxytetracycline or dihydrostreptomycin in all animals. Factors influencing persistence of resistant enteric organisms are discussed. Addition of the antimicrobials to the ration resulted in significantly greater weight gains for treated animals than for the controls but did not alter feed conversion.

Animal Feed↗
PubMed1976

Nonlactating-cow therapy with a formulation of penicillin and novobiocin: therapeutic and prophylactic effects.

An experimental product incorporating 500,000 IU of procaine penicillin G and 600 mg of sodium novobiocin in 2% aluminum monostearate-peanut oil gel (10-ml dose) was used to treat all quarters of 56 cows which were infected in at least 1 quarter at time of final mild-out at end of lactation. Treatment was withheld from 89 cows uninfected in all quarters. Quarter infection was determined by bacteriologic culturing of milk samples collected at the last regular milking, at intervals up to final milk-out (7 or 12 days later), at calving, and 1 week later. Clearance rates against Staphylococcus aureus, Staphylococcus epidermidis, streptococci other than Streptococcus agalactiae, and coliform bacteria in treated quarters were 83, 94, 88, and 71%, respectively. Subtraction of the spontaneous clearance rate of about 50% in untreated quarters resulted in values of 35 to 45% for drug efficacy against existing staphylococcal and streptococcal infections. Prophylactic efficacy was examined. In cows entering the true nonlactating period with 1 or more quarters infected, new infection rates across the period aming quarters uninfected at the beginning were 36.0% among untreated cows and 6.3% among treated cows (P less than 0.005). The comparable rates for cows entering the nonlactating period uninfected in all quarters were 5.7 and 0%. Staphylococcus aureus and streptococci, which comprised 38.5% of new period infections among untreated cows, were completely lacking among treated cows (P less than 0.025). Within the treated group of cows, 83.1% of infected quarters were cleared, and new infection rate in the non-lactating period was 50% less than the rate among untreated cows. Because the frequency of intramammary infection in this herd was quite low at "drying-off" (10.5% of quarters), the net effect on herd health of selective therapy of cows infected at end of lactation was a reduction in total quarter infection from 19.8 to 13.6%.

Animals↗
PubMed1976

Nonlactating-cow therapy with a formulation of penicillin and novobiocin: mammary irritation and residues.

An experimental product incorporating 500,000 IU of procaine penicillin G and 600 mg of sodium novobiocin in 2% aluminum monostearate-peanut oil gel (10-ml dose) was infused after the final milk-out at end of lactation into all 4 mammary quarters of 56 cows that were infected in at least 1 quarter. The therapeutic and prophylactic efficacies were published in the companion report. Infusion of the product in all quarters of 5 lactating cows resulted in only slight irritation. Penicillin was eliminated by the 11th milking and novobiocin by the 5th. After infusion in the dry udder, the antibiotics were no longer detectable in serous secretion after 14 days and failed to appear in urine at the earliest (7-day) sampling after administration. Neither antibiotic was detectable in the 1st postpartum milking after nonlactating periods as short as 3 weeks.

Animals↗
PubMed1975

Animal model for determining the no-effect level of an antimicrobial drug on drug resistance in the lactose-fermenting enteric flora.

Mature beagles were fed a ground-meal diet containing 0, 2, or 10 mug of oxytetracycline per g for 44 days. The 10-mug/g diet resulted in a shift from a predominantly drug-susceptible population of enteric lactose-fermenting organisms to a multiply antibiotic-resistant population which peaked at 78% resistant organisms. Since a shift to drug-resistant organisms did not occur in the group fed 2 mug/g, the level of oxytetracycline that results in increased incidence of antibiotic resistance lies between 2 and 10 mug/g in this dog model. Rats and hamsters fed diets containing oxytetracycline (10 mug/g or greater) or dihydrostreptomycin (10 mug/g), and provided suspensions of drug-susceptible Escherichia coli, did not develop a population of antibiotic-resistant organisms.

Animals↗