Management of poultry disease in large, commercially farmed flocks

Transcription

1 Vet Times The website for the veterinary profession Management of poultry disease in large, commercially farmed flocks Author : Wojciech Roman Idzinski Categories : Vets Date : May 24, 2010 Wojciech Roman Idzinski discusses the major points to consider when dealing with poultry disease among flocks, including environment, biosecurity, health plans, laboratory testing and drug administration POULTRY production in a contemporary, competitive market imposes high demands and expectation on both the poultry producer and veterinary surgeon. Very narrow production margins require a cost-effective approach to business. Anyone involved in the poultry business needs a twofold attitude: fulfilling needs of a particular production group of birds for example, broilers, layers and turkeys and, secondly, satisfying the market and its economical standards. The latter has a significant impact on how we manage poultry diseases and other pathological conditions. Market requirements have a significant impact on our approach to poultry prevention and treatment. Veterinarians need to apply a business-like approach to any commercial flock of birds (broilers, turkey growers or commercial layers) without welfare compromise of the birds. This approach is generally different to the one we exercise when dealing with small animals. As commercial birds and eggs are destined for human consumption, treatment choice is usually dictated by a remedy s effectiveness against bacteria in vitro and, more importantly, by the withdrawal period and general profitability. 1 / 7

2 A poultry flock should be perceived as one group of birds an entity, and that means we do not particularly focus on an individual specimen, but rather all the birds as a whole (except, maybe, for very expensive breeding flocks). This fact allows us to make a correct diagnosis by selecting a few representatives from the whole flock and checking them at postmortem examination thus, a few sacrifices for the benefit of the rest. This is, of course, not acceptable in the case of pet birds. Successful production in poultry depends vastly on meticulously applying and observing biosecurity rules. Effective biosecurity is the cheapest and most effective way of preventing disease. Although it cannot provide a 100 per cent guarantee for disease-free production, it can significantly reduce the risk of infection. Vaccination is the second aspect of prevention and is inseparable from biosecurity. Immediate treatment, usually with antibiotics, is the last measure in tackling infectious diseases. What are the main factors that influence flock health? The following is a list of a few of the most important: environmental conditions, such as air quality and stock density; chick quality (early infections, immunity status); water quality (biological and chemical quality); feed quality; biosecurity; and vaccination programme. Biosecurity In many instances, biosecurity remains the method of choice in the battle against pathogens. Some particular infections, such as Mycoplasma gallisepticum in a reproduction flock, usually means a death sentence for the birds, as the flock cannot satisfactorily recover. More importantly, the infection is passed to progeny in the egg. How can we define biosecurity? It is a complex of all measures aimed at the protection of a poultry flock from infectious pathogens (bacteria, viruses, parasites, protozoa and fungi) and pathogen vectors (wild birds, rodents and insects). Poultry veterinarians should, therefore, actively participate in assessing the potential effectiveness of the biosecurity system and spot any lapses and weak 2 / 7

3 points on the farm. It is the most crucial preventive method. A routine veterinary visit is a good opportunity to check the general state of biosecurity. It is important to bear in mind that each poultry farm should have an individual biosecurity assessment plan according to its potential biological risk. Recognising all biosecurity threats and communicating to a client any observed deficiencies is critical. When assessing biosecurity, one should take into consideration the following: localisation of the farm (the distance to the nearest poultry sites); movement of workers and visitors (they should generally be restricted); fencing, gates and protection from wild animals; quarantine, especially in case of parent and grandparent flocks (minimum of two to five days); foot baths, shower, etc; protective clothing (compulsory on any farm); visitors book; washing and disinfecting facility for vehicles (where applicable); strict policy for poultry workers (no private poultry kept); rodent and fly control; an all-in, all-out policy; and depletion/turnaround cleaning and disinfection policy. Not all of the above precautions are practically applicable on every site and this should be carefully examined. Health planning A health plan is an integral part of disease control. It is a good basis for all health-related decisions and records. A health plan should contain detailed information and instructions concerning a particular site and should be renewed annually to reflect the current health status of the flock and recent changes applied. 3 / 7

4 Typically, a health plan should contain basic information about the type of production, number of houses on site, flock details, vaccination details, procedures in certain situations (such as increased or decreased water consumption or increased mortality), worming programmes, control of a particular pathogen (such as E coli, Pastereulla, Brachyspira), any preventive use of microbials, water sampling, Salmonella testing, vitamin use, health visits and so on. Testing Another valuable tool in poultry management is the laboratory test, which should be perceived as a supplementary aid, helping us to interpret and make the correct diagnosis. The most common and basic laboratory tests for poultry include: water tests (TVC, full profile, mineral, etc); serological tests; environmental swabs; Salmonella tests; faeces samples (coccidial oocysts and worm eggs); and feed analysis. Histology, virus isolation, electron microscopy, PCR and other tests can help us make the correct diagnosis if necessary. Vaccination, as well as biosecurity, is of the utmost importance in poultry. The main route of administering vaccines in poultry is via water or in a spray. Injectable vaccines (in ovo in the hatchery or subcutaneously/ intramuscularly) are available. We should always bear in mind that poultry vaccines come in large-dose vials (the minimum is usually 1,000 or 5,000 doses), so their use in backyard or small flocks is limited. In many poultry disease textbooks we can find a vast spectrum of different diseases and pathological conditions. However, most occur infrequently, so the question that might come to our mind is: What pathological conditions are most common? Broiler chickens, as an avian production group, are characterised by having a short life span, limited physical exercise and prodigious growth rates. Therefore, certain diseases and abnormal conditions are characteristic to this particular group (for instance, ascites and skeletal pathology). Biosecurity and vaccination may have reduced the incidence of some endemic conditions, such as 4 / 7

5 Gumboro disease and Marek s disease. The most prevalent conditions in young chicks from all production groups are: omphalitis, yolk sac infection, starve-out, lung aspergillosis and early septicaemia. In older broilers we can often observe enteritis (this term comprises many conditions caused by different pathogens), coccidiosis (as separate to bacterial or viral enteritis), ascites, subclinical Gumboro disease, respiratory infections, septicaemias and femoral head necrosis. Commercial layers may suffer from E coli infections (egg peritonitis), intestinal worm infestations (especially free-range birds), enteritis (with Brachyspira as a common pathogen), viral infections (such as infectious bronchitis), histomoniasis, erysipelas and Pasteurella. Commercial turkeys can experience enteritis, haemorrhagic enteritis, coccidiosis, respiratory infections (oral rehydration therapy, Pasteurella), leg problems and so on. In free-range production, as biosecurity is compromised due to the fact birds are exposed to contact with other wild birds and their faeces certain pathogens, such as Mycoplasma, Salmonella and others, pose a real threat. Practically, there is no sure way of preventing certain infections. The approach to treating commercial flocks is somewhat different from the clinical treatment of pet animals. Efficacy dovetails in with withdrawal period and cost-effectiveness in determining the right stuff. A demonstration list of antibiotics found in a typical poultry practice and the doses for use in water are detailed below. The list is far from complete and can vary significantly. It should serve as an example only of what products might be used in poultry: enrofloxacin (Baytril, Enroxil) 1.0ml/10kg bodyweight; tylosin (Tylan) 20-40mg/kg (maximum 200mg/kg); lincomycin, spectinomycin (Linco-Spectin) mg/kg; apramycin (Apralan) 40-80mg/kg; amoxicillin (Amoxinsol, Octacillin) 20mg/kg; tiamulin (Denagard 12.5 per cent) 25mg/kg; colistin (Cofacoli) 37.5ml/ 1,000kg 5 / 7

6 tylvalosin (Aivlosin) 25mg/kg; tilmicosin (Pulmotil) 10-25mg/kg; chlortetracycline (Chlorsol 50) 20-60mg/kg; and erythromycin (Erythrocin) 25.5mg/kg. It is possible to use some of these products in feed instead of water, but take care in observing withdrawal times. On a longterm course of treatment, infeed administration is advisable. In early infections of broiler chickens or turkey poults especially associated with quite common bacterial conditions, such as yolk sac infection (YSI) or omphalitis lincomycin, spectinomycin or apramycin for the first three to five days may be considered. Fluoroquinolones should not be used preventively, but reserved for clinical cases poorly responding to other antimicrobials. Some schools do not recommend treating YSI, as it is believed infected chicks should be culled or die. However, it is likely these early bacterial infections can later develop into latent septicaemia or postponed complications (osteomyelitis). On postmortem examination, whenever possible, we should try to collect swabs from affected organs for bacteriology and sensitivity. However, the sensitivity test does not guarantee effectiveness of the treatment, as bio-availability and other kineticdynamic characteristics of antibiotics play a significant role. Farm visit Occasions where a site visit should be recommended include when the flock has an exceptional health problem, or as a routine annual visit. The aim of the latter is to assess environmental conditions and the effectiveness of biosecurity means implemented on the farm, and to expose any lapses or to spot specific clinical symptoms in birds. We should bear in mind that the practical application of such a visit as a diagnostic tool might be limited because birds, in most cases, do not show a wide range of clinical symptoms. In many instances, birds die without symptoms. Quarantine, especially in cases of high-value reproductive flocks, should also be applied. If we have to visit multiple flocks of different age groups, we should always start from the youngest, and potentially healthiest, flock. The wearing of protective clothes for example, blue disposable overalls, doublelayered overboots and face masks on site is compulsory. Treatment Four possible ways of administering medicines in poultry include: oral (water and feed), spray, topical or injection. Water medication is a faster and more efficient administration method 6 / 7

7 Powered by TCPDF ( compared to feed treatment. The latter may be considered in chronic cases or when a prolonged course is required. The accurate timing of medication is also significant. The most accurate method of calculating daily intake of a particular antibiotic is based on the live bodyweight of birds. Dosage calculation based on water consumption is acceptable, but less accurate. In cases of decreased water intake, our calculations may be incorrect. The author always prefers the live bodyweight method. Remember that critically ill birds do not benefit from water medication as they do not get a therapeutic dose. Therefore, some mortality is inevitable in the first days of treatment. We can easily calculate the required daily dose of a particular medicine by multiplying the number of birds by the average bodyweight and recommended dosage. Some medicines do not dissolve easily in water, so the piping system or nipple drinkers may get blocked. Monitoring the water usage during treatment is, therefore, paramount. Pulse or continuouspattern dosing can be applied. Of course, in cases of expensive birds (for instance, breeding grandparent flocks), individual treatment (injections) may be considered. We should ensure the water used for medication, especially vaccination, is of good chemical and biological quality. As time passes, water tends to become microbiologically contaminated in any piping system, so regular tests are strongly recommended. Simple total viable colonies or fullprofile water tests may give a valuable indication of its quality. The aim of this article was only to highlight the major points important for a veterinary surgeon caring for poultry flocks. Poultry disease management starts from effective biosecurity. Veterinary care of poultry comprises a comprehensive approach, including constant cooperation with the client and correct diagnosis based on postmortem examination, laboratory auxiliary tests and site visits. Treatment is, therefore, important, but it is only one of many components necessary for successful veterinary care. 7 / 7