Can We Farm Poultry Without Antimicrobials?Table of Contents
AbstractIt is not presently possible to economically raise commercial broiler chickens without antimicrobials. In confining poultry, we have increased risks of disease transmission. Even though the industry is applying many preventive and control measures, such as disease eradication, biosecurity, vaccination, etc.., antimicrobials are an important part of our prevention programs. Can we ethically withdraw these antimicrobials hence exposing susceptible birds to deadly infectious agents, deprive them from a cure, and still produce a low-cost source of animal proteins ? This becomes not only an economical, but also an ethical issue. Various tools, which could potentially decrease and/or prevent antimicrobials use, are being developed but further studies are needed before commercial applications. Antimicrobial resistance is a complex question and agriculture is not the sole culprit. Limiting our intervention to this aspect of the puzzle would be very near-sighted for a problem of that magnitude. The solution to the development of antibiotic resistance lies in the better use of antimicrobials, the creation of a national antibiotic resistance surveillance program (both human and animal), a better knowledge of drug pharmacokinetics in animals, the education of health professionals, and most importantly, of the public. IntroductionThe answer to this question is easy; no. At present, it is not possible to economically raise commercial broiler chickens without antimicrobials. Recent statistics show a steady increase in meat consumption per capita (Statistics Canada). Whatever advocates for healthier, greener food are preaching, the North American consumer wants to eat meat and does eat it in ever increasing volumes. This consumer also wants a safe quality product at the best possible price. The meat and poultry industries have to answer this demand. It is a market law. Are the governments, marketing agencies, producers, pharmaceutical companies, professional groups, and consumers ready to pay the price and markedly change their habits in the name of an antibiotic-free chicken? That question remains to be answered. The problem of antibioresistance is a complex one and simply banning the use of antibiotics in food animals would be very near-sighted for a problem of that magnitude. Unfortunately it is not presently possible to raise chickens without antibiotics for various reasons. There are different approaches that have been and will be considered by the industry. The purpose of this paper is therefore to bring the audience up to date with the use of antimicrobials in poultry in Canada, and discuss possible alternatives to the use and the better use of antimicrobials. Why Can't We Raise Poultry Without Antimicrobials?Over the past decades, agriculture has markedly improved its efficiency in order to provide for the ever-increasing nutritional needs of the human population. Thirty years ago, 90 days were necessary to produce a 2.25-kg chicken, whereas the 1999 broiler chicken reaches this weight in 41 days. Theses changes were made possible because of genetic selection for growth performance, better knowledge of birds dietary needs, different management systems such as confinement rearing, and better disease control measures. In confining poultry we have optimized growth and feed conversion ratios, decreasing the need for land space as well as the support of cropland. It has been estimated that if the United States was to raise its chickens on free range, it would take the land equivalent to the state of New Jersey (Avery, 1999). Confinement comes, however, with a cost. Increased densities enhance transmission of infectious agents. Prevention then becomes critical, especially in young susceptible birds. Most infectious diseases are enzootic in that many organisms are present and circulating in the flock. Anticoccidials are the most effective way to control coccidiosis, and similarly, with bacterial infections such as necrotic enteritis, prevention is economically and medically justifiable. To illustrate the importance of prevention, broiler chicks were vaccinated at three days of age against coccidiosis during an experiment. They were fed a non-medicated diet and raised according to commercial methods. Mortality increased markedly in the non-medicated group at ten days of age, with carcasses presenting lesions of necrotic enteritis. Remaining chickens were then treated with penicillin and the problem was resolved within a few days. Total mortality was 11.8% whereas one can expect 1.5 to 2% total mortality for a 6 week-period in a commercial broiler chicken flock. (Boulianne M., personal data, 1999). We are all aware that the European Union has recently banned the use of four antibiotic feed additives (virginiamycin, tylosin, spiramycin and zinc bacitracin). Recent conversations with french veterinarians has revealed that, while these additives are indeed out of the market, people are turning to those still available, such as avilamycin in poultry. However, the perception was that the number of cases of necrotic enteritis had markedly increased since the ban, necessitating greater use of water-soluble antibiotics. As one can see, a ban on antimicrobials used for prevention would increase dependence on therapeutic antibiotics (used at higher doses), more chickens would be exposed to the suffering caused by pathogenic bacteria and economic losses to producers would be greater. This would translate into a loss of economical high quality source of animal proteins. Are our consumers ready to pay the price? Present Strategies to Reduce Disease Occurrence in PoultrySome vertically transmitted diseases of economical importance have been eradicated from commercial poultry flocks. These programs, established by the industry, have seen the disappearance of Salmonella gallinarum, Salmonella pullorum, Mycoplasma gallisepticum, Mycoplasma synovia, and Mycoplasma meleagridis in all commercial poultry flocks. Mycoplasma synovia is the only mycoplasm that we very infrequently encounter in commercial laying hens. Similarly, the Québec Federation of table egg producers has made compulsory a detection and surveillance program for Salmonella Enteritidis for all producers. Flocks testing positive are destroyed and, since the implementation of this program in 1997, there has been no reported human cases of Salmonella Enteritidis poisoning related to egg consumption in the province of Québec. Various measures are used by the poultry industry to prevent disease occurrence and enhance performance. This includes decreasing bacterial pressure in poultry houses and is accomplished in various ways. In order to avoid building up that pressure, the husbandry is all-in, all-out i.e., birds from a barn are all placed and shipped to slaughter at the same time. There is also an increasing effort to concentrate birds' movement on a farm complex within a short period of time. Once the birds are gone, the manure is taken out and the building and equipment are washed, disinfected and fumigated. This is an ideal scenario, not always respected, but at the very least Canadian poultry producers remove the old litter and replace it with fresh one, contrary to their American counterparts who practice build-up of litter. Other basics that have been widely discussed and promoted are biosecurity measures and the importance of environmental quality. While implementation of biosecurity measures do markedly vary from one facility to the other, all producers know too well the cost of a poor environment on the health of their birds. Automatization of ventilation systems have eased the work, but a constant effort is needed in order to provide not only fresh air, but also clean water, adequate ambient temperature, comfortable bedding, etc... Primary viral diseases are too often complicated and exacerbated with secondary bacterial agents. These viruses can be prevented with vaccination. This is why breeders are submitted to a whole series of vaccines administered either via injection or drinking water. Broilers are vaccinated against Marek's disease and bronchitis, two viral diseases, at the hatchery and rely on maternal antibodies for the first two-week protection. If a specific viral challenge is present on the farm, water or spray vaccination will be necessary. A vaccine can prevent bacterial diseases such as pasteurellosis, bordetellosis and erysipelas, but otherwise there is so much variation and so little cross-immunity among bacterial strains, that vaccination against colibacillosis for example, has been unsuccessful. A vaccine for coccidiosis is also available and used in breeders that have the longevity to develop immunity against this parasite. The majority of the medication in poultry is used on a preventive basis. A large number of 18-day-old commercial chickens embryos are now vaccinated in ovo and simultaneously receive an antibiotic injection (ceftiofur or gentamycin) to prevent them from developing a potential infection which could occur secondarily to the break in the egg protective barrier. Day-old chicks still vaccinated subcutaneously at the hatchery are also injected with a single dose of antibiotic (also ceftiofur or gentamycin) to prevent omphalitis. This infection occurs when there is incomplete closure of the navel followed by contact with a contaminated surface. Since chicks are pulled out from the hatchery when about 95% of them are dry, hence mature, a certain percentage of the flock is still at high risk of developing omphalitis during the first hours of their life. Poults also receive a subcutaneous injection at the hatchery for the same reason. Broiler chickens receive anticoccidials (ionophores and/or chemicals in shuttle) to prevent coccidiosis during their growth, as well as so-called growth promoters. The two most commonly used feed additives i.e., zinc bacitracin and virginiamycin, have indeed been shown to improve growth performance. However, they are also preventive measures to the occurrence of a deadly condition named necrotic enteritis in broiler chickens caused by the bacteria Clostridium perfringens. Turkey feed is also medicated with anticoccidials, but only during the first few weeks of their life. The feed of replacement pullets, breeders and laying hens can also be supplemented during critical periods with chemicals in order to prevent and treat parasitism. When there is a disease outbreak in a flock, characterized by respiratory or digestive clinical signs and/or increased mortality, birds will be treated with antibiotics. Medication is administered either via the feed or the water and doses are calculated according to the MIB specifications and/or water consumption charts. If off-label use is necessary, a veterinary prescription will be necessary (except in Quebec where a prescription is compulsory in all cases of drug use). A table listing commonly used antibiotics in poultry is enclosed (Table 1). Different Approaches and Alternatives to the Use of Antimicrobials
Antibiotics Should be Under Professional SurveillanceAntibiotics in poultry should be viewed as health management tools; tools to be used with caution and under a regulatory system. Unfortunately, most of the medication used in the country is available without professional advice and it is only when first-line therapy fails that professional aid is sought. At the moment, it is only too tempting for the practitioner to use big-gun therapy, a mentality we have to change not only with our veterinarians and veterinary students, but also with our producers. In most provinces, feed additives and antimicrobials are added to poultry feed by feed companies, according to MIB specifications. This Medicated Ingredients Brochure is written and available from the Food Production and Inspection Branch of Agriculture Canada. A specific dose is recommended by the manufacturer rather than a range of doses as in the United States. Anything exceeding MIB specifications requires a veterinary prescription. Antibiotics used for therapy are available over the counter usually in animal feed stores and, in Ontario, in LMO (livestock medicine outlets). Interestingly, this province will, in the near future, create a course and certification for producers regarding drug use. Certification might then become compulsory for drug purchase, just like for pesticide use. In the province of Québec, all medication, whether for preventive or therapeutic purposes, requires a veterinary prescription, according to a provincial veterinary drug law passed in 1985. The veterinarian, in order to write the prescription, has to prove the existence of a veterinary client relationship. Thus it is impossible to obtain medication over the counter without a veterinary prescription. Importance of Identification and Sensitivity Testing in a Surveillance SystemFirst, when suspecting an infectious disease, therapy should be started; a) once the causal agent has been identified or, b) based on clinical diagnosis, if mortality is high and spreads rapidly, not allowing for the 48 hour-delay caused by laboratory procedures. In all cases, isolation, identification and sensitivity testing (antibiogram) should be performed to insure that the right therapy has been chosen. Unfortunately, there is very little if no support available from the governments in providing easy and non-expensive access to sensitivity testing. For example, the increase in laboratory fees in Québec has resulted in a marked decrease in number of submissions for antibiograms. This trend has been mostly observed in the number of dairy submissions whereas those of swine and poultry origins have remained stable (Dr. M. Nadeau, MAPAQ, personal communication). If we want to seriously establish effective monitoring programs of the development of antibioresistance in food animals, there should be a joint federal and provincial effort at; a) standardizing laboratory procedures not only within and between veterinary labs, but also with human labs (e.g. Kirby-Bauer vs. MIC standards), and b) develop and offer a national comprehensive monitoring program including sensitivity testing of not only sick but also healthy flocks/herds. Only then will we be able to speak with solid scientific data of the surveillance and development of antibioresistance in food animals in Canada. Decreasing services to the agricultural community by closing/reorganizing diagnostic laboratories for monetary reasons, as it has been observed in some provinces, does not reflect the economical importance of this activity sector nor its impact on human health. The Right Dose for the Right PeriodSecondly, the proper dose for a proper period, should be administered. If medicating feed is apparently a simple matter of applying MIB specifications, medicating via drinking water is a different story. Doses are based on a specific concentration of antimicrobials in the drinking water to be consumed by the birds. However, water consumption is dependent of body weight, environmental temperature, feed ingredients, water quality, breed and flock health (Wages, 1993). Unfortunately, finding a water-meter in a poultry barn is a rare event, and when present, the recording of water consumption data is exceptional. Dosage is based on water consumption charts which, in the poultry industry, vary from one company to the other. Use of a proportioner is also standard in the poultry industry. This equipment delivers a certain amount of the mother solution holding the medication, to a certain amount of drinking water. Many types of proportioners are available and they can be set at various dilutions: 1:100; 1:128, 1:256, etc... Very rarely are these proportioners checked and calibrated, and furthermore, rarely are water lines flushed before and after treatments. All these variables have the potential to seriously affect adequate drug delivery. Since many antibiotics utilized in the poultry industry have mg/kg dosage labelled for used in other food animals, Wages (1993) suggested a therapeutic regimen based on that method. However, can we extrapolate doses from mammalian species to a higher metabolism species such as poultry? Theoretically, how is the right dose calculated? The strategy for pharmaceutical companies when suggesting a dose, is to verify in vitro the Minimal Inhibitory Concentration (MIC) of the drug, and choose a dose exceeding X number of times this MIC for individual therapy. The main problem with large group treatment i.e., feed and water medication, is that those inhibitory concentrations are very difficult to reach. Yet, we can clinically observe therapeutic success with these lower doses. This stresses the problem of directly inferring from an in vitro test to an in vivo situation. In the past years the government regulations have become so strict that bringing a new drug or a new use of a drug to the market has become overly expensive. Besides, according to these regulations, a pharmaceutical company has to show that a drug is safe to be used in an animal, not that it is effective in treating a certain disease. Very little is known about the pharmacokinetics of the drugs presently used in feed and water medication. At what dose, when, and for how long do we reach effective blood levels? These types of questions are without answer for that there are very few pharmacokinetic studies. Can we also use other treatment concepts? For example, could we effectively use pulse-treatment in poultry i.e., repeated high doses administered for very short periods, and reach adequate antibiotic blood levels throughout the flock? As one can see, a serious effort is needed in the field of pharmocokinetics and this will not be possible without the joint efforts of the governments, pharmaceutical companies, universities and other concerned groups. Monitoring Antibiotic UseFinally, all use of antibiotics should be carefully monitored. Accurate
records of treatment and outcome should be used to evaluate therapeutic
regimens. Valuable data could be drawn from such surveillance and
ease tracking when repetitive problems occur. Again, this will only
be possible with a concerted effort of all partners of the industry.
Litter TreatmentsOther means of decreasing or preventing use of antimicrobials include
the reduction of pathogen pressure in the environment, either via
chemical treatment, competitive exclusion, etc... In the few past
years we have seen the emergence of various litter treatment, where
chemicals are added onto the litter to decrease the pH. This lowers
the number of pathogenic bacteria, such as E. coli and
Salmonella (Terzich, 1997), and decreases ammonia level, which
makes for a better environment quality. Unfortunately, these products
are costly and their efficiency is short-lived, ideally requiring
more than one application during a broiler chicken/turkey flock. ProbioticsThe concept of competitive exclusion has been suggested as an alternative to the use of antimicrobials. Early establishment of a non-pathogenic gut microflora, the probiotics, would avoid later attachment and multiplication of pathogenic bacteria. A similar concept has also been put forward with "litter vaccines," a mixture of non-pathogenic bacteria sprayed onto the litter to compete with pathogenic ones. Very little is known however about normal litter and digestive microflora, the nature of the strains used, stability during production and storage, their attachment and persistence in their new environment, and in presence or absence of other additives. Recent venues on the market of some of these products have generated interesting data, sometimes contradictory and conflicting, and caution should still be exerted. If exposure of pathogenic bacteria to antibiotics may eventually lead to the development of antibioresistance, what is the fate of these non-pathogenic bacteria? OthersOther non-conventional feed additives, such as enzymes, organic acids,
non-digestible oligosaccharides are also being studied. For example,
dietary mannan oligosaccharides apparently stimulate the liver to
secrete mannose-binding protein, which attaches to pathogens, triggering
the immune system to attack them. Oligosaccharides have to be given
continuously at a dose that is still uncertain and are still quite
costly. All of these upcoming non-conventional feed additives are
raising the need for a deeper understanding of the microflora physiology
and interaction with its host. Alternative Therapeutic MeasuresIn term of alternative therapeutic measures, homeopathy and essential oil therapy have been used in some small french « label » chicken flocks, but there have been no scientific studies of their efficiency. Better Regulations or the Implementation of HACCPThe objectives of the Hazard Analysis Critical Control Points (HACCP) system are to minimize transfer of potential foodborne bacteria from the intestines or feces to food items. The poultry industry is adjusting to these new demands and the Chicken Farmers of Canada have recently published their program. HACCP will work and should be effective in decreasing pathogen pressure only if critical points of potential transmission are known and well defined. This is almost achieved at the slaughter level but there is still work to do at the hatchery and the barn levels. ConclusionsAgriculture and the use of antibiotics in livestock have often been singled out as being responsible for the appearance of antibiotic resistance in human pathogens. Yes, it plays a role in the selection of antibiotic-resistant bacteria in animals (Nadeau et al., 1999). And even if evidence for the crossover of resistance from animal bacteria to human strains is scarce, we cannot pretend that the problem does not exist. Antibiotic usage needs rationalization, but not to the point of being detrimental to birds' health and at the expense of poultry farmers. Agriculture is not the sole culprit. In Europe, the use of avoparcin in livestock has been blamed for the appearance of vancomycin resistant enterobacteria in humans which has resulted in its total ban. Yet, vancomycin resistance is widespread in the USA (Coque et al., 1996), where avoparcin has never been licensed for veterinary use. Audits of antibiotic prescribing habits in french office-based medical practices revealed that about 40% of the prescriptions were delivered in cases of respiratory tract infections with a presumed viral etiology, thus inappropriately, and that the majority of antibiotic prescriptions (60 to 74%) for children were underdosed (Guillemot et al., 1998). The phenomenon of antibiotic-resistant bacteria should be viewed in its whole perspective and addressed as such by the medical, veterinary and agricultural communities. All have a responsibility in ensuring that antibiotics are used responsibly. Even small animal practitioners have a role to play for that their patients are also treated with antibiotics and come in very close contact with humans. Most importantly, human patients should not expect to receive antibiotics when the causal agent is viral and compliance to the prescription should be fully respected. There is still so much to do with public education. Total ban of antibiotics in food animals is not the answer to the problem of antibioresistance; it would have serious consequences for the economics of the food industry and animal welfare. AcknowledgementsThe author wishes to thank Drs J. Del Castillo, C. Klopfenstein,
R. Gauthier, R. Ouckama, S. Stevens, S. Ritchie, V. Dédet,
for providing information and useful comments.
ReferencesAMV, FIPA, COMISA (1999). Les grandes association mondiales publient leur position officielle sur l'usage prudent des antibiotiques: dix principes de bases. Le Vétérinarius, vol 15(2):26. Anonymous (1998). EU bans four antibiotic feed additives. Vet Record, Dec 19/26: 671. Avery D.T. (1999). Should we stop using antibiotics in livestock and poultry feed? Proceedings AASP Conference. St-Louis, Mo. p. 287. Coque, T.M., J.F. Tomakayo, S.C. Ricke, P.C. Okhuysen, and B.E. Murray (1996). Vancomycin-resistant enterococci from nosocomial, community, and animal sources in the United States. Antimicrob. Agents Chemother. 40:2605. Guillemot, D., C. Carbon, F. Vauzelle-Kervroëdan, B. Balkau, P. Maison, G. Bouvenot, and E. Eschwège (1998). Inappropriateness and variability of antibiotic prescription among french office-based physicians. J. Clin. Epidemiol. 51(1):61. Hooge, D.M (1999). Antibiotics and their alternatives for poultry examined. Feedstuffs, May 17th. p. 59. Nadeau, M., H. Bergeron, G. Côté, G. Arseneault, and R. Higgins (1999). Programme québécois de surveillance de la résistance aux agents antimicrobiens des bactéries d'origine animale et alimentaire. Proceedings Agriculture's role in managing antimicrobial resistance Conference. Toronto. Statistics Canada. Catalogue no. 32-229 (1979 to 1997) Terzich, M. (1997). The effects of odium bisulfate on poultry house ammonia, litter, pH, litter pathogens and insects. Proceedings 46th Western Poultry Disease Conference, Sacramento, Ca. p.71. Wages, D.P (1993). Volumetric vs. mg/kg dosing in poultry. Proceedings Symposium on Poultry Therapeutics. Columbus, Ohio, 22.
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