(Continued from Pago D 2) flock with chemotherapeutic drugs, it means that first-line pre vention did not work. Other con siderations such as benefit/cost ratios, antibiotic withdrawal times, and microbial antibiotic re sistance are important issues in this area. Limiting exposure to pathogens is accomplished by fol lowing the rules of biosecurity about which much has been writ ten. Cleaning and disinfection of the house and equipment, and ade quate down-time between all in-all out flocks are the adjuncts to biosecurity in this control cate gory. The general method of “decreasing stress” refers to ail of the good management practices aimed at providing the best quality environment, feed and water that the grower and flock supervisor can provide to the flock. On a day to-day basis, these items are the ones that the grower can impact the most. Lapses in those areas cannot be overcome by any of the other control methods. Vaccina tion of broilers for specific dis eases is also an extremely important, although often poorly understood method of control. Following are basic principles that apply to vaccination of broil ers. Vaccination of broilers Vaccination is a planned and controlled exposure to an antigen (infectious agent in some form) in order to stimulate proactive im munity against the particular anti gen. In broilers, most of the very early protection comes from the parent flock in the form of mater nal antibody passed to them in the egg. An important goal of the broiler breeder vaccination pro gram is to develop sufficient lev els of antibodies to particular disease agents’ that you want the progeny to be protected against early in life. This is referred to as “passive” immunity, because the broiler chick receives protection via the hen without encountering the pathogen and mounting an ac tive antibody response of its own. .While extremely important to the health of the young chick, passive immunity lasts a very short time and has poor cross protective ef fects on pathogens of multiple se rotypes. To continue protection for the rest of the life of the flock, vaccination of broilers with live vaccines is necessary' to cause an active immune response to the pathogens of concern. Timing of these vaccinations is in part based on predicted maternal antibody levels. At this point, proper han dling, dosing and application of the vaccine also becomes impor tant so that each broiler receives an effective dose in a short period of time. In broilers, we want to induce a sufficient amount of immune re sponse (usually measured by anti body titer), and we want it to last as long as the life of the broiler. Insufficient response is undesir able because the bird won’t have adequate protection for an adequate period of time. Over immunization (excessive field boosting) is wasteful because the bird develops more protection than will need in its short life span. Quality of response refers to the fact that some disease agents have multiple strains or serotypes. The type of vaccine used should con tain the appropriate strain or sero type that matches the field challenge strains or the bird may not be protected adequately. Broilers in our region are typi cally vaccinated for at least three viral diseases, Marek’s disease, Newcastle disease (NDV), and in fectious bronchitis (IBV). Some broilers are also vaccinated for in fectious bursal disease. Live Marek’s disease vaccine is injected into the incubating egg or into the newly hatched chick at the hatch ery. This should protect the bird for life against tumor formation and immunosuppresive effects. Live vaccines for NDV and IBV are given once or twice by mass application (spray or drinking wa ter) to protect against respiratory disease. They are generally applied together. Infectious bursal disease vaccines can be given once or sev eral times, depending on maternal antibody status and local chal lenge. The goal is to preserve the integrity and function of the bursa of Fabricius, a critical part of the bird’s immune system. Let’s take a closer look at the two respiratory viruses for which we vaccinate, IBV and NDV, and why they are so important. IBV and NDV can cause significant damage to the upper respiratory tract. They usually do not kill the birds, but they do allow secondary bacterial infections, especially E. coli, to flourish and cause signifi cant sickness, increased mortality, and/or condemnations, especially due to air sacculitis. In addition, certain strains of IBV damage the kidneys and can cause morbidity and mortality due to renal failure. Both IBV and NDV are highly contagious and übiquitous enough that vaccination is necessary to control them. Many broilers re ceive their first vaccination for IBV and NDV by spray cabinet at the hatchery. This vaccination can induce a good immune response, even in the presence of significant maternal antibody. However, pro tection will not last throughout the growing cycle from this day old vaccination. Therefore, if any level of challenge is present, a second application using IBV/NDV vaccine by spray or wa ter is necessary during the grow ing cycle, usually between 12-20 days of age. Immunity from this field boost should last another 5 weeks. A noticeable respiratory reaction is expected to develop a few days after vaccination, which should peak by 5 days and be gone by 8-10 days post vaccination. IBV and NDV live attenuated vaccines have the potential to cause “rolling reactions” that may be severe. A rolling reaction means that excessive and pro longed respiratory symptoms per sist in the flock, often accompanied by air sacculitis. There are multiple reasons for a rolling reaction to occur, but often improper vaccination technique is involved. To prevent these reac tions, all broilers in the house should receive an effective dose of vaccine m a short period of time. If some birds, but not all, drink the vaccine water or inhale the vaccine spray, they then propagate and shed viruses which pass to the next subset of birds, which in turn, shed to other birds, etc. There is evidence that these at tenuated live vaccine viruses may Wildlife Tops Concern At Annual Pesticide Conference CHESWOLD. Del. The Delaware Department of Agricul ture, (DDA) jointly sponsored the Bth Annual Delaware Pesticide Conference in cooperation with the University of Delaware Co operative Extension. Two hundred and forty-two people attended the conference Jan. 26 at the Delaware State Troopers Association Social Hall in Cheswold, Del. The morning sessions of this year’s conference focused on maintaining wildlife diversity and habitat and incidents involving in tentional and unintentional pesti cide misuse. The afternoon ses sion focused on the practical steps that an applicator can take to pro tect wildlife. Speakers at the event included Jack Tarburton, Delaware secre ary of agriculture, Dr. Pam Plot kin, assistant professor of wildlife conservation. University of Dela- become more virulent upon re peated passage in the flock, and may then cause a degree of disease that the vaccine was designed to protect against. Therefore, ensur ing adequate exposure of every bird to the fresh vaccine is para mount when vaccinating for these respiratory viruses. Strict attention to the details of biosecurity, environment and feed and water management, and vaccination will pay dividends to the broiler grower. Quality care is the key to protecting broiler health and turning out a quality product. PHONE: 717-626-1164 or 717-394-3047 PAX 717-733-6058 Mon,, Tuea.. Wed., Fri. 8 AM to 5 PM; Thurs. 7 AM to 5 PM ■ M CONSTRUCTION EQUIPMENT 10' snow plow w/trame and electric hydraulic pump, $l,lOO 080. (215)654-9237. 1970 Case 680 E backhoe, extend-ahoe, new tires, full cab, good condition, $ll,BOO 080. (610)847-8704. 1976 380 Timber Jack log akidder, also 1989 Morbark 12* hand tad chipper, both in VG condition. (717)769-7603. 1980 Gradall type excava tor, Detroit diesel up and down, 2-buckets, good condition, $ll,OOO. 610-562-5186 1983 Case 580 SE bock hoe, good tires, has plumb ing for braker, $13,500. (717)274-3306. 1984 JD 544 C, cab. bucket/forks, excellent condition, $32,000. 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