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Procedures are described for determining the effects of low level antibiotic feed additives in broiler chick rations when chicks are artificially infected with Salmonella typhimurium var. copenhagen and the effectiveness of the same antibiotics used therapeutically for salmonellosis. These procedures also permit study of development of antibiotic resistant enteric flora related to antibiotic feeding and the transferability of the resistance. Measures should be taken to monitor and assure minimal extraneous bacterial contamination of eggs, chicks, feed and facilities and minimize baseline antibiotics resistance. Facilities and equipment should be fumigated extensively, chicks should be from primary breeder flocks off antibiotics for two generations, handled minimally, and fed all-vegetable protein rations. Optimum procedures for oral induction of salmonellosis with a chick-virulent strain of Salmonella typhimurium var. copenhagen are reported. Effects of low level antibiotic feeding and subsequent therapeutic level feeding of infected and control birds are measured by mortality, feed efficiency and weight gain, and microbiological analyses of fecal samples, intestinal samples and necropsied dead chicks. Gathering all data possible from all facets of the trials is imperative for ascertaining antibiotic effects.

Three replicate trials were conducted with broiler male chicks to test the therapeutic efficacy of doxycycline, chlortetracycline and lincomycin-spectinomycin in water against an artifically induced Escherichia coli infection. Mortality, lesion scores (heart, liver and air sac), and performance data were the criteria in evaluating therapeutic efficacy of these drugs. Results indicated the therapeutic efficacy of doxycycline was greater than chlortetracycline and lincomycin-spectinomycin.

An experimental chick hatcher designed to filter recycled ventilation air was tested for its effectiveness in reducing the number of viable airborne microorganisms. Chicks in a filtered hatcher and a control hatcher (no filter) were artificially contaminated with Serratia marcescens as ventilation air was recycled in the hatchers for twelve hours. The number of viable S. marcescens particles in the filtered air of the conditioning chamber was less than detectable. The number of viable airborne S. marcescens particles in the hatching chamber of the filtered hatcher indicated a reduction of greater than 90 percent over the number in the unfiltered hatcher. The filter was effective in reducing the number of airborne particles carrying viable S. marcescens organisms in the hatcher.

The intestinal microflora of a group of broilers fed a diet containing .04% sorbic acid from Days 1 through 49 of their lives was compared with broilers given a diet without the fungistat. Four broilers from each group were killed at 7, 21, 35, and 49 days, and intestinal sections of the duodenum, the lower small intestine, and both ceca were removed aseptically. Samples of the contents of the intestinal sections were analyzed microbiologically. Groups of microorganisms analyzed included total aerobes, total anaerobes, coliforms, streptococci, lactobacilli, clostridia, Bacteroides, Bifidobacterium, yeasts, and molds. Generally, there was a large variation in viable counts of microorganisms for birds of the same treatment. Of the nine groups of microorganisms analyzed the highest counts obtained (greater than 10(6)/g) were for total aerobes, total anaerobes, lactobacilli, and Bifidobacterium. Coliforms, streptococci, and clostridia showed intermediate counts (greater than 10(3)/g), while yeasts and molds and Bacteroides showed the lowest counts (greater than 10(2)/g). Total microbial numbers, in most cases and irrespective of sorbic acid treatment, were highest in the ceca, lower in the small intestine, and still lower in the duodenum. There were no major trends of microbial population changes observed in a given treatment, intestinal location, or group of organisms with age and time on feed. Inclusion of sorbic acid in the feed did not influence total aerobes, total anaerobes, lactobacilli, streptococci, Bifidobacterium, and clostridia. However, broilers on sorbic acid-containing feed had, at 49 days of age, lower coliform counts in the duodenum, lower yeast and mold counts in the ceca, and higher Bacteroides counts in the ceca.

Bambermycins and bambermycins plus roxarsone were fed to broilers in ten consecutive experiments to determine if response (measured by body weight and feed efficiency) was continuous over a long term. Bambermycins was added at 1.1 ppm (1 to 44 days) and 2.2 ppm (45 to 51 days) to both test rations. In addition, one test ration contained roxarsone (3-nitro-4-hydroxyphenylarsonic acid) at 50 ppm (1 to 44 days). Each experiment was conducted with 1,080 commercial broiler cross-run chickens. Broilers fed bambermycins and bambermycins plus roxarsone were heavier (P less than .05) than controls in every experiment. Bambermycins plus roxarsone treated broilers were heavier (P less than .05) than bambermycins treated broilers in 2 out of 10 experiments. Broilers fed bambermycins converted feed more efficiently (P less than .05) than controls in 6 of 10 experiments and were more efficient (P less than .05) than bambermycins plus roxarsone fed broilers in 1 of 10 experiments. Bambermycins plus roxarsone treated broilers were more efficient (P less than .05) than controls in 5 of 10 experiments. These findings indicate that over a long term bambermycins and bambermycins plus roxarsone consistently and significantly (P less than .05) increased broiler body weights over controls, although the addition of roxarsone was not always effective in increasing body weights or improving feed efficiency over bambermycins fed alone.

A breeder flock and a control group of progeny birds were fed antimicrobial-free rations; a second group of progeny received rations supplemented with 50 g chlortetracycline (Ctc)/ton. Effects of dietary Ctc on the distribution of species and biotypes of faecal Gram-positive cocci and their relative resistance to 12 antimicrobial agents were studied. Antimicrobial resistance (AMR) pattern diversity and modal AMR patterns were determined for bacterial species common to all three groups. Numerical taxonomic analysis placed 1321 (97%) of 1360 isolates into eight species or biotypes. The largest cluster (n = 659, 48%) was a biotype of Streptococcus faecalis. Three clusters were biotypes of Streptococcus faecium and contained 580 isolates (42%). The isolates were susceptible to ampicillin and almost uniformly resistant to methicillin, neomycin, streptomycin, sulfadiazine and tetracycline. There were 54 and 47 different AMR patterns, including 0 to 11 and 1 to 11 resistance determinants, in isolates from control and Ctc-fed birds, respectively. Modal AMR patterns for Strep. faecalis and one biotype of Strep. faecium were very similar for all three groups of birds. However, modal patterns in a second biotype of Strep. faecium varied considerably for all three groups. Interpretation of AMR pattern diversities were equivocal among biotypes from both progeny groups. The variable distribution of isolates, proportions of resistant strains, modal patterns and diversity indices among the progeny were probably due to their exposure to different environmental sources of bacteria.

Twenty broiler chickens were fed bambermycins (Flavomycin; an antibiotic produced by Streptomyces) at the rate of 3 g/ton (US) for 63 days, and 20 control birds were fed nonmedicated feed. The birds were inoculated (dosed) on the 10th and 11th feeding day with Salmonella typhimurium. The study evaluated the effects of bambermycins on Salmonella incidence, shedding, and antimicrobial resistance. Bambermycins had no effect on body weights, duration of shedding of salmonellae, number of salmonellae shed on postdosing day 3, tissue recoverability of salmonellae, and total number of resistance patterns. Bambermycins resulted in the decrease of salmonellae to be more gradual; however, both treatments were comparable at the end of the study. The majority of S typhimurium from bambermycins-treated birds maintained the original antibiogram of streptomycin, sulfadiazine, and nalidixic acid. The salmonellae isolated from the control birds were more resistant to 2 drugs (varying antibiograms). Bambermycins as a feed additive in broiler diets given at the dose level of 3 g/ton had no detrimental effects based on salmonellae shedding and antimicrobial resistance.

An experiment was conducted to evaluate antimicrobial resistance of coliforms and streptococci isolated from feces of chickens fed salinomycin. Two groups of 20 chickens were fed either a control feed or feed supplemented with 80 g/ton salinomycin. Chicken fecal coliforms and streptococci were isolated at 5, 15, 19, 22, 26, 33, 40, and 47 days of age and their resistance to 11 or 12 antibacterial agents (coliforms and streptococci, respectively) were determined in both groups of chickens. Salinomycin significantly reduced the number of coliforms resistant to sulfadiazine and reduced the number of streptococci resistant to erythromycin and lincomycin. Streptococci from birds fed salinomycin had lower minimum inhibitory concentrations for streptomycin. No streptococci isolates developed resistance to salinomycin. Coliforms from birds fed salinomycin had more (P less than .05) resistance patterns involving two, five, and six drugs. Numbers of coliforms resistant to streptomycin, ampicillin, carbenicillin, and cephalothin were greater (P less than .05) from birds fed salinomycin.

Eighty broiler chickens were randomly assigned to each of 12 chambers in a controlled environment poultry facility. Ammonia gas was injected at 0, 50, or 100 ppm from 28 to 53 days of age. All chicks, except the control pens, were innoculated with coccidia at 36 days of age. No significant differences were found in mortality, but weight gains were significantly reduced in chambers that received ammonia gas. This was probably due to the increase in severity of air sac and intestinal lesions in the ammonia pens.

Two experimental chick hatchers in which ventilation air within the hatcher was partially recirculated in a positive pressure system, one with an air filter in the system and the other without a filter, were simultaneously tested to determine effect of the filter on quantitative reduction of viable airborne microorganisms. Chicks were artificially contaminated with either Escherichia coli or Staphylococcus aureus (coagulase-positive). Air was sampled for total test bacteria per cubic foot of hatcher air. The filter effectively reduced the number of viable airborne particles contaminated with E. coli and S. aureus contributed by chicks in the hatcher.

A comparison between fogged and nonfogged hatcher air was undertaken in 4 trials to determine effects on hatcher airborne bacteria, hatch statistics, and broiler performance. Eighteen day incubated eggs were artificially contaminated with a mixed Eschericia coli and Staphylococcus aureus culture when eggs were transferred to hatchers. Fogging with a disinfectant at 12-hr intervals during the hatching period caused significant reductions in total airborne bacteria and S. aureus counts. Counts of E. coli were not significantly affected. Growth data from 150 chicks from each hatcher from each trial showed 50-day feed efficiency and 50-day male body weights were significantly improved in chicks hatched in the fogged hatcher.

Duplicate trials were conducted with male broiler chickens to evaluate virginiamycin as treatment against experimentally induced necrotic enteritis infection. Each trial consisted of seven treatments, each replicated four times, with 10 birds per replicate. Two treatments were fed control ration (noninfected control and infected control) and the five remaining treatments were fed virginiamycin at 5, 10, 15, 20, or 40 g/ton. Birds were orally dosed with 10 ml of Clostridium perfringens culture at 14 days of age. At 5 weeks of age, surviving birds were killed and necropsied to obtain lesion scores. Birds fed virginiamycin had significantly less mortality and lower intestinal lesion scores than nonmedicated birds when experimentally infected with necrotic enteritis.

Twenty broiler chickens were fed 80 g/T salinomycin, an antibiotic produced by Streptomyces albus, and 20 birds were fed a control, unmedicated feed. The birds were experimentally infected with Salmonella typhimurium. The study evaluated the effects of salinomycin on Salmonella incidence, shedding, and antimicrobial resistance. Salinomycin had no effect on body weights, length of time salmonellae were shed, number of salmonellae shed on postdosing day 3, salmonellae tissue recoverability, or on the total number of resistance patterns. Salinomycin caused the decline of salmonellae to be more gradual; however, both treatments were comparable at the end of the study. The majority of isolated from birds receiving salinomycin maintained the original S. typhimurium antibiogram of streptomycin, sulfadiazine, and nalidixic acid. The salinomycin salmonellae were more susceptible to tetracycline, amikacin, carbenicillin, gentamicin, and cephalothin. The multiple resistance patterns of eight and nine drugs tended to be more prevalent among salmonellae from control birds than salinomycin treated birds. The antibiotic salinomycin appears to be an acceptable feed additive in broilers at the level of 80 g/T based on these results of its effects on salmonellae shedding and antimicrobial resistance.

A six-week trial was conducted to determine if therapeutic use of chlortetracycline (CTC) would be affected by previous use of the same antibiotics at subtherapeutic levels in the feed. Results indicated therapeutic effect of CTC on mortality was not compromised by the previous use of the low level antibiotic.