Antimicrobial Growth Promoters Research Articles

The control of microbial diseases in animals: alternatives to the use of antibiotics

In animal husbandry the control and prevention of infectious diseases is of basic economic importance. The introduction of antibiotics to treat bacterial infections almost 50 years ago led to a dramatic improvement in animal production. The emergence of antibiotic resistant strains demonstrates that the treatment of bacterial infections can not rely on the use of antibiotics without some critical consideration. Special attention has been paid to the use of antibiotics in animals including antimicrobial growth promoters because these can contribute to the problems with antibiotic resistance in humans. This has strongly emphasized the need to introduce disease preventive methods. A theory and methods for the prevention of diseases is presented that is based upon the effect on the target animal population of microbial exposure, defence and immunity to infections and combinations of these. It is emphasized that antibiotics should be an integral part of other disease preventive methods and used only when other methods have failed. They should not be included in the first line of action.

Effects of the antimicrobial growth promoter tylosin on subclinical infection of pigs with Salmonella enterica serotype Typhimurium

Abstract Objective To determine whether feeding tylosin, an antimicrobial growth promoter, to pigs was associated with increased risk of infection with and excretion of Salmonella enterica serotype Typhimurium. Animals 117 healthy pigs. Procedure A commercial pelleted dry feed was given in 2 feeding trials. In trial A, 11 pigs were given feed with tylosin, 11 pigs were given feed without tylosin, and 11 pigs were given feed with tylosin before and feed without tylosin after inoculation with S Typhimurium. In trial B, 44 pigs were given feed that contained tylosin, and 44 pigs were given feed without tylosin. Three weeks after the start of each trial, pigs were orally inoculated with approximately 5 × 106 colony-forming units of S Typhimurium. Feces were examined for S Typhimurium, using semiquantitative microbiologic techniques before and for 5 or 6 weeks after inoculation. Serum antibody titers against S enterica were measured by use of ELISA. Results None of the pigs developed clinical signs of salmonellosis. However, after inoculation, S Typhimurium was isolated from feces of most pigs, and all but 2 pigs developed serum antibodies against S enterica. Significant differences were not detected between experimental and control groups in either trial. Conclusions and Clinical Relevance Results indicate that tylosin fed as an antimicrobial growth promoter to pigs may not be an important factor in promoting infection with or excretion of S enterica serotype Typhimurium. (Am J Vet Res 1999;60:1201–1206)

Use of antimicrobial growth promoters in food animals and Enterococcus faecium resistance to therapeutic antimicrobial drugs in Europe.

Supplementing animal feed with antimicrobial agents to enhance growth has been common practice for more than 30 years and is estimated to constitute more than half the total antimicrobial use worldwide. The potential public health consequences of this use have been debated; however, until recently, clear evidence of a health risk was not available. Accumulating evidence now indicates that the use of the glycopeptide avoparcin as a growth promoter has created in food animals a major reservoir of Enterococcus faecium, which contains the high level glycopeptide resistance determinant vanA, located on the Tn1546 transposon. Furthermore, glycopeptide-resistant strains, as well as resistance determinants, can be transmitted from animals to humans. Two antimicrobial classes expected to provide the future therapeutic options for treatment of infections with vancomycin-resistant enterococci have analogues among the growth promoters, and a huge animal reservoir of resistant E. faecium has already been created, posing a new public health problem.

Antibiotic usage in animals: impact on bacterial resistance and public health.

Antibiotic use whether for therapy or prevention of bacterial diseases, or as performance enhancers will result in antibiotic resistant micro-organisms, not only among pathogens but also among bacteria of the endogenous microflora of animals. The extent to which antibiotic use in animals will contribute to the antibiotic resistance in humans is still under much debate. In addition to the veterinary use of antibiotics, the use of these agents as antimicrobial growth promoters (AGP) greatly influences the prevalence of resistance in animal bacteria and a poses risk factor for the emergence of antibiotic resistance in human pathogens. Antibiotic resistant bacteria such as Escherichia coli, Salmonella spp., Campylobacter spp. and enterococci from animals can colonise or infect the human population via contact (occupational exposure) or via the food chain. Moreover, resistance genes can be transferred from bacteria of animals to human pathogens in the intestinal flora of humans. In humans, the control of resistance is based on hygienic measures: prevention of cross contamination and a decrease in the usage of antibiotics. In food animals housed closely together, hygienic measures, such as prevention of oral-faecal contact, are not feasible. Therefore, diminishing the need for antibiotics is the only possible way of controlling resistance in large groups of animals. This can be achieved by improvement of animal husbandry systems, feed composition and eradication of or vaccination against infectious diseases. Moreover, abolishing the use of antibiotics as feed additives for growth promotion in animals bred as a food source for humans would decrease the use of antibiotics in animals on a worldwide scale by nearly 50%. This would not only diminish the public health risk of dissemination of resistant bacteria or resistant genes from animals to humans, but would also be of major importance in maintaining the efficacy of antibiotics in veterinary medicine.

Surveillance of antimicrobial resistance in bacteria isolated from food animals to antimicrobial growth promoters and related therapeutic agents in Denmark.

This study was conducted to describe the occurrence of acquired resistance to antimicrobials used for growth promotion among bacteria isolated from swine, cattle and poultry in Denmark. Resistance to structurally related therapeutic agents was also examined. Three categories of bacteria were tested: 1) indicator bacteria (Escherichia coli, Enterococcus faecalis, Enterococcus faecium), 2) zoonotic bacteria (Campylobacter, Salmonella, Yersinia enterocolitica), and 3) animal pathogens (E. coli, Staphylococcus aureus, coagulase-negative staphylococci (CNS), Staphylococcus hyicus, Actinobacillus pleuropneumoniae). All antimicrobials used as growth promoters in Denmark and some structurally related therapeutic agents (in brackets) were included: Avilamycin, avoparcin (vancomycin), bacitracin, carbadox, flavomycin, monensin, olaquindox, salinomycin, spiramycin (erythromycin, lincomycin), tylosin (erythromycin, lincomycin), and virginiamycin (pristinamycin). Bacterial species intrinsically resistant to an antimicrobial were not tested towards that antimicrobial. Breakpoints for growth promoters were established by population distribution of the bacteria tested. A total of 2,372 bacterial isolates collected during October 1995 to September 1996 were included in the study. Acquired resistance to all currently used growth promoting antimicrobials was found. A frequent occurrence of resistance were observed to avilamycin, avoparcin, bacitracin, flavomycin, spiramycin, tylosin and virginiamycin, whereas resistance to carbadox, monensin, olaquindox and salinomycin was less frequent. The occurrence of resistance varied by animal origin and bacterial species. The highest levels of resistance was observed among enterococci, whereas less resistance was observed among zoonotic bacteria and bacteria pathogenic to animals. The association between the occurrence of resistance and the consumption of the antimicrobial is discussed. The results show the present level of resistance to growth promoters in bacteria from food animals in Denmark. They will form the baseline for comparison with future prospective studies, thereby enabling the determination of trends over time.

Occurrence of glycopeptide resistance among Enterococcus faecium isolates from conventional and ecological poultry farms.

Occurrence of glycopeptide resistance among Enterococcus faecium isolates from conventional and ecological poultry farms.

Immunocorrection in the treatment of reproductive age women with inner genitalia

Numerous yeast products and yeast-containing feed ingredients are commercially produced, marketed, and used extensively in animal feeds around the world. Considerable research has been conducted to evaluate the potential animal growth performance and health benefits of adding yeast, yeast-derivatives, and yeast-containing ingredients into animal feeds. Active dry yeasts are commonly used solely or in combination with beneficial bacteria in probiotic products. Nutritional yeasts are used as supplements in animal feeds due to their relatively high protein and amino acid, energy, and micronutrient content compared with common feed grains and oilseed meals. Other important yeast-based products contain nutraceutical compounds present in yeast cells and cell walls (i.e. β-glucans, mannanoligosaccharides, nucleotides) that have generally been shown to improve animal growth performance and health. Specialty yeast products, such as selenium yeast (highly concentrated and bioavailable source of selenium) and Phaffia rhodozyma yeast (contains pigment that improves flesh color in salmon and trout) have specific applications in some animal feeds. Ethanol co-products such as corn distillers dried grains with solubles (DDGS) and new grains distillers dried yeast ingredients, containing more than 40% crude protein, also contain significant amounts of yeast cell and nutraceutical components. Therefore, because these yeast-based products have several nutritional and health benefits, they are becoming alternative supplements in animal feed due to restrictions on antimicrobial growth promoter use in many countries. However, it is difficult for nutritionists to differentiate the characteristics, composition, and optimal feeding applications among the diverse number of yeast-containing products available. Furthermore, most of these products contain combinations of probiotics and nutraceutical compounds with different modes of action, making it difficult to determine which compounds contribute to specific responses observed. Quantification of these nutraceutical compounds is difficult, and except for methods to determine viable yeast in dried active yeast products, there are no standard methods for determining dead yeast concentration or fast, inexpensive, and accurate methods to estimate the proportion of yeast components in various yeast-containing additives and feed ingredients. Due to the increasing popularity of using yeast-based products in animal feeds, development of analytical approaches to estimate yeast and its components in these products is greatly needed. In this review, various categories of commercially available yeast and yeast-containing additives and feed ingredients will be described along with our current knowledge about their role in improving animal growth performance, health, and proposed mechanisms of action, and challenges of quantifying yeast content and their biologically active components.

Future developments in the manipulation of growth in farm animals.

The anabolic steroid and antimicrobial growth promoters may be regarded as the first generation of animal growth promoters or performance enhancers. There is major investment in the development of new techniques to improve the efficiency of farm animal production. These techniques are reviewed under the headings of growth hormone (somatotrophin) and related techniques, immunological techniques, the beta-adrenergic agonists and the direct genetic manipulation of farm animals.

The energetic efficiency of growth

Metabolizable energy consumed by a growing animal is partitioned between heat production and gains in body tissues, principally protein and fat. The laws of growth that govern this partition are discussed. The apparent energy costs of protein and fat deposition in rats and pigs are about 53 kJ/g. Heat production is, however, related much more closely to total protein synthesis, most of which takes place in tissues other than ‘meat’. Ways and means of manipulating protein synthesis and the energy cost of growth by nutrition, anabolic agents and anti-microbial growth promoters are considered.

The energetic efficiency of growth

Abstract Metabolizable energy consumed by a growing animal is partitioned between heat production and gains in body tissues, principally protein and fat. The laws of growth that govern this partition are discussed. The apparent energy costs of protein and fat deposition in rats and pigs are about 53 kJ/g. Heat production is, however, related much more closely to total protein synthesis, most of which takes place in tissues other than ‘meat’. Ways and means of manipulating protein synthesis and the energy cost of growth by nutrition, anabolic agents and anti-microbial growth promoters are considered.