The Use of a Vaccine to Control Necrotic Enteritis in Broilers in Western Canada

Transcription

1 The Use of a Vaccine to Control Necrotic Enteritis in Broilers in Western Canada N. AMBROSE 1* Director of Veterinary Services, Sunrise Farms, A Avenue, Surrey, BC, V3W 1C9, Canada *Corresponding author: dr.ambrose@telus.net Necrotic enteritis (NE), caused by Clostridium perfringens bacteria, can be a devasting disease of broiler chickens resulting in high mortality, reduced feed intake and weight gain, and reduced profitability of a flock. Pathology is due to the potent exotoxins produced as C. perfringens grows in the intestine of rapidly-growing broilers. The problem is particularly difficult to control when wheat-based rations are fed to broiler chickens, despite the use of in-feed antibacterial medication and iophore anticoccidials. A vel approach to the control of NE losses has been developed: passive immunity to the C. perfringens Type A alpha toxin, induced by vaccination of parent flocks with a toxoid vaccine. On-going field trials in Western Canada are examining the ability of passive immunity to replace or augment in-feed antibacterial medication when broilers are fed a wheat-based diet. Broiler flocks composed of the progeny of parent flocks vaccinated with the C. perfringens toxoid are compared under rmal field growout conditions to control flocks from parents that were t vaccinated with the vel vaccine. Performance (mortality, weight, feed conversion, condemnation) of test flocks using vaccination for coccidiosis control will be compared to historical performance of the same farms. Performance of test flocks using infeed anticoccidials and antibacterials will be compared to concurrent control flocks. Results to date will be presented and discussed. Keywords: necrotic enteritis; broilers; vaccination; wheat Introduction Commercial production of broiler chicken meat without the aid of antibiotics, including iophore anticoccidials, is a goal of this Canadian poultry processor. The first step in this process is learning to produce broilers using a live coccidiosis vaccine in lieu of an in-feed anticoccidial program. Wheat-based rations predominate in western Canada, enhancing the susceptibility of broilers grown in this region to enteric pathogens such as Clostridium perfringens. C. perfringens Type A and Type C have been associated with the clinical disease, necrotic enteritis. Necrotic enteritis is characterized by sudden death of well-fleshed birds with fibrinecrotic lesions of the intestinal mucosa. These lesions are caused by biologically active substances produced by C.perfringens Type A and C, including alpha toxin and beta 2 toxin, rather than by the growth of the bacteria itself. Six sequential field trials at a registered commercial broiler farm in British Columbia, Canada evaluated production performance parameters of broilers vaccinated with a live coccidiosis vaccine together with recommended levels of in-feed antibiotics for the control of necrotic enteritis. Each of the vaccinated flocks experienced elevated mortality due to necrotic enteritis at two specific time periods corresponding to peaks in oocyst shedding from the live coccidiosis

2 vaccine. Recent field trials have added an additional layer of protection against Clostridium perfringens: passive immunity against the C. perfringens toxin. Broilers placed on the same farm in April and June 26 were the progeny of breeders vaccinated with a vel C. perfringens Type A alpha toxoid. Passive immunity against the alpha toxin of C.perfringens Type A was successfully used to augment protection of the broilers against necrotic enteritis in the preliminary field trial. Materials and Methods A registered commercial broiler farm in British Columbia, Canada grew six consecutive cycles of approximately 3, mixed sex broilers in two barns on a coccidiosis vaccine and medicated feed program in 25. These first six flocks are considered the control flocks. The control flocks were vaccinated with a n-attenuated, live sporulated oocyst coccidiosis vaccine containing E. acervulina, E. mivati, E. maxima and E. tenella (Coccivac-B, Schering-Plough Animal Health Corporation, Millsboro, DE, USA), and fed a regular medicated broiler ration. The base ration was formulated from wheat, and the feed medication was rotated per the routine practice of the feed company (Table 1A). The breeds used for the six test flocks were Ross 38 or Hubbard FF. A second series of production cycles began in March 26 (the Clostridium toxoid test flocks). Again, flocks were vaccinated with Coccivac-B, together with a medicated feed program (Table 1B). The broilers in the second series of trials, however, were progeny of breeder flocks vaccinated with a pre-licensing serial of a Clostridium perfringens Type A alpha toxoid (Netvax, Schering-Plough Animal Health Corporation). Breeder flocks were initially vaccinated with the alpha toxoid at 1 weeks and again at 17 weeks of age, prior to the onset of egg production. The breed used for these test flocks was Ross 78. The flock size in the second series of trials is 24 mixed sex broilers in a single 2-story barn: the marketing system in British Columbia dictates the number of birds placed per cycle and there is a contract in place with the processor that determines at what age birds will go to market. The coccidiosis vaccine was administered to each test and control flock at one day of age according to the manufacturer s instructions using a Spraycox (Schering Plough Animal Health Corporation) spray cabinet. Chicks were then delivered to the farm within 4 hours of vaccination and brooded and grown under rmal accepted husbandry practices. The broiler feed program was that of a regular wheat-based medicated diet formulated to meet the dietary specifications of a broiler grown in British Columbia. Wheat is a seed grain kwn to increase the viscosity of gut contents and slow intestinal passage in broilers creating an environment suitable for the proliferation of enteric pathogens such as Clostridium perfringens Type A which has been demonstrated to cause necrotic enteritis. The control flocks used the coccidiosis vaccine in lieu of anticoccidials for the first three cycles. However, in the next three production cycles, salimycin ( Bio Agri Mix, Mitchell, Ontario), a recognized feed anticoccidial, was added between 17 and 27 days of age in an attempt to control the necrotic enteritis mortality that had been experienced in the first three cycles (Table 1A and Figure 1). The addition of salimycin did t appear to prevent or reduce the incidence of necrotic enteritis. No salimycin was used in the ration of the Clostridium toxoid test flocks. During the growing cycle of all flocks in each trial series, birds were walked twice a day and mortality was collected. Dead birds were divided into four groups based on gross morphologic appearance; culls, leg abrmalities, flips, and others. Flips is a local term used to describe broilers that die of sudden death syndrome. A rule of thumb for rmal broiler mortality under the commercial setting is estimated to be.1% of the flock per day between two weeks of age and depletion. Mortality numbers were recorded and compiled into a six cycle summary

3 see Figure 1. For monitoring purposes only, mortality of unkwn subjective cause was necropsied on site for gross lesions related to coccidiosis or necrotic enteritis. Table 1 A and B Experimental Flock Placements Coccidiosis Control Program Flock Nonattenuated coccidiosis vaccine salimycin Starter Feed medications and level Grower A. Controls: six-flock sequence (25) yes bacitracin 1 bacitracin 1 a 11 mg/kg 11 mg/kg yes bacitracin 1 b 11 mg/kg yes c yes grower d ration salimycin 3 6 mg/kg yes grower e ration salimycin 3 6 mg/kg yes grower f ration salimycin 3 6 mg/kg B. Clostridium toxoid test flocks: 2-flock sequence 26 g yes bacitracin 1 bacitracin 1 11 mg/kg 55 mg/kg h yes bacitracin 1 bacitracin 1 55 mg/kg 55 mg/kg 1 BMD (bacitracin methylene disalicylate) 2 Stafac 3 Bio-Cox Results and Discussion Finisher bacitracin 1 11 mg/kg bacitracin 1 55 mg/kg bacitracin 1 55 mg/kg Withdrawal Progeny of toxoidvaccinated hens yes yes The first six consecutive production cycles ( controls ) experienced two consistent peaks in mortality attributable to necrotic enteritis, one at approximately 19 days of age, and a second peak at approximately 27 days of age (Figure 1). The first peak was generally a combination of flips and necrotic enteritis, as determined by post-mortem exam. The second peak was attributable to necrotic enteritis alone. The mortality pattern was consistent for all six flocks, and occurred regardless of the addition of salimycin to the ration. These two peaks in necrotic enteritis mortality roughly correspond to the expected peaks in coccidial cycling from the n-attenuated vaccine (Figure 2), as reported by the vaccine manufacturer. It is likely that the combination of intestinal viscosity associated with the wheat ration and the mucosal disruption caused by the rmal cycling of the coccidial vaccine allowed the overgrowth of C. perfringens, triggering the necrotic enteritis events. There was evidence of coccidial lesions outside of the rmal expected levels for the coccidial vaccine: the vaccine appeared to be performing rmally, with adequate development of immunity to coccidiosis. The in-feed medications (bacitracin, virginiamycin and salimycin) provided inadequate protection against necrotic enteritis outbreaks when the n-attenuated coccidiosis vaccine was

4 used in concert with a wheat-based ration. Production performance parameters for these six test flocks were below industry standards (Table 2) NE only 7 No. of Birds NE + flips AGE (Days) Normal mortality Flock A Flock B Flock C Flock D-sal Flock E-sal Flock F-sal Figure 1 Mortality Patterns: rmal flocks vs. test flocks with or without salimycin Oocysts per gram Day 1 Day 3 Day 5 Day 7 Day 9 Day 11 Vaccine oocysts per gram Day 13 Day 15 Day 17 Day 19 Day 21 Day 23 Day 25 Day 27 Day29 Day 31 Day 33 Day 35 Mortality (number of birds) Figure 2 Coccidial vaccine cycling (OPG) vs. Control 6-flock average mortality: corresponding peaks The production cycle placed in April 26 was housed in the same barn as the previous test flocks. This flock was also vaccinated with the n-attenuated coccidial vaccine at one day of age via spray cabinet. The flock was fed a wheat-based commercial ration medicated with bacitracin (Table 1B). The key difference was that the broiler chicks were the progeny of a Ross 78 breeder flock that had been vaccinated with a pre-licensing serial of a C. perfringens Type A Number of birds

5 alpha toxoid to induce high levels of maternal antibody against the C. perfringens alpha toxin. This invative approach to necrotic enteritis control uses antibody against the alpha toxin to prevent or reduce the severity of tissue damage caused by the toxin during C. perfringens blooms in the intestine of rapidly growing broiler chickens. The first production cycle was completed on 1 June, 26. Mortality was typically elevated at 17 to 2 days due to flips (Figure 3), but post-mortem examination of mortality, culls and random birds revealed evidence of necrotic enteritis (Figure 3). The growth rate of this Ross 78 flock was greater than the Ross 38 or Hubbard flocks, and the percentage of flips was correspondingly higher. Post-mortem examination confirmed that the coccidiosis vaccine was cycling as expected, based upon acceptable lesion standards provided by the manufacturer. The flock was severely heat-stressed at 27 days of age due to unseasonably high environmental temperatures. Post-mortem examination of 28-day old birds revealed that the flock had been off-feed during the heat episode, with gizzards impacted with litter and evidence of mild sloughing of the intestinal mucosa typical of heat-stressed birds. Nevertheless, there was evidence of necrotic enteritis in random birds, culls or mortality upon post-mortem examination. Post-mortem examination also verified continued cycling of the coccidiosis vaccine at acceptable standards per the manufacturer No. of Birds AGE (Days) Company avg Test Control Figure 3 Flock Mortality Summary: Company average (anticoccidial) vs. Clostridium Toxoid Test Flock and Controls (each with live coccidiosis vaccine) Passive immunity against the C. perfringens Type A alpha toxin appeared to successfully augment in-feed medication to prevent lesions of necrotic enteritis when a n-attenuated coccidiosis vaccine was used in concert with a wheat-based ration. The Ross 78 flock achieved growth performance meeting the breed standard. No loss in performance due to coccidiosis vaccination or necrotic enteritis was detected. The second in the series of test flocks will be placed on 15 June, 26. This flock will use a reduced level of bacitracin in the starter ration. Results will be presented in the oral paper. This study has been limited by the practical aspects of testing a product under regular production conditions. The first six flocks demonstrated a consistent pattern of necrotic enteritis breaks, hence serve as a basis for comparison for the subsequent progeny of toxoid vaccinates. Based upon the observations of the initial flock, passive immunity to the C. perfringens Type A alpha toxin appears to be a viable strategy for the control of necrotic enteritis in broiler chickens.

6 Further experimentation to examine the ability of passive immunity to control necrotic enteritis with reduced levels of in-feed medication or in the absence of in-feed medication will be conducted with successive 26 flock cycles. References WAGES, D. and OPENGART, K. (23) Necrotic Enteritis. In: Disease of Poultry, 11 th ed., (eds., Saif et al.), Iowa State Press, Ames, IA: QUINN, P.J., M.E. CARTER, M.E., MARKEY, B. and CARTER, G.R. (1994) Clostridium species. In: Clinical Veterinary Micrbiology, 1 st ed. Mosby, Toronto, ON: RIDDELL, C. (1997) Acute Death Syndrome in Broiler Chickens. In Diseases of Poultry, 1 th ed. (eds., Saif et al.), Iowa State Press, Ames, IA: SCHERING-PLOUGH ANIMAL HEALTH CORP. (21) Coccivac-B Normal Reaction: Oocyst shedding pattern. Technical service bulletin #366.