Genetic Analysis of Antibody Responses of Turkeys to Newcastle Disease Virus and Pasteurella multocida Vaccines1

BREEDING AND GENETICS Genetic Analysis of Antibody Responses of Turkeys to Newcastle Disease Virus and Pasteurella multocida Vaccines1 R. E. SACCO,2 K. E. NESTOR,3 Y. M. SAIF, H. J. TSAI, N. B. ANTHONY,4 and R. A. PATTERSON Department of Poultry Science and Food Animal Health Research Program, The Ohio State University, Ohio Agricultural Research and Development Center, Wooster, Ohio 44691

1994 Poultry Science 73:1169-1174

beneficial to the commercial industry. There are effective methods available for Selection for improved resistance of the control of a number of turkey diseases. turkeys to specific pathogens would be However, costs of medication, vaccination, and treatment and the reduction in performance of turkeys as a result of disease outbreaks can be substantial. Received for publication August 16, 1993. Accepted for publication March 30, 1994. In order to assess the feasibility of Salaries and research support provided by State developing lines of turkeys with improved and Federal Funds appropriated to the Ohio Agricultural Research and Development Center, The Ohio disease resistance, it is necessary that criteria for selection of disease resistance State University. Manuscript Number 145-93. 2 Present address: Department of Pathology, be established. Considering the complex University of Iowa, Iowa City, IA 52242. nature of host-pathogen interactions, 3 To whom correspondence should be addressed. selection for improved disease resistance 4 Present address: Department of Poultry Science, 202E Animal Science Building, University of Arkansas, in turkeys may be difficult. In addition to determining factors of selection, heritabilFayetteville, AR 72701. INTRODUCTION

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ABSTRACT Heritability (h2) of 16-wk BW and primary and secondary antibody responses and genetic and phenotypic correlations among these traits were estimated for 931 male and female turkeys vaccinated with Newcastle disease virus (NDV) and Pasteurella multocida. Turkeys from a line selected for 22 or 23 generations for increased 16-wk BW were vaccinated at 6 and 12 wk of age with blood samples collected 3 wk postvaccination. Antibody titers were determined using an ELISA method and transformed to loge for analysis. Heritability estimates for primary and secondary antibody responses to NDV were .380 ± .070 (SE) and .296 ± .063, respectively. For primary and secondary antibody responses to P. multocida, h 2 estimates were .458 ± .075 and .333 ± .066, respectively. Heritability estimate for 16-wk BW was .404 ± .071. The genetic correlation between primary and secondary antibody responses to NDV was .491 ± .150. There was no genetic correlation between primary and secondary antibody responses to P. multocida. Although the genetic correlation between primary antibody responses to NDV and P. multocida was .292 ± .159, the genetic correlation between secondary responses to the two antigens did not differ from zero. There were no genetic correlations between antibody responses and 16-wk BW. Similar results were observed for phenotypic correlations. Based on heritability and genetic correlation estimates, it would be possible to improve antibody responses to either NDV or P. multocida singularly; however, to improve antibody responses to both antigens, selection would have to be applied for each antigen. (Key words: heritability, genetic correlations, antibody response, Newcastle disease virus, Pasteurella multocida)

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MATERIALS AND METHODS Line of Turkeys

the present study) or 23 generations (2nd yr of the present study) for increased 16-wk BW. Further description of this line is given by McCartney et al (1968) and Nestor (1984). Management of Turkeys The breeder flocks that produced the poults used in the present study were vaccinated via aerosol mist with the La Sota strain of NDV in November of each year and with an inactivated NDV vaccine via the i.m. route in January of each year. Breeder flocks were not vaccinated for fowl cholera. Day-old poults were wing-banded according to dam and reared with feed and water available for ad libitum consumption. Diets were a multiration series with declining protein (Naber and Touchburn, 1970) that met or exceeded NRC (1984) requirements. Body weights were measured at 16 wk of age. Experimental Design The present study was conducted over a 2-yr period and included 464 and 467 turkeys in the 1st and 2nd yr, respectively. There was a total of 463 males and 468 females in the study. Line F was maintained with 36 pair-mated families (Nestor, 1977). A sire was randomly mated to two females to produce the offspring included in the present study with the exception that fullsib matings were prohibited. Vaccinations Poults were vaccinated at 6 and 12 wk of age with an inactivated NDV vaccine5 via s.c. route. In addition, poults received a P. multocida bacterin6 via i.m. route at the same time. Antibody Titers

Individual blood samples were collected The genetic line (F) of turkeys used in the present study was selected for 22 (1st yr of 3 wk after the vaccinations. Blood samples were allowed to clot, and after centrifugation sera were harvested and stored at -20 C. Antibody titers of individual serum 5 New cavac-T; Intervet America, Inc., Millsboro, samples collected at 9 and 15 wk of age DE 19966. 6 Maine Biological Laboratories, Waterville, ME were assayed using an avidin-biotin-based ELISA procedure, similar to that which has 04901.

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ity (h2) estimates and genetic and phenotypic correlations are needed for measures that might be considered as selection parameters. It is also imperative that correlations between selection criteria, other measures of responsiveness to pathogens, and production traits be determined prior to attempting to select turkeys for improved disease resistance. Significant genetic variation in antibody responses of chickens to a number of antigens has been reported (Peleg et al, 1976; Pevzner et al, 1978; Siegel and Gross, 1980; Van der Zijpp and Leenstra, 1980; Soller et al, 1981; Cheng et al, 1991). These studies and others have provided h2 estimates and genetic and phenotypic correlations for antibody responses of chickens to a number of antigens. Due to the reported variability in antibody responses of chickens and given that this variability seems to be related to resistance of chickens to diseases (Sharma and Stone, 1972; Wilson et al, 1984), directional selection for antibody response to specific antigens has been examined (Pevzner et al, 1978; Gross et al, 1980; Siegel and Gross, 1980). Genetic variation in antibody responses of turkeys to vaccination with Newcastle disease virus (NDV) and Pasteurella multocida has been observed (Sharaf et al, 1988; Sacco et al, 1994). However, h2 estimates and genetic and phenotypic correlations for antibody responses of turkeys to specific antigens are not available. The objectives of the present study were to: 1) provide h2 estimates for antibody responses of turkeys to vaccination with NDV and P. multocida; and 2) provide genetic and phenotypic correlations between antibody responses to NDV and P. multocida vaccines and between antibody responses and 16-wk BW.

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GENETICS OF ANTIBODY RESPONSE IN TURKEYS TABLE 1. Antibody responses ± SE of turkeys to Newcastle disease virus and Pasteurella multocida vaccines1 Antigen

Mean log,, 9-wk titer2

Mean loge 15-wk titer2

Newcastle disease virus Pasteurella multocida

3.66 ± .14 8.84 ± .09

7.33 ± .10 9.77 ± .04

1

Turkeys were vaccinated at 6 and 12 wk of age and blood samples were collected at 9 and 15 wk of age. Titers were determined by an ELISA method.

2

Statistical Analyses Antibody titers determined by ELISA were transformed to loge. Response variables included 16-wk BW and loge 9-wk and 15-wk serum antibody titers to NDV and P. multocida. Data were analyzed using a leastsquare and maximum likelihood program (Harvey, 1985). The following mixed model was assumed: Z

ijklm = M + Vj + Sjj + dijk + Xj + eijklm

RESULTS AND DISCUSSION Mean loge titers of Line F turkeys in response to NDV and P. multocida vaccines are shown in Table 1. Differences in antibody titers due to year effects were generally significant. The mean titers for primary and secondary response to P. multocida were 8.80 ± 13 (SE) vs 8.89 ± .13 (P > .05) and 10.3 ± .06 vs 9.51 ± .06 (P < .001) for Years 1 and 2, respectively. The respective yearly titers to NDV for primary and secondary response were 2.72 ± .20 vs 4.60 ± .20 (P < .001) and 7.08 ± .14 vs 7.58 ± .14 (P < .05). There was no twofactor interaction between years and the other variables. Random effect due to sires within year was not significant. With unequal subclass frequencies the tests of significance for years and sires within years are approximate (Harvey, 1985). Random effect of dams within sires within years was a significant source of variation. Female poults had significantly higher mean antibody titers to NDV. Males had significantly higher 15-wk titers to P. multocida. Mean 16-wk body weight for turkeys in the present study was 9.32 ± .05 kg. Year, dam, and sex effects were significant sources of variation in 16-wk BW. Mean body weights for Years 1 and 2 were 9.23 ± .07 and 9.41 ± .07 kg (P < .05), respectively. Body weights of males and females were 10.58 and 8.05 kg, respectively.

where Zijklm = observed value for a particular trait; \i = overall mean; Y, = fixed effect of the i* year; S;J = random effect of the j * sire within the i* year; d;jk = random effect of the k* dam within the j * sire within the i* year; Xi = fixed effect of the 1th sex of poult; an d eijkim = random residual effect associated with the ijklm* record. The h2 estimates and genetic and phenotypic correlations reported in the present study Heritability Estimates were determined using sire and dam variHeritability estimates and their standard ance components from full-sib data. errors for serum antibody titers to NDV and P. multocida vaccines and for 16-wk BW are 7 presented in Table 2. Heritability estimates Difco Laboratories, Detroit, MI 48233.

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been previously described for Bordetella avium (Tsai and Saif, 1991). The principal modifications in the ELISA method employed in the present study were the antigens used to coat microliter wells of the 96-well plates. For NDV ELISA, viral antigen was prepared as described by Tsai et al. (1992). A field isolate of P. multocida, capsular Serogroup A, somatic serotype 3,4 was grown in veal infusion broth7 for 24 h, adjusted to an absorbance of 1.0 at 540 nm, diluted in coating buffer, and used as antigen in the ELISA for P. multocida.

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TABLE 2. Heritability (h2) estimates and standard errors for antibody titers to Newcastle disease virus (NDV) and Pasteurella multocida vaccines and for 16-wk body weight1 h2 ± SE

Variable NDV 9-wk titer2 15-wk titer Pasteurella multocida 9-wk titer 15-wk titer 16-wk body weight

.380 ± .070 .296 ± .063 .458 ± .075 .333 ± .066 .404 ± .071

difference in the genetic regulation of the responses. However, there are other possible explanations for the difference, including sampling time postinjection and the test used to measure the antibody titers. Van der Zijpp et al. (1983) reported that there was considerable variation in the h2 estimates for antibody responses measured on different days postinjection. Genetic Correlations

:

for primary and secondary antibody responses to NDV and P. multocida ranged from .296 to .458. The estimates reported in the present study for P. multocida and NDV are within the range of h2 estimates reported in the literature for chickens when h2 estimates were based on sire and dam components of variance (Reta et ah, 1963; Peleg et ah, 1976; Gyles et ah, 1986; Cheng et ah, 1991). Higher estimates were observed for primary antibody responses to NDV and P. multocida compared to secondary antibody responses to these antigens. Whereas the primary antibody response is characterized by a predominance of IgM, the secondary antibody response is characterized by a more rapid response, a higher peak titer, and a greater production of IgG. Therefore, the h2 estimates for primary and secondary antibody responses may reflect a

Genetic correlations between 16-wk BW and antibody titers of turkeys in response to vaccination with NDV and P. multocida are shown in Table 3. A positive genetic correlation was found between primary and secondary antibody responses to NDV (.491 ± .150). Interestingly, there was no genetic correlation between primary and secondary antibody response to P. multocida. Primary and secondary antibody responses to NDV were positively correlated with primary antibody response to P. multocida. Soller et al. (1981) found no evidence of genetic correlation between antibody responses of chickens to NDV and Escherichia coli. The genetic correlations between 16-wk BW and antibody responses to NDV and P. multocida did not differ from zero. Phenotypic Correlations

Phenotypic correlations between 16-wk BW and antibody titers of turkeys to NDV and P. multocida vaccines are presented in Table 4. The phenotypic correlation between primary and secondary antibody

TABLE 3. Genetic correlations ± SE between antibody titers to Newcastle disease virus (NDV) and Pasteurella multocida vaccines and 16-wk body weight1

Variable NDV 9-wk titer 15-wk titer Pasteurella multocida 9-wk titer 15-wk titer

Pasteurellamultocida

NDV 15-wk titer2

9-wk titer

15-wk titer

Body weight

.491 ± .150

.292 ± .159 .308 ± .170

-.064 ± .184 .028 ± .194

-.042 ± .178 -.116 ± .187

-.144 ± .176

.057 ± .172 .087 ± .182

!Turkeys were vaccinated at 6 and 12 wk of age and blood samples were collected at 9 and 15 wk of age. 2 Titers were determined by an ELISA method.

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Turkeys were vaccinated at 6 and 12 wk of age and blood samples were collected at 9 and 15 wk of age. 2 Titers were determined by an ELISA method.

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TABLE 4. Phenotypic correlations between antibody titers to Newcastle disease virus (NDV) and Pasteurella multocida vaccines and 16-wk body weight1

Variable NDV 9-wk titer 15-wk titer Pasteurella multocida 9-wk titer 15-wk titer

Pasteurella multocida

NDV 15-wk titer2

9-wk titer

15-wk titer

Body weight

.338

.276 .137

.047 .032

-.033 -.040

.019

-.053 .007

'Turkeys were vaccinated at 6 and 12 wk of age and blood samples were collected at 9 and 15 wk of age. Titers were determined by an ELISA method.

2

either NDV or P. multocida by selection, for improvement in antibody response to both antigens, selection would have to be made for each antigen.

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response to NDV was .338. There was no phenotypic correlation observed between primary and secondary antibody responses to P. multocida. Primary antibody response to NDV was positively correlated with primary antibody response to P. multocida. There was no correlation between secondary antibody responses to the two antigens. Soller et al. (1981) reported that the phenotypic correlation between antibody responses to NDV and E. coli were small and nonsignificant. There were no phenotypic correlations between 16-wk BW and antibody responses to NDV and P. multocida. Results of the present study provide evidence for the importance of direct additive genetic variation for primary and secondary antibody responses of turkeys to NDV and P. multocida. Selection for improved antibody responses to NDV and P. multocida should be possible. However, the genetic and phenotypic correlations clearly indicate that selection based on secondary antibody responses to either NDV and P. multocida would not be expected to improve response to the other antigen or increase 16-wk BW. Selection based on primary antibody response to NDV and P. multocida could be achieved with a resultant improvement in the primary antibody response to the other antigen. However, selection for primary response would be complicated because the primary antibody response to an antigen develops at a slow rate, has a low peak titer, and the titer is not as persistent as the secondary antibody response. The results indicate that, although it would be possible to improve antibody response to

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