Antimicrobial substances and chick growth promotion: Comparative studies on selected compoundsin vitroandin vivo

Growth performance and immune response of two commercial broiler strains fed diets containing Lactobacillus cultures and oxytetracycline under heat stress conditions

1. Hubbard x Hubbard (HH) and Shaver x Shaver (SS) chicks given a dietary supplement of either 50 mg/kg oxytetracycline (OTC) or 1 g/kg Lactobacillus culture (LC) were exposed to 36 +/- 1 degrees C for 3 h daily from day (d) 21 to 42. 2. Prior to heat treatment, body weight (d 21) and weight gain (d 1 to d 21) of OTC and LC birds were greater than those fed the control diet. Chicks given LC had the best food efficiency followed by OTC and control birds during d 1 to d 21. Body weight (d 1 and d 21) and weight gain (d 1 to d 21) were greater for HH tlhan SS chicks. 3. After 3 weeks of heat exposure, birds receiving the LC diet had greater body weight and weight gain, higher food intake and lower food efficiency than OTC and control chicks. 4. Antibody production against Newcastle discase vaccine on d 21 was not affected by strain or diet. On d 42, while diet had negligible effect on this variable among the SS broilers, HH birds fed LC had higher antibody production than those on the control diet. 5. Neither strain nor diet had a significant effect on mortality.

Comparison of the supplemental effects of Saccharomyces cerevisiae and antibiotics in low-protein and high-fibre diets fed to broiler chickens

Two experiments were completed to compare the supplemental effects of yeast Saccharomyces cerevisiae and sub-therapeutic antibiotics in high-fibre and low-protein diets for broiler chicks. In experiment 1, yeast was added at 1.5, 3.0 and 6.0 g kg-1 while penicillin, tylosin or neoterramycin were added at 150 mg kg-1 into different batches of a high-fibre diet containing 250 g kg-1 palm kernel meal. Saccharomyces cerevisiae and antibiotics increased BW, BWG, FCR, feed intake, carcass and breast weights above the control. Small intestine weight was reduced by antibiotics, while yeast caused a lower deposition of abdominal fat. Liver weights of different treated broilers were similar. The performance indices were superior on penicillin and 3.0 g kg-1 yeast compared to other supplements evaluated. In the second experiment, 1.5 and 3.0 g kg-1 of yeast, and 0.75 mg kg-1 of procaine penicillin, zinc bacitracin and tylosin were separately added to a 180 g kg-1 crude protein diet. Performance of the chicks with additives was compared with unsupplemented negative and positive controls containing 180 and 210 g kg-1 crude protein respectively. Broilers fed with supplements had superior BW, BWG, FCR and feed intake compared to the negative control, but carcass data were similar. Dietary penicillin increased BW, BWG, feed intake more than other supplements, but yeast stimulated higher FCR. Data from both studies indicated that Saccharomyces cerevisiae comparatively increased growth and carcass weight and reduce abdominal fat, therefore, it can serve as a natural substitute for antibiotics in broiler diet.

Antimicrobials and competitive exclusion

The compatibility of commonly used antimicrobial feed additives with CE treatment are examined. It appears that additives permitted in the U.K. are without effect on CE, with the possible exception of avoparcin. However, a sharp difference has been found with the effect of antimicrobials on CE treatment cultures in vitro, and the in vivo effect; and it is postulated that these differences may be accounted for by the fact that the substances may not be 'caecum available' in the bird. When effects are observed in the bird they appear to be largely due to dose variation. In the case of adult birds already infected with Salmonella, the time lapse between completion of antimicrobial treatment and the administration of Broilact will be examined; as well as the selection of appropriate antimicrobial treatment in infected birds prior to the administration of replacement microflora.

Influence of peas (Pisum sativum) as a dietary ingredient and flavomycin supplementation on the performance and intestinal microflora of broiler chicks

1. Two experiments were carried out to study the effects of diets containing various concentrations of pea meal (Pisum sativum L.), with or without flavomycin supplementation, on the performance and intestinal microflora of broiler chicks. 2. During the 7 to 28-d period, chicks fed on diets containing 300, 600 and 800 g pea meal/kg consumed more food and gained more weight than chicks receiving a maize-isolated soyabean protein control diet. The addition of flavomycin to the diets had similar effects on the performance of both the control and the pea groups. 3. Pea diets, with and without supplemental flavomycin, had little influence on the composition of intestinal microflora. The counts of enterococci in the small intestine and Clostridium perfringens and coliforms in the caeca of pea-fed chicks exceeded those of control chicks.

Effects of dietary chlortetracycline on the antimicrobial resistance of broiler faecal Streptococcaceae

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.

Effects of diet and antimicrobials on growth, feed efficiency, intestinal Clostridium perfringens, and ileal weight of broiler chicks

Five experiments were conducted to evaluate the effects of diet and antimicrobials on weight gain, feed efficiency, ileal weight, and Clostridium perfringens in the ileum of broiler chicks. In the first experiment, glucose, sucrose, and fructose were added to a semipurified diet and the results were compared with those from a practical corn and soybean meal diet. All of the diets were fed with and without bacitracin at a level of 55 ppm. Fructose resulted in the greatest depression in weight gain, followed by sucrose. Bacitracin significantly improved weight gain and feed efficiency of chicks fed the fructose, sucrose, and practical diets. Highly significant inverse correlations were obtained between ileal weight and weight gain and the number of C. perfringens in the ileum and weight gain. In other experiments bacitracin, penicillin, chlortetracycline, oxytetracycline, erythromycin, tylosin, virginiamycin, lincomycin, bambermycins, and carbadox, all at a level of 55 ppm, improved weight gain and feed efficiency and significantly reduced the weight of the ileum and the number of C. perfringens in the ileum of chicks fed the practical diet. The antibacterial agents 3-nitro-4-hydroxy-phenylarsonic acid, arsanilic acid, furazolidone, and sulfathiazole had little to no effect on the 4 parameters evaluated. Virginiamycin and lincomycin at 16.5 and 4.4 ppm, respectively, were shown to be effective. In vitro activities of the antimicrobials against C. perfringens did not directly relate to in vivo activities and the effects on growth and feed efficiency. The results of these experiments support the concept of antimicrobials as growth permittants and provide further evidence for C. perfringens as a causative bacteria for growth depression.

Effect of the antibiotic thiopeptin on Clostridium perfringens and growth and feed efficiency of broiler chicks

Experiments were conducted to determine the potential of the antibiotic thiopeptin as a growth permittant for poultry. Thiopeptin as the semipurified antibiotic and as fermentation solids demonstrated activity against Clostridium perfringens at .03 ppm based on suppression of gas production in an anaerobic tube test. Supplementing a soybean protein and sucrose-based diet with levels of 2.2, 11, and 55 ppm of thiopeptin from each of the two sources resulted in significant improvements in weight gain and feed efficiency of chicks fed the higher levels. Computed indexes for each antibiotic treatment showed that the antibiotic as fermentation solids was slightly more active than the semipurified material at the lower levels. Supplementing the soybean protein and sucrose-based diet with 1.1, 5.5, 16.5, and 55 ppm thiopeptin reduced significantly (P less than .01) the numbers of C. perfringens organisms in ileal contents of chicks. Chicks fed 5.5, 16.5, and 55 ppm thiopeptin also had significantly fewer C. perfringens organisms in the intestine than those fed 1.1 ppm. A discussion is presented of the biological responses of thiopeptin relative to the antibiotics efrotomycin and bacitracin.