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Efficacy of Turkey Herpesvirus Vaccine Against Marek’s Disease in Broilers
Efficacy of Turkey Herpesvirus Vaccine Against Marek's Disease in Broilers C. S. EIDSON, 1 D. D. KING, 2 H. E. CONNELL, 2 D. P. ANDERSON 1 AND S. H. KLEVEN 1 Poultry Disease Research Center, College of Veterinary Medicine, University of Georgia, A thens, Georgia 30601 and Animal Health Division, Agricultural Research Service, U.S.D.A., Athens, Georgia 30601 (Received for publication November 8, 1972)
POULTRY SCIENCE 52: 1482-1491, 1973
INTRODUCTION
M
AREK's disease (MD) is of great economic importance to the poultry industry in the United States and, because of the economic pressures brought on by the losses due to MD, many attempts were made to control the disease by sanitation, isolation, rearing birds on eld litter, and inoculating birds with blood from turkeys or chickens. These measures were only partially successful; therefore, MD was still costing the poultry industry 200 million dollars annually. The first effective vaccine against MD was developed by Churchill et al. (1969) using a high-passage HPRS-16 strain of MD virus. These workers found that the high passage virus had lost its oncogenic 1
This project was supported in part by the National Poultry Research Foundation and through a memorandum of Understanding including the State Department of Agriculture, the Poultry Disease Research Center of the School of Veterinary Medicine, the Veterinary Science Research Division and the Animal Health Division of the Agricultural Research Service. 2 University of Georgia, College of Veterinary Medicine and Institute of Comparative Medicine, Journal Series Number 986, Athens, Georgia.
potential for chickens. More importantly, chicks of strains highly susceptible to MD gained a significant degree of protection against MD when vaccinated between 1 day and 2 weeks of age and then challenged with the virulent HPRS-16 strain of MD. Okazaki et al. (1970) using a turkey herpesvirus (HVT) isolated from turkeys by Witter et al. (1970), and Eidson and Anderson (1971) using a turkey herpesvirus isolated by Kawamura et al. (1969) found that HVT, administered intra-abdominally or subcutaneously gave protection against MD. Early in 1971 an HVT vaccine for MD was approved by the Biologies Division of the Agricultural Research Service for use in commercial flocks of breeders and pullet replacements. Since the HVT vaccine had been developed for breeders and pullet replacements, no data were available with regard to the effect of HVT on lesions in broilers at the time of processing (8-9 weeks). The vaccine had been approved on the basis of mortality and livability data of production age birds. To be economically advantageous to broiler pro-
1482
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ABSTRACT In three different broiler producing areas in Georgia, a total of 2,500,000 , broilers were vaccinated at one day of age with various doses of turkey herpesvirus (HVT) vaccine ranging from 200 to 2600 plaque forming units (PFU) per bird. Approximately 600,000 broilers reared in separate houses on the same farms served as unvaccinated controls. All groups were identified and processed separately. Very little effect on reduction of condemnations for Marek's disease was realized with doses of vaccine greater than 1000 PFU per bird. If the advantages of weight gains of vaccinated birds were not taken into consideration, 500 PFU per bird gave the best return on money invested for vaccine when the vaccine cost was $50 per thousand doses. However, when the cost of vaccine was reduced to ten dollars per 1000 doses the 1000 PFU dose was more advantageous. A dose of approximately 1000 PFU per bird also yielded a better return on money spent for the HVT vaccine because of the advantages of increased body weight and livability.
VACCINATION AGAINST MAREK'S DISEASE
ducers the dose of vaccine would have to be reduced and, in addition to death losses, development of MD lesions would have to be prevented at the time of processing. The objective of this report is to present data on broilers vaccinated with various doses of HVT. MATERIALS AND METHODS
Virus Assay. Primary chick embryo fibroblasts prepared from embryos of White Leghorn chickens were used for all titrations. Using 199 cell culture medium, 8% calf serum and 10% tryptose phosphate broth as the growth medium, 5 X 105 cells per ml. were started in 60 mm. glass petri dishes. The plates were incubated at 37°C. in a humidified atmosphere of approximately 5% C0 2 . After 18 to 24 hour incubation the chick embryo fibroblasts were used to titrate the HVT vaccine. Serial 10-fold dilutions (up to 10~6) were prepared in 199 cell culture medium with 2% calf serum. After the growth media was removed from the petri dishes, three
plates per dilution were inoculated with 1 ml. of the test material from each of the 6 dilutions. After the plates were inoculated they were rotated to give an even distribution of the inoculum. The plates were incubated at 37°C. for 30 to 60 minutes, and 4 ml. of maintenance media (199 medium with no serum) was added to each plate. After 24 hours the culture medium was removed and replaced with 199 cell culture medium (without calf serum or tryptose phosphate broth) and was changed every 2 days thereafter. Plaques were counted on the 5th or 6th day after inoculation. All plaques were counted in each of the 3 plates for the 4th, 5th or 6th dilution, and an average was taken. The number of plaques per vial was obtained by multiplying the average number of plaques by the dilution factor and the volume (ml.) of concentrated vaccine in the vial. Experimental Design. Three independent broiler integrators located in North Georgia's most concentrated areas of broiler production participated in this study. Company A's hatchery was located in Dalton and the poultry processing plant in Atlanta while the hatchery and the processing plant of Company B were located in Gainesville. Company C's hatchery was located in Royston; whereas, the processing plant was located in Greenville, South Carolina. Initially, program personnel provided proper equipment and instructed vaccination crews as to the proper handling and administration of the vaccine. The vaccinating equipment recommended is shown in Fig. 1. The equipment consisted of a magnetic stirrer and a 250 ml. bottle with a side arm at the bottom. The bottle contained a magnetic bar to the cells in suspension. A glass, automatic 2-ml. syringe with a 20 guage one-half inch needle was
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Source of HVT Vaccine. Vaccine was produced at the Poultry Disease Research Center. The HVT (FC126) isolate was obtained from Dr. William Okazaki, East Lansing, Michigan. The vaccine was prepared in cultured chick embryo fibroblasts (Eidson and Anderson, 1971). Infected monolayers were removed by trypsinization 72 hours post infection and were reconstituted to the desired dilution in 199 cell culture medium. Although the plaque forming unit (PFU) level of the diluted vaccine was not known at time of use, a sample of the vaccine was titrated at the time the vaccine was used. Two federally licensed vaccines and one state licensed vaccine were also used. All of the vaccines used in this study were titrated at the Poultry Disease Research Center.
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E I D S O N , K I N G , C O N N E L L , ANDERSON AND K L E V E N
connected to the side arm with rubber tubing. Farms selected for this study had at least two poultry houses so that one house could contain unvaccinated controls. On each farm the vaccine was administered on a complete house basis in order to eliminate any chance of mixing vaccinated and control birds. During the course of this study 2,500,000 birds were vaccinated with the H V T vaccine a t doses of 200 to 2600 P F U per bird while 600,000 birds served as non-vaccinated controls. All vaccination was done at 1 day of age. Each treatment group was identified separately as the birds were loaded and transported to the various processing plants. Program personnel accompanied the flocks to the processing plant to insure t h a t the identity of the lots was maintained. The vaccinated birds were usually the first birds to be processed t h a t day and
before the control birds were processed a complete break in the shackles of the processing line was made in order to reduce the chances of mixing the birds with other lots. Personnel of the Consumer and Marketing Service of the U.S.D.A. provided the inspection data. Records in addition to condemnation data, included body weight at time of processing and livability of the broiler flock. RESULTS
These trials were conducted to determine if less than a "breeder dose" could be used to vaccinate broiler chicks. Plaque forming units per bird close ranged from 200 to 2600. I n this study almost 3.1 million birds were utilized; however, several flocks were omitted from the data because of improper identity, lack of proper controls, sale to other processors,
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FIG. 1. Equipment used to vaccinate birds.
VACCINATION A G A I N S T M A R E K ' S D I S E A S E
I n conpanies B and C the condemnations due to M D in vaccinated birds
reached 2.0% at the 200-400 P F U level. However, the results (Fig. 5) indicate t h a t the optimum dose level of the H V T vaccine was between 500 and 1000 P F U . I n Fig. 6 an evaluation of the economics of vaccination is shown. This evaluation only took into consideration decreased condemnations at the various vaccine dosage levels. At the time this study was undertaken the cost of the vaccine (2500 P F U ) was approximately five cents per bird; whereas, at the present time the cost of the vaccine is one cent. Although t h e cost of the vaccine has changed, Fig. 6 still offers a base of comparison of cost figures. If only a reduction in condemnations is considered, a dose of approximately 500 P F U per bird is the most economically efficient level of application. I n
5.0
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200
400
600
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1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 PFU/BIRD DOSE
FIG. 2. Vaccination of broiler chicks with the HVT vaccine (company A).
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or other conditions which made the results questionable. The results of the trials of the individual companies (A, B a n d C) are shown in Figs. 2, 3, and 4, and the combined results of the trials are shown in Fig. 5. I n Fig. 2 (Company A), Fig. 3 (Company B), Fig. 4 (Company C) and Fig. 5 (Summary) the bold unbroken line shows the percent of control chickens condemned for M D on the same premises as vaccinated hatchmates. T h e number of control chickens (average for t h e trial) condemned for M D was greater than 4 percent whereas, the number of vaccinated birds (200-2600 P F U ) condemned for M D was less than one percent. !
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5.0
Q
4.0
o 3.0
2.0
1.0
200
400
600
800
1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 PFU/BIRD DOSE
FIG. 3. Vaccination of broiler chicks with the HVT vaccine (company B). this study it was found t h a t a dose of 500 P F U reduced the condemnations by 3.5 percent; whereas, the condemnations in birds vaccinated with 1000 P F U were reduced by 4 . 0 % . An analysis of the effects of H V T vaccine on body weight a n d livability m a y justify the application of higher dosages, (Figs. 7 & 8). T h e advantage of increased body weight of the average broiler vaccinated with 1000 P F U as compared to those receiving 500 P F U is approximately 0.08 pound per bird. At 12 cents per pound live weight, an increase of approximately 0.96 cents per bird was realized. T h e advantage of approximately 0.5 percent increased livability with 1000 P F U / d o s e as compared to 500 P F U / d o s e
resulted in an increased gross income of $2.50 per 1000 birds processed, or 0.25 cents per bird (Fig. 8). Table 1 summarizes the effect of the application of H V T vaccine at approximately 1000 P F U per bird. Condemnations due to M D were reduced by 4.0 percent or a savings of $20/1000 birds processed. T h e increased body weight of approximately 0.2 pound per bird added a saving of $25/1000 birds processed and the increased body weight of approximately 0.2 pound per bird gave an additional saving of $8 per 1000 birds processed. DISCUSSION Since the H V T vaccine was approved in 1971 by the Biologic Division of the
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1487
VACCINATION AGAINST MAREK'S DISEASE
5.0
4.0
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200
400
600
800
1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 PFU/BIRD DOSE
FIG. 4. Vaccination of broiler chicks with the HVT vaccine (company C).
Agricultural Research Service for use in commercial breeders and pullet replacements, the needs of the broiler industry were not satisfied because of the cost of the vaccine. Laboratory studies conducted by Okazaki et al. (1970) indicate that birds vaccinated at one day of age with 600 PFU were protected against MD when challenged with the virulent MD virus by intra-abdominal inoculation at 3 weeks of age or were challenged with the virulent MD virus by contact exposure as early as 2 weeks post vaccination. In field trials Purchase et al. (1972), using 8 different commercial breeders found that there was no apparent difference in protection against MD when birds were vaccinated
with 500, 2000, -ir 10,000 PFU per chick. Although the study by Purchase et al. (1972) indicates that less than a "breeder dose" would protect a chick against MD, many unanswered questions remained since this was a long term MD study. The question of whether a diluted dose of vaccine would protect a broiler chick against MD mortality as well as prevent MD lesions at the time of processing remained unanswered. The object of this study was to devise an MD vaccination program for the broiler industry that would be feasible economically. The three companies selected had birds in areas with histories of varying degrees of MD condemnations. As demonstrated in Fig. 2 (Company A)
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MD - Control Birds
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E I D S O N , K I N G , C O N N E L L , A N D E R S O N AND K L E V E N
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it I I I I i I I I M D - Vaccinated Birds 1.0
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400
600 800 1000 1200 1400 1600 1800 2000 2200 2400 PFU/BIRD DOSE
2600 2800
FIG. S. Summary of the broiler vaccination trials of the three companies involved in this study.
birds in one area were protected against M D by 200 P F U per bird dose; however, birds in Company B (Fig. 3) and Comp a n y C (Fig. 4) receiving 200 P F U did n o t receive the protection afforded the birds from Company A which would indicate the level of exposure to M D was apparently greater in the areas where birds from Company B and C were placed. I t is imperative t h a t each company keep accurate records on the dosage level of H V T vaccine because the level of exposure to the virulent M D virus m a y be greater in some areas t h a n others. Therefore, the dosage level of the vaccine must be varied accordingly. F r o m unpublished d a t a of field observations, it has been found t h a t the dosage level of vaccine should be increased during the winter
months, possibly because houses have less exchange of air and the level of exposure to M D is greater. At the beginning of this study the cost of the vaccine was approximately 6 cents per bird dose. As indicated by Fig. 6, 500 P F U would be more economical t h a n 1000 P F U . If the cost of 500 P F U were 1 cent and the condemnations due to M D were reduced b y 3.5 percent, a savings of $7.50 per thousand chickens processed would be realized; whereas, if 100 P F U cost 2 cents and the condemnations due to M D were reduced b y 4.0 percent then the company would save $20 per 1000 birds; however, the profit would be negated since it would cost $20 per thousand to vaccinate the birds. However, now t h a t the cost of the vaccine is approximately 1
1489
VACCINATION AGAINST MAREK'S DISEASE
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FIG. 6. The cost of the HVT vaccine at graded doses and percent decrease in condemnation that must be realized in order to pay for the vaccine. cent per "breeder dose" (approximately 3000 PFU) it is more economical to use 1000 PFU. If birds received 500 PFU costing 0.18 cents (1/6 dilution) and the condemnations were reduced by 3.5 percent then the savings would be $15.85 per 1000 birds; however, if 1000 PFU (1/3 dilution) costing 0.33 cents were used and the condemnations were reduced by 4.0 percent then the savings would be $16.70 per 1000 birds. Also Figs. 7 and 8 indicate that there is an increase of 0.08 pound per bird in body weight broilers vaccinated with 1000 PFU as compared to those receiving 500 PFU. At 12 cents per pound live weight, an increase of approximately 0.96 cents per bird can be realized. The advantage in livability of birds vaccinated with 1000 PFU was increased by 0.5 percent (0.25 cents
per bird) when compared to birds vaccinated with 500 PFU. Therefore, if birds were vaccinated with 1000 PFU costing 0.33 cents then the increased livability and increased body weight would mean a savings of 0.88 cents as compared to the advantage returned on the application of 500 PFU per bird dose. If birds receiving 1000 PFU are compared with the controls as shown in Table 2 the total increase in gross income was $53 per 1000 birds processed. If the vaccine cost of 1000 PFU were $20 per 1000 birds processed then the increase in net income was $33 per 1000 birds; however, at the present time the cost of 1000 PFU is 3.30 per 1000 birds; therefore, the increase in net income is $49.80 per 1000 birds processed rather than $33 per 1000 birds.
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«2-5 \
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EIDSON, KING, CONNELL, ANDERSON AND KLEVEN
1000
1500
2000
2500
PFU/BIRD DOSE FIG. 7. The effect of HVT vaccine on body weight of broilers as compared to unvaccinated controls of the same age.
This study indicates that the most economical dose of HVT vaccine for the broiler chicks is 1000 PFU. It was also shown that birds properly vaccinated with the HVT vaccine (1000 PFU) are not only protected from mortality due to MD. In
addition, the lesions characteristic of MD that are responsible for condemnations at the processing plant are also eliminated. ACKNOWLEDGMENT
The cooperation of the Georgia poultry
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500
VACCINATION AGAINST MAREK'S DISEASE
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TABLE 1.—The effect of the application of approximately 1000 PFU of HVT vaccine per bird Results Compared to Unvaccinated Controls
Factors Considered Condemnations for Marek's Disease Livability Body Weight
Increased Income Above Unvaccinated Controls $20/1000 birds processed' $8/1000 birds processed" $25/1000 birds processedb
4 . 0 % decrease 1.6% increase 0.2 lbs. increase
Total increase in gross income Cost of 1000 PFU
$53/1000 birds processed $20/1000 birds vaccinated
Increases in net income
$33/1000 birds processed
* Based on 1% of flock being equal to $5/1000 birds processed. Based on a 4.0 lb. bird @ 12.5 cents/lb.
b
REFERENCES Churchill, A. E., L. N. Payne and R. C. Chubb, 1969. Immunization against Marek's disease using a live attenuated virus. Nature, 221: 744747. Eidson, C. S., and D. P. Anderson, 1971. Immunization against Marek's disease. Avian Dis. 15: 68-81.
Kawamura, H., D. J. King, Jr. and D. P. Anderson, 1969. A herpesvirus isolated from kidney cell culture of normal turkeys. Avian Dis. 13: 853863. Okazaki, W., H. G. Purchase and B. R. Burmester, 1970. Protection against Marek's disease by vaccination with a herpesvirus of turkeys. Avian Dis. 14: 413-429. Purchase, H. G., W. Okazaki and B. R. Burmester, 1972. Long-term field trials with the herpesvirus of turkeys vaccine against Marek's disease. Avian Dis. 16: 57-71. Witter, R. L., K. Nazerian, H. G. Purchase and G. H. Burgoyne, 1970. Isolation from turkeys of a cell-associated herpesvirus antigenically related to Marek's disease virus. Am. J. Vet. Res. 3 1 : 525-538.
NEWS AND NOTES (Continued from page 1481) oratories Inc. in a technical service capacity for the southeastern region, with headquarters in Gainesville, Georgia. He did diagnostic laboratory work with a national company, and had field service experience throughout the eastern part of the United States. He will provide technical assistance to poultry companies on health and production problems, and will work with them in the development of poultry health programs. Dr. Anthony received a D.V.M. degree from the University of Georgia, after graduating there in agricultural economics. He later received a M.S. degree at the University of Missouri. MAAG AND EASTERBROOKS S. Frank Moore has been named President of
Maag & Easterbrooks, Inc., a biological and agricultural research, development and manufacturing company currently specializing in veterinary and poultry vaccines. Dr. T. A. Maag, Chairman of the Board, said Moore will serve as President of the parent company and three subsidiary companies with operations in Georgia and Alabama. Moore was with Cotton, Incorporated, where he was Director of Research and Technical Services. Dr. Hsi-tang Tung has been appointed Director of the Laboratory Section of Maag & Easterbrooks, Inc. He joined the company in April, 1972, and was assigned to duties in microbiology relative to quality control. In his new position, he will be respon-
(Continued on page 1509)
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industry, the Georgia Poultry Federat i o n , t h e S t a t e D e p a r t m e n t of A g r i c u l t u r e , t h e Consumer a n d M a r k e t i n g Service, t h e V e t e r i n a r y Science R e s e a r c h Division a n d t h e A n i m a l H e a l t h D i v i s i o n of t h e A g r i c u l t u r a l R e s e a r c h S e r v i c e is g r a t e f u l l y acknowledged.
POULTRY SCIENCE 52: 1482-1491, 1973
INTRODUCTION
M
AREK's disease (MD) is of great economic importance to the poultry industry in the United States and, because of the economic pressures brought on by the losses due to MD, many attempts were made to control the disease by sanitation, isolation, rearing birds on eld litter, and inoculating birds with blood from turkeys or chickens. These measures were only partially successful; therefore, MD was still costing the poultry industry 200 million dollars annually. The first effective vaccine against MD was developed by Churchill et al. (1969) using a high-passage HPRS-16 strain of MD virus. These workers found that the high passage virus had lost its oncogenic 1
This project was supported in part by the National Poultry Research Foundation and through a memorandum of Understanding including the State Department of Agriculture, the Poultry Disease Research Center of the School of Veterinary Medicine, the Veterinary Science Research Division and the Animal Health Division of the Agricultural Research Service. 2 University of Georgia, College of Veterinary Medicine and Institute of Comparative Medicine, Journal Series Number 986, Athens, Georgia.
potential for chickens. More importantly, chicks of strains highly susceptible to MD gained a significant degree of protection against MD when vaccinated between 1 day and 2 weeks of age and then challenged with the virulent HPRS-16 strain of MD. Okazaki et al. (1970) using a turkey herpesvirus (HVT) isolated from turkeys by Witter et al. (1970), and Eidson and Anderson (1971) using a turkey herpesvirus isolated by Kawamura et al. (1969) found that HVT, administered intra-abdominally or subcutaneously gave protection against MD. Early in 1971 an HVT vaccine for MD was approved by the Biologies Division of the Agricultural Research Service for use in commercial flocks of breeders and pullet replacements. Since the HVT vaccine had been developed for breeders and pullet replacements, no data were available with regard to the effect of HVT on lesions in broilers at the time of processing (8-9 weeks). The vaccine had been approved on the basis of mortality and livability data of production age birds. To be economically advantageous to broiler pro-
1482
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ABSTRACT In three different broiler producing areas in Georgia, a total of 2,500,000 , broilers were vaccinated at one day of age with various doses of turkey herpesvirus (HVT) vaccine ranging from 200 to 2600 plaque forming units (PFU) per bird. Approximately 600,000 broilers reared in separate houses on the same farms served as unvaccinated controls. All groups were identified and processed separately. Very little effect on reduction of condemnations for Marek's disease was realized with doses of vaccine greater than 1000 PFU per bird. If the advantages of weight gains of vaccinated birds were not taken into consideration, 500 PFU per bird gave the best return on money invested for vaccine when the vaccine cost was $50 per thousand doses. However, when the cost of vaccine was reduced to ten dollars per 1000 doses the 1000 PFU dose was more advantageous. A dose of approximately 1000 PFU per bird also yielded a better return on money spent for the HVT vaccine because of the advantages of increased body weight and livability.
VACCINATION AGAINST MAREK'S DISEASE
ducers the dose of vaccine would have to be reduced and, in addition to death losses, development of MD lesions would have to be prevented at the time of processing. The objective of this report is to present data on broilers vaccinated with various doses of HVT. MATERIALS AND METHODS
Virus Assay. Primary chick embryo fibroblasts prepared from embryos of White Leghorn chickens were used for all titrations. Using 199 cell culture medium, 8% calf serum and 10% tryptose phosphate broth as the growth medium, 5 X 105 cells per ml. were started in 60 mm. glass petri dishes. The plates were incubated at 37°C. in a humidified atmosphere of approximately 5% C0 2 . After 18 to 24 hour incubation the chick embryo fibroblasts were used to titrate the HVT vaccine. Serial 10-fold dilutions (up to 10~6) were prepared in 199 cell culture medium with 2% calf serum. After the growth media was removed from the petri dishes, three
plates per dilution were inoculated with 1 ml. of the test material from each of the 6 dilutions. After the plates were inoculated they were rotated to give an even distribution of the inoculum. The plates were incubated at 37°C. for 30 to 60 minutes, and 4 ml. of maintenance media (199 medium with no serum) was added to each plate. After 24 hours the culture medium was removed and replaced with 199 cell culture medium (without calf serum or tryptose phosphate broth) and was changed every 2 days thereafter. Plaques were counted on the 5th or 6th day after inoculation. All plaques were counted in each of the 3 plates for the 4th, 5th or 6th dilution, and an average was taken. The number of plaques per vial was obtained by multiplying the average number of plaques by the dilution factor and the volume (ml.) of concentrated vaccine in the vial. Experimental Design. Three independent broiler integrators located in North Georgia's most concentrated areas of broiler production participated in this study. Company A's hatchery was located in Dalton and the poultry processing plant in Atlanta while the hatchery and the processing plant of Company B were located in Gainesville. Company C's hatchery was located in Royston; whereas, the processing plant was located in Greenville, South Carolina. Initially, program personnel provided proper equipment and instructed vaccination crews as to the proper handling and administration of the vaccine. The vaccinating equipment recommended is shown in Fig. 1. The equipment consisted of a magnetic stirrer and a 250 ml. bottle with a side arm at the bottom. The bottle contained a magnetic bar to the cells in suspension. A glass, automatic 2-ml. syringe with a 20 guage one-half inch needle was
Downloaded from http://ps.oxfordjournals.org/ at NERL on June 18, 2015
Source of HVT Vaccine. Vaccine was produced at the Poultry Disease Research Center. The HVT (FC126) isolate was obtained from Dr. William Okazaki, East Lansing, Michigan. The vaccine was prepared in cultured chick embryo fibroblasts (Eidson and Anderson, 1971). Infected monolayers were removed by trypsinization 72 hours post infection and were reconstituted to the desired dilution in 199 cell culture medium. Although the plaque forming unit (PFU) level of the diluted vaccine was not known at time of use, a sample of the vaccine was titrated at the time the vaccine was used. Two federally licensed vaccines and one state licensed vaccine were also used. All of the vaccines used in this study were titrated at the Poultry Disease Research Center.
1483
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connected to the side arm with rubber tubing. Farms selected for this study had at least two poultry houses so that one house could contain unvaccinated controls. On each farm the vaccine was administered on a complete house basis in order to eliminate any chance of mixing vaccinated and control birds. During the course of this study 2,500,000 birds were vaccinated with the H V T vaccine a t doses of 200 to 2600 P F U per bird while 600,000 birds served as non-vaccinated controls. All vaccination was done at 1 day of age. Each treatment group was identified separately as the birds were loaded and transported to the various processing plants. Program personnel accompanied the flocks to the processing plant to insure t h a t the identity of the lots was maintained. The vaccinated birds were usually the first birds to be processed t h a t day and
before the control birds were processed a complete break in the shackles of the processing line was made in order to reduce the chances of mixing the birds with other lots. Personnel of the Consumer and Marketing Service of the U.S.D.A. provided the inspection data. Records in addition to condemnation data, included body weight at time of processing and livability of the broiler flock. RESULTS
These trials were conducted to determine if less than a "breeder dose" could be used to vaccinate broiler chicks. Plaque forming units per bird close ranged from 200 to 2600. I n this study almost 3.1 million birds were utilized; however, several flocks were omitted from the data because of improper identity, lack of proper controls, sale to other processors,
Downloaded from http://ps.oxfordjournals.org/ at NERL on June 18, 2015
FIG. 1. Equipment used to vaccinate birds.
VACCINATION A G A I N S T M A R E K ' S D I S E A S E
I n conpanies B and C the condemnations due to M D in vaccinated birds
reached 2.0% at the 200-400 P F U level. However, the results (Fig. 5) indicate t h a t the optimum dose level of the H V T vaccine was between 500 and 1000 P F U . I n Fig. 6 an evaluation of the economics of vaccination is shown. This evaluation only took into consideration decreased condemnations at the various vaccine dosage levels. At the time this study was undertaken the cost of the vaccine (2500 P F U ) was approximately five cents per bird; whereas, at the present time the cost of the vaccine is one cent. Although t h e cost of the vaccine has changed, Fig. 6 still offers a base of comparison of cost figures. If only a reduction in condemnations is considered, a dose of approximately 500 P F U per bird is the most economically efficient level of application. I n
5.0
4.0
§o
3.0
a u o
2.0
1.0
200
400
600
800
1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 PFU/BIRD DOSE
FIG. 2. Vaccination of broiler chicks with the HVT vaccine (company A).
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or other conditions which made the results questionable. The results of the trials of the individual companies (A, B a n d C) are shown in Figs. 2, 3, and 4, and the combined results of the trials are shown in Fig. 5. I n Fig. 2 (Company A), Fig. 3 (Company B), Fig. 4 (Company C) and Fig. 5 (Summary) the bold unbroken line shows the percent of control chickens condemned for M D on the same premises as vaccinated hatchmates. T h e number of control chickens (average for t h e trial) condemned for M D was greater than 4 percent whereas, the number of vaccinated birds (200-2600 P F U ) condemned for M D was less than one percent. !
1485
1486
E I D S O N , K I N G , C O N N E L L , A N D E R S O N AND K L E V E N
5.0
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4.0
o 3.0
2.0
1.0
200
400
600
800
1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 PFU/BIRD DOSE
FIG. 3. Vaccination of broiler chicks with the HVT vaccine (company B). this study it was found t h a t a dose of 500 P F U reduced the condemnations by 3.5 percent; whereas, the condemnations in birds vaccinated with 1000 P F U were reduced by 4 . 0 % . An analysis of the effects of H V T vaccine on body weight a n d livability m a y justify the application of higher dosages, (Figs. 7 & 8). T h e advantage of increased body weight of the average broiler vaccinated with 1000 P F U as compared to those receiving 500 P F U is approximately 0.08 pound per bird. At 12 cents per pound live weight, an increase of approximately 0.96 cents per bird was realized. T h e advantage of approximately 0.5 percent increased livability with 1000 P F U / d o s e as compared to 500 P F U / d o s e
resulted in an increased gross income of $2.50 per 1000 birds processed, or 0.25 cents per bird (Fig. 8). Table 1 summarizes the effect of the application of H V T vaccine at approximately 1000 P F U per bird. Condemnations due to M D were reduced by 4.0 percent or a savings of $20/1000 birds processed. T h e increased body weight of approximately 0.2 pound per bird added a saving of $25/1000 birds processed and the increased body weight of approximately 0.2 pound per bird gave an additional saving of $8 per 1000 birds processed. DISCUSSION Since the H V T vaccine was approved in 1971 by the Biologic Division of the
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a o.
1487
VACCINATION AGAINST MAREK'S DISEASE
5.0
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400
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800
1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 PFU/BIRD DOSE
FIG. 4. Vaccination of broiler chicks with the HVT vaccine (company C).
Agricultural Research Service for use in commercial breeders and pullet replacements, the needs of the broiler industry were not satisfied because of the cost of the vaccine. Laboratory studies conducted by Okazaki et al. (1970) indicate that birds vaccinated at one day of age with 600 PFU were protected against MD when challenged with the virulent MD virus by intra-abdominal inoculation at 3 weeks of age or were challenged with the virulent MD virus by contact exposure as early as 2 weeks post vaccination. In field trials Purchase et al. (1972), using 8 different commercial breeders found that there was no apparent difference in protection against MD when birds were vaccinated
with 500, 2000, -ir 10,000 PFU per chick. Although the study by Purchase et al. (1972) indicates that less than a "breeder dose" would protect a chick against MD, many unanswered questions remained since this was a long term MD study. The question of whether a diluted dose of vaccine would protect a broiler chick against MD mortality as well as prevent MD lesions at the time of processing remained unanswered. The object of this study was to devise an MD vaccination program for the broiler industry that would be feasible economically. The three companies selected had birds in areas with histories of varying degrees of MD condemnations. As demonstrated in Fig. 2 (Company A)
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MD - Control Birds
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it I I I I i I I I M D - Vaccinated Birds 1.0
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400
600 800 1000 1200 1400 1600 1800 2000 2200 2400 PFU/BIRD DOSE
2600 2800
FIG. S. Summary of the broiler vaccination trials of the three companies involved in this study.
birds in one area were protected against M D by 200 P F U per bird dose; however, birds in Company B (Fig. 3) and Comp a n y C (Fig. 4) receiving 200 P F U did n o t receive the protection afforded the birds from Company A which would indicate the level of exposure to M D was apparently greater in the areas where birds from Company B and C were placed. I t is imperative t h a t each company keep accurate records on the dosage level of H V T vaccine because the level of exposure to the virulent M D virus m a y be greater in some areas t h a n others. Therefore, the dosage level of the vaccine must be varied accordingly. F r o m unpublished d a t a of field observations, it has been found t h a t the dosage level of vaccine should be increased during the winter
months, possibly because houses have less exchange of air and the level of exposure to M D is greater. At the beginning of this study the cost of the vaccine was approximately 6 cents per bird dose. As indicated by Fig. 6, 500 P F U would be more economical t h a n 1000 P F U . If the cost of 500 P F U were 1 cent and the condemnations due to M D were reduced b y 3.5 percent, a savings of $7.50 per thousand chickens processed would be realized; whereas, if 100 P F U cost 2 cents and the condemnations due to M D were reduced b y 4.0 percent then the company would save $20 per 1000 birds; however, the profit would be negated since it would cost $20 per thousand to vaccinate the birds. However, now t h a t the cost of the vaccine is approximately 1
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VACCINATION AGAINST MAREK'S DISEASE
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FIG. 6. The cost of the HVT vaccine at graded doses and percent decrease in condemnation that must be realized in order to pay for the vaccine. cent per "breeder dose" (approximately 3000 PFU) it is more economical to use 1000 PFU. If birds received 500 PFU costing 0.18 cents (1/6 dilution) and the condemnations were reduced by 3.5 percent then the savings would be $15.85 per 1000 birds; however, if 1000 PFU (1/3 dilution) costing 0.33 cents were used and the condemnations were reduced by 4.0 percent then the savings would be $16.70 per 1000 birds. Also Figs. 7 and 8 indicate that there is an increase of 0.08 pound per bird in body weight broilers vaccinated with 1000 PFU as compared to those receiving 500 PFU. At 12 cents per pound live weight, an increase of approximately 0.96 cents per bird can be realized. The advantage in livability of birds vaccinated with 1000 PFU was increased by 0.5 percent (0.25 cents
per bird) when compared to birds vaccinated with 500 PFU. Therefore, if birds were vaccinated with 1000 PFU costing 0.33 cents then the increased livability and increased body weight would mean a savings of 0.88 cents as compared to the advantage returned on the application of 500 PFU per bird dose. If birds receiving 1000 PFU are compared with the controls as shown in Table 2 the total increase in gross income was $53 per 1000 birds processed. If the vaccine cost of 1000 PFU were $20 per 1000 birds processed then the increase in net income was $33 per 1000 birds; however, at the present time the cost of 1000 PFU is 3.30 per 1000 birds; therefore, the increase in net income is $49.80 per 1000 birds processed rather than $33 per 1000 birds.
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«2-5 \
1490
EIDSON, KING, CONNELL, ANDERSON AND KLEVEN
1000
1500
2000
2500
PFU/BIRD DOSE FIG. 7. The effect of HVT vaccine on body weight of broilers as compared to unvaccinated controls of the same age.
This study indicates that the most economical dose of HVT vaccine for the broiler chicks is 1000 PFU. It was also shown that birds properly vaccinated with the HVT vaccine (1000 PFU) are not only protected from mortality due to MD. In
addition, the lesions characteristic of MD that are responsible for condemnations at the processing plant are also eliminated. ACKNOWLEDGMENT
The cooperation of the Georgia poultry
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VACCINATION AGAINST MAREK'S DISEASE
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TABLE 1.—The effect of the application of approximately 1000 PFU of HVT vaccine per bird Results Compared to Unvaccinated Controls
Factors Considered Condemnations for Marek's Disease Livability Body Weight
Increased Income Above Unvaccinated Controls $20/1000 birds processed' $8/1000 birds processed" $25/1000 birds processedb
4 . 0 % decrease 1.6% increase 0.2 lbs. increase
Total increase in gross income Cost of 1000 PFU
$53/1000 birds processed $20/1000 birds vaccinated
Increases in net income
$33/1000 birds processed
* Based on 1% of flock being equal to $5/1000 birds processed. Based on a 4.0 lb. bird @ 12.5 cents/lb.
b
REFERENCES Churchill, A. E., L. N. Payne and R. C. Chubb, 1969. Immunization against Marek's disease using a live attenuated virus. Nature, 221: 744747. Eidson, C. S., and D. P. Anderson, 1971. Immunization against Marek's disease. Avian Dis. 15: 68-81.
Kawamura, H., D. J. King, Jr. and D. P. Anderson, 1969. A herpesvirus isolated from kidney cell culture of normal turkeys. Avian Dis. 13: 853863. Okazaki, W., H. G. Purchase and B. R. Burmester, 1970. Protection against Marek's disease by vaccination with a herpesvirus of turkeys. Avian Dis. 14: 413-429. Purchase, H. G., W. Okazaki and B. R. Burmester, 1972. Long-term field trials with the herpesvirus of turkeys vaccine against Marek's disease. Avian Dis. 16: 57-71. Witter, R. L., K. Nazerian, H. G. Purchase and G. H. Burgoyne, 1970. Isolation from turkeys of a cell-associated herpesvirus antigenically related to Marek's disease virus. Am. J. Vet. Res. 3 1 : 525-538.
NEWS AND NOTES (Continued from page 1481) oratories Inc. in a technical service capacity for the southeastern region, with headquarters in Gainesville, Georgia. He did diagnostic laboratory work with a national company, and had field service experience throughout the eastern part of the United States. He will provide technical assistance to poultry companies on health and production problems, and will work with them in the development of poultry health programs. Dr. Anthony received a D.V.M. degree from the University of Georgia, after graduating there in agricultural economics. He later received a M.S. degree at the University of Missouri. MAAG AND EASTERBROOKS S. Frank Moore has been named President of
Maag & Easterbrooks, Inc., a biological and agricultural research, development and manufacturing company currently specializing in veterinary and poultry vaccines. Dr. T. A. Maag, Chairman of the Board, said Moore will serve as President of the parent company and three subsidiary companies with operations in Georgia and Alabama. Moore was with Cotton, Incorporated, where he was Director of Research and Technical Services. Dr. Hsi-tang Tung has been appointed Director of the Laboratory Section of Maag & Easterbrooks, Inc. He joined the company in April, 1972, and was assigned to duties in microbiology relative to quality control. In his new position, he will be respon-
(Continued on page 1509)
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industry, the Georgia Poultry Federat i o n , t h e S t a t e D e p a r t m e n t of A g r i c u l t u r e , t h e Consumer a n d M a r k e t i n g Service, t h e V e t e r i n a r y Science R e s e a r c h Division a n d t h e A n i m a l H e a l t h D i v i s i o n of t h e A g r i c u l t u r a l R e s e a r c h S e r v i c e is g r a t e f u l l y acknowledged.